Understanding Pressure Regulators

Natural gas is distributed through the city gas lines at a higher pressure than your typical residential gas furnace can properly handle. Any excessively high gas pressure and gas pressure variations are detrimental to the operating efficiency and safety of a gas-fired furnace, boiler or water heater. This means we need to ensure a standard gas pressure (no high or low extremes) is distributed to all of our hvac equipment burners.

A gas-pressure regulator is a device created to do just that. It controls manifold gas pressure to all of our HVAC equipment. Gas is distributed to the burners from the outlet orifice of the regulator at a single, nonfluctuating constant pressure regardless of inlet pressure changes. It is the regulators responsibility to sense all of the changes in gas pressure and be able to adjust the gas flow as needed. The sensing device used for this job is attached to a valve ball or disc to restrict gas flow through the seat.

How A Gas Regulator Works
A pressure regulator uses the available gas pressure as the primary force to open or close the valve. Outlet gas pressure presses against the diaphragm and spring. If the gas pressure is weak to overcome the force of the spring, the attached ball or disc is pushed away from its seat. This enlarged opening will allow more gas to flow. If the pressure is too high the valve ball or disc is brought towards its eat, restricting the amount of gas. As gas pressure against the diaphragm equals the force exerted by the spring, the ball or disc is so positioned to maintain a steady downstream pressure. This is a basic principle of operation used by all diaphragm valves.

The spring-loaded side of the diaphragm must be vented or the movement of the part will be restricted. Proper venting allows the valve diaphragm to move freely in either direction depending on the pressure of gas in the line. The use of a vent hole orifice also prevents the rapid and potentially dangerous escape of gas in the event of a rupture. Both internal and external bleed systems are used to vent the gas from the spring-loaded side of the diaphragm valve.

When to Use A Regulator
nstalling a separate pressure regulator after the combination gas control can sometimes result in over gassing the main burners. This will occur when the regulator remains in a wide-open position when the main gas valve remains closed. When the gas valve open,s over-gassing can result from the delay of the regulator valve in resuming regulation. A combination gas control can eliminate this problem.

Some gas-fired water heaters use a balanced pressure regulator. This type of pressure regulator uses two internal diaphragms to control gas pressure. The operating principle is quite different from that described for the regulators used on gas fired hvac equipment.