Piston Pumps

Given that the oil is maintained in good condition (ie: clean, dry and fit for use) then acceptable pump life can be expected from all the types of you mentioned. Pump selection is most often dictated by the application. Consult an expert in hydraulic systems design and give him what you want the system to do they will be able to tell you the best pump for the application.

I am not looking for a pump for a certain application. I have several different pumps running on different systems. On some systems the pumps have been running for at least eight years. On other systems similar pumps have run for only two years. I feel that if the system is properly cared for and the pumps are not abused, you should see 6-8 years of useful life before the pump shows signs of loss of flow or internal leakage that will prevent the system from reaching pressure. I am interested in what others have experienced on their systems.

I do have a similiar situation to the one you described. We have a piston pump that is lubricated with mineral oil and has a working pressure of around 2,000 psi and potential to raise. This is the only unit in the plant,therefore I have no other application to compare it to. Although since you are interested in what we have expirenced so far, I would be glad to share with you. This paticular pump has been rebuilt atleast every 2 years. Even since we started our oil analysis program it has been rebuilt one time. We have made modifications to this unit in order to filter and sample the oil more efficiently. Trend information will be watched closely.

Looking at the conditions of working I would expect a piston pump to work for two years or more for a low volume high pressure application system.

One more factor that I have experienced is positive suction( Suction point below oil level) instead of forced suction ( Suction point above oil level )helps the piston pump to run free of cavitation.

Usually the piston pumps are precision type and high pr and low volume pumps and would be apprpriate if we are talking in terms of running hours
I have experience radial piston pumps of 300 bar pr. running with postive feed of 5 bar giving a pump life of 60000 hrs considering oil is clean and there is no internal leaks and sump temperature upto 50 deg c
However gear pump can tolerate more contamination and vane pumps inbetween.With a vickers vane pump with good oils I have seen system running for 10 yrs and gear pumps upto 15yrs but piston pumps are sensitive due to their finer tolerance and radial pump is extreme ly sensetive.
regards
Arupanjan

To be honest Marty, I think that's a difficult question to answer. Even if the oil is well maintained, other factors can significantly reduce the life of a pump. I have seen gear pumps last for 10 years and still going strong yet on an identical machine about 50 meters away, the pump has been rebuilt 4 times in the last 10 years. Both systems have been running between 13/10 and 15/12 for most of this time.
In my opinion, I have always favoured gear pumps. They tend to more forgiving then other pumps but every time I try to back a winner, Murphy steps in and proves me wrong.

MC and Marty you need to take into account the design of modern day hydraulic pumps, the gear pump by design is of the unbalanced type and fatigue will get you sooner or later every time. The failure rate is somewhat dependant upon the operating pressure. Yes they are a little more forgiving of contaminants, however you will not find a gear pump capable of higher pressures that are common today i.e. 3000 psi or above. Piston pumps are more sensitive to contamination because of the design that is employeed to manufacture them and the tighter tolerances involved. With good clean systems it is not uncommon to get 7 to 10 years or more of useful life out of a quality built piston pump, provided the oil is kept clean, dry, and not allowed to run hot. Also there is a consideration that should be given to the additive package with respect to anti-wear. However you must remember that metalurgy can not engineer out eventual fatigue, only retard the fatigue for a little while. With respect to the useful life of a piston pump, this is somewhat of an objective question. If the pump gives good service for say 3 years before failure at one facility, that facility may say that the pump performed well, however another facility may expect the pump to run indefinetly, and if it fails at 6 years say that they did not get the expected life out of it. I guess it is all based upon your perticular expectation and assumptions. Just as a note we have several different facilities across the US that are running large Oilgear "D" pumps that have ben running for between 20 and 28 years with only one failure. The systems operate at 2200 psi and a final system pressure of 3600 psi. It is a high low circut design on multi opening presses. The circut is handled by Dennison double vane pumps and the "D" pump. In answer to the final question on Martys original post, You should never expect a gear pump to last longer than a good vane or piston pump, provided fluid conditions are optimal and mantained in that condition for the system. A gear pump as I said is of the unbalanced design and although it may continue to create flow the efficiencies of the pump will decrease to a greater extent, before that of a vane or piston pump when failure starts to occur.

piston pump life is depend on oil condition,filters , and the working pressure , and the worjking temp. of pump. Its hard to say what should be the life of pump. If you can run the pump cooler , life will incfeased . So cooling system also play the big roll for the total life cycle of pump.