hydrostatic issue

[SSdoxie]

The 2 small lines from motors back to tank are case drain, a small amount of the oil going through the motor is sent to the output bearing for lubrication then returned through these lines to keep motor case pressure at a minimum and prevent blowing out the seals. If you haven't changed the filter do so, it could some restriction not allowing an even flow of oil through to the charge pump.

 

[mikehaugen]

that's what I am hoping, but do you think it would cause it to surge? I would expect just a minimized top speed, I guess I would think it would be more consistent is all. As I stated before I have very limited experience with anything hydrostatic.

 

[oldnslo]

Air in oil does strange things so if the filter is partially plugged it may cause the surging.

Roy

 

[mikehaugen]

well thanks, I am definitely hoping the filter will help. It sure us hard to find parts for these old buntons.

Btw Roy, where about in northern IL are you at? if you don't mind me asking

 

[J_J]

Case drains allow for motor lubrication. Fluid flows around the motor and helps carry off some heat .

Do not block this line and it should go directly to tank.

Do you not have two large lines and one small line?

Some hyd motors have them.

All 4 of my hyd wheel drive motors have these lines.

Excerpt:

Piston pump and motor case drain lines should be returned to the reservoir through dedicated penetrations. These penetrations must be higher than the unit’s case port and be connected to a drop-pipe inside the reservoir that extends below minimum fluid level. Due to the reasons above, filters are not recommended on case drain lines.

High case pressure results in excessive load on the lip of the shaft seal. This causes the seal lip to wear a groove in the shaft, eventually resulting in leakage past the seal. If case pressure exceeds the shaft seal’s design limits, instantaneous failure can occur. The subsequent loss of oil from the case may result in damage through inadequate lubrication

 

[mikehaugen]

thanks JJ, yes there are 2 large lines and 1 small line on each motor. It is the smaller line I was curious about. Like I said hydrostatic pumps are new to me and I know there are some differences. I did not know what these lines did, but it sounds like it isn't anything that is necessarily specific to hydrostatic, I could see these being useful on any hydraulic motor. And yes these lines have dedicated penetrations into the tank, whether or not they have a drop pipe inside the tank or not I could not tell you but the fluid level i the tank is above them anyway.

On a side note, what kind of pumps are these usually. I doubt that it's a gear pump, I am thinking it's an axial piston pump but not sure why it would need such large return line if it were.

 

[J_J]

It is probably a hydrostatic pump, one pump for each side.

http://www.surpluscenter.com/MorePhotos.asp?ITEM=9-8238-R

http://www.surpluscenter.com/Instruct/I9-8238-R.pdf

Ports appear to be same size.

 

[CJONE]

like oldnslo said a partially plugged filter on the intake will cause surging or complete failure if it is run like that for long. Put a restriction gauge [vaccume hg] on the inlet line at the pump, that will tell you the story. CJ