3-39. HIGH-PRESSURE RELIEF VALVE. (Figure 3-47)
a. General. The high-pressure relief valve provides safety release if pressure produced by the R.O. pump
rises above 1100 psi (77.33 g/cm2), as read on the R.O. pressure psi gage. The R.O. pump normally produces
about 900 psi (63.27 kg/cm2). This paragraph describes testing and servicing of the high-pressure relief valve.
When relief valve trips, it shoots out a high-pressure jet of water
which could cause physical injury to personnel. During test, aim
output port away from personnel.
(1) Attach valve port (8) to metered high-pressure water source.
(2) Increase pressure gradually. Valve should open at 1100 ± 25 psi (77.33 ± 1.76 kg/cm2).
(3) If valve fails to open between 1075 and 1125 psi (75.57 and 79.09 cm2), adjust valve:
(a) Loosen locknut (2).
(b) To raise activation pressure, turn adjusting screw (1) clockwise.
(c) To lower activation pressure, turn adjusting screw (1) counterclockwise.
(d) After adjustment, tighten locknut (2).
(4) Reduce pressure and repeat test two more times.
(5) If valve cannot be adjusted to specified pressure range, return valve to next higher level of
(6) At end of test, check weep-hole (7) for moisture. If water has seeped through weep-hole, change
O-ring (6), as described in subparagraph c. below.
c. Servicing. (Figure 3-47)
(1) Disconnect valve from water source.
(2) Loosen locknut (2). Remove adjusting screw (1) with locknut (2) from valve cap (3).
(3) Remove valve cap (3) from valve.
(4) Remove keeper (4) with disc springs (5) from valve.
b. Testing and Adjustment.