Common Problems in Pressure Reducing Valves (PRV)

There are many common problems in pressure reducing valves that water treatment plant operators may encounter. Which must be known to avoid plant shutdown. If noticed, they must be solved immediately and not wait for the periodic maintenance date.

What are pressure reducing valves?

A pressure reducing control valve is a hydraulic control valve that reduces the high inlet pressure value to the lower required pressure value. The pressure reducing control valve maintains the required outlet pressure value to be set at a constant rate without affecting the pressure reducing control valve current and the inlet pressure value. When there is no flow in the system, the valve closes itself automatically and without any leakage. When the valve inlet pressure value in the system drops to less than the required inlet pressure value, the valve opens itself completely. The valve can be used in a horizontal or vertical position in the system. There are different ways to apply pressure reduction: mechanical, electronic, and hydraulic.

In this article, more about pressure reducing valves and their importance.

Pressure Reducing Valves Applications

In municipal networks

Pressure reducing valves (PRV) are required at the inlet of pressure zones or DMAs (area measuring zones). On the one hand, to protect downstream equipment and household plumbing from overpressure. On the other hand, to ensure sufficient and reliable pressure for consumers.

Irrigation

Pressure reducing valves are required at the inlet of low-rise fields, pivot machines, low-pressure systems such as drip lines and more.

In high-rise buildings

Pressure reducing valves are located on every floor or every few floors. To protect the section plumbing and low-rated fixtures and connections from overpressure.

How do pressure reducing valves work?

Hydraulic pressure reducing valves are equipped with a pressure reducing sensor designed to sense the pressure downstream hydraulically.

The pressure in the valve is reduced by throttling/closing when the downstream pressure increases above the sensor pressure setpoint and opening the valve when the downstream pressure drops below the sensor pressure setpoint.

Valve Closed Condition

If the downstream pressure is higher than the required set point. The pilot allows water to flow from the downstream direction into the control room and the valve tends to close.

Regulation Only Condition

When the downstream pressure is equal to the required set point, the valve keeps the water in the control room and the valve remains in the same position, neither opening nor closing, thus maintaining the set pressure.

Valve Open Condition

When the downstream pressure is lower than the required set point, the valve discharges water from the control room to the atmosphere and the valve opens.

In waterworks and buildings, two-way control is also common. It has somewhat different operating principles.

This video explains how a pressure reducing valve works

What are the common types of pressure reducing valves?

System pressure can vary due to many different reasons. Pump start-up, changes in terrain, pipe characteristics, resistance of equipment along the system, leaks water theft and of course, the pattern of demand flow which has a direct impact on pressure loss through the pipeline.

In water plants and buildings, some systems provide water 24/7, and the flow is constantly changing throughout the day.

While in irrigation and fire protection, the flow is constant and occurs in shifts/pulses, depending on crops or fire emergency events.

Based on this understanding, there are many different types of pressure reducing valves and configurations that ideally suit these diverse requirements.

Some rely on a three-way control loop and others on a two-way loop. Others are full bore for minimal pressure loss during insufficient inlet pressure and others are reduced bore for effective pressure regulation.

Some have chokes to handle low flows, and others have different mechanisms to eliminate/limit cavitation.

Important Instructions for Installation

1. The nominal diameter of the valve must be the same as the diameter of the line or a smaller nominal diameter.
2. You must install the valve horizontally in the direction of the arrow mark on it.
3. It is recommended to use an isolation valve (butterfly valve or slide valve, etc.), an air relief valve, a rapid pressure relief control valve, A dirt stop valve when installing the valve on the line.
4. Cavitation hazards pose a risk to the valve body during pressure drops. You must adjust the required outlet pressure value by looking at the cavity table or asking for help from the technician.

Operation Steps

1. Turn on the pump or supply water to the system by opening the main valve in the network.
2. Open the circular valve located at the valve inlet and close the circular valve located at the valve outlet.
3. You must wait for a period of time for the water to reach the valve control chamber. When the water reaches the control chamber, the pressure gauge will show a specific pressure value.
4. You must adjust the required outlet pressure value by using the adjustment screw by looking at the pressure gauge.
5. When the adjusting screw is turned clockwise, the outlet pressure value increases, and when turned counterclockwise, the outlet pressure value decreases.
6. After setting the desired outlet pressure value, you must tighten the tightening nut located under the adjusting screw. The role of the circular valve is to pump water into the system. After closing the valve, the pressure gauge will indicate zero.
7. You must check the outlet pressure value continuously.

Maintenance Steps

1. You must check and clean the valve parts according to the water quality. Do not clean them more than once every few months unless the water is very dirty.
2. You must empty the water in the valve actuator and valves not used in the winter season.

Some Common Problems

If the valve does not work:  The ball valve at the valve inlet and outlet may be closed. The valve outlet pressure may be too low, or the pilot valve adjusting bolt may be too loose.

Maintenance: Check the ball valve, if it is closed, open it, set the adjusting bolt to the desired value, and tighten the tightening nut.

Valve does not close: The diaphragm may be torn, or there may be foreign matter in the diaphragm position. The pilot valve connection may be clogged with foreign matter.

Maintenance: Check the diaphragm and if it is torn, replace it with a new one. Then check the diaphragm position and clean foreign matter if present, check and clean the connections.

Valve operation is irregular: The moving parts of the pilot valve may be clogged due to calcification. The needle valve or nozzle at the inlet of the pilot valve may be clogged, and the pressure gauge may be faulty.

Maintenance: Replace damaged parts, and clean them only if they are clogged.

Conclusion

The hydraulic pressure reducing control valve operates fully automatically with the main pressure without the need for any external power.

The two-way pressure reducing pilot valve used in the control valve reduces the outlet pressure to the desired value without being affected by the flow rate changes in the network.

When the inlet pressure value in the network drops below the desired outlet pressure value, the valve opens fully.

In water transmission networks with variable flow rates. It is recommended to connect a pressure reducing control valve with a smaller diameter than the existing pressure reducing control valve to the network as a bypass.