Energy Currents
A Blog by Enerdynamics

Natural Gas Regulators Are a Critical Safety Device: Here’s How They Work

by Bob Shively, Enerdynamics President and Lead Facilitator

The number of accidents on the gas transmission and distribution system are low given the 3 million miles of pipeline in the U.S. But over the last 10 years, gas distribution and transmission systems have caused incidents resulting in an average of 11 fatalities and 48 injuries per year according to the U.S. Pipeline and Hazardous Materials Safety Administration (PHMSA). Gas operators strive to continually drive these numbers to zero. A key device in preventing accidents is the gas regulator, which is found throughout the system from the wellhead to the customer meter. Everyone involved in the natural gas business should understand what a regulator is, how it works, and how it is critical for ensuring a safe gas system.  

A 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. Correct operation of regulators is critical to ensure that downstream pressures do not exceed pipe maximum allowable operating pressure (MAOP) while also keeping pressures high enough to reliably serve customers.

The type of regulator used depends on the application. The two most common types are spring-loaded regulators and pilot-operated regulators.

Spring-loaded regulators

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 regulators

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 upstream pressure, the loading pressure, and the downstream 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 downstream pressure will go up. If less gas flows, the downstream pressure will go down. 

How regulators ensure safety

Pipeline pressures that exceed MAOP risk rupturing pipes causing leaks and potential explosions or fires. Regulators are the key component that prevents this. They are installed in configurations to ensure downstream pressures remain at safe levels. In locations where single regulators are installed, they are designed to fail shut, meaning that if the regulator is failing to control downstream pressure it will shut a valve and cut gas flow downstream. This is how the regulator on your house keeps you safe.

     A district regulator station with a parallel run

For more critical regulators that serve many customers, such as regulators at a district regulator station, duplicative regulators are placed in line in a single pipe run. If one regulator fails, a second regulator will take over the job of controlling downstream pressure until a crew is dispatched to address the failure. Often a second parallel run will be installed so that gas flow can be switched to the second line while maintenance is performed. This provides continuous service while safety is ensured. Such critical regulators are checked and maintained regularly to make sure they will continue to operate as designed.