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The (e,2e) spectrometer vacuum chamber (figure 1) is manufactured from 304 grade stainless steel, the construction being carried out by Vacuum Generators using a design of Jones, Read and Cvejanovic, full details of which may be found in T.
3mm thick mu-metal magnetic shielding is placed both internally and externally to decrease extraneous external magnetic fields to less than 5mG at the interaction region.
All inputs and outputs to the spectrometer pass through the vacuum chamber via feedthroughs on the top flange. The top flange of the vacuum system is a 25mm stainless steel flange with 11 conflat CF70 flanges arranged around a central 200mm flange designed for locating a hydrogen source. Two flanges are used for the high voltage channeltron and photomultiplier tube inputs and pulse outputs. Three rotary motion feedthroughs allow the analysers and electron gun angles to be changed externally via stepper motors for both analysers and for the electron gun.
The ionisation gauge is placed at right angles to the main flange to prevent light from the thoriated iridium filament entering the vacuum system, which would increase noise on the photomultiplier tube.
The ionisation gauge feedthrough is sooted, and a loose cover is placed over the entrance in the chamber flange to prevent stray light from the ion gauge entering the vacuum system. The target gas enters the system via a CF70 flange which has two 6mm stainless steel tubes welded into the flange. The other gas feed is connected to a hypodermic needle set at 90A° to the incident beam for measurements in other geometries.
The gas jet which is not currently used in the interaction region can be used to non-locally fill the chamber with gas for background counting measurements. The final CF70 flange is used when the photomultiplier tube is cooled, usually during baking of the system following exposure to atmosphere. The tube is cooled by passing vapour from a liquid nitrogen source through expansion coils wrapped around the photomultiplier tube housing. The electron gun is a two stage non-selected gun designed by Woolf (Ph.D thesis, University of Manchester) (see figure 3).
The gun consists of a filament, grid and anode source which is focussed using a triple aperture lens through two 1mm defining apertures in the centre of the gun.
The apertures define the electron beam pencil and beam angles, and are focussed onto the interaction region using a second triple aperture lens located between the apertures and interaction region. The electron gun is shielded using advance (constantin) sheet which is grounded to the body of the gun mounting.
The gun is mounted onto an x-y translation table to allow placement of the electron beam as accurately as possible to the centre of rotation of the analysers and electron gun rotation axis. The gas jet is mounted from the electron gun using a narrow support of 310 stainless steel, and the Faraday cup can be attached to this support. The original unselected electron gun built by Woolf was completely rewired and a custom built PTFE 25 way inline wire-wrap plug and socket was placed between the 52 way vacuum electrical feedthrough and the electron gun. The wiring from the 52 way feedthrough to the inline plug is shielded colour coded 30 awg PTFE coated advance wire, and the inline plug and socket connectors are non-magnetic gold plated wire wrap pins. The electron analysers are constructed from molybdenum and are mounted from two rotating gear plates controlled externally via the rotation feedthroughs on the top flange (see figure 2). The input electrostatic lenses for each analyser are three element cylindrical lenses as shown in figure 4. The interaction region is focussed onto the entrance aperture of the hemispherical energy analysers with a beam angle of around zero degrees, the image of the analyser entrance aperture being larger than the size of the interaction region. Field gradients around the input and exit apertures are corrected using standard Jost correctors. The energy selected electrons passing through the exit apertures are finally collected by Mullard X919BL channel electron multipliers which amplify the single electron to produce a current pulse at their output. A principle source of noise on the signal pulses arises from the turbo-molecular pump motor. The noise from the turbo pump is reduced to ~ 5mV using these techniques, and as the average pulse height from the saturated multiplier is around 20-40 mV, this allows adequate discrimination following amplification.
The pre-amplifiers located external to the vacuum system are commercial 100X preamplifiers with 400pS rise-times, manufactured by Phillips Scientific. The NIM signals produced by the discriminators drive two ORTEC 437 Time to Amplitude Converter's via appropriate delay cables and an ORTEC pulse delay unit. The main TAC output feeds an ORTEC Multichannel Analyser card located in the PC controlling the experiment, whereas the second monitor TAC drives an external MCA, allowing convenient monitoring of the coincidence signal as the experiment progresses. The high voltage supplies to the electron multipliers are two Brandenberg 5kV supplies controlled by the main PC via serial DAC's.
Principally the filter is used to reduce pickup noise from entering via the HT cable onto the multiplier output.
Secondly, the filter has a slow response time for high voltage spikes, and reduces the probability of damage to the pulse electronics should the EHT supply suddenly turn on or off. Capacitor C2 decouples the 1kW load resistor to earth for high frequency pulses from the CEM's, and the voltage appearing across this load is connected via the capacitor C3 to the input of the 6954 preamplifier. Since the input impedance of the preamplifier is 50W and the CEM is effectively an ideal constant current supply, most of the current passes through to the preamplifier.
Finally, the 10M resistor prevents the output to the preamp from rising above ground when the preamp is disconnected from the circuit and is therefore a safety device for the preamplifier when initially connected. The original design placed the atomic beam nozzle and Faraday cup on the same support structure fixed to the body of the electron gun, with the atomic beam direction being in the detection plane when the perpendicular plane geometry is chosen (see figure 2). A second configuration is adopted for exclusively perpendicular plane coincidence experiments, the atomic beam nozzle being oriented at an angle of 45A° to the detection plane so that the gas effusing from the nozzle does not fill the analysers when they oppose the nozzle (see figure 6). In this configuration the support strut for the atomic beam nozzle is terminated lower than the detection plane, as is the nozzle itself. For non-perpendicular plane measurements the Faraday cup is once mounted from the support strut and the gas effuses perpendicular to the electron beam direction.
One difficulty when aligning an (e,2e) coincidence experiment lies in the focussing the incident electron beam and analysers onto the interaction region. The throughput of electron current as detected by the Faraday cup is insensitive to both position and focusing of the electron beam, since the cup opening is usually made quite large (in this case 6 - 10mm) and the bias voltage applied to the cup to prevent electrons returning to the interaction region allows all electron trajectories within this opening to be detected. Conventionally, following maximisation of the Faraday cup current, the beam is steered and focussed onto the gas jet as detected by counts in the analysers. This has the disadvantage that the overlap volume is maximised for both atomic and electron beam density, which tends to place the interaction volume as close as possible to the output of the atomic beam nozzle, which is almost certainly not in the centre of the detection plane. To eliminate the need for time consuming iterative techniques and the associated errors due to detection geometry, a separate method for tuning the electron gun is adopted that does not depend upon the analysers. The interaction between the target and the electron beam not only produces ionisation, but the valence states of the target also are excited with various probabilities depending upon the incident energy of the electron beam. These photons are detected by the photomultiplier tube, by placing a 450nm A± 50nm optical filter in front of the photocathode. The interaction region is therefore defined where an aperture in front of the photocathode is focused by the lens. The plano-convex focussing glass lens is covered by a grounded fine tungsten mesh to eliminate surface charging. The photomultiplier tube may be cooled by circulating nitrogen gas boiled off LN2 through copper coils encircling the photomultiplier tube housing. The photomultiplier tube used in the experiment is a 9789QB EMI photomultiplier tube with a bi-alkali photocathode peaking in the blue region of the optical spectrum.
As with the electron multiplier circuitry, it is important to optimise the load of the photomultiplier tube so that reflections along the feeder line to the counting electronics are minimised.
The 1nF 6kV capacitors across the dynodes close to the output stage are used as charge storage pumps that quickly refurbish the surface charge on the dynodes, allowing increased counting rates. The dynode resistors are 1% tolerance metal film resistors as these are more stable with temperature. The EHT supply to the photomultiplier tube is a Brandenberg 2kV supply operating at 1500V for this tube. The negative going output pulses from the tube measure typically 200-500mV in height, and therefore are able to directly drive an ORTEC 473A constant fraction discriminator located in one of the NIM crates. All resistors and capacitors for the dynode chain are soldered to the photomultiplier tube base internal to the vacuum system, using standard 5-core solder. Typical pulse heights from the electron multipliers in saturation mode are 25-40mV, whereas the typical height of the photomultiplier tube pulses is of the order of 250mV. The electron multiplier pulses are obtained from the multiplier supply circuitry as explained above. The amplified pulses from the 6954 amplifiers pass along doubly shielded RG-58 cable to the input of the ORTEC 473A discriminators.
The two analyser discriminators are located in separate NIM crates to increase isolation and reduce common mode pickup.
The slow rise-time positive outputs from the 473A discriminators pass to three ORTEC 441 rate-meters which allow counting and monitoring of the pulses. The fast NIM pulses from the analyser 473A CFD's pass through appropriate delay lines to two 437 TAC's.
This second multichannel analyser allows the operator to monitor the total accumulated coincidence signal during operation. The lens supplies that control the voltages impressed onto the lens elements and deflectors in the experiment were developed over a number of years, and therefore take different forms. Three of these supplies feed the deflectors in the electron gun, the other two supply the input deflectors in the analysers.
In a second 19" crate is located the gun lens high voltage supplies together with the high voltage supplies for the Faraday cup. In a third 19" crate is located the analyser voltage supplies together with a set of serial loading supplies that control the electron multiplier EHT supplies. A further supply controls the current boost circuitry located in the filament constant current supply unit (see below).
The outputs of each computer controlled supply that drives an individual lens element or deflector are connected to a 70 relay switching board. The Digital voltmeter is in turn accessed via an IEEE-488 interface which is addressed by an 8086 slave PC which converses with the central PC which controls the experiment. The outputs from the relay board connect to the spectrometer via shielded multicore cables which take the gun voltages to the 52 way feedthrough and the analyser voltages to the two 19 way feedthroughs located on the vacuum flange. The gun supply multicore also carries the filament supply current to the 52 way feedthrough.
The Faraday cup current is measured by the Keithley Digital voltmeter when under computer control but this can also be measured by an external pico-ammeter.
In addition to the analyser electrostatic lens and deflector voltage connections, the 19 way CF70 feedthroughs are used to control signals from internal sensing opto-isolators which control the stepper motor interlocks. The stepper motors that drive the analysers and electron gun around the detection plane are five phase motors with integral 10X reduction gearboxes driving the rotary motion feedthroughs.
The intelligent stepper motor drivers are addressed via a serial port located on the controlling PC bus. An additional interference problem was traced to the RS232 serial line from the controlling PC.
The PC bus was found to be poorly earthed due to very little copper being used for the bus earth. This was cured by decoupling the 0V RS232 line from the main 0V line for the stepper motors, as is shown in figure 10.
The analyser stepper motor supplies have a facility for halting the motors using limit switches which are optically coupled to the internal 68000 logic circuits driving the supplies. The SD5443-3 phototransistor normally illuminated by the TEMT88PD photodiode during operation ensured a fail-safe mechanism should any of these components fail (this automatically prevent the motors from running). Should the analysers move into a position as defined by the four criteria (a) - (d) above, a shutter located on the analyser turntables moves between the appropriate photodiode and phototransistor, shutting off the light and thereby shutting down the stepper motor current. Only motion in the opposite direction is allowed by controlling logic, allowing the analyser to move away from the point of imminent collision but no closer. The six pairs of optocouplers that prevent the analysers moving into the Faraday cup, electron gun and gas jet support are located on the mounting struts supporting the main body of the spectrometer. Two optocouplers are located on the side of analyser 2, and two shutters are located on the sides of analyser 1 to prevent the analysers colliding with each other. Finally a ninth optocoupler is located over the electron gun counterweight which monitors when the gun is at an angle less than 65A°, where the sweep angle around the detection plane is reduced. The current boost circuit operates from a serial driven supply card as detailed previously. The main filament drive is through six power diodes that feed the current from the constant current supply to the filament. The Darlington transistor T1 feeds additional current to the filament via three parallel 10 turn 100W trim resistors through a 1N4007 diode. As the constant current supply acts as an infinite resistance source, the boost circuit supplies additional current only when the voltage at the anode of the feed 1N4007 exceeds the output voltage of the constant current supply. Finally, the filament bias voltage (and hence energy of the electrons) is set to the midpoint of the filament by two 100W balancing resistors located across the terminals. In addition to the ADC buffer card, three independent isolated regulated supplies drive REF01 voltage reference sources for measurement of the positions of 10 turn potentiometers located on the analyser and electron gun rotary drive shafts.
The angular position of the electron gun and analysers is calibrated when the system is opened using visible laser diodes that define these angles to an accuracy of A±0.2A°. Figure 13 shows an overall block diagram detailing the computer control and high speed pulse interfacing to the spectrometer. September 2012 - In this installation the plumber installed a PVC vent inside of a clay lined double flue chimney.
In the May 2011 issue of Plumbing Engineer magazine, I wrote a column titled, a€?Is PVC an acceptable vent material for flue gases?a€? in which I pointed out many problems and challenges associated with venting flue gases with polyvinyl chloride (PVC) pipe. AHRI is an advocate on behalf of their members; they lobby at all levels of government, including at model code hearings. Some people have asked why I am making such a big deal over using PVC for venting combustion gases. Recently, I received a call from someone on behalf of a woman who had suffered a serious debilitating illness.
In exposed locations, the PVC pipe was tan colored; above the drywall and below the second floor decking in the area of the break, it was a very dark brown. The pipe was brown and discolored in the vicinity of the two water heaters, and two yellowish fittings were cracked and completely separated.
There is not much data on discoloration of PVC pipe or on ambient air cooling requirements for PVC flue pipes. There is no standard for PVC pipe for use as a flue material for combustion gases and there is no testing for these conditions.
When the home was being sold, an inspector found significant water damage in the lower levels.
She was amazed to hear this, because he was describing many of the symptoms she had been experiencing for several years.
PVC pipe has a temperature limit of 140 F; most water heaters and boilers have thermostats that exceed this temperature.
Plumbing engineers typically design hot water systems to store hot water about 140 F in water heaters to minimize Legionella bacteria and other organic pathogen growth in the hot water tank. If a fuel gas appliance was 100% efficient, the flue gas temperature would be the same temperature as the thermostat setting or fluid temperature in the water heater or boiler. I serve on an industry committee that is developing guidelines for minimizing Legionella in building water systems. Water heater, boiler and furnace manufacturers have gone to great lengths to promote and use PVC plastic flue pipes in applications that exceed the temperature ratings of the product. This standard specification does not include requirements for pipe and fittings intended to be used to vent combustion gases.a€?a€?The cost of PVC plastic pipe cost is a fraction of the cost of stainless steel. There is no testing for a water heater, boiler or furnace that has a system set at the upper temperature settings with a build-up of scale on the heating surfaces or with a plugged air filter.
He said that the company has had numerous complaints about PVC pipes used for venting flue gases, and that they always point out that they do not recommend this usage and that there is no listing for it in their manual.
The piping manufacturer recommends that inquiries about the suitability of plastic piping systems for venting combustion gases should be directed to the manufacturer of the water or space heating equipment being installed.
Furthermore, several of the ASTM standards applicable to PVC plastic pipe and fittings that this company manufactures their pipe to include the following note: This standard specification for PVC pipe does not include requirements for pipe and fittings intended to be used to vent combustion gases.
There is no standard referenced in any of the codes in the United States for a plastic flue vent for combustion flue gas piping, although many water heater and boiler manufacturers recommend this.
The maximum temperatures listed in the ABS, PVC and CPVC pipe manufacturersa€™ technical literature are shown in the following table. Generally, for a new condensing water heater or boiler, the stack temperature will be about 20 degrees higher than the water temperature.

Some boiler and water heater manufacturers offer stack or flue gas temperature gauges as a way to see whether the unit is scaling up and losing efficiency, which is helpful for monitoring the flue condition.
This control would shut off the burner if the flue gas temperature exceeds the temperature rating of the flue pipe. A standard will be needed for plastic flue pipes that should include a temperature gauge and a high limit probe. Without a standard for proper use of these safety devices in combination with plastic flue gas piping or without the use of stainless steel flues, plastic flue materials can melt as flue gas temperatures rise. A family of four died in Aspen, Colorado, in 2008, of carbon monoxide poisoning from the failure of PVC plastic flue pipes on a condensing snow melting boiler system in a rental property. I have heard arguments by many contractors that do not believe PVC flue venting for combustion gases is a problem, but I have seen melted and discolored piping in many of my investigations, so I know it is a problem. This approach seems to be a way to lessen the initial cost of installing a high efficiency boiler or water heater.
Some people argue that the mechanical code allows you to follow the manufacturera€™s recommendations. Exception: Where a code provision is less restrictive than the conditions of the listing of the equipment or appliance or the manufacturera€™s installation instructions, the conditions of the listing and the manufacturera€™s installation instructions shall apply. I have not seen any testing data or an independent test report from a boiler or water heater manufacturer that shows that PVC piping has been tested and approved for the conditions it will likely see in a water heating or boiler installation. This temperature limit was intended to allow the use of PVC pipe for use as a flue gas material. This temperature limit was intended to allow the use of CPVC pipe for use as a flue gas material.
This temperature limit was intended to allow the use of Polypropylene (PP) pipe for use as a flue gas material. I am not aware of any plastic pipe manufacturers that meet this sub-section of the standard. Interestingly, although the CO levels were elevated to dangerous levels, they were not high enough to trip a carbon monoxide alarm. This standard specification does not include requirements for pipe and fittings intended to be used to vent combustion gases.The cost of PVC plastic pipe cost is a fraction of the cost of stainless steel. The test does not test for long term thermal cycling of the PVC pipe where the pipe becomes discolored. Scale on heating surfaces and higher system water temperatures that increase scale production are not extreme cases but are normal conditions expected over the life of a water heater or boiler.
Scale deposits occur when calcium, magnesium and silica, commonly found in most water supplies, get cooked onto the heating surface and form a continuous layer of material on the waterside of the water heater or boiler heat exchanger surfaces. The National Institute of Standards and Technology, Handbook 115, Supplement 1 addresses the loss of efficiency based on scale formation. A flue pipe should not be allowed to fail and cause an injury or death from a normal system temperatures, location of a flue in a concealed space, or a normal build-up of scale on the heating surface. At the ASHRAE show in Chicago, I asked every water heater and boiler manufacturer that was exhibiting PVC flues on their equipment to show me any testing data they might have that shows the PVC material was not going to exceed 140 F. The fuel-fired appliance manufacturers, in their quest to use PVC pipe as an inexpensive flue material, realized that no piping manufacturer was going to go out on a limb and certify their pipe for use as a flue gas material, so a proposal for a code change was submitted to the International Fuel Gas Code to allow an exception for the listing requirements for flue gas materials. The AHRI representative went on to talk about dilution air being mixed with the flue gas temperatures. Until any fuel burning appliance manufacturer can produce an independent engineering lab test report that shows that the appliance will shut down if the flue gas temperatures exceed 140 F, an engineer or the inspector has every right to reject the PVC flue materials as not being in compliance with the requirements for listed flue pipe materials in the International Fuel Gas Code.
Fuel burning appliance manufacturers should change their installation literature to prohibit PVC pipe and fittings.
The manufacturers and AHRI have created an unsafe condition by lobbying for a material that is not suited for this application.
Data also needs to be published showing the dilution air requirements at the maximum possible ambient air conditions. At BMA, design solutions are arrived at by a cultivated and experienced team of professionals.
BENEFITS Bill Moore and Associates offers a long term career opportunity with growth potential, medical benefits, a 401(K) plan and profit sharing. As service manager, Jason handles repairs and maintenance of BMA client signage nationwide. One of these is internally connected to a gas jet which can be set at 45A° to the incident electron beam and is used in the perpendicular plane experiments. These stainless steel feeder tubes are connected to the nozzle using grounded shielded PTFE hose. One follows the anode, another corrects the beam direction between the apertures and a third steers the beam onto the interaction region. This shield is coated with aerodag colloidal graphite to reduce patch fields on the surface of the metal, and is made as small as possible to allow the analysers to approach the gun as close as is feasible when non-perpendicular plane geometries are selected (see figure 2). The XY translation table is mounted from the rotating yoke, to which is attached the photomultiplier tube. This allows the gun to be dismounted from the system without the need for rewiring of the feedthrough when the need arises (filament changes, cleaning etc).
The wiring between the gun and inline socket is also shielded colour coded PTFE coated advance wire facilitating spot welding to the electrostatic lens elements of the gun.
The analysers are mounted onto x-z translation tables that allow them to view the interaction region accurately over the full range of angles accessible.
These lenses have a capability for energy zooming of around 10 : 1, and have a maximum entrance acceptance angle of A±3A° as defined by the entrance apertures. This ensures that the overlap volume accepted by each analyser encompasses the interaction volume for all detection angles as the analysers move in the detection plane.
These devices use an activated lead glass internal surface which has a high coefficient of secondary electron emission when a high voltage (around 3000V) is applied across the multiplier.
This noise may be picked up by the channel electron multiplier and the high voltage feed to the multiplier, and is generated internally in the vacuum system. The CFD's are operated in NaI mode as this has a 2ms dead time following the initial pulse, thus reducing the possibility of false triggering due to any mismatching impedance reflections along the delay cable. These EHT supplies are connected via VERO 200 high voltage couplings to high voltage cable connecting to the pickoff circuitry located on the high voltage feedthroughs. This allowed the analysers to roam the detection plane over a complete 360A° angular range. The configuration of the target source hypodermic when perpendicular plane measurements are conducted.
The common procedure is to initially maximise the current from the gun onto the Faraday cup, then onto analyser counts as the electron beam is moved through the gas jet.
Maximising the Faraday cup current is therefore only a crude preliminary alignment of the incident electron gun beam.
This therefore assumes that the analysers are initially focused onto the interaction region, and a slow iterative technique must be adopted where the analysers and electron gun are tuned so as to maximise the signal from both analysers.
In this case a true differential cross section is not obtained, since the scattered and ejected electron trajectories lie in a different plane than defined in the initial experimental alignment. An EMI 9789QB reduced photocathode photomultiplier tube is installed in the vacuum system together with optical focussing and defining elements (figure 2). A group of these excited states decay back to lower valence states with the emission of visible photons at wavelengths around 450nm for both helium and argon targets. Tuning of the electron gun to PMT counts therefore guarantees that the electron gun is steered and focussed to the point at the centre of the detection plane independent of the analysers or gas beam density.
This is mainly used when the vacuum system is baked at temperatures above 55A°C, since the photocathode is rapidly damaged by temperatures exceeding this. The tube is a venetian blind dynode construction, and has a reduced photocathode to decrease the noise on the output of the tube to less than 20Hz.
The photomultiplier tube base was thoroughly cleaned in an ultrasound following location of these components, to displace any flux residue from the solder joints. It is therefore necessary to amplify the channeltron pulses prior to transmission to the discriminators, whereas the photomultiplier tube pulses are sufficiently large to not require further amplification.
These pulses are amplified by Phillips Scientific 6954 100X amplifiers located external to the EHT feedthroughs connected by 10cm lengths of RG-58 cable. These crates are further decoupled from the AC mains supply using filter circuitry on each supply line. Internal to these rate-meters buffer 7400 TTL chips have been added to send to 32 bit counters located in the main PC via RG-58 cable. These supplies are fully floating, their mid-point voltage being equal to the lens element voltage in which the deflectors are housed. All these supplies are fully computer controlled isolated units with low output impedance to reduce noise and eliminate current loops.
This relay switching unit allows either the voltage or the current on each lens element to be measured by a Keithley Digital voltmeter. This drive is further reduced internally by 10X reduction gears, resulting in a reduction ratio of 100:1. This led to the ground line of the RS232 serial line moving around with respect to the 0V stepper motor reference as drive current to the motors returned along the ground line.
The optocoupler logic circuit circuit that controls the stepper motors and avoids collisions between the analysers, the electron gun, the Faraday cup and the hypodermic support.
Added to this filament supply is a computer controlled current boost circuit that can be used to increase the filament current during electron gun tuning. The additional current then returns to the 12V DC regulated supply via a second 1N4007 diode. This therefore depends upon both the current driving the filament, as well as the resistance of the filament when hot (typically 4W - 6W). This supply feeds current to the filament without changing the characteristics of the main constant current supply used while operating the spectrometer. These high stability reference sources ensure that the analyser and electron gun positions are accurately measured with time.
A datalogger internal to the controlling PC establishes a cubic spline relationship between the measured angles and the corresponding ADC conversion from the potentiometers. This PC also controls the selection of the relay motherboard for measurement of the required lens element either in voltage or current mode when a request is sent from the controlling computer via an RS232 serial line. The other flue in the chimney vents a fireplace, the problem we are finding is when homeowners light a fire in their fireplace the PVC in the heating system flue can melt and cause a serious carbon monoxide and flue gas danger. The school had hundreds of apartments in numerous buildings with high efficiency water heaters that were installed more than 10 years ago. Although the water heater installation manual we obtained recommended using PVC pipe as a flue material, PVC pipe manufacturers do not recommend this. He has asked every major manufacturer of boilers and water heaters for data to support the recommendations in their literature for the use of PVC pipe for combustion flue materials but has not received any replies.
Just because a manufacturer recommends using PVC does not mean that it is acceptable or safe.
There is a Canadian standard, ULC S636, but that standard has several flaws in that it allows flue gas temperatures that exceed the temperature limits of the pipe material manufacturers. Any temperatures above the rated temperature will allow the pipe to melt, sag and, possibly, collapse or pull apart. The design and efficiency of the unit, along with several other factors, including water quality, will affect the stack temperature. A temperature sensor or probe with a high-limit control could be inserted into the flue at the flue connection to the boiler or water heater. Then PVC, CPVC and polypropylene flue gas piping can be safely used on high efficiency boilers and water heaters. Not only is energy lost when this happens but flues can become blocked or disconnected, which can be a carbon monoxide or a fire danger.
The plastic pipe manufacturer was not at fault, because they had published limitations on the use of their piping, and they had not recommended PVC piping for that application. I also see the proliferation of recommendations from high efficiency, condensing boiler and water heater equipment manufacturers for the use of combustible and unlisted PVC piping products as corrosion resistant combustion flue venting. High efficiency equipment will cost significantly more than less efficient models, so there seems to be a movement by manufacturers to promote these unlisted and, therefore, non-code-approved materials over code approved and listed stainless steel flues, which are corrosion resistant. Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturera€™s installation instructions. Where conflicts between this code and the conditions of listing or the manufacturera€™s installation instructions occur, the provisions of this code shall apply.
The water heater manufacturera€™s installation instructions conflict with the requirement in section 802.1 that requires all vent systems to be listed and labeled for the application. The code restriction requiring all flue materials to be listed and labeled for their intended purpose is more stringent language, so the more restrictive code requirement requiring listed and labeled flue pipe materials would apply.
Any testing should include the extreme conditions when scaling occurs and flue gas temps rise, near the end of the equipmenta€™s service life.
The temperature limit for PVC pipe is 140 F, and the allowable temperature in the ULC S636 standard exceeds the temperature limits set by PVC pipe manufacturers. There is currently one manufacturer listed to this standard, but the potential for the flue gases to exceed the 230 F is still there. There are forces pulling each way, and I believe that a significant change will be coming within the next few years. He has served as Chairman of the International Residential Plumbing & Mechanical Code Committee. In the March 2012 issue, a representative of the Air-Conditioning, Heating and Refrigeration Institute (AHRI) wrote a letter supporting the use of PVC pipe on behalf of their appliance manufacturer members that use PVC as an alternative to the stainless steel or high temperature plastic flue venting materials that are listed for use.
AHRIa€™s government affairs staff works closely with congressional staff on legislation that impacts the industry. I would love to tell them it is OK to use these materials, but health and safety trump saving a few bucks on pipe material.
I photographed, took temperature recordings and used a multi-gas detector to take readings.
Dark areas on the decking and floor joists indicated that high temperature flue gases had possibly cooked the sugars or sap in the wood to a dark caramel color. Testing the flue gases in this case revealed that flue gas temperatures after the dilution air was added was still much higher than the 160 F hot water temperature and far in excess of the temperature rating for PVC pipe.
It appears that PVC flue pipes should not be located in concealed spaces such as the space between a ceiling and a floor deck, near insulation or floor joists or in wall cavities that have no ambient air cooling capability. A plumbing contractor opened the drywall ceiling on the lower floor and found the two completely separated PVC flue pipes pumping carbon monoxide and moisture into the home. The combustion gases that were venting into the floor space and coming up through a floor register into the living space had oxygen levels that dropped to well below 18 percent in some areas. Furnaces can have flue temperatures well above 140 F when the air filters are dirty and the air flow drops off. They typically use thermostatic mixing valves conforming to industry standards to reduce domestic hot water temperatures to safe delivery temperatures. Since 100% efficiency is not really possible, all flue gas temperatures will exceed the thermostat setting. The committee includes representatives of ASHRAE, ASPE, water heater manufacturers, plumbing designers, CDC, EPA, several pathologists and microbiologists and many other experts. They cannot use traditional galvanized flues because the condensation produced is pure water and very aggressive and would corrode or rust the flue in a very short time.
I am guessing that there was a meeting after the May 2011 article and that AHRI decided to defend the use of PVC plastic for venting combustible gases. According to him, the test involves setting the thermostat to the highest setting and flowing water continuously to keep the burner on. Scale creates a problem because it typically possesses a thermal conductivity, an order of magnitude less than the corresponding value for bare steel. This is a serious life safety issue that the appliance manufacturers apparently would like to sweep under the carpet.
Some looked at me like deer in the headlights, others rolled their eyes, and a few said they didna€™t know and suggested I talk to a€?that guy over there.a€? The guy over there did not know either. The exception allows for non-metallic flue materials to not be required to be listed for the application if the manufacturer of the equipment certifies their equipment for use with non-metallic flue materials.
This dilution air is often drawn into the water heater through openings in a hood on top of the water heater.
They should require other more suitable high temperature non-metallic pipe materials or stainless steel flue materials. They should issue a recall letter to every business and every homeowner that has PVC flue pipes installed on equipment designed for non-metallic flue pipes if the equipment does not have temperature sensors or limit switches in the discharge flue that shuts down the burner if the flue gas temperatures exceed 140 F.

Recent weather events in Southern states have shown that ambient air conditions can get close to 115 F or higher. He has served as chairman of the International Residential Plumbing & Mechanical Code Committee. The premise was simple: Put together a pool of innovative design and manufacturing talent and provide clients with a total service at a national level. The results of the BMA business doctrine carried out by a collective talent pool have been tremendous. Bill Moore and Associates is a multidisciplinary retail sign and environmental graphic design-build firm that works for prestigious and high profile national and regional retail clients. Albany's small town atmosphere in direct proximity to cultural centers, such as Berkeley and San Francisco, offers the ideal context for the 21st century career. He is responsible for researching and maintaining a library of vendor contacts and material specifications to ensure that the signs BMA installs are fully functional and looking good 10, 15, even 20 years later.
The spectrometer is shown configured in the perpendicular plane, the electron gun being placed in the vertical position with respect to the analysers which span the horizontal detection plane.
The electron source is a heated tungsten hairpin filament heated by passing around 2A of DC current through the filament. The saturated gain of these devices yields around 1E8 electrons in the output current pulse for a single electron which enters the input cone. This allows the analyser to roam over a complete 360 degrees of the detection plane when in this geometry (apart from the position where the analysers would clash wth each other). The analysers are then adjusted for maximum signal count and the procedure is iterated until a maximum is found. The dark noise count is also reduced when cooled, however since the reduced cathode PMT only produces dark counts of less than 20Hz at room temperature, this is not necessary during routine operations.
The 1.82M resistor was chosen to optimise the single photon counting efficiency of the tube. It is not found that these solder connections significantly affect the ultimate vacuum pressure in the system. Isolated DC supplies to these amplifiers is obtained from a standard +15V supply, the circuit diagram being given in figure 8.
The power supply to these TTL buffers is derived from the rate-meter supplies via 7805 5V regulators located internally.
This supply boosts the current without changing the main supply, thus ensuring supply stability before and after the electron gun is tuned. Whether you are storing small parts, tools, or medium size items, modular steel drawer cabinets will increase productivity and protect inventory from dust and pilferage.
In these (now common) types of installations we strongly recommend the replacement of PVC vent with a chimney liner made from a stainless steel alloy such as AL29-4C which is specifically made for venting condensing heating systems and usually comes with a lifetime guaranty (from many manufacturers) against corrosion in that type of application.
A maintenance man for the university said that some really bad pipes had come apart at the fittings and melted.
I called the manufacturer of the PVC pipe in this case and asked the representative a few questions about using PVC pipe as a combustion flue for fuel gases. Just because PVC works in new installations does not mean that a condition cannot occur in which scale builds up over a short time in hard water areas and causes high flue gas temperatures.
There are serious consequences with carbon monoxide asphyxiation and fire that cannot be ignored. If a water heater is set to store water at 140 F to minimize Legionella bacteria growth, the flue gas temperature will be about 160 F when the heater is new.
The boiler manufacturer that recommended using PVC pipe as flue material was a target of the liability claim by surviving family members. PVC pipe is not listed and labeled as a combustion flue pipe material, as noted in the piping manufacturera€™s notes above, yet manufacturers of the water heaters and boilers seem to be avoiding the issue, and they continue to recommend the use of PVC flue venting in their installation instructions. The ULC S636 standard allows the material to exceed the limit for CPVC piping by 10 degrees Fahrenheit. I hope the industry can develop a standard to allow low cost, high temperature plastic materials. In this case, it appears that they were lobbying the readers of Plumbing Engineer on behalf of the manufacturers of fuel burning appliances such as water heaters, boilers and furnaces that are recommending use of PVC pipe for venting combustible gases. The caller went over some of the comments that were addressed in the article and explained that a woman had become seriously ill and permanently disabled from what is believed to be exposure to the combustion gases from two failed PVC plastic flue vent pipes in her home. The two PVC flue vents were connected to two water heaters that were piped together in the garage of a three-story townhome.
Apparently, the ambient air had a cooling effect on the pipe in exposed areas; that is why the exposed pipe was a lighter brown color.
The water heater manufacturer's literature recommended the use of PVC pipe and made no mention of system design temperature limitations or installation requirements for the PVC flues with respect to the location in a concealed space or adjacent to insulation. There was black mold throughout the floor space and on the exterior walls, where the wood structure and siding was rotted.
Low oxygen levels combined with elevated CO levels can be a deadly combination and can lead to brain damage. The maximum temperature setting for residential water heaters is 160 F, for commercial water heaters it is 180 F and for boilers it is 200 F, all above the maximum recommended PVC temperature of 140 F. So, if a water heater is set at 160 F and the thermostat allows the fluid temperature to overshoot the set point by about 10 degrees F plus or minus, the flue gas temperatures on a very efficient residential water heater would be higher than 170 F. They have recently tentatively agreed that the minimum storage temperature for water heaters should be 140 F in order to make sure that all parts of the domestic hot water system are well above the ideal growth temperatures for Legionella. When galvanized steel flues develop rust holes, people may start suffering from carbon monoxide poisoning. He then goes on to mention that AHRI uses the ANSI Z21 series of standards for appliance testing as the basis for acceptance of PVC flue piping.
In this condition, enough water can be flushed through the water heater or boiler to keep the water temperatures low enough to keep the flue gases cooled and relatively low. I would like to see a manufacturer provide a copy of testing and certification for any fuel burning appliance with PVC pipe testing for these conditions.
An often stated rule of thumb is that boiler efficiency can be increased by 1% for each 15% reduction in excess air or 40 F reduction in the stack gas temperature.
The flue gas temperatures rise, and the burner stays on longer in order to transfer heat through the scale and the heating surface. A few said, a€?Yeah, everyonea€™s using PVC now, and I have never heard of a failure.a€? Not one manufacturer could produce any technical data or a report addressing the temperature limits that the fuel burning appliance manufacturers are required to have for non-metallic PVC flue materials. They are claiming that they have a certification test, but the test that the AHRI representative cited does not test for the proper temperature limits for PVC pipe.
It is a function of the size of the combustion air fan which, in many cases, is located on the flue outlet so there can be a negative pressure zone on top of the water heater where dilution air can be drawn into the flue. They should also address all of the thermal expansion, ambient cooling and stress cracking issues with non-metallic systems.
With combustion gases close to 200 F, you would need a pretty big combustion air opening to bring in enough 115-degree cooling air to bring the temperature down to a safe level.
The only place that PVC is addressed is in Table XII, which gives the maximum allowable temperatures of typical nonmetallic vent material used in water heaters. Our office resources and policies provide for an innovative, supportive and progressive working environment, while the opportunity to travel throughout the US consistently refreshes one's attitude and perspective. The electron gun is a two stage non-energy selected gun that produces an incident electron beam current of up to 4 microamps at an incident energy from around 30eV to 300eV. The 470k resistors bias the dynodes to achieve saturation of the current pulse at the output of the tube, hence biasing the tube for single photon counting applications.
This was found to be necessary to eliminate problems associated with current loops from the 20A peak motor current feeding the common point of the logic circuitry. We also recommend moving the intake vent out of the chimney to prevent the corrosive by-products of combustion from being drawn into the heating system intake which can actually damage the heating system over time. He was quite familiar with this issue and emailed me a link to the companya€™s technical manual, which discussed all of the physical and temperature limitations of the piping.
Most boiler and water heater manufacturers list other ways of venting with stainless steel, but they seem to always recommend the cheapest way in their literature, in an attempt to make the boiler seem more affordable to consumers. I believe that we will see a few code changes on this topic in the next round of code hearings. The plumber had found that the flue pipes in separate joist spaces were completely separated and that what appeared to be carbon monoxide poisoning and oxygen deprivation may have caused the womana€™s illness; she apparently has brain damage and is now permanently disabled.
In the floor cavity, the temperature on both sides of the flue pipe wall was the flue gas temperature. It also did not list any temperature limitations for a maximum thermostat setting on the water heater for systems using PVC flues. Boiler water temperatures are typically in the 180 to 200 degree range, because most HVAC hydronic heating coils are designed for these higher water temperatures in order to reduce the heating coil sizes and to reduce the gpm pumping requirements.
The committee is also looking at minimum hot water return temperatures above the ideal growth temperatures for legionella bacteria. These standards only test for deflection at 157 F, although he claimed that they test to 158 F. The test does not allow real-world conditions in which commercial water heaters reach the shut-off temperature of 180 F.
Numerous documents, research reports and papers address the insulating effects of scale formation on the heat transfer surfaces and the waste of energy associated with scale on heating surfaces. Energy losses and increased flue gas temperatures are a function of scale thickness and composition. There are acceptable non-metallic flue materials such as high temperature polypropylene and new, high temperature plastics that have higher temperature ratings than PVC. The dilution air imposes an additional CFM demand on the unit that is not covered in the manufacturera€™s installation data. A consensus standard for non-metallic flue venting systems is really needed now if they are going to continue to promote the PVC material. As scale builds up and the heater efficiency falls off, the flue gas temperatures can easily increase to over 350 degrees F. There is no justification for the 157-degree temperature, which exceeds the piping manufacturera€™s temperature rating. The decision to use PVC pipe for venting flue gases is purely a monetary decision; it totally disregards public health and safety.
Our eclectic, collaborative team is composed of architectural graduates, graphic designers and fine artists.
The analysers are identical, and consist of a 3-element electrostatic lens focussing the interaction region onto the entrance of a hemispherical electrostatic energy analyser. The Anode deflector pair corrects for any misalignment of the filament emission point with respect to the axis of the electron gun.
Even though PVC pipe should not be confused with other non-metal (plastic) vent products that some companies are manufacturing such as polypropyIene vent systems, these other non-metal (plastic) vent products should still never be put in a multi flue chimney that vents a fireplace or solid flue appliance because those types of non-metal vent products are still not designed for use near such high temperatures and this is an application that manufacturers dona€™t even test.
The water heater had scaled up due to minerals in the water supply; this caused the flue gas temperatures to rise, which created the noted problems. Even if someone had their water heater set at 120 F, with scaling, the flue gas temperatures can rise well above 300 F. Wherever the pipe was near a floor joist or near insulation, the piping appeared to be darker in color. The PVC flue pipe separations above the drywall ceiling allowed products of combustion, including carbon monoxide and water vapor, to vent under positive pressure into the house over several years. The broken PVC flue pipes caused the plumbing contractor to wonder whether the building occupants had experienced any symptoms of carbon monoxide poisoning. When this standard is published, storage type water heaters will have minimum storage temperatures of 140 F or higher; flue gases are typically much hotter than the water temperature.
Stainless steel flues are an option but, compared to galvanized steel or PVC plastic, they are very expensive. The insulating effect of scale on water heater and boiler heating surfaces results in increased flue gas temperatures.
The result is overheating of the water heater or boiler tube metal, tube failures and loss of energy efficiency, which is commonly diagnosed by an increase in flue gas temperature. There is rarely manufacturera€™s data on what the fan CFM is and how that affects the combustion air requirements for the water heater or appliance. The International Fuel Gas Code exemption for non-metallic flue pipe materials is not safe and, in my opinion, should be repealed as an emergency code change. To be accurate, just enough hot water should be flowed to cause cold water to enter the bottom of the heater and cause the burner to come on; then the flow of water should be shut off until the burner shuts off.
Bill Moore and Associates has been in the retail sign and design business for over 35 years. The Chamber is lined internally with 3mm thick mu-metal, and a mu-metal cylinder encloses the chamber externally as shown.
The electrons selected in angle and energy are amplified using Mullard 919BL channel electron multipliers. The defining apertures limit the pencil and beam angles of the electron beam following focussing by lens 2 onto the interaction region. The load is set by the 50W resistor across the anode to the HT feed, the pulse being decoupled to ground via the 1nF capacitor. For more information on whether PVC should even be used at all to vent flue gases (never mind in a double flue chimney) I suggest reading the following two articles from Plumbing Engineer Magazine, which is a leading publication in the heating industry. Boiler thermostats or burner controls are generally limited to 200 F, commercial water heater thermostats or burner controls to 180 F and residential water heater burner controls to 160 F, and all can overshoot by several degrees. These symptoms include the following: headaches, dizziness, nausea, flu-like symptoms, fatigue, shortness of breath, impaired judgment, chest pain, confusion, depression, hallucinations, agitation, vomiting, abdominal pain, drowsiness, visual changes, fainting, seizures, memory and walking problems. High-temperature plastic flues were used briefly in Canada but were recalled after a series of flue failures. If there are two appliances located in the same closet and both rely on cooling air mixing with the combustion gases, where are the additional requirements for combustion air openings and dilution air requirements? I also feel that manufacturers should immediately discontinue recommending the use of PVC pipe for venting combustible gases. This reduces the magnetic field at the interaction region to less than 5mG, an acceptable level for the electron energies used in this experiment. The interaction region defined by the interaction of the gas target beam and the electron beam is focussed onto the photocathode of an EMI 9789QB photomultiplier tube via a lens, 450nmA±50nm optical filter and defining aperture.
Placement of the apertures ensures that the beam angle is close to zero degrees at the interaction region over a wide range of energies, whereas the aperture opening reduces the pencil angle to around A±2 degrees over this energy range.
It is my hope that the building code will soon ban the use of PVC and plastic vents in multiple flue chimneys where melting of the heating system vent pipe by the use of another flue is a possibility. As scale builds up on the heating surfaces, the scale insulates the flue gases from the hot water in the system, causing the flue gas temperatures to increase.
Not knowing her condition, the plumber contacted the homeowner and asked whether she had experienced any of these symptoms.
In the beginning, flues were cobbled together out of whatever flue materials they could find and PVC was included even though it is not rated for the system temperatures commonly experienced in flues.
Each time the water heater cycles, the hot water rises to the top of the heater; each consecutive cycle overheats the water in the top of the heater and, with each consecutive stacking cycle, the water temperature will be 5 to 10 degrees hotter. If a closet or space is designed for only enough air for the combustion requirements, and the hood is drawing many times more cubic feet of air than the combustion air requirement from the same space, the burner can starve, and improper combustion can cause soot conditions that will increase flue temperatures. Today, Skip and Alastair lead an organization that combines talent from the fields of graphic design, architecture and the sign industry. The target gas effuses from a 0.6mm ID hypodermic needle constructed from platinum iridium alloy.
The 10MW safety resistor prevents the output charging up to a high voltage if the feed is disconnected. The deflectors between the apertures correct for space and surface charge beam variations inside the field free region, whereas the final deflectors allow the beam to be steered onto the interaction region defined by focussing a 1mm aperture in front of the photomultiplier tube onto the gas target beam.
Water heater and boiler manufacturers began listing the ASTM standard numbers for PVC DWV pipe and PVC water pipe as the material to use for venting their appliances. Improper airflow to the closet or room containing the high efficiency equipment can starve the dilution air ports reducing the cooling capability of the dilution air that is intended to help cool the combustion gases. The electrons passing through the interaction region which are not scattered are collected in a Faraday cup opposite the electron gun. The gun, photomultiplier tube, gas hypodermic and Faraday cup all rotate on a common yoke with an axis through the centre of the horizontal detection plane, allowing all geometries from the perpendicular plane to the coplanar geometry to be accessed.

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