Hale MG - Manual (Page 25)

Muscle Pumps
1-18
During normal operation, both the QG relief valve
and PG30 relief valve are closed (as shown in
figure 1-17).
The TPM system functions by monitoring and
controlling pump pressure and relieves excessive
pressure by first utilizing the internal relief valve
(QG) (returning flow to the pump suction, see
figure 1-18). If excessive pressure remains and
there is positive pressure on the suction, a
secondary external relief valve (PG30) responds by
discharging excessive pressure to the atmosphere
(shown in figure 1-19). The staging of the internal
and external relief valves to operate in series
ensures maximum protection against over pressure
and eliminates the indiscriminate discharging of
water to the ground.
The external relief valve (PG30) is mounted on the
discharge side of the pump where discharged water
flowing through the valve provides a self-cleaning
process and virtually eliminates the possibility of
the valve remaining in an open position due to
contamination.
The amber light on the PMD control illuminates
when the QG relief valve is open. The same light
flashes when both the QG and PG30 valves are
open.