Bleeding lines on new grapple install

[RickB]

Todays hyd systems that are self bleeding have check valves in the system that allow air to breathe out, usually in the actuating cylinders themselves. Aircraft hydraulic systems do the same; they also maintain a pressure in the header tank to ensure positive flow.

I'm not going to pretend to work for NASA or know about aircraft hydraulics, but common hydraulic circuits and cylinders on tractors don't have check valves in them. If they did have devices on the cylinders to bleed off air, which they don't, those devices would not be called check valves. Tractor hydraulic systems seldom have pressurized reservoirs, but a lot of construction equipment does.
It sure would be helpful if the information posted here could at least be factual as applied to the equipment being discussed.

 

[wdchyd]

I'm not going to pretend to work for NASA or know about aircraft hydraulics, but common hydraulic circuits and cylinders on tractors don't have check valves in them. If they did have devices on the cylinders to bleed off air, which they don't, those devices would not be called check valves. Tractor hydraulic systems seldom have pressurized reservoirs, but a lot of construction equipment does.
It sure would be helpful if the information posted here could at least be factual as applied to the equipment being discussed.

:thumbsup:

 

[Mike476]

It sure would be helpful if the information posted here could at least be factual as applied to the equipment being discussed.

It isn't something that is easily found on the web unfortunately. I bought the manual for my 1660 but I'm away from home to see whether the check type of vent valve I'm referring to is located on the control valve, the pump or where exactly.

One thing is certain, the seals in the cylinder will not permit air to pass but maintain their integrity and keep the hydraulic oil from bypassing as well.

 

[RickB]

It isn't something that is easily found on the web unfortunately. I bought the manual for my 1660 but I'm away from home to see whether the check type of vent valve I'm referring to is located on the control valve, the pump or where exactly.

One thing is certain, the seals in the cylinder will not permit air to pass but maintain their integrity and keep the hydraulic oil from bypassing as well.

Go ahead & check on that. The only certainty here is the absolute fact that a double acting hydraulic cylinder or a pair of cylinders connected in parallel will purge itself (or themselves) of air by simply being cycled a number of times with the minimum possible load. Been true forever, and all the commentary here doesn't change that. No check valves or bleeders required.

The claim that cylinder seals do not pass air is bogus. If that were true, equipment manufacturers would not have specifications detailing acceptable rates of fluid bypassing cylinder piston seals. And as a point of fact, many do indeed have those leakdown allowances.

 

[Tx Jim]

I'll 2nd,3rd & 4th what RickB stated!!!!!!!!!!!!!!

 

[Mike476]

I will, for the benefit of the OP.

Double acting cylinders will eventually bleed air without the aid of vent valves, or the need to bleed from the installed component for that matter.

Priming installed components / lines helps reduce the risk of pump cavitation or damaging other componenets. Whether open or closed systems, there are componenets that don't like air, another basic fact. All the commentary in the world won't change that.

 

[xtn]

Priming installed components / lines helps reduce the risk of pump cavitation or damaging other componenets.

Forgive me if I've misunderstood. Doesn't the pump draw from a (hopefully full) reservoir? It's not like an air-filled return line is plumbed directly into the pump's inlet, right?

xtn

 

[Groo]

If you are dealing with a long line and a small volume cylinder, you could easily get air trapped in a cylinder that would not self bleed. Air in there won't necessarily hurt anything, but it will have it moving a little weird, especially under load. Single acting mufti-stage cylinders often (always as far as I've seen) have bleeders built into them.

 

[Wa11banger]

RickB,

Thanks for your input I had thought it might pass through the seals but had been told the it would not. However if your valve block and pump are lower than the devices circuit how does air get passed when it settles out of the fluid and at a high point in the line? Or does that matter

 

[RickB]

RickB,

Thanks for your input I had thought it might pass through the seals but had been told the it would not. However if your valve block and pump are lower than the devices circuit how does air get passed when it settles out of the fluid and at a high point in the line? Or does that matter

Having gravity in one's favor is helpful when it is possible. If not, the velocity of the oil returning through the lines from the cylinder to the tank carries the air along. Several cycles are always recommended to purge the air completely.