Hydraulic Top Link Drawbacks

[MtnViewRanch]

I was not using my small tractor there for awhile and I tested both top & side links for a 3 month period, now there was only a couple of hundred pounds on the hitch, but after 3 months the only movement was 1/16" and that was on the first day. Never moved after that.

Maybe Harry and I are just lucky.

 

[ovrszd]

Brian,

Luck is your middle name.

In my World, more hydraulic systems drift than not. If you have a system(cylinder/valve) that doesn't leak off a little you are very fortunate indeed.

 

[MtnViewRanch]

Brian,

Luck is your middle name.

In my World, more hydraulic systems drift than not. If you have a system(cylinder/valve) that doesn't leak off a little you are very fortunate indeed.

Good luck, or bad luck?? :confused3:

Actually we were talking about the cylinders drifting when unplugged from the QDs. Now my rear remotes on my 75hp tractor, for the side link with a 1000lb implement hanging on it will drift about 5/32" in an hour which I feel is acceptable, now on my 32hp tractor, it drifts down at a rate of about 3/4" per hour when setting, but for what ever reason when actually working the tractor it seems to be less and at an acceptable rate. I really need to get into that valve and check it out, but currently no time to do such things.

 

[ovrszd]

Yep I realize you were talking about cylinder drift. Just saying, some drift is acceptable. Most people expect a system to be "drift free". That's rare. I accept it and never worry about it.

 

[bumperm]

Can't help thinking there must be some confusion going on w/regards the two disparate situations being discussed, 1) cylinder under load with hoses connected to tractor, and 2) cylinder under load with hose quick connects disconnected from tractor.

With the cylinder connected to the machine's hydraulic system, it's indeed likely there will be some creep. Most often this is due to leakage within the spool valve that controls that cylinder. In my new Kubota, creep was significant on the 3 point tilt cylinder, more than 1/2" an hour - disconnecting the quick connects locked the cylinder in place, which is prima facia evidence that spool leakage was at fault.

When cylinder plumbing is disconnected, as Brian (Fit Rite) says, most cylinders drift little if any. To move a significant amount. the cylinder's piston seals would have to be leaking and/or the hose connections are lose or quick connects would have to be leaking. Even then, due to the dissimilar displacement ratio between rod side compared to cylinder side within the cylinder, significant creep when disconnected should still be minimal unless the cylinder and quick connects are leaking like a sieve.

 

[thirdroc17]

I've always wondered how unhooked cylinders could move, the differing volumes of oil on different sides of the seals, but, I've parked many an implement with the cylinder holding it up. I'm lazy, and it's just easier that way, ok?! LOL While I've never seen any oil leak out, other than the small loss occurring during the unhooking process, I have yet to see an implement not settle to the ground after anything from a couple days to a month.

 

[MtnViewRanch]

I've always wondered how unhooked cylinders could move, the differing volumes of oil on different sides of the seals, but, I've parked many an implement with the cylinder holding it up. I'm lazy, and it's just easier that way, ok?! LOL While I've never seen any oil leak out, other than the small loss occurring during the unhooking process, I have yet to see an implement not settle to the ground after anything from a couple days to a month.

It happens, there is no denying it. But typically it takes a long time and this is with poorer quality units. Hydraulic cylinders that are normally on implements are not of the best quality and are often only rated for 2500PSI. The sun and the cold will do some amazing things. Good units will hold for a long long time. Our 580 Case TLB will hold the bucket up for months with ZERO leak down, and that is connected through the control valve. Gives you an idea of the quality difference with AG stuff vs Industrial stuff.

 

[Fallon]

My Fitrite TnT setup will drop a good few inches in a week or so, but that's hooked up to the valve (also Fitrite). I'm pretty sure unhooking would stop it, but why bother. It causes no operational issues leaking that slow.

 

[Threepoint]

Can't help thinking there must be some confusion going on w/regards the two disparate situations being discussed, 1) cylinder under load with hoses connected to tractor, and 2) cylinder under load with hose quick connects disconnected from tractor.

With the cylinder connected to the machine's hydraulic system, it's indeed likely there will be some creep. Most often this is due to leakage within the spool valve that controls that cylinder. In my new Kubota, creep was significant on the 3 point tilt cylinder, more than 1/2" an hour - disconnecting the quick connects locked the cylinder in place, which is prima facia evidence that spool leakage was at fault.

When cylinder plumbing is disconnected, as Brian (Fit Rite) says, most cylinders drift little if any. To move a significant amount. the cylinder's piston seals would have to be leaking and/or the hose connections are lose or quick connects would have to be leaking. Even then, due to the dissimilar displacement ratio between rod side compared to cylinder side within the cylinder, significant creep when disconnected should still be minimal unless the cylinder and quick connects are leaking like a sieve.

Bumperm, I only know enough about hydraulics to be dangerous to myself and others, but I think you nailed it. With the QDs disconnected, seems to me the fluid has virtually very little place to go, which I think was the point originally made. With the hoses connected, that's a different story. In that case, a check valve on the cylinder will help in the case of a leaky spool valve. No?

 

[bumperm]

Bumperm, I only know enough about hydraulics to be dangerous to myself and others, but I think you nailed it. With the QDs disconnected, seems to me the fluid has virtually very little place to go, which I think was the point originally made. With the hoses connected, that's a different story. In that case, a check valve on the cylinder will help in the case of a leaky spool valve. No?

Exactly. A DPOCV (dual pilot operated check valve) will lock the cylinder in both directions, while a POCV will lock it in just one. The POCV acts as a one way check valve until pressure is applied to its pilot port - that allows flow in both directions.

The POCV is useful in that it stops the sometimes incessant creep when you have the bush hog or box blade adjusted just right, but still allows you to easily adjust same. But, if you need the float function, it won't work with a POCV. Also, if you are in the habit of shutting the tractor down, then trying to extend the top link to completely lower the implement, that doesn't work, as with no pressure to unlock the check valve, the cylinder stays locked in position. Start the tractor, adjust cylinder as required, shut down again :c)

I have a DPOCV on my top link, came that way, and I added a POCV on my tilt cylinder. Completely eliminated the creep . . . now if we could just do that in the Whitehouse . . . (in a non-violent hydraulically acceptable manner of course)

bumper