Nidum said:
Then it is a suction side problem and not a delivery side problem ?
A possibility. Seems more likely, at least to me. It could also be a problem in the hydraulic drive.
A possible test: On a normally operating system, preferably with a short hose, you may be able to hear a difference in engine speed or sound
- when idling
- when dispense pump is operating but the nozzle closed
- when actively dispensing.
Listen to the engine at idle without the pump engaged.
With the pump operating but not dispensing, I would expect the engine to be 'laboring', pumping product thru the pressure relief (unloading) valve. You MAY be able to hear some turbulent flow thru the relief valve too.
While dispensing, the engine would not be working quite as hard and the governor would close the throttle a bit to maintain engine speed. This may make a detectable difference in engine sound.
Compare the listening results between a good system and one that is not dispensing correctly.
If the bad system has less change between condition #1 and condition #2 above, then it's either a, suction side problem, a bad relief valve, or a pump drive problem (mechanical or hydraulic).
If the bad system matches the good one for #1 and #2 above, try changing the nozzle, and then the hose, to see if the problem is corrected. If corrected, either tear apart the offending item and find out why, or return to the manufacturer and let them figure it out.