Hale Q Series Muscle - Manual (Page 39)

39 MUSCLE (Midship) Pumps Installation, Operation, and Maintenance Manual
p/n: 029-0020-63-0
Accessories / Options 
3.3 PRESSURE AND RELIEF VALVE CONTROL
Relief Valve System
The Hale Standard Relief Valve System consists of a panel mounted control valve
(PM) and an internal relief valve, either a QG or a QD.
The relief valve system works as follows: The
strainer mounted in the pump discharge pressure
tap provides pressure to the diaphragm in the PM
Control Valve. The handwheel on the PM control
either increases or decreases spring tension on the
diaphragm. The seat of the QD or QG relief valve is
kept closed by pump discharge pressure.
As pump pressure increases, more pressure is
applied to the diaphragm in the PM Control Valve.
As the pressure on the diaphragm increases
beyond the set point, the stem will move off its
seat, allowing pump pressure to push on the piston
in the relief valve. The pressure on the piston will
cause the relief valve seat to lift, allowing excess
discharge pressure to dump back to the pump suc-
tion.
The amber indicator light on the PM control illumi-
nates when the relief valve is open.
Thermal Relief Valves (TRV)
Thermal Relief Valves (TRV) protect the pump from overheating. (See Figure 3-4:
“Thermal Relief Valve, TRV,” on page 40.)
The valve monitors the water temperature in the pump. When temperatures exceed
120°F (49°C), the valve automatically OPENS. When the temperature returns to a
safe level, the valve CLOSES.
Figure 3-3: PMD Series Relief Valve
Control (Shown)