Terex PT110 Forestry hydraulic problems.

[wlhequipment]

Hi folks,

I mistakenly originally posted this in the “other earthmoving” forum; meant to post it here, so this is a bit of a repeat post, but at least now it’s in the right place.

I have a Terex PT110 Forestry that is having really high back pressure on the return circuits of the high flow only. The HF circuit is reversible in the cab, and I have high return back pressure going both ways. 900 psi of back pressure to be precise. That ain’t no clogged filter. In full bypass, they won’t go over 150 or so psi.
What do you guys think might be causing the problem? Am I looking at a valve body issue? Maybe a solenoid? I think there are 2 spools in the valve body that switch the high flow. As far as I can tell, that’s the only thing that could be causing such a back pressure. Thoughts?

thanks!

 

[Tones]

If you are using a mulcher check the casedrain. To do this unplug the hose off the machine, remove the quick connect. Now get a pail , put the hose into it, with the hiflow engaged run the machine at full revs for 1 minute then shut it down. If there is more than a gallon of oil it indicates a worn hydraulic motor.

 

[wlhequipment]

If you are using a mulcher check the casedrain. To do this unplug the hose off the machine, remove the quick connect. Now get a pail , put the hose into it, with the hiflow engaged run the machine at full revs for 1 minute then shut it down. If there is more than a gallon of oil it indicates a worn hydraulic motor.

Thanks, but this isn’t a case drain issue, it’s back pressure on the return circuit issue. It shouldn’t be more than about 100 psi back to the tank, and I have almost 900.

 

[Tones]

Is there a loop flushing line on the hydraulic motor?

 

[wlhequipment]

There may be flushing on the drive motors on the machine, but that’s not the circuit I’m having trouble with. This is just a high flow circuit problem. I know I have all that back pressure because I made a hose with quick disconnects and a gauge and connected across the quick disconnect ports at the front of the machine, so the attachments are out of the equation. In networking terms, we call that a loopback. So the fluid leaves the QD port at the front of the machine, goes through a short hose, and right back to the machine. The gauge reads 900.

 

[lantraxco]

Probably the restriction in the quick disconnects. Why is the back pressure an issue, are you losing motor seals on an attachment?

 

[wlhequipment]

Probably the restriction in the quick disconnects. Why is the back pressure an issue, are you losing motor seals on an attachment?

That might be - of course it shows restriction in forward and reverse, so both QDs would have to be restricted, otherwise I'd show high pressure going one way and low pressure going the other way (gauge in the same place in the circuit). The problem with high return pressure is the machine is not able to do as much work to the attachment if it has to work that hard on the return. I did lose a couple seals too. So, really f@%*ing annoying thing today - no problems. Back pressure is probably below 100 and the machine works just fine. So, my problem is intermittent.

 

[lantraxco]

That might be - of course it shows restriction in forward and reverse, so both QDs would have to be restricted, otherwise I'd show high pressure going one way and low pressure going the other way (gauge in the same place in the circuit). The problem with high return pressure is the machine is not able to do as much work to the attachment if it has to work that hard on the return. I did lose a couple seals too. So, really f@%*ing annoying thing today - no problems. Back pressure is probably below 100 and the machine works just fine. So, my problem is intermittent.

More likely the spools aren't shifting completely then, or a spool in the stack(s) isn't returning to neutral exactly. Hydraulic issues are bad enough to troubleshoot, intermittents will make you Lanway, er, crazy.