As UK plumbing systems become ever more advanced and plumbing equipment becomes more sophisticated, mains pressure is being used increasingly in situations that used to be the domain of low pressure gravity systems: typically to accommodate unvented hot water heaters, continental style multi outlet showers, and electronic controls, for example. As the use of such systems and specialised fittings spreads, so too is the use of pressure reducing valves in order to control and regulate the pressure and flow to the terminal fittings.
Why reduce pressure?
A fundamental question! Most people in the UK probably feel they have spent far too much of their time chasing about in their shower trying in vain just to get wet. Water pressure is so low in some cases the tendency is to think that if you have the chance to get high pressure, why in the world would you want to limit it? In this technical spotlight, we will look at the question of why pressure needs to be controlled as well as explain the basic function of a Reliance Pressure Reducing Valve (PRV) and the different valve characteristics for different applications.
How much is too much?
In the UK, water pressure from the mains can vary by location from between 1 Bar to 10 Bar, and in some places at low usage times the pressure can be even higher than that. The water pressure is also variable throughout the day, with pressures increasing at night and in the middle of the day but dropping at high usage times: eg first thing in the morning and late in the afternoon.
Generally speaking for most domestic applications a pressure of around 3 Bar is sufficient if the internal plumbing system is designed and installed correctly. Water pressures above 3 Bar can start to cause problems such as excessive noise from high flow velocity, water hammer from ceramic disc taps, solenoid valves on dishwashers and washing machines or other quick closing valves. It is also wasteful, as higher pressures mean higher flow rates and ultimately higher water bills. Also, modern plastic plumbing products may be susceptible to rapid deterioration if exposed to water pressures above 10 Bar for any length of time, which can result in potentially catastrophic failure and significant property damage if their allowable pressure/temperature envelope has been exceeded.
One simple way to prevent these difficulties and protect the plumbing system from overpressurisation is to install a pressure reducing valve at the entrance to the property which will limit and maintain the incoming mains pressure at the desired level.
What is a PRV?
The Reliance range of Pressure Reducing Valves (PRVs) are balanced spring and diaphragm type valves, which will limit the downstream pressure to a predetermined maximum under flow and no-flow conditions. A valve that works under flow and no-flow conditions is also said to be ‘drop tight’. The most important criterion for a pressure reducing valve is that the valve must be drop tight, i.e. pressure does not increase downstream of the valve under no-flow conditions. It must be emphasised that 99% of pressure reducing valve applications require the pressure to be limited to a maximum predetermined level under flow and no-flow conditions.
Another term that is used in relation to the operation of a pressure reducing valve is ‘creep’. This is a slow or small increase in downstream pressure under no-flow conditions. Creep may be caused by the valve seat being compressed, in which case there will only be a small increase in downstream pressure. This can occur with all drop tight valves with resilient (soft) seats under changes in inlet pressure. What should not occur is a slow creep in outlet pressure until it equals the inlet pressure.
Applications
There are many different applications for PRVs: they can be used just about anywhere that water pressure needs to be controlled. There are however certain types of Reliance PRV which have been developed with particular applications in mind.
Commercial Sector
The Reliance 315 HC series PRV is very popular for the commercial market and is used extensively in areas such as high rise property developments, hotels, sports stadiums, schools, prisons and leisure centres.
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| RWC-SYR Commercial 315 HC Dial-Up Series Pressure Reducing Valve |
Reliance Commercial/Industrial 6247 Series Pressure Reducing Valve |
Several features make the 315 HC series attractive to the commercial market:
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It is a dial-up type PRV. This means the valve has an indicator dial on the valve which will move as the adjustment knob is turned; this indicator will show the downstream pressure that the valve is set at to within 0.2 of a Bar. This feature can save significant time and cost when commissioning a large system.
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The valve is full cartridge-type construction, which means only one spare part ever needs to be kept to fully service the valve. It also saves significantly on downtime if repairs are ever required, as a full cartridge change can be done in less than a minute.
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The 315 HC series is suitable for cold and hot water up to 80 ° C , meaning that only one valve needs to be specified and only one range of spares needs to be stocked.
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As this valve is targeted specifically at the commercial sector, which can have significantly higher peak time demand for flow rates, the valve has been designed to give maximum flow with the absolute minimum pressure loss.
Reliance has also developed a new valve group called the Tenant Valve Assembly , around the 315 HC PRV cartridge. This is a combination type valve which incorporates an isolating ball valve, a double check valve, a pressure reducing valve: with all the benefits of the 315 HC PRV and a provision for a water meter cartridge in one compact valve. It is ideal for any multi-unit development for: zone isolation, backflow protection, pressure control, and if required, water metering
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Reliance Tenant Valve Assembly, shown with optional pulse output cap and water meter cartridge.
Domestic Sector
NEW Easiset 320 Series Domestic Pressure Reducing Valve from Reliance
Reliance’s new 320 Easiset PRV is the latest addition to the range of pressure reducing valves for the domestic market. Because issues such as servicing and maintenance are just as important in domestic property as they are in commercial environments, the 320 Easiset range also incorporates our patented one piece cartridge-type construction and the valve is available for temperatures up to 80 ° C . Its biggest innovation though is the pull and twist adjustment mechanism which eliminates the need for cover caps and difficult-to-reach adjustment screws. When the cap is pulled up and turned, the pressure is adjusted; when finished, the cap is pushed back down and automatically locks in position. This new range is available in 1/2”, 3/4”, 15mm and 22mm compression sizes and in hot or cold water versions
As the UK moves progressively towards the North American/Continental style of high pressure water systems, new and innovative products will need to be developed to ensure that the provision of water to the end user is achieved in a controlled and efficient manner. Reliance has been at the forefront of pressure control in the UK for over 20 years and will continue for many years to come to provide reliable, high quality products which are easy to use and maintain, to achieve pressure reduction.
Written by Eric Winter, Technical Manager, Reliance Water Controls
Copyright - Reliance Water Controls Ltd - November 2005
Reliance, RWC-Syr and Tenant Valve Assembly are all registered trademarks of Reliance Water Controls Ltd
Easiset is a trademark of Reliance Water Controls Ltd |
