Thanks for the replies. I have read that thing about how to tell the difference. I do understand cavitation in
principle, but yeah not as it applies here and what the symptoms are.
Here is where it stands. As soon as I run the engine, the pump immediately makes a hissing sound as if air of some sort is running through it, from whatever source. That is at idle speed. If I use the rams, I get a whining noise, again even at idle. This was not happening before I had the tractor repaired. So AFAICS it's behaving like a leak, but sounding like cavitation.
OK. I added trannie oil, because I could hear what sounded almost like a sucking sound if I removed the filler and the oil was a _bit_ low. It did not help. Now the oil level is higher, I can see _lots_ of bubbles in the trannie oil if the engine is running, regardless of whether the rams are in use or not.
Regarding centrifugal cavitation, I could see that the extracted air bubbles _may_ remain, as there is not so much high pressure compared to a positive displacement pump.
I suppose if I used a remote reservoir of oil and fed oil into the pump from that, simply feeding the return line back into the bucket or whatever, then I can see if it's the pump, cavitation, or air.
I understood that cavitation causes the extracted air bubbles to collapse on the high pressure side: therefore it seems to me that I should not be seeing so many bubbles coming out, when the rams are not even in the circuit, but are being bypassed totally by the spools.
In that article it says that oil will not leak out of a hole that lets in air, because the pressure is lower in the inlet than atmospheric. Surely that only applies if the pump is running? With the engine stopped, I would have though that there would be _some_ sign of oil along the intake. I can get to all of it ans can neither see nor feel and signs of oil.
Thanks again. If the bucket trick does not work I will have to start cracking the gearbox and look at the inlet inside there.
