A natural gas regulator is a device used to reduce pressure in the gas delivery system. Regulators are commonly located at the interconnect between the transmission and distribution system, at locations in the distribution system where higher-pressure pipes are connected to lower-pressure pipes, and where the gas enters an end-use consumer premises.
The type of regulator used depends on the application. The two most commonly used types of regulators are spring-loaded regulators and pilot-operated regulators.
Spring-loaded:
A spring-loaded regulator, also called a direct-operated regulator or a diaphragm regulator, is the simplest of the two types. The spring-loaded regulator is a self-contained device that partially opens or closes a valve to control or regulate the flow of gas through the regulator. The position of the valve is automatically adjusted to allow more or less gas to flow depending on the pressure downstream of the regulator. If more gas flows through, downstream pressure will rise. If less gas flows through, downstream pressure will drop.
The spring is set so the force of the spring determines the position of the diaphragm, which in turn controls the lever to determine the valve position. Downstream pressure presses against the bottom of the diaphragm, which is balanced by pressure from an adjustable spring. The opposite reaction will occur if downstream pressure falls below a set point, resulting in the valve opening further to allow more flow, thus increasing pressure.
If downstream pressure rises beyond the desired set point the extra pressure pushes on the diaphragm, compressing the spring and causing the regulator mechanism to partially close the opening. This reduces flow and returns the downstream pressure to the desired level. Spring-loaded regulators are typically used for regulating pressure into a customer facility and as part of a more complex regulator called a pilot-operated regulator. The advantage to this type of regulator is that it has few components and is the lowest-cost option.
Pilot-operated:
A pilot-operated regulator is more complex than the spring-operated regulator and provides more precise pressure control of gas flow by continually making small adjustments to downstream pressure. They are more expensive and require more maintenance than spring-loaded regulators. Thus, they are used in situations where the extra expense is justified given the need for precise control for safety or operational efficiency.
These applications include use in transmission pressure limiting stations and in district regulator stations, and for other applications with high flow rates such as power plants and large industrial customers.
The two key components that make up a pilot-operated regulator are a main valve that controls the downstream pressure and a pilot regulator that controls the amount that the main valve is open. By controlling the position of the main valve, the pilot regulator determines the amount of gas flow the main valve lets through, thus controlling the downstream pressure.
The position of the main valve is determined by the relationship between inlet pressure, the loading pressure, and the outlet pressure. The more the main valve is open, the higher the downstream pressure. Changes in downstream pressure result in a series of reactions that change the position of the main valve. When the downstream pressure changes it changes the position of the pilot regulator. This controls the amount of downstream gas that bleeds into the loading pressure, thus increasing or decreasing the loading pressure. In turn, the change in loading pressure changes the position of the main valve, thus changing the amount of inlet gas that flows through the regulator. If more gas flows through, the outlet pressure will go up. If less gas flows, the outlet pressure will go down.