the engine running or motored around, it is possible to measure the petrol
rate of flow and compare the result with the standard rate for the type of
pump. The pump delivery pressure is measured with the gauge. This
should be within 1.1/2 and 2.1/2 lb. per square inch. If too low the cause may
be a defect in the diaphragm or rocker arm—due to excessive wear or
incorrect assembly of the pump after overhaul. It will also show whether
the pump is responsible for any tendency to carburettor flooding.
The flow-rate test will indicate whether there are faults in the fuel-
feed system, such as air leaks due to loose or faulty connections and wear in
the fuel pump itself.
It should be emphasised that it is only necessary to release one union
on the engine in order to connect up the pump analyser. Full operating
instructions are supplied with the apparatus.
Testing with the A.C. Petrol-pump Test Stand
In order to illustrate the method of using the petrol-pump test stand
previously described, the example of the Austin car and commercial A.C.
petrol-pump tests will now be considered. For the purpose of the test the
suction side of the pump is piped to a tin of paraffin at floor level and the
outlet side of the pump connected to a stop tap and pressure gauge.
First, flush the pump through to wet the valves and seats, and then
completely empty it again by continuing to operate the rocker arm by
hand with the suction pipe clear of the paraffin. Again operate the pump.
Not more than twenty strokes should be necessary to secure delivery of
paraffin from the pump outlet.
With the same apparatus a second test can be made by working the
pump with the tap on the delivery side closed, pressure then being recorded
on the gauge. After ceasing to work the pump it should take several seconds
for this pressure to return to zero, thus denoting that the valves are seating
properly. Also, while there is pressure, the outer edge of the diaphragm—
visible between the two clamping flanges—should be carefully examined
for leakage, and the retaining screws tightened if necessary. When
working a pump by hand a somewhat longer stroke is obtained, and the
pressure developed is apt to be higher than when the pump is fitted to the
engine.
When the above apparatus is not available the pump should be tested,
using a pan of clean paraffin, as follows:
First, flush the pump by immersing it in the paraffin and working the
rocker arm half a dozen times; then empty the pump by continuing to
operate it while held above the bath. Then with the pump clear of the
paraffin bath place the finger over the inlet union (marked "in") and
work the rocker arm several times. Upon removing the finger a distinct
suction noise should be heard, denoting that a reasonable degree of suction
has been developed. Afterwards the finger should be placed over the
outlet union and, after pressing the rocker arm inwards, the air drawn into
the pump chamber should be held under compression for two or three
seconds; this should also be done with the pump immersed in paraffin, and
the clamping flanges of the diaphragm watched for any signs of air leakages.