Hydraulic Pressure Reducing Valve

What is hydraulic pressure reducing valve?

This is a self-contained and automatic pressure reducing valve that operates by use of hydraulic fluid. This valve is used to reduce high fluid pressure to consistent and usable pressure. This valve consists of a flexible diaphragm that controls the valve via an interconnected pin and a compression spring. The spring is loaded via a metallic screw that moves up and down to control the fluid pressure as necessary. The use of this valve is important in that reduction of the high pressure to constant and usable pressure prevents losses that may occur due to leakage or due to damage on fixtures downstream. Also, the use of this valve helps to reduce noise levels that emanate from high fluid flow velocities. Hydraulic pressure reducing valve manufacturers produce various types of this valve. Such valves are made of different materials and they are meant for use in different industrial applications. 

Figure: Hydraulic pressure reducing valve.

Components of hydraulic pressure reducing valve 

Body 

This component is made of strong metallic materials such as stainless steel, nickel alloy, carbon steel, brass, and other strong materials. Hydraulic pressure reducing valve manufacturers design the body from such materials to ensure it is strong to withstand the fluid pressure as well as the impact of falling objects. The body houses internal parts of the valve and it also contains the valve inlet and outlet ports. 

Pilot valve 

This valve regulates fluid flow into and out of the control chamber to enhance fast response and constant flow.

Adjustment spring 

This is a coil spring that connects the valve diaphragm to the hydraulic system via a screw. It transmits the force necessary to press the diaphragm to vary fluid pressure. 

Diaphragm 

This component is used to allow fluid flow through the valve. The inlet fluid pressure pushes up on the diaphragm against the spring tension. This forces the valve to open and then fluid flows downstream. 

Screw 

This is a metallic component with threads that assist in compressing or elongating the spring to push the diaphragm up or down to vary fluid pressure. 

Gaskets 

These components are placed between the pipe and valve mating surfaces. Their function is to prevent fluid leakage through the connections. 

Figure: Components of a Hydraulic pressure reducing valve.

How does a hydraulic pressure reducing valve work? 

Hydraulic pressure reducing valves operate by converting high fluid pressure at the valve inlet to low pressure at the valve outlet. To start the valve, the user sets the required exit pressure on the valve. As such, the hydraulic system adjusts the valve to the set pressure. This works via a compression spring that holds the diaphragm in its position. Hydraulic pressure reducing valve manufacturers design the valve such that if the entrance pressure is below or is at the set point for downstream pressure, fluid will still flow through the valve. This means that the pressure will not be at the level it can force the spring back to close the valve. It is the demand on the outlet side which causes pressure drop which would mean the hydraulic pressure reducing valve will remain open. When the inlet pressure exceeds the required exit pressure, it overpowers the tension on the valve spring. This spring tension is due to the value of pressure set by the user. As such, the exit pressure forces the valve diaphragm to move upwards where it effectively closes the valve. This occurs mostly when there is low or no demand from the exit side. 

Figure: Working of a hydraulic pressure reducing valve.

Types of Hydraulic pressure reducing valves 

Plastic hydraulic pressure reducing valve 

This is a hydraulic pressure-reducing valve that is made of plastic materials such as polyvinyl chloride (PVC) and propylene. Such materials have high strength enough to withstand moderate pressure and impact damage. Hydraulic pressure-reducing valve manufacturers design these valves for use in applications that have moderate pressure and low temperature. Use of these valves in high temperatures causes damage to the valve because of the poor thermal properties of plastic materials. High pressure can cause damage to the valve and excess fluid leakage. However, this valve is very good for controlling flow of corrosive product because the corrosion resistance of plastic materials is more than that of metallic materials. Also, these valves are cheaper compared to their metallic counterparts. 

Figure: Plastic hydraulic pressure reducing valve.

Pilot-operated hydraulic pressure reducing valve

This is a hydraulic pressure-reducing valve designed for use in large loads that need close control. This valve has a fast response to variations in load and it is best for a wide range of fluid flow rates compared to other valve types. Hydraulic pressure reducing valve manufacturers design this valve with large size to enhance large fluid flow rates. The large size makes the valve more expensive relative to other valves. Hydraulic pressure reducing valve manufacturers use an auxiliary valve known pilot valve to operate this valve. The pilot valve is used to load a diaphragm or a piston to increase downward force. This force is used to open the main valve to allow fluid flow. Such design enhances large fluid flow at low-pressure variation. 

The control of the pilot valve opening and closing is enhanced by balancing force between the secondary pressure and the spring force. The pilot valve is meant to deliver pressure to the diaphragm or piston of the main valve. It creates a downward force which is then amplified by the diaphragm or piston area. This helps in the opening of the main valve which facilitates a high fluid flow rate. As such, this hydraulic pressure-reducing valve has a fast response over a wide range of fluid flow rates. Another advantage of this valve is tight pressure on the downstream side. 

Direct-acting hydraulic pressure reducing valve 

This is a hydraulic pressure-reducing valve that is used for small loads. This valve is the simplest of the hydraulic pressure-reducing valves and it uses convoluted bellows or flat diaphragm to operate. The accuracy of this valve relative to the downstream set point is around +/- 10%. This valve does not offer precise fluid flow control. This hydraulic pressure-reducing valve is cheaper relative to the piloted-operated type. Also, this valve is of compact design and it is easy to install. However, this valve has more pressure variation compared to the pilot-operated type.

This valve operates by using a spring adjustment force triggered by the hydraulic actuator to open the valve directly. The spring employs its compressive properties to create the opening force on the valve which results in the fluid flow. As the pressure increases downstream, it creates balancing where it feeds the downstream pressure to the underside of the spring where upward force balances against the compressive force. This compressive force is restricted to enhance enough spring sensitivity to balance with downstream changes of pressure. 

Factors considered when purchasing a hydraulic pressure-reducing valve 

Type of media 

Hydraulic pressure reducing valve manufacturers design various types of these valves for use in different applications. Each valve is meant for use in specific fluid. Some of these valves are meant for corrosive fluids while others are not. So, it is very important to know the type of fluid the valve will be exposed to before purchasing.

Operating temperature 

Hydraulic pressure-reducing valve manufacturers use different metallic or soft materials to make the valve. Soft materials can are meant for use in low-temperature applications while metallic ones are meant for use in high temperatures. Using the valve at the wrong temperature will of course damage it even during the first day of work.

Pressure

Each hydraulic pressure reducing valve has its highest level of pressure to which it can operate comfortably. Using the valve at the wrong pressure levels will cause malfunction or excessive leakages which will lead to losses in the fluid being transported or other damages to the environment. 

Applications of hydraulic pressure reducing valves 

• Hydraulic pressure-reducing valves are used in fire-suppression systems to help reduce inlet pressure to stable and safe outlet pressure.
• These valves are used in domestic and commercial water supply systems. 
• Hydraulic pressure reducing valves are used in mining operations.
• They are used in the control of chemicals in industrial applications. 
• These valves are used in hospitals to control the flow of oxygen. 
• Hydraulic pressure reducing valves are used to control the flow of steam and water in steam power plants. 
• They are used in oil and gas industries. 
• They are used in compressed air and gas systems. 

Advantages of hydraulic pressure reducing valves 

• These valves are free from fluid leakage. 
• Hydraulic pressure-reducing valves prevent damage to plumping fixtures. 
• They are fast in operation. 
• They are operated using a hydraulic system. 
• They allow consistent and safe fluid flow. 
• Hydraulic pressure-reducing valves are of simple and compact design.
• Their repair and maintenance operations are easy and cheap. 
• They are free from blockage as they use a strainer to filter foreign materials. 
• They are highly reliable as no excess fluid can flow through the valve. 

Disadvantages of hydraulic pressure reducing valves 

• These valves are more expensive compared to other valves. 
• They are of large size relative to other valves and thus they occupy large installation area. 

Troubleshooting hydraulic pressure reducing valves 

Controlled pressure exceeds limits under normal loads 

• There is a blockage in the pressure sensing line or orifices. Remove the blocking materials. 
• There is dirt or foreign materials between the head and pilot valve sear. Open the valve and clean off the dirt or foreign materials. 
• There are foreign materials between the seat and main valve head. Open the hydraulic valve and clean the foreign materials. 

Controlled pressure exceeds the limit on light loads 

• Dirt between the seat and main valve head. Open the valve and clean off the dirt. 
• Leakage on the bypass valve. Repair the bypass valve as necessary. 

The hydraulic pressure reducing valve does not open 

• Defective main valve diaphragm. Replace the diaphragm. 
• Blocked orifice. Remove the blocking materials. 
• Blocked strainer. Remove the blocking materials. 
• Dirt on the pilot valve seat. Clean off the dirt. 

Low delivery pressure 

• Defective main valve diaphragm. Replace the diaphragm. 
• Undersized valve. Ensure the load matches the recommended valve ratings by the hydraulic pressure reducing valve manufacturer. 

Valve does not close 

• Leakage via the bypass valve. Repair bypass valve. 
• Blocked pilot sensing line. Clean off blocking materials. 

Summary 

A hydraulic pressure reducing valve is a self-operating valve used to reduce excess pressure in a piping system to stable and safe working pressure. Hydraulic pressure-reducing valves operate by using a flexible diaphragm that controls fluid flow via an adjusting spring and screw. The diaphragm pressure side connects to the exit end of the valve to exert controlled pressure on the diaphragm. Hydraulic pressure reducing valve manufacturers design this valve such that when there is no load on the valve spring, the valve closes. The hydraulic system applies torque on an adjusting screw and thus to the spring to transmit force to the valve diaphragm. This forces the diaphragm to open the valve and allows fluid to flow from the valve. 

Hydraulic pressure reducing valve manufacturers design these valves using different materials from metallic to plastic materials. The materials used to make the valve determines the area of application and thus it is important to enquire from the hydraulic pressure reducing valve manufacturer or valve vendor on the application of the valve. The factors to consider when purchasing hydraulic pressure-reducing valves are operating pressure, temperature, and type of media. The various types of hydraulic pressure reducing valves are plastic hydraulic pressure reducing valves, direct-acting hydraulic pressure reducing valves, and pilot-operated hydraulic pressure reducing valves among others. Applications of hydraulic pressure reducing valves are fire-protection, compressed air and gas systems, mining, hospitals, chemicals, oil, and gas among others. Advantages of using hydraulic pressure-reducing valves are reliability, versatility, zero leakage, easy installation and repair, free from blockage, and fast operation.