Altecnic: An overview of PRVs

Ed Morris, Technical Manager at Altecnic, explains the basics of PRVs. Ed has worked in the heating, ventilation, air conditioning and plumbing industry for over 25 years and joined Altecnic more than seven years ago as Technical Manager.

Ed Morris
Technical Manager

What is a PRV?
A Pressure Reducing Valve (PRV) is a frequently misunderstood product. The operating principle is simple enough; they reduce the incoming pressure from a mains supply or a boosted pumped supply within a building. Their purpose is equally obvious – limiting high-pressure water that can seriously damage components in heating and potable water systems, which can lead to damage or even burst pipes and ruptured seals. A PRV reduces the pressure to a required value, but what frequently causes confusion is the difference between dynamic and static pressure.

Why should I install a PRV?
PRVs are installed in residential, semi-commercial and public buildings to reduce and stabilise the inlet water pressure.

If the pressure is too high it may prevent control valves from operating or isolating and on potable water application, the force of water from the tap or other outlet may be too fierce which could cause localised flooding.

PRVs are designed to reduce water pressure and maintain it to a set level preventing damage to those components installed downstream of the PRV.

PRVs are generally used on water and potable water applications. Some PRVs are also used on compressed air, natural gases and natural non-adhesive fluids. Importantly, they should not be used on salt water, petrol or diesel.

What is the difference between dynamic and static pressure?
Static pressure is the head or pressure of water in a system when that water is at rest. Static pressure control is therefore the maintenance of a set pressure within a system when there is no demand, i.e. no flow. This is particularly useful for single point of use outlets, especially where protection is required due to low pressure rating of, for example, washing machines and showers.

Dynamic pressure, in comparison, is the static pressure of the body of water but it also includes the momentum of the fluid in motion. Therefore, dynamic pressure control is the maintenance of a set pressure within a system when the water is moving.

The key difference is that a dynamic PRV will only control the pressure when water is moving. If there is no demand the pressure can creep up without regulation. Setting is done using a Pressure Gauge installed in the pipework or in the valve. Ideally the Pressure Gauge should be upstream of the valve.

How do I know which PRV to install?
There is a selection to choose from based on the application (cold water or hot and cold water service), with or without a pressure gauge, set using a screwdriver or a Dial up setting.

When it comes to static control valves, the Caleffi PRESCAL 535 series of pressure reducing valves are a high quality WRAS approved example. This series of pressure reducing valves have the feature to be pre-adjustable. The pressure reducing valve can be set to the desired pressure value before installation, using an adjustment knob with a pressure setting indicator. After installation, the system pressure will automatically adjust itself to the set value. The internal cartridge containing all the regulating components is pre-assembled as a “self-contained unit”, to facilitate inspection and maintenance procedures.

Find out more at altecnic.co.uk or head to stand 5E30 at InstallerSHOW.
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