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.

 

[Wa11banger]

Understood but I do believe my supply ckts are longer than the cylinder movement on the curl and dipper. I didnt think any cylinders were recirculatory

 

[RickB]

Understood but I do believe my supply ckts are longer than the cylinder movement on the curl and dipper.

Most are. It's not about length, it's about volume. And cycling the cylinder(s) more than once. Which I have mentioned more than once. I'm drawing on 40 plus years of practical experience here, as well as 20 years of equipment dealership experience which includes being familiar with factory recommendations and service procedures from a wide range of manufacturers. If that's not good enough for the theorists, NASA employees and aircraft engineers here, I can't help it. I'm getting along just fine, thanks.

 

[Wa11banger]

Haha RickB I do thank you for sharing your knowledge and I will even apologize for getting your panties in a wad. I am just trying to understand why. I am not questioning your advise simply asking you to expound on why, if you can. Telling someone to cycle it several times and it will work itself out does nothing to explain why.

Thanks again for your insight but if our/my questions bother you so much are you sure a forum is the place for you? With over 6k post i am sure you do know it is a place to ask your questions, share your knowledge, and overall comunicate with like minded people or at least people with the same interests.

I've never owned a dealership, and do not have 40 years experience with hydraulics but thanks to you and others I have at least a better working knowledge of many things I have never been familiar with before. Im still ignorant on tractors and their systems but less and less everyday

 

[J_J]

Just cycle the hyd circuits about 10 or more times, and be done with it.

If you continue to have air in the circuits, you might want to check the suction side of the pump.

 

[RickB]

Haha RickB I do thank you for sharing your knowledge and I will even apologize for getting your panties in a wad. I am just trying to understand why. I am not questioning your advise simply asking you to expound on why, if you can. Telling someone to cycle it several times and it will work itself out does nothing to explain why.

Thanks again for your insight but if our/my questions bother you so much are you sure a forum is the place for you? With over 6k post i am sure you do know it is a place to ask your questions, share your knowledge, and overall comunicate with like minded people or at least people with the same interests.

I've never owned a dealership, and do not have 40 years experience with hydraulics but thanks to you and others I have at least a better working knowledge of many things I have never been familiar with before. Im still ignorant on tractors and their systems but less and less everyday

My panties aren't in a bunch.
Every time the volume of air contained in the cylinder exits and returns to the reservoir, it carries a percentage of the volume of any air present with it. Cylinder size, hose diameter and length, as well as elevation between the valve and cylinder are some of the variables that determine how many cycles of cylinder stroke are required to remove all the air present. If you take your fingers off the keyboard for a minute and actually think about what happens when a cylinder is cycled, I'm pretty certain you can understand how the oil moves the air out and back to tank.
Pardon the pun, but it really isn't rocket science.

 

[murphy1244]

Pardon the pun, but it really isn't rocket science.:laughing::thumbsup:

 

[Wa11banger]

Lol no pardon needed but unfortunately rocket science isnt my specialty either.. So that explanation did open my eyes.. I kept thinking once everything was up to pressure you had what you had.. taking my hand off the keyboard partially got me stuck in this rut a couple weeks ago when I originally asked. I got myself lost drawing it on the whiteboard.. I drew a cylinder and ckt, put a diff color dot at a specific distance from it in the cylinder. (This is where I went totally wrong and got my blinders stuck on hard) I tried to demonstrate to myself that ckt exercising and that dot would move into the cylinder. Then back to where it originated when relaxed. I completely overlooked the fact that the volume difference would probably put that dot someplace else. because of my cylinder orientation I was also leaning towards all air getting pushed past piston seals and exiting the flange seal. Couldnt see the forest for the trees thing.. thanks for the explanation I do truly appreciate it.

 

[Gary Fowler]

Air cycles out of the system without any bleeding required. I know this from experience. I don't need to know how it does it or the hydraulic fluid theory to know that it does. I don't know how my computer puts these letters on this thread but I know that it does put a D on the screen when I hit the letter on the keyboard and it has no wires so it transmits wireless. I don't need to know how that works either, it just does. One does not need to know theorem mechanics about tractors to know that if I pull back on the FEL lever, I expect the FEL to raise. I don't need to know how the pump is powered, fed, pressure delivered etc., just that it will work just like the air being removed from the new cylinder.

Fluid level being maintained with correct type in your tractor is about all you need to know as long as it is working which 99.99% of the time it will continue to work as long as all fluids are maintained and serviced as recommended.

 

[Wa11banger]

Air cycles out of the system without any bleeding required. I know this from experience. I don't need to know how it does it or the hydraulic fluid theory to know that it does. I don't know how my computer puts these letters on this thread but I know that it does put a D on the screen when I hit the letter on the keyboard and it has no wires so it transmits wireless. I don't need to know how that works either, it just does. One does not need to know theorem mechanics about tractors to know that if I pull back on the FEL lever, I expect the FEL to raise. I don't need to know how the pump is powered, fed, pressure delivered etc., just that it will work just like the air being removed from the new cylinder.

Fluid level being maintained with correct type in your tractor is about all you need to know as long as it is working which 99.99% of the time it will continue to work as long as all fluids are maintained and serviced as recommended.

You are absolutely right some do not wish to know and thats fine for sure. I asked the question because if someone here could answer I wanted to know.. On top of that it was a great ride to get there I learned something new today. I also learned I need to better communicate where I came to my conclusion from a little better. Many things learned in just a couple of banterings back and forth.

I also learned I really need to apologize to the OP for totally highjacking his thread very sorry RJ

 

[k0ua]

I have always like to know how things work, even things that probably won't really profit me to know. I like to know just for the "knowing". I always have.