Hale Rear Mount - Manual (Page 7)

GAUGES & LAYOUTS
To accurately test a pumper for performance, a pitot gauge and a pump pressure gauge, both
gauges tested for accuracy, are required. Gauge testing can be done with a dead weight gauge
tester. Pumpers should be tested from draft at not over a 10 foot lift with 20 feet of suction hose.
1500 GPM and higher rated pumpers frequently require two separate 20 foot lengths of suction
hose and larger pumps utilize lower lifts down to 6 feet.
Smooth bore nozzles of accurate size should be used with the pitot gauge. The volume pumped is
then determined by referring to tables which show GPM flow in relation to nozzle size and the pitot
gauge reading. Nozzles should preferably be used on a siamese deluge gun for greatest accuracy.
A stream straightener, just upstream of the nozzle, is advisable.
For the 500 and 750 test, two 2-1/2" lines should preferably be laid from the pumper to the nozzle.
Since deluge guns are not always available, other hose layouts may be made such as one 2-1/2"
line to a 1-3/8” tip for 500 GPM. In general, the nozzle used on one 2-1/2" hose should not be
larger than 1-1/2" for accuracy of measuring GPM. For another example, two separate 2-1/2" lines
with a 1-1/4” nozzle on one and a 1-1/2” nozzle on the other would pass 1000 GPM flow. The sum
of the flow from both nozzles is, of course, the GPM delivered by the pump. For good pitot gauge
accuracy the nozzle pressures should be between 40 and 85 PSI.
Since the underwriters ratings specify both GPM and pressure, it is usually necessary to restrict the
flow somewhat in order to build up the pump pressure. In normal pumping, this restriction would be
caused by the friction loss in the lines. However, depending on line loss alone would require a large
amount of hose for some tests. For example, testing a 500 GPM pumper at 250 GPM and 250 PSI
requires 72 PSI nozzle pressure on a 1" tip. To reduce the pressure from 250 PSI at the pump to
72 PSI at the nozzle would require over 1300 feet of 2-1/2" hose. Therefore, it is common practice
to use 50 feet or 100 feet of hose and gate the discharge valves as required.
TESTING AT CAPACITY
The pumper should first be tested for capacity, for instance, 750 GPM at 150 PSI. It is best to run
at capacity for 20 to 30 minutes to be sure there will be no overheating or loss of power. If the
pumper will not reach capacity at the rated pressure, it needs a thorough check-up.
Assuming the pumper does reach capacity, it is then desirable to know how much reserve is
available. If there is some reserve at capacity the engine throttle will not have been wide open.
Now open the throttle wide. The pump pressure will increase, and the flow will also increase. Gate
the discharge valves slightly until the nozzle pressure (and flow) is the same as during the capacity
run. A 10% increase in pressure (150 to 165 PSI) indicates that the pumper has reasonable
reserve and that the engine is delivering ample power and that the pump is in good condition. No
increase, or a one to two percent increase in pressure when the throttle is opened wide may
indicate that performance has dropped.
Test performance should be compared to the performance at the time of delivery. Test records
should be on file with the pumper delivery papers. If not, they may be procured from the
manufacturer of the apparatus or from the local Underwriters. If the pumper performance has
dropped appreciable compared to its original performance, it is in need of service.
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