Third Functions Hydraulic Fittings Difficult to Engage

[ericm979]

I'm not sure how that would put air in the system.

 

[ovrszd]

I think, by not having the tractor running, it won't supply fluid to the opposite side of the cylinder????

So his assumption is that it will suck a bit of air into the cylinder??

Only way that will happen is after it has sucked all the fluid out of the hose from the valve to the cylinder, and all the fluid out of the valve tank return line.

I'm afraid the vacuum will be gone before any air gets to the cylinder.

 

[npalen]

Letting the grapple clamp free fall the last few inches by shifting the valve with the engine/pump shut off would cause a vacuum in the hose supplying the base end of the cylinder in this case. The vacuum is created because the pump isn't supplying fluid that would normally fill the base end of the cylinder when the valve is shifted.
So with the vacuum (negative pressure) in the circuit, any increase in temperature when the grapple is disconnected would only slightly reduce the negative pressure. There would be no positive pressure in the hoses to cause difficulty when reattaching the grapple to the tractor.
Does that make sense?

 

[ovrszd]

Letting the grapple clamp free fall the last few inches by shifting the valve with the engine/pump shut off would cause a vacuum in the hose supplying the base end of the cylinder in this case. The vacuum is created because the pump isn't supplying fluid that would normally fill the base end of the cylinder when the valve is shifted.
So with the vacuum (negative pressure) in the circuit, any increase in temperature when the grapple is disconnected would only slightly reduce the negative pressure. There would be no positive pressure in the hoses to cause difficulty when reattaching the grapple to the tractor.
Does that make sense?

Vacuum cannot be created within fluid. There must be air. So back to my earlier description, you would have to suck all of the fluid out of the system into the cylinder and still have enough vacuum to bring in some air from your Tank. Not sure you can get that much fluid movement. But maybe??? I've never tried it.

 

[npalen]

Think of another instance such as when you let the loader down after shutting the tractor off. The valve spool is shifted and letting fluid out of the base end of the lift cylinders but the non-rotating pump can't replenish fluid to the rod end of the cylinders. This create a vacuum like what I'm referring to in earlier posts. Some fluid probably sneaks by the non-rotating pump especially a vane or gear type but still leaves some vacuum. Right?

Shifting the valve spool in the other direction after the loader is all the way down would tend to equalize the vacuum between the rod and piston sides of the cylinder, I would think. Even a tiny amount of vacuum would be better than a tiny amount of pressure that makes it difficult to reattach the quick couplers.

 

[ovrszd]

Think of another instance such as when you let the loader down after shutting the tractor off. The valve spool is shifted and letting fluid out of the base end of the lift cylinders but the non-rotating pump can't replenish fluid to the rod end of the cylinders. This create a vacuum like what I'm referring to in earlier posts. Some fluid probably sneaks by the non-rotating pump especially a vane or gear type but still leaves some vacuum. Right?

Shifting the valve spool in the other direction after the loader is all the way down would tend to equalize the vacuum between the rod and piston sides of the cylinder, I would think. Even a tiny amount of vacuum would be better than a tiny amount of pressure that makes it difficult to reattach the quick couplers.

I totally understand the dynamics. I'll leave it to you to do a test and get back to us. This time of year would be a great time on a sunny day.

 

[ericm979]

There's a lot of oil in the lines and hoses leading to the grapple's cylinders. The closest air is in the tank, on the other side of the loader valve that is opened. I don't see it getting to the grapple from just the action of the cylinders extending under the weight of the lids, there's just not enough oil being moved.

Maybe if you left the grapple lids up, then unplugged the couplers, a small amount of air might leak in past the seat on the coupler on the suction side as it's being uncoupled. But the system will also be lightly pressurized by the weight of the lids on the cylinders so it may be hard to unplug the pressure side coupler.

 

[npalen]

I'm guessing that the amount of vacuum left in the base of the cylinder is limited by the spring in the coupler after "uncoupling". But, then again, we don't need a great amount of vacuum left after "dropping the lid" with the engine off. We just need enough to allow room for a tiny amount of thermal expansion of the fluid in the grapple when stored.

 

[the old grind]

Sounds a bit more practical than having to lug another bulky tool around on implement-changing day.

Think about which way is faster, easier to learn, and that you're sure to get right first time every time. :scratchchin:

Take the 'tool money' saved and buy your wife something to keep her company while you perfect the air/vacuum process.

btw, and way OT, but what's so QA about something if a guy has to get out of the cab so danged often. :confused2: