What is a pressure regulating valve?
At a basic level, a pressure regulating valve is a mechanical device designed to control upstream or downstream pressure in response to changes in the system. These changes may include fluctuations in flow, pressure, temperature or other factors that occur during routine system operation. The purpose of the pressure regulator is to maintain the required system pressure. Importantly, pressure regulators differ from valves, which control system flow and do not adjust automatically. Pressure regulating valves control pressure, not flow, and are self-regulating.

Pressure regulator type
There are two main types of pressure regulating valves: pressure reducing valves and back pressure valves.

Pressure reducing valves control pressure flow to the process by sensing outlet pressure and controlling the pressure downstream of themselves

Back pressure regulators control pressure from the process by sensing inlet pressure and controlling pressure from upstream

Your ideal pressure regulator selection depends on your process requirements. For example, if you need to reduce the pressure from a high-pressure source before the system media reaches the main process, a pressure reducing valve can do the job. In contrast, a back pressure valve helps control and maintain upstream pressure by relieving excess pressure when system conditions cause pressure to be higher than required. When used in the right environment, each type can help you maintain the required pressure throughout your system.

Working principle of pressure regulating valve
Pressure regulating valves contain three important components that help them regulate pressure:

Control components, including valve seat and poppet. The valve seat helps control pressure and prevents fluid from leaking to the other side of the regulator when it is shut off. While the system is flowing, the poppet and valve seat work together to complete the sealing process.

Sensing element, usually a diaphragm or piston. The sensing element causes the poppet to rise or fall in the valve seat to control inlet or outlet pressure.

Loading Elements. Depending on the application, the regulator may be a spring-loaded regulator or a dome-loaded regulator. The loading element exerts a downward balancing force on the top of the diaphragm.

These elements work together to create the desired pressure control. A piston or diaphragm senses upstream (inlet) pressure and downstream (outlet) pressure. The sensing element then attempts to find balance with the set force from the loading element, which is adjusted by the user via a handle or other turning mechanism. The sensing element will enable the poppet to open or close from the valve seat. These elements work together to maintain balance and achieve set pressure. If one force changes, some other force must also change to restore equilibrium.

In a pressure reducing valve, four different forces must be balanced, as shown in Figure 1. This includes the loading force (F1), inlet spring force (F2), outlet pressure (F3) and inlet pressure (F4). The total loading force must be equal to the combination of inlet spring force, outlet pressure, and inlet pressure.

Back pressure valves operate in a similar manner. They must balance spring force (F1), inlet pressure (F2) and outlet pressure (F3) as shown in Figure 2. Here, the spring force must be equal to the sum of the inlet pressure and the outlet pressure.

Making the Right Pressure Regulator Selection
Installing a properly sized pressure regulator is key to maintaining the required pressure. The appropriate size generally depends on the flow rate in the system – larger regulators can handle higher flows while controlling pressure effectively, while for lower flow rates, smaller regulators are very effective. It is also important to size the regulator components. For example, it would be more efficient to use a larger diaphragm or piston to control lower pressure applications. All components need to be appropriately sized based on the requirements of your system.

System pressure
Since the primary function of a pressure regulator is to manage system pressure, it is critical to ensure that your regulator is sized for the maximum, minimum, and system operating pressures. Pressure regulator product specifications often highlight the pressure control range, which is very important for selecting the appropriate pressure regulator.

System temperature
Industrial processes can have wide temperature ranges, and you should trust that the pressure regulator you select will withstand the typical operating conditions expected. Environmental factors are one of the aspects that need to be considered, along with factors such as fluid temperature and the Joule-Thomson effect, which causes rapid cooling due to a drop in pressure.

process sensitivity
Process sensitivity plays an important role in determining the choice of control mode in pressure regulators. As mentioned above, most regulators are spring-loaded regulators or dome-loaded regulators. Spring-loaded pressure regulator valves are controlled by the operator by turning an external rotary handle that controls the spring force on the sensing element. In contrast, dome-loaded regulators use the fluid pressure inside the system to provide a set pressure that acts on the sensing element. Although spring-loaded regulators are more common and operators tend to be more familiar with them, dome-loaded regulators can help improve accuracy in applications that require it and can be beneficial in automatic regulator applications.

system media
Material compatibility between all components of the pressure regulator and the system media is important for component longevity and avoiding downtime. Although rubber and elastomer components undergo some natural degradation, certain system media may cause accelerated degradation and premature regulator valve failure.

Pressure regulating valves play a vital role in many industrial fluid and instrumentation systems, helping to maintain or control required pressure and flow in response to system changes. Choosing the right pressure regulator is important for your system to remain safe and perform as expected. The wrong choice can lead to system inefficiencies, poor performance, frequent troubleshooting, and potential safety hazards.