- Determine standpipe or sprinkler riser residual pressure for each valve location.
- Turn to appropriate valve chart, based on valve size and body style. The
valve flow range for each chart is indicated in the lower right corner of the chart. Be
sure to use the correct chart for the designed flow rate through the valve.
- Locate the valve inlet residual pressure on the vertical axis of the chart and
draw a line from this pressure horizontally across the chart.
- Locate the desired valve outlet residual pressure on the chart horizontal
axis and draw a vertical line from this pressure value across the chart.
- From the intersection of the inlet and outlet pressure lines constructed in
3 and 4 above, move horizontally to the nearest valve performance curve. This will be
the appropriate valve for the chosen location.
- To determine the valve static outlet pressure, refer to the appropriate
static chart. Locate the standpipe or sprinkler riser static pressure on the vertical
axis of the chart. Follow across to the appropriate valve curve and drop down to the horizontal
axis to read valve outlet static pressure.
When sprinkler system supply pressure exceeds the maximum allowable static
pressure on the system, it is recommended that a small relief valve be installed on
the discharge side of each pressure reducing valve. Since the pressure reducing valve
may be subjected to a large static pressure differential from inlet to outlet,
the outlet pressure can easily build up to an undesirable level due to pump tests or
slight leakage. Due to the incompressibility of water, a very minute amount of leakage, or
even "O"-ring deformation, can produce a large pressure increase on the downstream side
of the valve.
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