Pressure control: solving water system problems

The water systems in domestic, commercial and industrial properties can present unique problems and challenges as plumbing fittings become ever more sophisticated.

The water supply pressure in the UK can vary from 1bar to 20bar (or even higher in some low usage areas). The water pressure will also tend to vary through the day, for instance at high usage times (typically mornings and late afternoons),the pressure may drop by comparison with low water usage times (throughout the night, for example), when the pressure may increase dramatically.

Such periods of high pressure can cause several problems: excessive noise from high flow velocities, water hammer from quick closing taps or solenoid valves, plus the risk of water wastage is particularly great because higher pressure means higher flow rates.

The water supply usually enters domestic dwellings beneath the kitchen sink so the first effect of high pressure is often experienced at that point; when the cold tap is turned on too quickly or too far, this creates a gush of water which hits the bottom of the sink and bounces back, soaking the user and creating a wet mess!

The best way to control high pressure is by installing a pressure reducing valve. These take a high pressure at the inlet, then the valve reduces it to a lower pressure at the outlet as desired, under both flow and no-flow conditions.

All Reliance pressure reducing valves are WRAS approved: this means that they have undergone independent third party testing to ensure that they comply with the current. UK water regulations for pressure reducing valves. It also ensures that all materials used within the make-up of the valves have been verified as safe for potable water systems.

How do pressure reducing valves work?

A pressure reducing valve is a valve which takes a high inlet pressure and reduces it to a lower outlet pressure. When it does this under both flow and no-flow conditions, the type of control is known as ‘drop tight’.

reducing valves use a balanced spring and diaphragm to control the downstream pressure.

This ‘drop tight’ feature is one of the most important criteria for any pressure reducing valves, as this stops the pressure from ‘creeping’ - a term which is used when an increase in the downstream pressure occurs under no flow conditions.

A valve which will allow this ‘creep’ cannot be known as 'drop tight' or in fact a true pressure reducing valve, as it will eventually allow the pressure to creep up to equal the upstream pressure, which can cause significant problems and essentially negates the point of using a pressure reducing valve in the first place.

The diaphragm effectively separates all of the water contact parts and the pressure from the water supply away from the control spring and associated mechanism. The body is then protected from debris by the use of a stainless steel strainer. Under no flow conditions the downstream pressure puts back-pressure on the seat and diaphragm of the valve, which in turn overcomes the spring pressure. This means the seat moves up, forcing it to seal against the diaphragm, therefore not allowing the downstream pressure to increase.

Under flow conditions the back pressure against the seat is reduced thus allowing the seat to open and water to flow through the valve.