my freinds old yale has its pump cavitating when you load it. tilt or raise. it foams the oil till it comes out the breather. i have never seen this happen before. the condition is getting worse. im pretty sure its not sucking air through the pickup, and there is no pickup restriction. does he need to get a new pump?
This doesn't add up to me, usually you have problems sucking air when the machine first starts with cold oil. Is there some unusual plumbing arrangement for the filter? and has the filter been changed and cut open? Water in the oil will make cavitating and foaming worse, wouldn't hurt to check the tank drain and/or drain/flush/refill.
If air, in fact, is getting into the system it has to be entering on the suction side of pump or through the pump shaft seal, it's not really possible for air to enter in the pressure side of the system, that would be an oil leak. How are you pretty sure the pickup line has no restriction? I can't say about this particular machines, but many forklifts have a suction strainer inside the tank and some cover to remove to access the strainer. It could be something like a rag or a plastic bag inside tank blocking suction strainer. All kinds of weird stuff will happen then.
pump 10-4 on the pump shaft seal, seen that b4. Its been my experience that excess air entrainment does not accompany cavitation much less enough air to create foam. Also check your tank ALL lines entering or exiting your tank need to be below the minimum fluid level. Made a service call on a combine once where the diffuser had come off inside the tank, little foam and a lot of oil coming out the top of the tank. Good luck in your endeavor, Tom
the plumbing is simple. oil into the pump, then to the control valve, on to functions or return through filter and back to tank. i visited this lift about a year ago when he first got it and it would only suck air when tilting. now it sucks air lifting. i replaced the rubber elbow on the suction line cause it was hard as rock and i wanted to eliminate the chance of it being the problem. i told him then that its probly a pump issue. a lull in business made him not get the pump then. as i recall there was no pickup tube problem. being that this is a constant flow system wouldnt a rag cause the problem all the time?? im not a hydraulic specialist. i was also thinking its the seal but it sound hooky cause im not familiar with the fluid dynamics of what the pump is going through. i would just tear it apart cause its a direct drive and you cant see the seal. problem is he parks it indoors each day. im gonna see if he can live with it parked for a week or two and get to the bottom of this. maybe a twenty dollar seal will work for him instead of an $1800 pump. thanks for the input guys. one other thing, where can i get a decent price on a pump for this old yale?