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Gas pressure regulators for heaters & appliances:
This article explains LP or Natural Gas Pressure Regulators used on building appliances such as gas fired furnaces, boilers, water heaters, and stoves:
How to Inspect & Test LP or Natural Gas Valves Regulators, or Gas Controls at Appliances.
We provide descriptions and photographs of unsafe gas piping, regulators, or controls on heating systems, indications of unsafe or improperly operating gas appliances, gas meters, and other gas installation defects.
This document also provides free sample draft home inspection report language for reporting defects in oil and gas piping at residential properties.
Photo at left: a gas pressure regulator for a gas cook top or range. Page top photo: gas control & pressure regulator for a gas fueled furnace.
[Click to enlarge any image]
Watch out: improper installation and even improper inspection and testing methods involving natural or "LP" gas can involve dangerous conditions and risk fire or explosion.
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.
From a safe location, call your gas company's emergency line and/or your fire department.
The gas fired furnace gas regulator photograph shown just above is a typical gas valve assembly such as those used on most household appliances such as gas cooktops and gas ranges.
This gas fuel regulator can be converted to work with either natural gas or LP gas (propane) as we discuss separately
at CONVERT NATURAL GAS to LP GAS / PROPANE.
Gas regulators are needed at both LPG or propane gas fueled appliances and at natural gas fueled appliances to assure a smooth delivery of fuel at the pressure and flow rate required by the heater or appliance.
The gas pressure delivered to a heating appliance (gas range, clothes dryer, gas heating furnace, gas fired water heater, etc) needs to be both constant and at the proper pressure for that appliance.
Because of varying outdoor temperatures, the LP gas pressure inside the storage tank may be as low as 10 psi in freezing weather or as high as 200 psi with the tank exposed to sunlight in hot weather.
See LPG PROPANE TANK PRESSURES for more details.
And in natural gas fuel systems the gas pressure delivered from the gas main in the street can also vary widely by area, season, time of day and for other reasons and may range from 60 psi down to as low as 0.25 psi of natural gas pressure in the piping system.
In addition to those external sources of variation in the pressure of the fuel gas supplied to the heater or appliance, the actual gas pressure right at the heating appliance also varies because of gas type (LPG, propane vs natural gas), source pressure variations, gas piping distance, gas piping diameter, and other gas appliances that are in or out of use and fueled by the same building gas piping system.
In sum, a gas appliance regulator must deliver gas at the proper gas pressure and flow rate specified by the manufacturer for the particular appliance.
In addition, at some appliances such as gas fired boilers and furnaces, the job of the gas regulator includes automagically "turning on" the gas when the thermostat calls for heat and turning the gas supply off when the call for heat is satisfied (at the thermostat) OR when a flame sensing safety device or flue gas spillage device detects that the heater is not operating safely.
The LP, propane, or natural gas regulator(s) have to keep gas flowing to the appliance(s) at that pressure even as pressure in the storage tank or gas piping system changes and even when the number of appliances consuming gas changes (as devices turn on and off in the building).
[At above left: the gas pressure regulator for a gas fired heater.]
For that reason the gas regulator will increase the gas flow through itself according to pressure drops on the "low pressure" side of the regulator.
The regulator above is shown removed from the appliance where it will be used. The photo of the gas regulator shown at above left and some of the content in this article are thanks to Charles or Mike Trumbature.
Gas regulator leaks or damage: improper installation, including use of wrong type of fittings, improper thread size, cross-threading, or over-tightening fittings at the gas regulator can damage the connectors, pipe or fitting threads or can even crack the gas regulator body. That is going to cause dangerous gas leaks risking fire or explosion.
Be sure to check all fittings and components for gas leaks after converting, installing, or adjusting a gas regulator.
[Click to enlarge any image]
Watch out: typical instructions on the package of a replacement or OEM gas appliance regulator will include this warning:
CAUTION DO NOT OVER-TIGHTEN. Secure regulator to cooktop gas inlet using pipe-joint compound (resistant to LP and natural gas). Turn to hand tight plus 1/4 turn, not exceeding 1 turn for alighment. Check inlet fittings & regulator for leaks. - Maxitrol gas regulator package instructions for Maxitrol RV47CL US 1/2 psig Nat 6.0" LP 10.0"
Gas pressure too high: Some technicians have informed us that as the gas valve regulator on some gas furnaces or boilers age over several years, the spring inside the regulator (and determining the regulator output pressure) can weaken.
A weakened spring inside of a gas regulator can allow the gas pressure to increase beyond the BTU rating of the heat exchanger.
This same condition could occur if the regulator is simply not properly adjusted in the first place. Adjustment of a gas regulator might also be necessary if the gas piping from source (meter or tank) to the appliance is long or is too small in diameter.
If the gas regulator delivers gas at too high a pressure the gas flame may be also too big (and too hot), which can accelerate rusting and can warp the heat exchanger at its lower joints causing a "crack" to appear.
A cracked heat exchanger on a gas appliance is unsafe. Our correspondent, Charles commented that:
After loosing three heat exchangers in two different homes that had routine maintenance inspections, I decided to look into it and check the gas regulator pressure myself. The same problem can occur with gas water heaters.
Gas pressure too low: if the gas regulator is not properly adjusted or if there are other problems in the gas piping or supply system the gas pressure may be too low, providing an inadequate and possibly unsafe flame.
Depending on the cause of the problem, it may be possible to correct this at the regulator, but don't try boosting pressure at a gas regulator unless the pressure has always been too low.
Otherwise when the underlying cause for low gas pressure is corrected elsewhere, the flame will be too big and pressure too high at the burner - an unsafe condition.
Immediate LP or natural gas safety hazards: if there is evidence of an LP or natural gas leak at a building, gas odors, for example, you should:
Gas regulator noises: while many gas grill and some other appliance manufacturers say a bit of humming at the gas regulator for appliances is normal and harmless, not everyone agrees.
Certainly if there is a gas odor or gas leak, the gas supply should be shut off immediately and you need to call a professional for diagnosis and repair of the trouble.
Some experts explain that over time a humming gas regulator may become unsafe; and there are other noises that have other meanings at gas regulators, pipes, and LP gas tanks.
See GAS REGULATOR NOISES for complete details.
Also see THE TRUTH ABOUT GAS LEAKAGE COMPLAINTS and GAS VALVES [PDF] - original source: Honeywell Corporation (1994), www.graycoolingman.com/uploads/1/0/6/6/10667336/honeywell_gas_valve_leakage.pdf
The pressure delivered to a gas-fired heating boiler or furnace is typically 3" to 3.5" water column for 100K BTU gas fired furnaces or boilers.
(LP gas and piped-in natural gas do not provide the same pressures from the source which is why regulators and orifices must be properly installed and adjusted depending on the type of gas fuel in use (Propane or LP gas from a local gas tank vs. natural or piped-in gas).
The large screw on top of the gas regulator shown in the photograph above is a "cap screw" which can be removed by (a trained) heating technician when it is necessary to access the LP or natural gas pressure regulator adjusting screw inside.
SAFETY WARNING: If you lack the training and equipment, do not attempt to disassemble or mess with a gas regulator as you could create a very dangerous or even fatal problem.
Under the "cap screw" on the gas regulator there a plugged NPT tap (usually 1/8") used to install a hose barb and manometer (a very low pressure gage) in order to check gas pressure right at the heating furnace or boiler.
[Gas regulator valves such as this one usually have a 1/8" NPT plug which is remove by the technician in order to connect a manometer to measure the gas pressure being delivered right at the appliance.]
For connecting the manometer to measure gas pressure, the technician may obtain a hose barb and plastic hose form a hardware store in order to make these connections.
The actual gas pressure setting for the regulator is on the gas valve. Inexpensive manometers such as those made by Dywer Instrument CO. are good for checking and setting the regulators.
See the 2T650 and 3T292 models, probably best suited depending on the ranges needed. [Available from Granger Corp., a supplier of HVAC testing equipment.] Since the pressures for gas furnaces (and boilers) can vary above or below the 3" water column (WC), the 7" manometer is probably a better one fits all choices when checking gas regulator assemblies.
Charles, a fire pump and sprinkler system inspector in Houston Tx, our correspondent on this topic commented:
One of the things I've noticed about home inspections are the A/C contractors inspecting gas furnaces. They have no problem identifying a cracked heat exchanger but never check the gas pressure to the burner.
Checking the pressure delivered to a furnace by a gas regulator valve is beyond the scope of a normal home inspection. However certain clues such as defects in gas flame or rusty gas burners can suggest that there is a problem with the adjustment of the gas pressure (the regulator's job) or with the combustion air supply (potentially a fatal mistake).
Not only are there dusty cobwebs over the gas regulator, but a chewing gum wrapper and a scrap of green foam have fallen into the furnace and may be blocking air intake to the right hand gas burner tube.
Not only might this interfere with proper burner operation by obstructing combustion air to the burner, but combustible trash at any gas burner is a potential fire hazard.
The gas burner flame color, pattern, height, or the presence of rust on a gas burner can also indicate potentially dangerous operating problems with a gas furnace or boiler.
These concerns are discussed in more detail
at GAS FLAME & NOISE DEFECTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Gas Cylinder or Tank Regulators: Readers concerned with installing, inspecting, or testing LP Gas regulators which are found on outdoor above ground or buried gas cylinders used for storage of LP Gas on site should also
see GAS REGULATORS for LP TANKS
Readers concerned with changing the fuel type between LP gas and natural gas for a gas fired appliance should see our safety warnings
at GAS APPLIANCE CONVERT LP-NATURAL GAS.
This discussion has moved to GAS REGULATOR ADJUSTMENT PROCEDURE - separate article
Details about the different pressures found or set for LP gas, propane, and natural gas including before and after different gas pressure regulators are
Continue reading at GAS REGULATORS for LP TANKS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
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