Adjusting Pressure Reducing Valve

What is adjusting pressure reducing valve?

This is a pressure-reducing valve that can be adjusted to vary the fluid pressure as necessary. This is a pressure control valve. Adjusting pressure reducing valve manufacturers produce this valve for use in different applications where it ensures constant reduced pressure in a piping system. It helps to correct fluid flow pressure which then helps to safeguard plumping fixtures against damage by the pressure. Excess pressure can also cause leakage through valves and other faucets. Adjusting pressure reducing valve employs a spring-loaded spool to regulate downstream pressure. If the valve setting is above the downstream pressure, the fluid flows from inlet to outlet freely. The pressure is reduced by the use of an adjusting screw via a handle mounted on top of the valve. Adjusting pressure reducing valve manufacturers produce different types of these valves for use in various applications. The valves are produced using various materials and meant for specific use. These valves are used in applications such as water, steam, air, and gases among others. 

Figure: Adjusting pressure reducing valve.

Components of an adjusting pressure-reducing valve 

Valve body 

This is the main part of an adjusting pressure-reducing valve used to cover internal parts. The body is usually strong and it is made of metallic materials like brass, stainless steel, and carbon steel among other strong materials. The body also contains the valve ports where fluid enters and leaves the valve. 

Adjustment handle 

This is the component placed on top of the valve and it is where the valve operator applies force to turn a screw to either increase or reduce fluid pressure leaving the valve. 

Adjustment spring 

This spring connects the diaphragm to the handle and adjusting screw. The spring helps to press the diaphragm to vary the pressure as necessary. 

Adjustment screw 

This is a screw that connects the handle to the adjustment spring. The screw helps to transmit torque applied by the valve operator on the handle to the valve diaphragm via the spring. 

Seats 

Adjusting pressure reducing valve manufacturers design these valves with several seats. The seats help to provide tight seals that prevent fluid leakage for example between the valve disc and the valve body. 

Gaskets 

Gaskets are components used to prevent fluid leakage. The gasket can be metallic or soft material depending on the operating temperatures. The gaskets are placed between the valve and pipe mating surfaces. 

Pilot valve 

This is a small valve within the pressure-reducing valve which determines the flow of fluid into and out of the control chamber. It helps to regulate fluid flow and maintain constant fluid pressure. 

Figure: Components of an adjusting pressure reducing valve.

How does an adjusting pressure-reducing valve work? 

Adjusting pressure-reducing valves operate by converting high pressure to low pressure. Fluid enters the valve at high pressure and exits via the outlet port at low and constant pressure. As such, adjusting pressure-reducing valve manufacturers aim to produce a valve that can lower inlet fluid pressure to a manageable and consistent level through a spring-loaded diaphragm and piston arrangement. 

To start an adjusting pressure-reducing valve, the valve operator sets the outlet pressure required. This is done using a wheel or dial on top of the valve. As such, the compression spring adjusts its tension holding the diaphragm in place. Adjusting pressure reducing valve manufacturers design the valve such that fluid can flow through the valve when the upstream pressure is below or remains at settings for downstream fluid pressure. In such cases, the pressure will not be sufficient to force the spring back which can effectively close the valve. Demand on the outlet end causes pressure drop which keeps the valve open. When the inlet pressure exceeds the outlet pressure, it overpowers the spring tension set up by the operator. As such, the downstream pressure forces the diaphragm to move upwards effectively closing fluid flow. 

Figure: Working of an adjusting pressure reducing valve.

Types of Adjusting pressure reducing valves 

Direct-acting adjusting pressure reducing valve 

This is the most basic type of an adjusting pressure-reducing valve. This valve is categorized based on diaphragm type and piston type. Of the two, the diaphragm type is mostly used because it has tight seals and long service life. Adjusting pressure reducing valve manufacturers design this valve for use in small loads and where precise fluid pressure control is not so important. This valve is the simplest of all adjusting pressure-reducing valves and it is meant for point-of-use installation. It is the cheapest among all the adjusting pressure-reducing valves. However, this valves has more pressure variation from the set point compared to other valves. Direct-acting adjusting pressure reducing valves accuracy is around +/- 10%.  

The fluid entering the valve flows through the valve strainer where any dirt or other foreign materials are filtered out. The fluid then proceeds into the valve where it pushes on a seating disc to force it to open. This valve works through force equilibrium system that is diaphragm force operates an adjusting spring. The downstream fluid pressure pushes on a large area of the diaphragm where it tries to close the valve. The point at which the valve shuts off is the set point. This set point is created by adjusting spring tension. More tension helps to open the valve and raise the set point. Low tension reduces the force attempting to open fluid flow and thus it shuts off a lower set point. An increase in demand reduces the downstream pressure and hence the pressure trying to close the fluid flow. This forces the adjusting pressure-reducing valve to open and then restore the required fluid pressure. 

Figure: Direct-acting adjusting pressure reducing valve.

Pilot-operated adjusting pressure reducing valve 

This is an adjusting pressure-reducing valve that is used for large loads. Due to the large loads associated with this valve, it needs close pressure control. This valve has a fast response to changes in load and it can operate in a wide range of fluid flow rates relative to the direct-acting valve. The size of this valve is also large and this increases its cost. Adjusting pressure reducing valve manufacturers design this valve with another small valve known as a pilot valve. This valve loads a diaphragm or piston to increase the downward force used to open the main valve. It is through this pilot valve that this valve gets its name “pilot-operated” which helps to enhance large fluid flow at low-pressure variation. The closure and opening of this pilot valve are controlled by balancing between secondary pressure and adjustment spring force. The pilot valve assists in delivering pressure to the main diaphragm or valve piston. The pilot valve creates downward force that is amplified by use of a diaphragm or piston. This then helps to open the main valve which enhances high fluid flow capabilities. 

Through the force amplification, the application of a small change on the pilot valve yields a large change in downstream pressure and fluid flow via the main valve. Therefore, it is through the pilot valve that this valve can have a fast response over a broad range of fluid flow rates. Adjusting pressure reducing valve manufacturers produce two types of this valve that is internally piloted piston operated type and an externally piloted valve. The difference between these two is that the externally piloted valve uses a double diaphragm while the internally piloted uses a piston for its operation. 

Figure: Pilot-operated adjusting pressure reducing valve.

Applications of adjusting pressure-reducing valve 

• Adjusting pressure-reducing valves are used in the commercial and domestic water supply. 
• They are used in the mining operations. 
• These valves are used in steam power plants to control steam and water flow. 
• Adjusting pressure-reducing valves are used in hospitals to control the flow of oxygen. 
• They are used in oil and gas industries. 
• They are used to control ram pressure in hydraulic presses. 
• Adjusting pressure reducing valves are used to control pressure in unit heaters, humidifiers, and sterilizers. 
• They are used in the food industry for cooking which makes the operation faster compared to one done at atmospheric pressure. 

Advantages of adjusting pressure-reducing valves 

• Adjusting pressure-reducing valves are versatile as they can be used in different applications. 
• They are fast in operation.
• Adjusting pressure-reducing valves are of simple and compact design. 
• They do not need separate feedback controllers or measuring elements. 
• These valves are easy to operate and maintain.
• They are highly reliable. 
• They are free from blockage due to the use of a valve strainer. 
• Adjusting pressure-reducing valves enhance stable and reliable pressure. 
• These valves help to reduce high noise levels frequent in piping systems with high fluid flow velocities. 
• These valves help to reduce the possibility of fluid leakage due to high pressure which then saves the user in terms of material loss. 
• Adjusting pressure-reducing valves help to stop water hammer and related effects due to pressure build-up in closing valves and taps. 
• These valves help to reduce energy consumption in applications that use heaters such as dishwashers, showers, and washing machines among others. 
• It prevents damage to other plumping fixtures due to high fluid pressure. 

Disadvantages of adjusting pressure-reducing valves

• These valves are of large sizes and thus they consume a lot of installation space. 
• They are more expensive relative to other control valves. 

Troubleshooting adjusting pressure-reducing valves 

Valve does not close 

• Bypass valve leakage or it is open. Check this valve and repair it as necessary. 
• Blocked pilot sensing line or it is not installed. Open the valve and remove the blockage or install it as necessary. 
• Ruptured pilot. Replace the pilot diaphragm components. 

Low delivery pressure 

• The pilot valve was adjusted to the wrong pressure. Adjust the pilot valve to the pressure recommended by the adjusting pressure reducing valve manufacturer.
• Undersize valve. Check the valve rating against the actual load to ensure they match the adjusting pressure reducing valve manufacturer’s instructions. 
• Low fluid supply pressure. Check the supply pressure and rectify it. 
• Ruptured main valve diaphragm. Replace the diaphragm. 

The valve does not open

• The orifice is plugged. Open the valve and remove the blocking materials. 
• Defective main valve diaphragm. Replace the diaphragm. 
• Blocked strainer. Open the strainer and remove blocking materials. 
• Dirt in the pilot valve seat. Clean the dirt. 

Light loads cause overshoot of controlled pressure 

• Dirt between the seat and main valve head. Clean the dirt. 
• Severely over-size valve. Adjust the screw to enhance the required fluid pressure for light loads. 

Overshoot of controlled pressure under normal loads 

• Dirt between the head and pilot valve seat. Clean the dirt. 
• Blockage on the pressure sensing line orifices. Remove the blockage. 
• Foreign materials between the seat and the main valve head. Open the valve and clean the foreign materials. 

Summary 

Adjusting pressure reducing valves are used to reduce incoming fluid pressure to a predetermined and safe constant downstream pressure level. Adjusting pressure reducing valve manufacturers design this valve with an adjusting mechanism to help adjust the required downstream pressure. The working components of this valve include a flexible diaphragm used to control the valve together with a compression spring. The spring is loaded by use of an adjusting screw. The diaphragm’s pressure side is connected to the outlet end of the adjusting pressure-reducing valve to ensure the controlled pressure is exerted on the diaphragm. The valve closes once the adjustment screw is retracted to ensure no load is applied to the valve spring. The valve opens once the adjustment screw is rotated where it applies force on the spring to the diaphragm which then forces the valve to open. 

Adjusting pressure reducing valve manufacturers produce two main types of this valve that is pilot-operated and direct-acting adjusting pressure reducing valves. These valves are used in applications such as commercial and domestic water supply, steam power plants, oil and gas, compressed air systems, hospitals, and mining operations among others. Advantages of purchasing an adjusting pressure reducing valves are fast operation, versatility, reliability, ease of repair, no blockage, and no damage to downstream pipes and valves.