Three top tips on installing PRVs

Close Button

The primary purpose of installing a pressure reducing valve (PRV) is to ensure homeowners’ water systems are kept safe, stable and protected from costly remedial work. It’s a safety feature within all plumbing and heating systems that stops too much pressure from damaging your pipes, fittings and applications whilst minimising injury. Not only that, PRVs play an important part in today’s increasing need to conserve water. In this blog, we look at three top tips on installing PRVs.


PRV held by a plumber with copper pipe connections

1. Size matters


Choosing the correct size of PRV is crucial to ensure the valve can perform at its optimum valve performance. The sizing of PRVs cannot be underestimated. If the flow rate is constantly low and the PRV is oversized, the seat of the valve can erode over time. This means that the PRV will not be ‘drop tight’ and would allow the downstream set pressure to ‘creep.’ A PRV is considered ‘drop tight’ if it can perform two important functions. One, that the set outlet pressure remains un-affected by fluctuations of inlet pressure, and two, any pressure that rises occurs downstream of the valve.

However, if the valve is undersized, it can become very noisy every time the outlets are opened and shut. This is due to the large volume of water squeezing through the valve, which causes the internal spring to vibrate under strain, in turn creating a ‘water hammer’ effect in the pipework.

Flow rate is the most important factor when deciding which size PRV to install. To work out the correct size, you must identify how many outlets are required and what the combined maximum flow rate will be.

PRVs are sized by DN (Diameter Nominal). The following chart shows the maximum flow rates when you consider the nominal size of the PRV and pipe:


Nominal size Maximum flow rates (residential)
PRV size (DN) Pipe size (inches) Litres per minute
15 1/2 30
20 3/4 48
25 1 78
32 1 1/4 120
40 1 1/2 138
50 2 216
65 2 1/2 390
80 3 540
100 4 750
125 5 1050
150 6 1500
200 8 2400
250 10 4500



The minimum pipe length downstream of the PRV, before any elbow fitted, must be no less than five times the pipe work size. This is to protect against noise and to ensure a laminar flow.


2. PRV placement


PRVs can be used with any hot or cold-water system. Installing them to the mains supply after the main shut off valve will accurately control the system pressure. PRVs will also control the flow rate of the water running through the system – this protects fittings and appliances from experiencing blowouts of water at a fast rate at any outlet.

Installing a PRV to the main water source system protects the home from the high-water pressure coming from the main road supply. For example, if a number of homes have their water turned off for a length of time, a huge amount of pressure can build up. Without a PRV, this could cause outlets within the home to blowout at an uncomfortable pressure.

This is another reason why it’s good practice to choose a PRV that is drop tight. It will maintain system pressure under no flow conditions, even if the supply to the PRV has significantly increased due to an extended period of inactivity.


3. Check, then check again


Commonly installed prior to a water meter on entry to the house, PRVs need to be placed in a position where they can be easily tested and maintained if needed. When installing a new PRV to a system, it must be cleaned and flushed as outlined in the Water Regulations 1999, to ensure contamination of the mains supply does not occur. Best practice is to make sure the valve is cleaned every year, eliminating any system debris that could have built up.

Most valves include an integral strainer that that prevents debris affecting the valves function, and can be removed, cleaned and de-scaled if necessary.

You should always ensure a gauge is used when commissioning the valve. This makes sure the valve pressure is set accurately, and to check that the outlet pressure remains unaffected during normal operating conditions.

When an outlet is opened, the pressure in the valve will slowly drop off as water flows out. Once the tap is closed, the pressure should return to its normal ‘set pressure’. It is recommended that installers check the PRV 24 hours after installation, to ensure no creeps in this set pressure occur.

The best practice would be to always check the pressure once installed. As the pressure builds within the valve, the tap will open until the pressure of the tank decreases to reach the minimum setting. After you close the tap the pressure should build back up, showing that the system can hold at the required pressure. It’s recommended to leave the PRV on a test run overnight, to make sure it’s holding steady.

It is not a legal requirement to install a PRV, however, it’s in the best interest of future-proofing plumbing and heating systems. This valve eliminates water waste and damage, providing a sustainable solution for the modern-day water system.

At RWC, our team of technical experts are with you all the way to offer advice on installation best practice to future-proof plumbing and heating systems and to help build energy-efficient homes. If you’ve got any questions, please contact us here.


See also…

Speeding up plumbing installations in multi-occupancy buildings

Simplifying installations for new plumbers

Introducing Reliance Valves with JG Speedfit connections – Part 1 the Easifit TMV

Reliance Valves with JG Speedfit connections – Part 2: 312 Compact PRVs

How to prevent backflow in the home

Backflow prevention and why it’s important while battling a crisis

Author: JG Marketing