Depth of Hydraulic Suction & Return in Reservoir?

[IceStationZebra]

You want at least one diameters worth of oil above and below the inlet. So if you have a 1" suction you want at lease 1" of oil above and below. More is better. You don't want it on the bottom so you have some place for water and debris to settle out. The return can go back anywhere as long as it is below the fluid level, and ideally as far from the outlet as practicle.

ISZ

 

[MHarryE]

It's really recommended to baffle a tank between the suction and return but since you are using the compressor thank that's not possible. We use diffusers on our returns - tubes into the tank with holes in the tubes so the oil enters at several points along the width of the reservoir. That you could do by securing a diffuser tue to a reducer fitting and screwing that into the tank, then the return line attaches to the female portion of the reducer. That is what we do but they are all designed for the particular machine. The book says to have at least 30 seconds of oil flow in the reservoir to allow air bubbles to disperse after their return, the reason for baffles and diffusers. Actually my primary design manual says 2 minutes worth but that is not practical for our stuff although they may get it on a large hydraulic press.

 

[IceStationZebra]

The book says to have at least 30 seconds of oil flow in the reservoir to allow air bubbles to disperse after their return, the reason for baffles and diffusers. Actually my primary design manual says 2 minutes worth but that is not practical for our stuff although they may get it on a large hydraulic press.

I have never had the pleasure to work on a machine with 2 minutes worth of reservoir, usually more like 20-40 seconds worth. I have never used a baffle nor a diffuser.

On one prototype we actually replaced the side wall of the reservoir with plexiglas (perspex to those outside North America). We ran the machine with either ISO 32 or 46 hydraulic oil, can remember which. With approximately 100°F/40°C oil and the machine turned off it took several minutes for some of the air bubbles to rise to the serface. Even after 5 minutes a good portion of the bubbles were still in the oil. We did not pursue any remediation methods so I can't comment on what worked or didn't work.

What I learned is:
- It is not easy to remove entrained air.
- You have to minimize any chance to create air bubbles.
- My first try with a problem machine would be to use the pressure in the return flow to release the air bubbles. One example is race cars do with dry sump oil reservoirs - the return flow is spun around a cylindrical tank as it returns. The centrifigal force helps get the bubbles out.

ISZ

 

[triptester]

Used air tanks contain a lot of rust which can cause pump damaged. A inspection opening should be put in the top for proper cleaning before using as a hydraulic reservoir.

 

[N8ghz]

Depending on what you end up with for a filler port, diameter wise, you might want to drop a magnet into the tank. It may require a wooden dowl or something else non-magnetic to get it down in there.....ask me how I know that....

 

[IceStationZebra]

Depending on what you end up with for a filler port, diameter wise, you might want to drop a magnet into the tank. It may require a wooden dowl or something else non-magnetic to get it down in there.....ask me how I know that....

I make a tube out of stiff paper or light cardboard. Then just drop it where you want it. ISZ