How Do Gas Pressure Regulators Work?

Working with gas pressure regulators can be daunting if you’re new to the field. Regulators handle the important task of keeping a system operating at maximum efficiency while avoiding a dangerous buildup of pressure. Unchecked, this buildup could cause a rupture to equipment, costing downtime and maintenance as well as posing a risk to operators. To answer the question “how do gas pressure regulators work?”, it’s important to understand both the mechanisms and function of the devices, design style, and how to troubleshoot some common issues.

How Do Gas Pressure Regulators Work: The Basics

Pressure regulators operate under the concept of a system in equilibrium. With the exception of instantaneous changes, axially-aligned forces must vectorially sum to zero for the system to dynamically respond and remain balanced. In real-world applications, both the sensitivity and precision of the equipment must be considered to determine how quickly the sensor can restore itself to mechanical equilibrium. To answer the question “how do gas pressure regulators work?'', it is best to start by describing what comprises a gas pressure regulator. Regardless of style, regulators consist of three distinct components:

• Loading mechanism: Responsible for a force antiparallel to the inlet/outlet pressures. A screw-adjustable spring or gas-fed dome provides the force; in some designs, a combination spring and dome load are utilized.
• Sensing mechanism: The barrier between the load force and inlet/outlet pressures. This mechanism is able to sense changes in pressure and act to restore the displacement from equilibrium. Physically, it exists as a diaphragm for low-pressure, spring-loaded regulators and all dome-loaded regulators or a piston for high-pressure, spring-loaded applications.
• Control mechanism: A poppet is used to reduce high inlet pressure to lower outlet pressure. The poppet can either be balanced or unbalanced. The balanced design features an orifice through the poppet which reduces the area on which the inlet pressure can act. A balanced poppet is less susceptible to the effects of dependency, where outlet pressure can change seemingly paradoxically to a change in inlet pressure. Meanwhile, unbalanced poppets see usage in smaller regulators and low-pressure environments.

The operation of the gas pressure regulator follows the flow of the inlet and outlet pressure. This is sampled continuously by the sensing mechanism and balanced against the loading mechanism. Depending on the type of gas pressure regulator, the poppet will either open or close to regulate inlet or outlet pressure. The damping level of the regulator also plays an important role in selection. An underdamped regulator may be susceptible to ringing due to a rapid, sudden change in inlet pressure, while an overdamped regulator could exhibit hysteresis (a dependency on prior system states).

Pressure-Reducing or Back-Pressure Regulator?

As important as the construction and mechanics of a gas pressure regulator is its type: pressure-reducing or back-pressure. Pressure-reducing, as one may deduce, reduces an inlet pressure to a fixed preset outlet pressure. The poppet defaults to an open position to allow pressure to flow from inlet to outlet but closes to reduce outlet pressure when inlet pressure increases beyond the fixed outlet pressure value. The pressure-reducing regulator is installed upstream of sensitive equipment as a means of protection. 

In contrast, the back-pressure regulator’s role is to maintain the inlet pressure below a preset value. The poppet’s position is normally closed, but the poppet can toggle between an open or closed position to release or build pressure, respectively. As its role is to maintain inlet pressure, the back-pressure regulator is installed downstream from the components it protects.

Due to their alternate placement in systems around sensitive equipment, pressure-reducing and back-pressure regulators may face unique difficulties during use. While the following list is not inclusive of every challenge an operator could encounter, being able to correctly diagnose these issues will help reduce maintenance downtime.

• Accumulation: A condition of back-pressure regulators whereby inlet flow causes an increase in inlet pressure
• Creep: An increase in outlet pressure, genuinely due to leakage of the regulator seat
• Droop: When outlet pressure decreases in a pressure-reducing regulator following an increase in flow rate
• Lockup: When Outlet pressure increases as flow rate decreases to zero
• Supply pressure effect: A change in the outlet pressure opposite the direction of a change of inlet pressure in pressure-reducing regulators; also known as dependency

Have an Expert Vendor Answer Your Pressure Regulator Questions

Gas pressure regulators play a key role in protecting your equipment and workers. For questions beyond the introductory “how do gas pressure regulators work?”, you can contact one of our Field Advisors for an in-depth consultation of your specific system and pressure regulators that will keep your operation running smoothly.