Knocking noises in hydraulic power unit

Good possibility yes...

The vickers type variable displacement pumps are oftentimes quite obnoxious upon startup so I'd suggest wait till you're pretty sure all air been purged from the system before getting overly concerned.

Ignoramus29686 fired this volley in news:IMudnSIgDI-kNBXSnZ2dnUVZ snipped-for-privacy@giganews.com:

Not "air pockets" per se, but probably a combination of too-cool (too viscous) fluid and too-low level.

When the tank level is - ehh... - just a _little_ low and the fluid is cool, it tends to suction a vortex from the top of the vessel down to the suction line... and it sucks up some air.

Run the thing until the viscosity decreases a little from heat, and it'll stop.

Even in warm Florida, I have to run a dipstick heater in each of my hydraulic tanks during the cooler months in order to use the higher- viscosity oil that's appropriate for our hot summer days.

LLoyd

Yes, and this is, indeed, a vickers pump. Additionally, there is probably not enough fluid in the tank.

Ignoramus29686 fired this volley in news:5eCdnYUN7sBlIxXSnZ2dnUVZ snipped-for-privacy@giganews.com:

Bingo... except... I don't buy that thing about Vickers V/D pumps "getting air-bound". Where would the air come from, unless it was drawing it from the surface level of the fluid? It's all about level and viscosity. The higher the displacement of the pump, the worse the problem.

One of my tanks is outdoors (under cover, but in non-conditioned space). IF I keep the fluid level high enough, even if it's cold, it will stall the motor before it will suck air. Let the fluid get within about 5" of the suction port, though, and it will draw air almost to the exclusion of oil (when cold).

LLoyd

LLoyd

Yep, I will put more oil in there, indeed. There is a forklift that I will be scrapping soon, hopefully it will provide some oil.

Pretty sure mine has an air leak in the suction line, and the fluid = drains back into the tank overnight.

I could be wrong though--I've never really worried about it enough to = check the fittings...=20

It's all about level and=20

Except, the noise goes away in half a minute or so on mine, which IMO is = not nearly enough time for the fluid to have warmed appreciably...that = is, unless it's been sitting for several months, in which case it could = take a minute or two.....

One thing for certain, is they oftentimes do sound downright obnoxious = upon startup...=20

"PrecisionmachinisT" fired this volley in news:Zaadnd4FF6UGRhXSnZ2dnUVZ snipped-for-privacy@scnresearch.com:

ANY pump will make a racket if it's sucking air. If your suction line drains, you have a leak.

Fix the leak, fix the noise.

LLoyd

Why ?

--It's been doing this s*it for ~ 20 years still running fine...

"PrecisionmachinisT" fired this volley in news:DM-dnTrNTKelIBbSnZ2dnUVZ snipped-for-privacy@scnresearch.com:

Because YOU said -- "they oftentimes do sound downright obnoxious upon startup"

Your using that term means you don't like it; you find it offensive, unpleasant.

If you'd said, "yeah, they're a little noisy on startup, but it doesn't bother me", I'd have assumed differently.

To me, the sound is not obnoxious, it's just information about what's going on inside the system. I am only perturbed if it continues after warmup.

LLoyd