Water supply to a house doesn’t always come at the perfect pressure; the municipal water main pressure may be too high or too low for a home’s needs. Different regulating devices are available to compensate for the various problems with water supply pressure. The following lists the basic types of devices and their uses.
Pressure Reducing Valve: These devices can lower the pressure in your house by about 10 to 15 psi. Most residential plumbing codes require a pressure reducing valve to be installed, directly after the water meter, if the incoming water supply pressure is more than 80 psi. There are many types and brands on the market, but most consist of an adjustable spring loaded diaphragm in a bell shaped housing which acts to reduce water pressure between the inlet and outlet. They will also regulate pressure in the system to a constant, regardless of changes of pressure in the main supply line. A side benefit of installing a pressure reducing valve is that it will help to prevent or lessen the occurrence of water hammer noise in your lines.
Booster Pump: When a house’s plumbing system has a lot of plumbing fixtures, like sinks, toilets, whirlpool baths and showers and the supply main has low pressure, a booster pump can be added to the system to raise the pressure. A drawdown tank, such as a hydro-dynamic bladder, and a pressure switch starter disconnect will also need to installed. Alternately, you can purchase an integrated system, like the ones manufactured by Amtrol, which contain a pump, tank and controls all in one unit.
Sizing a booster pump involves calculating both the flow required, in gallons per minute, for the system, and the system pressure, in pounds per square inch (psi), required. Determining required system pressure involves 3 main factors: friction loss in the piping, static height of the fixture located furthest vertically, and minimal required residual pressure at the fixture located highest and furthest away from the supply. The International Plumbing Code spec includes guidelines on requirements and should be consulted. Once requirements are determined, booster pump manufacturers have sizing tables in their catalog, website or brochure that will help find the correct pump for any given system flow and pressure requirement.
Vacuum Breaker: These act as backflow prevention devices. Backflows happen when water is siphoned back into the home’s system during a shut down or interruption of the main water supply service. If a home’s water supply also supplies its landscape irrigation system, there is the possibility that toxic herbicides, pesticides and other contaminants could be introduced into the home’s fresh water system and consumed. Therefore, many plumbing codes require a backflow prevention mechanism. The codes usually include specific rules on how and where the backflow prevention device is installed. For example, a shutoff valve should never be installed downstream of a vacuum breaker, since that would create continuous pressure on it. Vacuum breakers (also called Atmosphere Vacuum Breakers, or AVBs) are an inline valve, usually constructed from brass, with a sealed chamber which opens when water pressure drops too low, thus breaking the siphonage effect.
Pressure Balanced Shower Valve: Required by some local codes, it provides constant water pressure to showers to avoid fluctuations in water temperature, such as when a toilet is flushed. The intent of the local requirement is usually to prevent injury from scalding to people taking a shower. A pressure-balanced shower valve compensates for changes in water pressure with a diaphragm or piston inside which reacts to changes in hot and/or cold water pressure to balance the pressure. These valves keep water temperature constant, within a few degrees Fahrenheit.
Thermostatic temperature control valves are another anti-scald device which accomplishes the same function. They offer more control but are more expensive. Anti-scald devices are required for new construction only, where regulated by code, but they can be retrofit to an older shower without too much difficulty.