4 Post hydraulic lift question ?

[1956f100]

Just set-up a new to me 4 post lift ( Backyard Buddy ) , but could be same issue with other brands. When raising the lift to maximum height, loaded and unloaded, the plastic reservoir tank severely deforms inward as the fluid is drawn out, and returns to normal or slightly bulges out when the lift comes down. Checked for proper oil level in system. Factory suggested air in system, and to run up and down with tank cap off to bleed. Did this numerous times. Lift operates properly with a vehicle on it. Can get tank to not deform if I crack the fill cap to draw air in on the up cycle and expel air on the down cycle. I feel I am missing something fundamental in the operation.
Any hydraulic gurus online that may be able to provide some info? Thanks

 

[bobscogin]

Since the volume of fluid changes, shouldn't the reservoir be vented?

Bob

 

[gnpenning]

^^^ the cap should be vented.

 

[Bad Eye Bill]

Yep, needs a vent somewhere.

 

[Candoo]

Cap should be vented, if not drill a hole in the hyd fill cap.

 

[1956f100]

Thanks guys, I kinda felt that way too , but could not get anyone to reinforce
my thinking.

 

[Oilguy]

There may be some sort of temporary dust plug in the breather. But as stated above, the breather is not breathing. That should be obvious to the vendor. You should be able to blow through it easily if it is not defective. I would like to see a photo of it; never heard of this happening and just curious. I could also recommend a replacement and where to purchase one if the vendor is no help.

 

[1956f100]

Where would the breather be that you are referring to? I am assuming inside the tank probably? There is also a small filter looking piece on the back end of the lift cylinder. At work now. Will try to get pics this evening or tomorrow if you can point me in the right direction.

 

[Oilguy]

The tank cap you refer to is most likely the breather. I am unable to post photos on this site for some reason otherwise I could nail it down better for you. The breather is usually made of plastic for these units and has NPT (pipe thread) on the stem which screws into the top of the tank. If that is what you removed and all was fine then for some reason it is not letting air in/out of the tank which is a mandatory function on a hydraulic unit. The piece you spoke of on the back of the cylinder is also a breather but it's job is to let air in/out of that side of the piston. It is a single-acting cylinder and the back (cap end) only has air in it, no oil pressure. That breather, which is quite often bronze material prevents vacuum/pressure from building up as the piston reciprocates in the cylinder. Plus, if the piston seals become worn, any oil that bypasses the seal will escape through that breather rather than lock the cylinder up.

 

[1956f100]

Got around to taking a few pics of my pump. The red fill cap is what I may drill a small hole and see what the results are. Unfortunately, I can't get pics to post either. If it works, I may tap and install a small sintered bronze breather I can source from work.

 

[Oilguy]

Do a search for SPX/Stone and look at their breathers. I don't believe a sintered bronze unit will be large enough. Most breathers on small power units are at least 1/2NPT thread.

 

[1956f100]

OK, Will do some research on them.

 

[1956f100]

OK, solved my problem, thanks to you guys and especially Oilguy for his input. I did some research on the SPX breather cap, and then called the pump mfg again to talk to a tech. This time the tech confirmed also that the tank needs a breather cap and gave me the cap part number. I searched for it and found several places with pictures to get it.
Then the light bulb came on. When I got home from work, I went to the lift and confirmed what I realized. The solid fill cap and the drain cap were reversed from the factory. I removed the drain cap and found the tank had a molded in partition that will need to be removed when it comes time to drain the fliuid. Reversed the caps and all is now good. Instructions from the factory would have saved some frustration. Thanks again for the good input.

 

[Oilguy]

Very cool. Thanks for letting us know what you found; glad it works.