Then the controlling pressure in tank is maximum allowable case drain pressure.
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Is the 5 psi absolute or gauge pressure?
John C.
Senior Member
Most of the stuff I've worked with in hydraulics are done at gauge pressure. The absolute pressure given for the minimum feed is using absolute pressure to account for differences in elevation that the machine may be worked at. Most hydraulics systems for some reason like to have 14 PSI in the hydraulic reservoir. In your case, I would say any positive pressure is going to work better than what you had.
As far as case drain filters go, many of the systems I've worked on in the past never had them. Basically, if that pump is making metal, that filter isn't going to prevent contamination of the system.
As far as case drain filters go, many of the systems I've worked on in the past never had them. Basically, if that pump is making metal, that filter isn't going to prevent contamination of the system.
From this forum suggestions my main cause of 2nd and 3rd failures most likely have been contamination. The first in my opinion was cavitation because the pump was making gun like noises. This may have been due to someone draining tank oil to container with water. Also the fluid level in may not have been kept properly within limits.
In a nut shale, I will modify the inlet as suggested, the Dayton filter I posted looks promising because has a strainer and pressure relief. Meaning introduction of dirt in tank is minimal. How about your opinions with this dayton breather?
On cleaning the tank today, the returning lines and the tank refill/inlet are on one end of tank where I found a hole drilled at the bottom and big chunks of pump wear material was trapped. The opposite end is the suction manifold.
Also to note is oil main return line from filter goes to cooler thereafter before entering tank (approximately 2" metallic pipe) ;are provisions for case drain line. One port was plugged so introduced another case drain line meaning now each pump has its own case drain line connected to this 2" line in effort to reduce case drain pressure.
Nige
Senior Member
I would agree that the 2nd & 3rd failures could have most likely been caused by system contamination remaining from the 1st failure.
However IMHO what you should not lose sight of is that you have a tank cap that apparently should generate (a small amount of) pressure in the tank to aid pump suction. That cap was not functioning as designed if you could blow through it in both directions. That failing should be addressed at the same time you are decontaminating the system. Piston pumps don't suck too well. They like a postive flow of oil into them under pressure, either from the oil level in the tank being significantly above pump suction port height (not possible in your case) or by a system that generates pressure in the hydraulic oil tank. Out of those two options only one appears to be available to you.
Tones
Senior Member
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Totally agree with Nige. The pump height has a lot to do with this kind of failure. A machine I owned had the load sense piston pump mounted above the tank oil level, it $hit it self twice. To fix that problem I put a radiator cap on the tank and ran I hose from the engine inlet manifold to the tank with a pressure reducing valve so now the turbo charges the tank. Oh and that machine was Made in America (with pride) apparently. The idiot company who made it still dose the same crap.
Nige
Senior Member
Similar case - Cat 994 wheel loader (all models). The implement pumps (four of them) suction ports are probably a couple of feet above the oil level in the tank. The breaker relief valve in the tank is set to relieve at 35psi. 'Nuff said.....
You did not have any issue on case drain after raising the tank pressure?
Nige
Senior Member
Gauge pressure.
Finished the modifications
