1. THE PRESSURE REDUCING VALVE: DEFINITION

Pressure reducing valves are used throughout high-rise buildings to prevent excess pressure and to thwart pressure surges and water hammers caused by pump stops and starts.

What does a pressure reducing valve do?

A reducing valve or pressure reducing valve (PRV) is a type of safety valve used to control or limit the pressure in a system; pressure might otherwise build up and create a process upset, instrument or
equipment failure.

What is PRV in plumbing?

A pressure reducing valve (PRV) is a mechanical device designed to lower the working pressure of a fluid from the supply side to the point of use side in a system. Pressure reducing valves
operate by using an opposing force to act against the supply water pressure by means of a spring-loaded diaphragm.

What is a PRV and where is it located?

They are most often close to the house near the point where the incoming water pipe enters. Pressure reducing valve is also located on your water heater, it is actually a temperature/pressure reducing valve. Sometimes a "pressure only" reducing valve will be located on supply piping also.

What causes a pressure reducing valve to leak?

If a recently replaced reducing valve starts leaking again, it probably means that the reducing valve is only doing its job; it relieving excess pressure in the water heater. When this happens, the fix gets a little bit more involved. When a water heater heats up the water in the tank, the water expands.

2. TYPES OF PRV

There are three types of PRV

1. Diaphragm or Convoluted Bellows
2. Internally piloted piston-operated
3. Externally piloted

                                                                                        

 

Diaphragm or Convoluted Bellows

                                                                         

This valve reduces the pressure of the water that goes through it and is used to obtain a regulated and constant value at its outlet.

It is installed at the water mains (for a bungalow as for a flat). It protects the whole installation from problems due to excess pressure: noises in the pipes, water hammer, splashes, premature wear of household electrical appliances and taps.

 

3. WATER SAVING:

• Water represents a major part of project & facility management budgets.
• Not wasting it makes for real solving.
• Less pressure means less water used, and therefore less energy consumed.

Through its low load losses, the pressure reducing valve allow the obtaining of a normal flow rate when water in drawn in several places simultaneously.

 

• Example with a tap running for 10 minute

• A considerable amount of the distributed water is directly dumped into the sewer without even having been truly used (see illustration above).
• Reducing the pressure, all in obtaining comfort in use, allows for real savings.
• In all cases, make a regular check of the condition of the tap and toilet flusher seals: a leak consumes a lot more water than you think.

 

4.PRESSURE REDUCING VALVES OR REGULATORS?

We use the standardized official term « REDUCER », but a pressure reducing valve is highly sensitive to upstream pressure variations and regulates badly without water flowing.

The direct action pressure reducing valves regulate the downstream pressure as well with or without water flowing. The downstream pressure only varies by 8% from the upstream pressure variation. These appliances are therefore PRESSURE REGULATORS.

 

5.HOW TO CHOOSE THE DIAMETER OF PRESSURE REDUCING VALVES?

• Practical rule: the pressure reducing valve is generally chosen according to the diameter of the installed pipe, provided, of course, that the latter is of the right size.
• The choice of pipe diameters must follow the rules of the trade and must conform to the standards in force. Refer to the flow rate curves of each pressure reducing valve, given in the technical documents.

                                                                                     

INSTALLATION:

• Reducing valves may be installed in all positions.
• They are generally installed directly after the water meter, and thus protect the whole installation.
• Advantage of a pressure gauge connection on the front : when 2 tubes are parallel with the wall, one above the other

 

7. HOW TO ADJUST A PRESSURE REDUCING VALVE?

• The Pressure reducing valves are factory preset at 3 bar. They remain adjustable within a 1.5 to 5 bar range or can be adjusted as per building requirements.
• To increase the pressure, tighten the adjusting screw (clockwise as you look at the screw from above).
• To reduce the pressure, undo the adjusting screw (anticlockwise as you look at the screw from above), slightly open a tap for a moment, close again, and then tighten the screw again until you obtain the desired pressure.
• Two 1/4" gauge ports are located on each side of the valve when a pressure gauge is required to be fitted.

When opening the downstream tap (drawing), it is normal to see the pressure drop: this is the load loss of the appliance. This value is given in the appliance flow rate curves (see technical documents).

8. PRECAUTIONS

• Direct action water pressure reducing valves are insensitive to scale or impurities, and need no maintenance or particular precautions provided that they are installed according to the rules of the trade.
• However, if there is a risk of back pressure or water hammer in the downstream circuit, you are advised to protect the pressure reducing valve by a non-return valve placed immediately downstream.

 

 

9. PRESSURE GAUGE: THE ESSENTIAL ACCESSORY

• The pressure gauge allows direct reading of the pressure, and thus allows precise adjustment of the pressure reducing valve to local installation conditions.
• The pressure gauge should not remain under pressure – the installation of an isolating valve is recommended.

 

                                                                            

10. CASE STUDY: 43-STOREY BUILDING - « NORMAL » WATER MAINS PRESSURE: 6 BAR - DESIRED PRESSURE IN EACH FLAT: 2 BAR

• In the case of a residential building, it is advisable to install a pressure reducing valve at the input of each riser in the plumbing shaft.
• Each PRV will serve a zone of 7 floors. Outlet pressure of PRV is set to 1.5 bars so that maximum pressure at the lowest floor will not exceed 3.3 bars. This is safe working pressure for all CP sanitary fixtures.