gas oven safety valve leaking free sample

Pilot ignition systems use a flame sensing element to sense whether the pilot is lit and the safety valve can open. The sensing element sits right in the pilot flame.

Just exactly where the sensor sits in the pilot flame is important. (See figure 6-A) If the sensing bulb is not in the right part of the flame, or if the pilot is adjusted too low or too high, it will not get hot enough and the safety valve will not open.

When two dissimilar metals (for example, copper and steel) are bonded together electrically, and then heated, they generate a tiny electrical current between them. The voltage is very small, measured in millivolts. This is the basis for a millivolt oven ignitor system. All that"s needed is a safety valve that will sense this tiny voltage and open the valve if it is present. If the pilot is out, there is no millivoltage and the safety valve will not open. See figure 6-B.

If the burner in a millivolt system will not start, typically the problem is the gas valve. Occasionally the problem might be the pilot generator or thermostat. The thermostat in these is just a temperature-sensitive on/off switch. To test, turn it on and test for continuity.

If that doesn"t work, we have a minor dilemma in determining whether the problem is the pilot generator or the safety valve. The dilemma here is that the voltages are too small to be measured with standard equipment. VOM millivolt adaptors cost nearly as much as the pilot generator itself. And the safety valve, which is usually the problem, costs twice as much as the pilot generator. So usually you just replace either or both of them. But don"t forget they are electrical parts, which are non-returnable. What I recommend is just to replace the gas valve first; that usually will solve the problem. If not, replace the pilot generator. You just ate a gas valve, but trust me, you"d have bought one sooner or later anyway.

When installing the pilot generator, screw it into the safety valve finger tight, plus 1/4 turn. Any tighter than that and you can damage the electrical contacts on the valve.

In some systems the sensor is a liquid-filled bulb, with a capillary to the safety valve or flame switch. When the liquid inside heats up, it expands and exerts pressure on a diaphragm, which opens the valve or closes the switch.

It is important to know that these sensor bulbs do not cycle the burner on and off to maintain oven temperature. That is the thermostat"s function. It has a sensor bulb too, but it senses oven temperature, not pilot flame. The only function of these pilot sensing elements is to prevent gas flow to the burner if the bulb does not get hot enough to assure burner ignition.

In flame switch systems, hydraulic pressure from the capillary physically closes the switch, which completes an electrical circuit to the safety valve. The safety valve is electrical and operates on 110 volts. See Figure 6-D. If the pilot is out, the flame switch does not close and the 110 volt heating circuit is not complete, so the safety valve will not open.

Some of these direct-pressure (hydraulic) systems use a two-level pilot. The pilot stays at a very low level; not even high enough to activate the safety valve. This is called the constant pilot, or primary pilot. Gas for the primary pilot may come from either the thermostat or directly from the gas manifold.

When the thermostat valve is turned on, the pilot flame gets bigger, heating the sensor bulb, which activates the safety valve (hydraulically) and the burner ignites. This is called the heater pilot, or secondary pilot. Gas for the secondary pilot comes from the oven thermostat itself.

When the gas oven reaches the correct temperature setting, the thermostat drops the pilot flame back to the lower level, the safety valve closes and the burner shuts off. See figure 6-E.

If you do have a good strong pilot that engulfs the pilot sensing bulb with flame, then odds are that the sensing element and/or whatever it is attached to are defective. If it is a flame switch, replace the flame switch. If it is a safety valve replace that.

In a two-level pilot system, remember that the main oven thermostat supplies the secondary pilot with gas. So if you cannot get a good secondary pilot the problem may be the pilot assembly, or it may be the thermostat. If you do get a good secondary pilot, you"re back to the sensing bulb and safety valve.

Spark ignition systems use a spark module to generate a pulsing, high-voltage spark to ignite the gas. The spark module is an electronic device that produces 2-4 high-voltage electrical pulses per second. These pulses are at very low amperage, measured in milliamps, so the risk of shock is virtually nil. But the voltage is high enough to jump an air gap and ignite gas. The spark ignition module is usually located either under the cooktop or inside the back of the stove. The same module is used for both the surface burner ignition and the oven burner ignition.

However, the spark is not certain enough to light the oven burner, and the gas flow is too high, to rely on the spark alone. Remember, in an oven, before the safety valve opens, you need to be assured of ignition. So the spark ignites a low-gasflow pilot, and then the safety valve opens only when the pilot is lit.

This is the same two-level pilot system described in section 6-2(b), with a few important exceptions. The constant or primary pilot does not stay lit when the oven thermostat is turned off. It does, however, stay lit the whole time the oven thermostat is turned on.

When the gas oven is turned on, a switch mounted to the oven thermostat stem signals the spark module. These are the same switches as shown in section 5-3.

When the thermostat calls for more heat in the oven, the heater or secondary pilot increases the size of the pilot flame, which heats the sensing bulb, which opens the safety valve and kicks on the burner.

Yup, this ol" boy"s got it all. Spark ignition, a pilot, a flame switch and TWO - count "em - TWO safety valves; one for the pilot and one for the burner. (Figure 6-H)

The operation is actually simpler than the diagram looks. When you turn on the oven thermostat, a cam on the thermostat hub closes the pilot valve switch. This opens the 110 volt pilot safety valve and energizes the spark module, igniting the pilot. As in the other spark system, the pilot flame provides a path that drains off the spark current, so the ignitor stops sparking while the pilot is lit. As long as the oven thermostat is turned on, the pilot valve switch stays closed, so the pilot valve stays open and the pilot stays lit.

When the pilot heats the pilot sensing element of the flame switch, the flame switch closes. This completes the 110 volt circuit to the oven safety valve, so the valve opens and the burner ignites.

When the oven temperature reaches the set point of the thermostat, the thermostat switch opens, breaking the circuit and closing the oven safety valve, and shutting off the burner.

Now that you know how the system works, first look to see what is not working. When the oven thermostat is on, and there isn"t a pilot flame, is the electrode sparking? Is there spark, but no primary pilot? Is the primary pilot igniting, but not the secondary? Is there sparking after the thermostat is shut off?

(The pilot may or may not light, but the main burner is not lighting) Remember that the thermostat supplies the pilot with gas in these ovens, and only when the thermostat is on. So if you don"t have a primary and secondary pilot flame, odds are the problem is the pilot orifice or oven thermostat. Try cleaning the pilot assembly and sensor bulb as described in section 6-5. If that doesn"t work, adjust the secondary flame a little higher. If that doesn"t work, replace the pilot assembly.

If you do have a good strong secondary pilot that engulfs the pilot sensing bulb with flame, then odds are that the oven safety valve (or flame switch, whichever is attached to the pilot sensing bulb in your system) is defective. Replace the defective component.

Something is wrong with the high-voltage sparking system. If you are in a hurry to use your oven, you can turn on the oven thermostat, carefully ignite the primary pilot with a match and use the oven for now; but remember that the minute you turn off the thermostat, the pilot goes out.

Are the cooktop ignitors sparking? If so, the spark module is probably OK. What typically goes wrong with the sparking system is that the rotary switch on the valve stops working. Test continuity as described in section 5-3(a). If that isn"t the problem, check the electrode for damage and proper adjustment. The spark target (the nearest metal to the electrode) should be about 1/8″ to 3/16″ away from it, (about the thickness of 2-3 dimes) and directly across the primary pilot orifice. Replace or adjust the electrode as appropriate. When replacing, make sure you get the right kind of electrode (there are several) and do not cut the electrode lead; follow it all the way back to the spark module and plug the new lead into the proper spark module terminal.

Most modern appliances have safety features built in, but your gas oven safety valve is arguably the most important. If an electrical appliance malfunctions, it can cause a fire, but a misfiring gas oven could potentially blow up your house. You don"t ​really​ need to know how the safety mechanism works to use your oven, but you may find that it gives you some extra peace of mind.

Broadly speaking, there are two ways a built-in safety mechanism can work. One option is that it remains "open" by default and to shut off if certain conditions are met. That"s how fuses and circuit breakers work in an electrical circuit: Ordinarily, the electricity is free to flow, but if the current grows too large, the fuse or breaker will blow and cut off the circulation of electricity.

The other option is for your safety mechanism to be "closed" by default and allow a device to operate only when the correct conditions are met. That"s how a gas oven safety valve works. Gas ordinarily is prevented from flowing, and if the valve is working correctly, it opens only when you want to light your oven.

Many gas stoves use what"s called a "hot surface igniter," a bar or element (similar to the ones on your stovetop) that gets hot enough to ignite the gas on contact. Gas oven safety valves on stoves with this type of ignition system take a couple of different approaches.

In one approach, a bimetallic strip operates the valve. It harnesses a simple scientific principle: Metals expand and contract at different rates when they"re heated and cooled. If you bond two suitable metals together in one strip, that strip will flex to a predictable degree as the temperature goes up and down. Wall-mount thermostats often use this principle, as do analog oven thermometers and the thermometer in the lid of your gas grill.

As appliance-repair website PartSelect explains, turning on your gas oven causes electricity to flow into the heating element of your hot surface igniter. As the igniter heats up, it warms a bimetallic strip inside your gas oven safety valve. When the igniter reaches its operating temperature, the bimetallic strip opens the valve and allows the gas to flow, igniting as it crosses the heated surface.

According to heating-equipment vendor Anglo Nordic, gas oven safety valves use a variation of that principle to operate. In these stoves, the flow of electrical current through the hot surface igniter becomes the control mechanism. The igniter"s bar is made of a material that offers less and less resistance to electricity as it heats. When it reaches the temperature required to ignite the gas, its resistance becomes low enough to trip the safety valve and open the flow of gas.

More modern ranges use an electrical igniter. When you turn on your oven, the gas begins flowing immediately, and it sends an electrical current to a piezo electric igniter. The current makes the igniter spark (like the manual igniter on your gas grill) and lights the oven"s burner. In this case, the safety valve works in the opposite way: An electronic sensor checks for the heat caused by ignition after a few seconds, and if it"s absent, it will close the valve and shut off the flow of gas.

It"s worth pointing out that not all gas ovens have a safety valve in the conventional sense. Older stoves simply use a pilot light, a small but constant flow of gas, which, in turn, feeds a small, candle-like flame. You essentially ​are​ the safety mechanism in this system: It"s up to you to check that the pilot is lit. When you turn on the gas manually, the small pilot flame ignites the main flame. It"s a mechanically simple system, which makes it durable, and for that reason, you"ll still see it used on commercial restaurant ranges, which must stand up to decades of heavy use.

Safety is of the utmost importance when dealing with pressure relief valves. The valve is designed to limit system pressure, and it is critical that they remain in working order to prevent an explosion. Explosions have caused far too much damage in companies over the years, and though pressurized tanks and vessels are equipped with pressure relief vales to enhance safety, they can fail and result in disaster.

That’s also why knowing the correct way to test the valves is important. Ongoing maintenance and periodic testing of pressurized tanks and vessels and their pressure relief valves keeps them in working order and keep employees and their work environments safe. Pressure relief valves must be in good condition in order to automatically lower tank and vessel pressure; working valves open slowly when the pressure gets high enough to exceed the pressure threshold and then closes slowly until the unit reaches the low, safe threshold. To ensure the pressure relief valve is in good working condition, employees must follow best practices for testing them including:

If you consider testing pressure relief valves a maintenance task, you’ll be more likely to carry out regular testing and ensure the safety of your organization and the longevity of your

It’s important to note, however, that the American Society of Mechanical Engineers (ASME) and National Board Inspection Code (NBIC), as well as state and local jurisdictions, may set requirements for testing frequency. Companies are responsible for checking with these organizations to become familiar with the testing requirements. Consider the following NBIC recommendations on the frequency for testing relief valves:

High-temperature hot water boilers (greater than 160 psi and/or 250 degrees Fahrenheit) – pressure test annually to verify nameplate set pressure. For safety reasons, removal and testing on a test bench is recommended

When testing the pressure relief valve, raise and lower the test lever several times. The lever will come away from the brass stem and allow hot water to come out of the end of the drainpipe. The water should flow through the pipe, and then you should turn down the pressure to stop the leak, replace the lever, and then increase the pressure.

One of the most common problems you can address with regular testing is the buildup of mineral salt, rust, and corrosion. When buildup occurs, the valve will become non-operational; the result can be an explosion. Regular testing helps you discover these issues sooner so you can combat them and keep your boiler and valve functioning properly. If no water flows through the pipe, or if there is a trickle instead of a rush of water, look for debris that is preventing the valve from seating properly. You may be able to operate the test lever a few times to correct the issue. You will need to replace the valve if this test fails.

When testing relief valves, keep in mind that they have two basic functions. First, they will pop off when the pressure exceeds its safety threshold. The valve will pop off and open to exhaust the excess pressure until the tank’s pressure decreases to reach the set minimum pressure. After this blowdown process occurs, the valve should reset and automatically close. One important testing safety measure is to use a pressure indicator with a full-scale range higher than the pop-off pressure.

Thus, you need to be aware of the pop-off pressure point of whatever tank or vessel you test. You always should remain within the pressure limits of the test stand and ensure the test stand is assembled properly and proof pressure tested. Then, take steps to ensure the escaping pressure from the valve is directed away from the operator and that everyone involved in the test uses safety shields and wears safety eye protection.

After discharge – Because pressure relief valves are designed to open automatically to relieve pressure in your system and then close, they may be able to open and close multiple times during normal operation and testing. However, when a valve opens, debris may get into the valve seat and prevent the valve from closing properly. After discharge, check the valve for leakage. If the leakage exceeds the original settings, you need to repair the valve.

According to local jurisdictional requirements – Regulations are in place for various locations and industries that stipulate how long valves may operate before needing to be repair or replaced. State inspectors may require valves to be disassembled, inspected, repaired, and tested every five years, for instance. If you have smaller valves and applications, you can test the valve by lifting the test lever. However, you should do this approximately once a year. It’s important to note that ASME UG136A Section 3 requires valves to have a minimum of 75% operating pressure versus the set pressure of the valve for hand lifting to be performed for these types of tests.

Depending on their service and application– The service and application of a valve affect its lifespan. Valves used for clean service like steam typically last at least 20 years if they are not operated too close to the set point and are part of a preventive maintenance program. Conversely, valves used for services such as acid service, those that are operated too close to the set point, and those exposed to dirt or debris need to be replaced more often.

Pressure relief valves serve a critical role in protecting organizations and employees from explosions. Knowing how and when to test and repair or replace them is essential.

This article describes how to find gas leaks on LP or natural gas piping, regulators, or appliances, and it provides free sample draft home inspection report language for reporting defects in oil and gas piping at residential properties.

This article series provides descriptions and photographs of unsafe gas piping, indications of unsafe or improperly operating gas appliances, gas meters, and other gas installation defects are provided.

These questions & answers about tools & procedures used to test gas piping and fittings for leaks were posted originally at GAS LEAK DETECTION, LP / NG - you will want to see the guidance there.

If you smell gas you should leave the building immediately and should do so without doing anything that could create a spark such as operating a light switch or telephone.

This indeed sounds really annoying, I agree. The gas company is locking out the meter because they think the system the gas system unsafe. Nothing in your message tells us what the gas company found and is worried about, though presumably it"s a gas leak.

It is possible to pressure test a piping system that is not in use, something your plumber could do. But what I would do at this point is call the gas company to ask them how they want you to proceed.

So the gas company won"t turn the gas on, and put a bolt in it. Then my plumber says he can"t detect the gas if it"s turned off, and he can"t turn it on. I am clueless on what to do.

By completely isolating all of the building gas piping, you can watch the meter and if it continues to run then you know there is actually a gas leak at the meter itself. That would be a reason to ask for help from your gas company.

If there is no gas usage when the main valve is turned off, and usage resumes when the main gas valve is turned on, then there is a leak to be found in the building piping, valves, or in one of the appliances.

At that pointI would follow the gas line from the meter onwards, and one by one check off every length of piping and every connector to each shut off valve.

For example, I have found that soap testing, while traditional and a perfectly good gas leak testing method, can be difficult to perform with complete accuracy.

While all the cocks of gas are off but still the meter is showing reading. We have check all points with soap aolution they are not liking is it possible that whole internal house fittings in cements could be liked if then whats a solution. Plz tell me

I don"t quite follow what"s happening from your brief text, but I suspect that your gas company thought that there was a gas leak somewhere inside your home, and to prevent blowing up the home they shut off your gas supply, perhaps also removing their meter at the same time.

Watch out: if you smell gas do not do anything that could cause a spark or flame as that can cause a fatal explosion: get everyone to leave the home and call emergency services from a distant, safe location.

After smelling gas in the garage, the gas company found leaks in two of the 21 lines and proceeded to turn off the gas to the entire building. After the leaks are repaired, what test procedures should be followed before the gas can be turned back on? The system has shutoff valves for each metered line.

In my experience very small leaks at the shutoff valves on LP tanks are quite common and might even be appreciated by the gas companies as long as the leak is both outdoors and small enough as to avoid a fire or explosion. In some communities an owner has probably to make a fuss to get a gas company to find and fix such leaks.

The legal question of who pays for lost gas fuel or other losses, assuming the total cost is big enough to be worth the heartache, expense, and delays, is one to discuss with your attorney, with your lease contract in-hand.

If a service tech comes and inserts a t connector to be able to switch between two lp tanks, one leased and one owned and does not test the valve on the leased tank while it was in the closed position( or on position either) and it causes a loss of lp from the private tank who is liable for the lost fuel?

The tech is "sort of" right. I have confirmed by field test and by speaking with other inspectors and plumbers that a *small* gas leak at the gas control/valve on gas-fueled water heaters is so common that I"m cautious about calling it out. We have replaced a valve only to find the very same leak at the new one.

- even if the only detectable leak point is the case seam on the gas control, the leak seems larger than common and risks a worsening and thus dangerous condition.

I am a home inspector using a Tif 8800, I detected a leak (propane)at a gas valve on a water heater, detector was set at a slow tick, when I found the leak the detector screamed and all six lights lit up. The technician told the home owner this is normal for this valve. Is this right?

On 2015-09-26 12:05:36.085898 by I had a 1mm sq hole ina domestic Gas pipe that went undetected for 4 years if on average the gas heating was on for 1 hour every day how much gas would i have lost at 1/4PSI

I had a 1mm sq hole in a domestic Gas pipe that went undetected for 4 years if on average the gas heating was on for 1 hour every day how much gas would i have lost at 1/4PSI

The gas will dissolve the oil in the galvanizing. If the ceiling is drywall and not readily accessible, the plumbers should make sure the leak is not in an exposed line first before tearing out ceiling. It may just be a flare nut that needs tightening or a leaky regulator on an appliance.

They didn"t identify where but they turned off gas valve and said to have a heating professional find & fix it. TWO visits by plumber and heating specialist failed to find a leak with both a pressure test and a gas meter.

However we still smell gas in the heater area but it appears to be intermittent. Is this possible? I"m concerned about the safety of my family. Should we be in the home? What steps can we take?

Sounds as if you need to get the gas company back to perform more testing using combustible gas analyzers not just a pressure test. How those instruments are used and how carefully and how thoroughly makes a lot of difference in reliability of the result.

Unless the gas leak is due to an improperly-tightened fitting or a poorly-made flange on gas piping that can be corrected, you"ll have to replace the valve. Sorry. NO external fix such as a patch, tape, or goop would be safe.

Any piping or gas line can be repaired using proper fittings and safety measures (like turning off the gas supply and testing the repair for leaks), but the question of how much line needs replacement should be decided *after* an assessment of the condition of the rest of the piping; if it"s deteriorated it"s unsafe and thence patching an immediate leak is inadequate and also unsafe.

I have a gas leak in my trailer (propane). I took it back to the dealer, who said they could find nothing.After going through 7 tanks in a season, with most of the cooking on a separate BBQ, something is wrong.

If I shut the tank off for a couple of days then turn it on, you can hear a gush of gas coming from the tank; re-filling the plumbing. This tells me there is a leak. I plan on putting on a new tank, and weighing it. Turn on the valve when I am not using the trailer, and weigh that tank daily.

Kenneth we have not found a recommended replacement age for gas piping, and if there were to be one developed it would have to consider variations in pipe material. Black iron pipe is often in use for more than 50 years.

I have a gas piping system installed at my small restaurant, the materials used for the pipes were schedule 40 BI pipes and the installation is about 5 years now, I have checked the system for leaks, but so far, I didn"t find any leaks on the system.

I ran all new black iron pipe in my house for a remodel. I pumped 100 psi in the pipes and had a couple of small leaks. I fix those, but still get a 10 pound drop over night. Since the natural gas pressure is so low should I worry?

First you"ll want to have an expert trace the odor to its apparent source. Gas like odors may be from an LP or natural gas supply - most people can recognize the odor of the mercapatan odorant placed in gas supplies but not everyone.

Third: wind or other conditions can make tracking down a gas leak tricky, and unfortunately I"ve found that the expertise of gas company field people varies from really expert to inept. But the gas company has a huge interest in avoiding a catastrophe.

Both independent inspectors and gas company employees should be equipped with gas leak detection instruments (not just a cigarette lighter, nose, or soap solution) that can help pinpoint the presence of a leak.

I have had intermittent gas smell near the front door of my house over the past ten years or more. The gas meter is halfway around the house from the front door. The gas company has been out here on four occasions and has found no leak. T

oday, my plumber again mentioned the odor and suggested that it may signal a danger. What to do if the gas company is again unable to find a leak???? Thanks.

To inspect gas piping for leaks when gas service has ben turned off one would begin with a visual inspection of the piping and connections, but that process alone would be inadequate. The gas piping system will need to be tested under pressure, using air or an inert tracer gas.

Monitor for a pressure drop when using air; use a tracer gas such as used in HVAC testing. Test pressures? We will need to check the AGA specifications on leak testing.

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Simply put, a valve-proving system is a safety control used on gas fuel-fired industrial heating equipment that verifies the effective closure of two safety shutoff valves in series by detecting gas leakage.

In the 1950s and "60s, as the gasification of Europe began, the European code bodies adopted the U.S. safety standards and practices for gas combustion. Europe simply had little experience with natural gas at that time, and the U.S. safety practices, which applied redundant safety controls, were adopted. As a result, Europe adopted the "double block and vent" and "proof-of-closure" concepts as a means to validate the prepurge cycle.

As Europeans gained experience with fuel-fired equipment, incidences occurred that illustrated the shortcomings of proof-of-closure switches and vent valves, which could allow the system to operate under unsafe conditions. This provided the impetus for European manufacturers to look for other solutions, and the concept of a valve-proving system (VPS) was introduced in Germany in the early 1970s.

The active valve-proving system detects gas leakage by verifying flow through an orifice of known diameter and proves both safety valves simultaneously (figure 2). The active valve-proving system confirms the effective closure of both safety valves by:

Starting an internal pump and simultaneously starting an internal timer. The pump pressurizes the volume between the two main safety valves using gas pressure from upstream of the first main safety valve.

If the differential pressure between the safety valves reaches approximately 0.5 psi over the inlet pressure within the specified time, both safety valves are proven closed. If the pressure between the safety valves fails to reach the overpressure level within the specified time, the valve-proving system detects a leak and locks out the system.

Rather than proving both safety valves at the same time, the passive valve-proving system proves each safety valve separately (figure 1). When proving the No. 1 main safety valve, the passive valve-proving system detects gas leakage by monitoring for pressure rise between both safety valves; and subsequently when proving the No. 2 main safety valve, it monitors for pressure decay between both safety valves. The passive valve-proving system may have its own auxiliary safety valves that bypass main safety valves, or it may simply cycle the main safety valves during valve proving. However, to illustrate the valve proving sequence, it is easiest to show auxiliary safety valves. During valve proving, the passive valve-proving system proves the effective closure of the No. 2 main safety valve by:Opening the No. 1 auxiliary safety valve and allowing upstream gas pressure to fill the volume between both main safety valves.

Essentially, the same process is repeated for proving the No. 1 main safety valve, but this time, the No. 2 auxiliary safety valve vents the volume between the main safety valves and the No. 2 pressure sensor monitors the manifold for pressure rise. If the No. 2 pressure sensor does not detect pressure rise within the specified time, the first main safety valve is proven closed.

A valve-proving system currently is used on gas-fuel-fired equipment in Europe, Australia, China, Russia and in South and North America (figure 3). The following codes and standards that apply the use of valve-proving systems can be used as reference:European Standard EN 746-2 for industrial thermoprocessing equipment.

In the United States, a valve-proving system can be used as an alternative to a vent valve in the following standards:NFPA 85 (when venting of gas is prohibited).

Also in the United States, a valve-proving can be used as an alternative to proof-of-closure in the following standards:Fuel-fired equipment insured by FM.

One major hazard with fuel-fired equipment is having an explosive mixture of fuel in an enclosed, or semi-enclosed, area that cannot safely relieve the expansion forces of the gas when ignited. Historically, the number of boiler and furnace explosions were reduced by requiring certain safety practices and incorporating certain safety controls into the fuel-fired equipment. This was done to provide an acceptable level of risk to the public.

For fuel-fired equipment, a high risk of incident occurs during burner lightoff. One important practice to reduce the risk of explosions is to prepurge the combustion chamber. The intent of prepurge is to remove all combustible gases from the combustion chamber before introducing an ignition source; the common four air-change prepurge is based on a worst-case scenario of having a burner chamber completely filled with fuel gas.

If both safety valves did not leak gas, there would actually be no reason to prepurge. However, loss experience has shown that safety valves can fail to close and can leak gas into the combustion chamber; therefore, the chamber is prepurged to provide redundant safety in the system in case both safety valves leak gas into the combustion chamber. The addition of proof-of-closure switches and/or a vent valve provides an additional level of safety to simply validate prepurge.

Before introducing an ignition source, prepurge should be validated. Validate does not imply guarantee but rather implies a high degree of confidence that the risk to introduce an ignition source in the combustion chamber is considered negligible. For example, a prepurge is not valid if the safety valves were wide open during prepurge.

To validate the prepurge, a combustion air switch verifies adequate airflow. In addition, there should be some means to verify that gas is not flowing into the combustion chamber at a rate such that prepurge is not able to remove enough gas from the chamber to remain far below the lower explosive limit (LEL) during ignition. A proof-of-closure switch on a safety valve provides a degree of confidence in the "validity" of the prepurge by verifying that the valve is in its fully closed position. A proof-of-closure switch on each safety valve provides even a higher degree of confidence.

A normally open vent valve mounted in between both safety valves also provides a degree of confidence in the "validity" of the prepurge. This valve prevents the buildup of pressure between the safety valves and thus minimizes gas leakage to the burner if both the No. 1 valve leaks and the No. 2 valve leaks in the closed position.

In the case that No. 1 valve and the No. 2 valve leak in the closed position, the vent valve mounted in between two safety valves provides a degree of validity to the prepurge. The vent valve minimizes the potential for leakage into the furnace by diverting any leaking gas to a safer location. Unlike a vent valve, the valve-proving system does not allow for ignition if either valve is detected as leaking, thereby validating the prepurge cycle. Furthermore, a vent valve will not interrupt the limit circuits; thus, ignition is still allowed. By contrast, a valve-proving system locks out the ignition sequence when a problem is detected.

Unlike a valve-proving system, a vent valve allows ignition under conditions when far more gas can leak to the burner. Instances when a vent valve would allow ignition include:Both valves, which have severely damaged valve seats, leak in the closed position.

A proof-of-closure switch validates prepurge by proving that the valve stem is in the minimum (closed) position. The valve stem position is related to the valve seat position. If a switch indicates that the valve stem is closed, there is a high degree of certainty that the valve seat is not leaking gas into the burner.

Similarly, a valve-proving system provides a high degree of certainty by directly verifying the position of both valve stems. If a valve stem does not close all of the way, the valve seat is not in contact with the valve disc, and the valve-proving system detects an open valve due to gas leakage. The valve-proving system also verifies the valve seats. If the valve stem closes 100 percent but the valve seats are damaged, a valve-proving system will detect a problem and prevent ignition.

A proof-of-closure switch does not detect problems with a valve seat but only verifies the position of the valve stem. Figure 4 shows a relationship between valve seat closure and valve stem closure. Illustrated is a 0.25 mm dia. wire inserted below the valve seat of an energized (open) valve. The valve then is de-energized (closed), and the valve stem fully closes while at the same time the valve seat does not. The amount of gas leakage due to the 0.25 mm dia. wire is detected by a valve-proving system but not a proof-of-closure switch.

The valve seat "bubble" test is an annual maintenance requirement for installed safety valves in most fuel-fired equipment standards and generally a requirement or recommendation of safety valve manufacturers. The allowable valve seat leakage rates on installed safety valves are determined by the safety valve manufacturer, who typically applies the same requirements as specified in the safety valve standard ANSI Z21.21/CGA 6.5. This standard is applied to new safety valves leaving the factory. The allowable rates for installed valves typically are not more stringent than ANSI Z21.21/CGA 6.5 requirements.

A valve-proving system is not designed to detect leakage rates less than or equal to the ANSI Z21.21/CGA 6.5 standard; it is designed to detect leakages above the ANSI Z21.21/CGA 6.5 standard. Therefore, a valve-proving system, which is intended to prove the effective closure of both safety valves by detecting leakage, is not currently an alternative to the annual valve seat bubble test.

Generally speaking, a valve-proving system"s detection limit is the maximum amount of gas leakage at which a prepurge can still be validated. A valve-proving system should take into account application-specific variables such as operating pressure, fuel gas type and the manifold volume. To simplify this, the European standard EN 1643, "Valve Proving Systems," adopts a maximum rate of 1.76 ft3/hr (50 l/hr) or 0.10 percent of burner capacity. In combination with a prepurge, this maximum rate still provides a high degree of certainty to allow burner ignition.

A common error in thinking is that a valve-proving system should detect leakage rates to the ANSI Z21.21/CGA 6.5 safety valve standard. This might be applicable if a valve-proving system were used as an alternative to the annual valve seat bubble test. However, no equipment standard requires a valve seat bubble test at every burner startup or shutdown.

A valve-proving system provides several safety benefits. It actively checks the integrity of both safety valves on every startup or shutdown. It detects safety shutoff valve problems that other safety controls ignore. It is equally safe with heavier-than-air fuels as with lighter-than-air fuels. Also, it gives the user at least some idea of the condition of the safety valve seat leakage rate.

When a valve-proving system is used as an alternative to a vent valve, no gas is released to the atmosphere. As a result, it is environmentally friendly. Furthermore, unlike a proof-of-closure switch, a valve-proving system is a "self-checking" safety control, which means that the system faults and does not allow ignition if its internal proof-of-closure signal fails to change state.

Natural gas is a colorless, odorless fuel. As a safety precaution, we add a chemical odorant called mercaptan that gives natural gas an odor often associated with rotten eggs. This distinctive scent allows you to smell a potential leak if it occurs. Always leave if you suspect a leak. Natural gas is non-toxic, lighter than air and displaces oxygen. In severe cases, if not used properly, it may lead to asphyxiation, and has a risk of ignition near a spark. It"s important to know that some people may not be able to detect the odorant because they have a diminished sense of smell, known as olfactory fatigue, or because the odor is being masked by other odors in the area. Certain conditions may cause the odorant to diminish so that it is not detectable. Never try to find the leak yourself.

SMELL for the distinctive, rotten-egg odor associated with natural gas. You should act any time you detect even a small amount of this odor in the air.

AVOID using any sources of ignition, such as cell phones, cigarettes, matches, flashlights, electronic devices, motorized vehicles, light switches or landlines, as natural gas can ignite from a spark or open flame, possibly causing a fire or explosion. Natural gas is non-toxic, lighter than air and displaces oxygen. In severe cases, if not used properly, natural gas can also lead to asphyxiation.

CALLAtlanta Gas Light at877.427.4321or911 once you are out of the area of the suspected leak and in a safe place. Stay away until Atlanta Gas Light or emergency personnel indicate it is safe to return.

WITT is a manufacturer of Pressure relief valvesor Safety relief valves for technical gases. They are designed to protect against overpressure by discharging pressurized gases and vapors from pipelines, pressure vessels and plant components. Safety relief valves (SRV) are often the last line of defense against explosion – and such an explosion could be fatal. Other common names for safety relief valves are pressure relief valve (PRV), safety valve, pressure safety valve, overpressure valve, relief valve or blow-off valve.

WITT safety valves are very precise. They are individually preset to open at a predetermined pressure within the range 0.07 to 652 Psi. Their small size and orientation-independent installation allow a wide range of connection options. WITT relief valves also stand out due to their high blow-off flow rates of up to 970m³/h. They can be used within a temperature range of -76° F to +518°F and even with very low pressures.

For maximum safety, WITT undertakes 100 % testing of each safety relief valve before it is delivered. In addition, WITT offers individual testing of eachsafety valveby the TÜV, with their certificate as proof of the correct set pressure.

WITTsafety relief valvesare direct-acting, spring-loaded valves. When the preset opening pressure is reached, a spring-loaded element in the valve gives way and opens, and the pressure is relieved. Once the pressures are equalized, the valve closes automatically and can be reactivated any time the pressure rises again. Depending on the application and the nature of the gas, the safety relief valvescan either discharge to atmosphere, or via a connected blow-off line. The opening pressure of the safety valves is preset by WITT at the factory according to the customer’s requirements.

Safety relief valvesare used in numerous industries and industrial applications where, for example, gases pass through pipelines or where special process vessels have to be filled with gas at a certain pressure.

For most industrial applications using technical gases, brass is usually the standard material of construction of thesafety relief valvebody/housing. For the use of pressure relief valves with aggressive and corrosive gases, the housings are made of high-quality stainless steel (1.4541/AISI 321, 1.4404/AISI 316L, 1.4305/AISI 303 or 1.4571/AISI 316Ti). The use of aluminium as a housing material is also possible.

Depending on the type of gas used and individual customer requirements, various sealing materials and elastomers are available to ensure the safety of your systems under even the most difficult conditions.

WITT pressure relief valves are available with different connections. In addition to the standard versions with the usual internal or external threads, special versions with KF or CF flanges, VCR or UNF threads can also be ordered. Special adapters for connecting the safety relief valve to a blow-off line are also available.

Natural gas connectors, like those used on ranges, water heaters and clothes dryers, must be inspected regularly and replaced as needed. Only a qualified professional should check for and replace your connector. Certain flexible connectors manufactured between 1970 and 1980 may fail over time and need to be replaced.

If your home or business was built after 1990, or you’ve had work done to the natural gas system, it is likely that corrugated stainless steel tubing (CSST) was installed. If lightning strikes a structure containing improperly installed CSST, the lightning will travel along the structure’s natural gas piping and could cause a leak or fire.

Some homes and businesses have privately buried natural gas or fuel lines that run to an unattached garage, grill or pool. Customers, not Alliant Energy, are responsible for natural gas lines after the meter. Customer must maintain, operate and know the location of buried lines. A qualified technician should regularly inspect it for leaks. If the pipe is metallic, inspect it for corrosion. Repair if unsafe, or shut off the flow of gas. Prior to excavating, have the piping located and marked. Excavating performed near the pipe should be done by hand.