What is a Pressure Reducing Valve?

In a fluid system pulsating high pressure is a cause of maximum damages occurs. Also, if the pressure is very high in comparison to what is required for a system, it will cause the wastage of fluid (in domestic water system), leakages in the long run as the system is designed for handling lower pressure, and it can also lead to a pipe burst or system breakdown. All this will ultimately reduce the efficiency of the system and will contribute to the higher operating cost for a business.

This reduction in efficiency of a fluid system can be controlled by a constant and reduced pressure supply in a system. This can be achieved by using an Automatic pressure regulator or a Pressure Regulating Valve.

The basic function of a Pressure regulating valve in a fluid system is to convert a pulsating & high inlet pressure to a constant & reduced (or pre-set) pressure.

How does a Pressure Reducing Valve work?

If there is a requirement for pressure reduction between two components of a process, a pressure regulating valve will open. These valves can lower liquid or gas pressure to a predetermined level.

The pressure reducing valve is a hydraulically powered, diaphragm actuated control valve that decreases greater upstream pressure to lower constant downstream pressure of variable demand or varying upstream pressure. It is designed to resist even the harshest conditions. Essentially, the valve maintains a constant downstream pressure regardless of flow.

The operation of pressure reducing valve is dependent on the balance of fluid pressures acting over and under the piston, as well as the spring force. If the low-pressure fluid and spring force are more than the high-pressure supply, the piston will close the valve. When the low-pressure fluid force is reduced, the new fluid pressure and spring force are less than the high-pressure supply fluid, causing the piston to open the valve. The valve will frequently open and close in order to maintain the pressure under control. The valve’s outlet pressure may be adjusted by changing the spring to a stronger or weaker one as needed. In certain situations, the spring force is adjusted via an adjustable screw. Some reducing valves employ several pistons as well as diaphragms to improve performance.

Types of Pressure Reducing Valve

Pressure reduction valves are categorized into two main categories based on the mechanism that controls the valve opening:

• Direct-acting Pressure Reducing Valve

Direct-acting Pressure Reducing Valve: Direct-acting pressure reduction valves are excellent for lower pressures that do not require precise pressure control. They are made in a small size, are cheaper, and are easy to set up. In comparison to their pilot-operated counterparts, they often have higher fluctuation from the set pressure. This is the most basic form of a pressure-reducing valve, with either a flat diaphragm or a bellows. Because it is self-contained, it does not require an external sensing line downstream to function.

The amount of valve opening in the direct acting pressure reduction valve is regulated directly by the movement of the adjustment spring. When the spring is compressed with the help of an adjusting screw, it generates an opening force on the valve, causing the flow to rise. As pressure develops downstream, equalization is done by transferring the downstream pressure to the underneath of the adjustment spring, where its upward force counterbalances the compression of the spring. The spring compressive force that opens the valve is restricted to provide for adequate spring sensitivity to equalize with variations in downstream pressure. As a result, pressure is simply controlled by a valve opening, where excessive flow rates might result in pressure drop.

• Pilot Operated Pressure Reducing Valve

Pilot operated Pressure Reducing Valve: These valves are often utilized for higher loads that need precise pressure control. When compared to direct-acting models, they give a quicker reaction to load fluctuation and are suited for a larger range of flow rates. They are larger and more expensive.

A pilot valve is used in pilot-operated pressure reducing valves to load a piston or diaphragm, increasing the downward force required to open a larger main valve. In the same way that a direct-acting valve functions, the pilot valve’s opening, and shutting are regulated by the balance of force between the adjustment spring and the secondary pressure. In a pilot-operated valve, however, the opening and shutting of the pilot valve are done on purpose to supply pressure to the main valve piston or diaphragm. This pilot flow pressure generates a downward push, which is magnified by the area of the piston or diaphragm, allowing for the opening of a much bigger main valve, allowing for extremely high flow rates.

A minor change in the pilot valve opening can result in a substantial change in flow and downstream pressure via the main valve because the downward force is magnified by the employment of a piston or diaphragm. As a result, the adjustment spring force on the pilot only needs to be changed a little to achieve rapid reaction over a wide range of steam flow rates. The major benefits of this type of valve over direct-acting valves are quick reaction and precise delivered pressure control.

Pilot operated pressure reducing valves are further divided into two types:

• Internally piloted pressure reducing valve, and
• Externally piloted pressure reducing valve.

Pressure reducing Valve Applications

These valves are used in various sectors such as water services, Air & Gas Services, Hydraulic systems, Steam services, Fuel oil systems in IC engines and Boilers, etc.

• For Air & Gas Services: Compressed air systems, power tools, pneumatic control systems, and control valves for industrial gas storage and distribution systems all utilize both direct-acting and pilot-operated pressure reduction valves for air and gas services. The type of pressure-reducing valve used for these services is determined by the level of control necessary.

• For water services: Pressure-reducing valves are widely used in household and industrial water distribution systems, as well as fire prevention systems. For these services, direct-acting pressure-reducing valves are often recommended. Maintaining system pressures becomes extremely challenging in high-demand circumstances. In those lines, pressure reduction valves are utilized to effectively regulate the pressure downstream to an acceptable limit.

• For Steam Services: Pressure reducing valves are used for various steam applications like steam supply, steam turbines for power generation, steam engines, etc.

Advantages of a Pressure Reducing Valve

• It safeguards the system components and pipelines from hammering.
• No external power source is required to operate the valve.
• It has a very simple design and operates with very little maintenance & lower cost.
• Separate measuring elements and controllers are not required as it is a self-contained valve.

Disadvantages of a Pressure Reducing Valve

• Blockages: A pressure reducing valve may develop blockages that will restrict the valve to open or close to maintain the desired pressure. This can be caused by salt deposits or suspended solids in the fluid medium.
• As internal components are exposed to the system fluid, they are prone to damage in a long run.
• Manual pressure setting is to be done by adjusting the screw.

How to select a Pressure Reducing Valve

When choosing a pressure reducing valve, make sure you obtain a product that is of good quality, is cost-effective and will last for many years.

1. First, choose between Diaphragm or a Piston sensing regulating valve according to your requirement. A diaphragm has greater sensitivity and has a wide choice of material of diaphragm. On the other hand, a piston valve can handle high-pressure regulation but has less sensitivity as compared to diaphragm sensing regulators.
2. Sizing of a pressure regulator: Any process engineer’s objective is to select the smallest valve that will serve the function. The smallest valve is sometimes the most affordable. It is, however, critical that you understand the pipe’s exact dimensions. Choosing the incorrect size might result in inefficiencies and operational issues. The best way to select a proper size is:

• Find minimum and maximum system flow that a valve can experience.
• Calculate the pressure differential between upstream and downstream pressures.
• Using the following formula find the flow coefficient, C

Flow (Q) = Cv × (square root Pressure Differential)

• You can choose a valve with a slightly larger Cv than you calculated, allowing you to handle higher flows in the future.
• Lastly, make sure that the provided flow rate is appropriate and documented, as well as the pressures. To achieve optimum efficiency, always choose accurate calculations over informed approximations.

Pressure Reducing Valve maintenance

While doing the maintenance on these valves, consider the following points.

• Find leakage or breakage in the pilot system.
• Check if the strainer screen is clean and free from dirt.
• Check for air pockets in the pilot valve and remove them.
• Inspect the diaphragms of the main valve and pilot valve for any damage, make sure it’s not leaking.
• Check the pilot line for any blockage and make sure it has a free flow.