Maintenance Technician I
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Ensuring Practical, Safe Working Water Pressures Municipal and private water supply companies use pumps and pumping stations to boost water supply pressures in supply mains to be able to supply water for fire fighting, high rise buildings to overcome loss of pressure as the elevation increases, and to maintain water supply in water towers and supply tanks. Pressure in water supply mains can exceed 200psi. Most plumbing codes require water pressure reducing valves on domestic systems where the municipal water main’s pressure exceeds 80psi. Higher pressures could rupture pipes, damage fixtures,and injure the people using them.
High water pressures waste water. Many municipalities today not only charge homeowners and businesses high rates for water consumption, but also charge consumers equally high rates for the disposal of wastewater. Furthermore, reducing water consumption, reduces the excess energy required for heating additional hot water.
There are two types of water pressure reducing valves, direct acting and pilot operated. Both use globe or angle style bodies. Valves used on smaller piping diameter units are cast from brass; larger piping diameter units are made from ductile iron. Direct acting valves, the more popular type of a water pressure reducing valves, consist of globe-type bodies with a spring-loaded, heat-resistant diaphragm connected to the outlet of the valve that acts upon a spring. This spring holds a pre-set tension on the valve seat installed with a pressure equalizing mechanism for precise water pressure control.
Installed in series directly after the water meter in homes, commercial buildings, and manufacturing plants, a water pressure reducing valve automatically reduces the pressure fromthe water supply main to alower, more sensible pressure.
Water entering the valve from municipal mains is constricted within the valve body and directed through the inner chamber controlled by an adjustable spring loaded diaphragm and disc. Even if the supply water pressure fluctuates, the pressure reducing valve ensures a constant flow of water at a functional pressure, as long as the supply pressure does not drop below the valve’s pre-set pressure.
A properly sized valve prevents noisy operation or premature valve failure. Over sizing water pressure reducing valves can lead to problems such as wire draw under low flow conditions. In general, the minimum flow through a water pressure reducing valve should be 10% to 15% of the maximum flow rate desired in the system. Also, water pressure reducing valves should be selected based on the flow and pressure ranges listed in the literature, not the size of the pipe to which they will be attached. You should select a regulator whose operating pressures fall within the middle of its rated range.
Watts water pressure reducing valves can increase your water system’s performance, reduce operating costs, and ensure a longer life for other plumbing fixtures. Most simple pressure reducing applications require the installation of a single regulator. However, there are applications that require the use of more than one unit installed in a specific system configuration. When there is wide variation in pressure between the municipal main’s inflow pressure and the functional pressure needed within the building, or when the main’s pressure exceeds 200psi, you should consider using a two-stage, serial reduction configuration. When you want to maintain a continuous supply of water at reduced pressures, you should consider a parallel installation.
The two-stage serial reduction approach uses two valves in series to reduce or eliminate extreme variations between the water main’s inflow pressure and the desired, final reduced pressure. Two stage reduction is recommended when initial pressures are 200psi or greater, or when the desired pressure reduction ratio is greater than 4:1, e.g., from 200psi to 50psi, or where the inflow pressure fluctuates greatly. The advantage of two-stage serial reduction is that neither valve is subjected to extreme pressure differentials, thus prolonging valve life and delivering more precise pressure regulation.
The parallel installation makes use of two or more smaller size water pressure reducing valves serving a large size supply pipe main. This approach should be used wherever there is a wide variation of reduced pressure requirements such as an apartment building where demand could be .5 gpm at 1am and 100 gpm at 6am and where you must maintain a continuous water supply. Parallel installations also offer the advantage of providing increased capacity where needed beyond that provided by a single valve. In addition, the parallel configuration improves valve performance for wide variable demands and permits servicing of an individual valve without shutting down water flow to the building completely, thus avoiding costly shutdowns.
To facilitate installation and servicing of the regulator, Watts offers a variety of end fitting configurations, which include union fittings (female threaded, solder, cpvc, and pex), flanged valves, water meter threads and special lay lengths for water meter installations. Please refer to the valve model for specific availability of end connection options.
Using Performance Curves
To match the valve characteristics to system requirements Watts provides performance curves on WPRV specification sheets for each type and size of valve giving the capacities of each with reduced pressure fall-offs up to 25psi. By the use of these charts, the most suitable and economical valve can be selected to satisfy the job requirements. The charts or curves for all types are plotted on a simple basis of rate of flow plotted against the reduced pressure fall-off. In the left hand column, the reduced pressure fall-off is listed up to 25psi. Along the bottom, is listed capacity in terms of gallons per minute flow. In the reduced pressure fall-off column, the “0” represents the reduced pressure setting of the valve when there is no flow (reduced lock-up pressure).
Want more information?
For more information please see our Watts Water Pressure Reducing Valves product guide.