PRESSURE REDUCING VALUES

PRESSURE REDUCING VALUES

There are two general types of PRwile those that reduce pressure only while water is flowing, and those that regulate the pressure under both flowing and nonflowing (static) conditions. PRVs are used in both sprinkler and standpipe* systems to prevent system overpressurization.

1. The type found in most standpipe systems is the orifice disc. This PRV is a restricting orifice that is calibrated fo£ the standpipe hose outlet on which it is placed. When the normal hydrostaticpressure at a 2V.2-inch hose outlet valv£ exceeds 55 psi, each valve is equipped with an adjustable-orifice, disc-type PRV” that will reduce the pressure on th* downstream side of the PRV to not more than 50 psi when the discharge is 200 gpm from a one-inch nozzle at ^tached to 100 feet of 2 inch, unlined hose. This type of PRV reduces the pressure by regulating the flow, and therefore is only effective when water is flowing. (This is the reason that the nozzle required on hose outlets as , house lines do not have a shut-off on the nozzle.) These PRVs must be removed from the standpipe hose outlet valve when operating a hoseline from the standpipe and when supplying a standpipe system through a hose outlet valve. These PRVs should be marked with the address of the premises and with the floor location and setting for the location at which it is to be used. These PRVs are not interchangeable without being recalibrated.
2. Another PRV found in use is a type of adjustable, restricting orifice valve that is incorporated into the hose outlet valve stem. This type of PRV restricts the flow of water to the downstream side by permitting the hose outlet valve to be opened only to a desired preset, and is calibrated the same as the orifice disc PRV. To operate a line off this type of PRV, the pin that restricts the opening of the valve is removed, allowing the fire department to open this hose outlet valve all the way or set a desired flow’ condition. This PRV will only control the pressure when water is flowing. It will not reduce the static pressure.

When supplying a standpipe through a hose outlet valve equipped with this type of PRV, the pin should be removed and the valve opened all the way.

3. Another newer type of PRV is being installed on standpipe systems. It reduces the pressure both in a static and flowing condition. ‘Phis type of PRV, under normal conditions, cannot be removed from the standpipe hose outlet valve. If the flow or pressure desired is greater than the valve permits, a fire department override is provided. When this override is used, there is no overpressurization protection for the hoseline being operated from it. When it is necessary to supply the standpipe through a hose outlet fixed with this type of PRV, the override provision must be used.

When a sprinkler system supply is taken off of the standpipe riser, a PRV should be installed to prevent overpressurization of the sprinkler system. This type of PRV valve will operate both in a flowing and in a static condition.