Hydraulic System question

[Yardscaper]

I have a 2445 that, for lack of a better word, has a spongy effect. Let me explain. When the lift arms are lowered into position, the arms will drift upwards approximately 2 to 3 inches and stop. If you put them back to the position that you want, they do it again. This seems to only happen after lifting something heavy or when the machine is hot. I am really just curious if this is a quirk of the machine or if anyone else has experienced this. It gets annoying and I would like to fix it! This same machine will also continue to spin an auger bit or run the trencher bar even after the pto switch has been shut off. It does not spin it with the torque that it has when it is on, but it does continue to run. I did contact Power Trac on that one and was told that this was normal. I have a 1430 as well, and it does not do this. Anyone else have this issue? This one is really a pain, especially when you are trying to reposition or get a rock out of the trencher bar when it becomes jammed. Any help that you guys can give me woulod be great!

 

[J_J]

This is a safety issue and should be corrected as soon as possible.

This could be caused by a leaking control valve.

There might be some air in your cylinders.

 

[JimR]

You have a problem with your tractor if things move and spin when dis-engaged. PT is full of it that this is normal. That' s like saying my car moves in park and GM says it is normal.

 

[J_J]

You should have replied to Yardscaper, but that's allright. When PT technicians don't have an answer, they say that's normal.

Some one also told me that PT chose control valves that leak down. Why would any one want their cylinders to leak down. A lot of PT owners have noticed that the lift arms will leak down, some rather fast. Mine will leak down over night. I think maybe from wear and tear.

I have never had the lift arms to go up by them self. If they go up with the motor running, fluid is getting by a valve some where.

 

[blackwell]

This is caused by lowering a heavy load too fast which causes the return oil to rush out of the cylinders faster than the pump can replenish the cavity causing cavitation and traps air in the cylinders. Just raise the arms all the way up and then lower them all the way down and the cylinders should refill and stop the sponge filling. This can be eleminated by adding small orrifice in the tube end of the cylinders, but it slows the cylinder speed and causes heat which is probally why PT does not add them.
You might also check the caps on the end of the spools of the lift valve, if the bonnet is loose the spool can shift slightly off center and cause more drift.
As to the arms leaking down, the cylinders are not leaking but fluid is bypassing inside the lift valve and blieve it or not this is normal. A spool inside a housing must have clearance in order to slide in and out, oil then slips thru that clearance causing the cylinder to collapes. A PO check or counterbalance valve can be inserted between the valve and cylinder to stop this, BUT the arms could not be used in float position. The average spool valve will leak about one cubic inch per minute per 1000 psi. PT's operate steering and lift at low flow high pressure which causes the leakage to be more noticeable. Some backhoe manufactures publish a leakage rate, i.e. how long the arms can hold a certian weight in the air for a given time.
EB

 

[MossRoad]

EB,
It's good to have someone with your knowledge around here. Thanks for taking the time to explain things so well. /forums/images/graemlins/wink.gif

 

[cqaigy]

I agree w/Mossy. Nice post!!

 

[Yardscaper]

Thanks for the info!

I figured that this is what caused the leakdown. I have had other equipment that was much worse and some that never leaked down, no matter what. As for the lift arms feeling spongy, one of my employees pointed out the all the way up, all the way down cure. Thank you for sharing your knowledge!

 

[outridder]

When I hauled my PT out of Tazwell the mower wheels couldn't rest on the tailgate so they just had the mower cranked all the way up and tilted. The further I drove the lower the deck went and I wasn't sure if that was normal and didn't know about leakdown. I would hit the rest stops, check the strapping and see how low the deck was. I didn't want to have to jump on the PT and start it and raise the arms since I wasn't used to the tractor but I decided if it below the level of the tailgate I would have to do it. Seven hours later I was back home and it wasn't even near that mark.

Dan