Options for dealing with pressure build up in disconnected hydraulic lines

[jinman]

When you hook hoses together, you don't accomplish anything as far as pressure relief. The pressure still builds up inside the hoses on both sides since they both get the same heat. The reason hooking the hoses together works is the fraction of a second when you disconnect that the pressure can relieve itself inside the fitting from both the male and female side.

I think on our compacts with male fittings on the attachment side, nothing could be simpler than installing an open ended female quick connector; however, the connectors can be expensive.

 

[newbury]

I use either time or a garden hose. If I can put off hooking it up I wait till morning when it's cooled down. If I HAVE to move it I'll carefully run a garden hose with cool water drenching as much hydraulic as possible.

Both work, but since I retired I wait till morning, or maybe winter

 

[ptgdigger]

When you hook hoses together, you don't accomplish anything as far as pressure relief. The pressure still builds up inside the hoses on both sides since they both get the same heat..

At least from my experience with industrial equipment , backhoes , skid steers and excavators, I disagree. I can't remember the last time BOTH hoses were difficult, always one tough hose and one easy one , along with heat I believe trapped pressure plays a large role and by hooking the hoses together trapped pressure is equalized. If it were just heat both hoses should be a bear, but I don't ever remember in my 20 some years that being the case.

Also on the tractors how well is the hydraulic system designed? If you run the 3 point or front loader up or down until the stop and the relief kicks in are you getting some pressure build in the remote lines? I know in our machines where the auxiliary is on a toggle switch if someone bumps the switch and pressurizes the lines with nothing connected (deadhead) that pressure will last through several on/off cycles of the machine or most of the day unless someone runs the bleeding routine on the auxilary.


Ray

 

[J_J]

You can usually relieve the pressure by pushing the ball or poppet on a flat steel surface.

When the male and female QD's are connected, the temp will increase and decrease. The pressure would be the same in the hyd loop, whatever the temp, and probably becomes atmosphere pressure when the QD's are separated.

If the hoses are separated hot, when the temp subsides, they could draw in some air, or rain water if QD's are face up, or laying in water.

 

[kco]

Ray, in my case both hoses had high pressure. I tried opening each by pressing against a birch block. Once the pressure was relieved using the mallet I was able to finish with the birch block. I checked the other hose of the pair and the pressure was already off it too. Could it be that industrial equipment has a more sophisticated system that isolates different parts of the circuit? (might be a dumb question--I have virtually no knowledge of hydraulics)

I like JJ's suggestion of a T connector/needle valve but will likely stick with just trying an open female QD, if I do anything. For now I'll just see if this is a rare occurance and, if it happens again, hope to remember to use a rag to prevent the hydraulic shower.

The garden hose idea is interesting too, but I remove the loader a long way from a water supply.

JJ's T connector suggestion got me looking at the hydraulics closer (as wasn't sure what a T connector looked like). I notice there are two of them to carry the curl and raise circuits from the right to the left side. Is there such a thing as a 4-way connector(I couldn't find one)? If so, one might use it to replace the T and put the needle valve there since it is in a handier location on the loader arm.

 

[J_J]

Just add another tee in line.

 

[jinman]

At least from my experience with industrial equipment , backhoes , skid steers and excavators, I disagree. I can't remember the last time BOTH hoses were difficult, always one tough hose and one easy one , along with heat I believe trapped pressure plays a large role and by hooking the hoses together trapped pressure is equalized. If it were just heat both hoses should be a bear, but I don't ever remember in my 20 some years that being the case.

Certainly, one tough hose and one easy one.:thumbsup: That's because as soon as you relieve the pressure on one hose, it automatically reduces the hydraulic lock pressure on the other. Think about the structure of a hydraulic cylinder. If you have pressure on both sides of the ram and relieve one side, it reduces the pressure on the other side in a static disconnected circuit. It can't help but work that way. It doesn't matter what generated the pressure, relieving one side affects the other side as well.

I don't know about the tractor side and am making no claims to how pressure has to be equalized there. I'm only talking about a grapple or loader with simple double-acting hydraulic cylinders.

 

[oldnslo]

I agree with ray66v in post #10. Use the connect under pressure QD's if this is an ungoing problem. All of the tees and bleed valves are just more leak points and cluster of fittings to get snagged on something.

Just do some research and see what the connecting force is at different pressures.

 

[namesray]

i guess i am not understanding you guys. call me crazy, but seems o me everyone is over engineering this thing. the op stated having problems with heat expansion in uncoupled hydraulic lines and reconnecting was hard due to the expansion putting more pressure on the qc's then what is easily pushed together by hand force. you all lean towards buying valves and time consuming modifications. if you just work the function of the hoses repeatitly you are going to dissconnect right before you dissconnect them, you HEAT up the fluid. that hot fluid is already expanded when you dissconnect. cools off then super easy to reconnect later. even if the outside temps warm up, there is room for the expansion and still easy to reconnect. this has worked for me 100% of the time since i started doing it lately. i see jj reason of drawing in air=can be purged through normal operation or an easy procedure. as for water getting in, just don't let the couplers near water or expose it to it. wrap a plastic bag around it. i am not saying the valve ideas are silly to releave pressure, just seems like it would be easier to work the fluid until warm, and then shut the engine/pump off, move valve in all directions to releave all pressure or potential gravity leak down that can lead to pressure build up and then dissconnect. doesn't cost anything either. just my 2 cents.

 

[grsthegreat]

i guess i am not understanding you guys. call me crazy, but seems o me everyone is over engineering this thing. the op stated having problems with heat expansion in uncoupled hydraulic lines and reconnecting was hard due to the expansion putting more pressure on the qc's then what is easily pushed together by hand force. you all lean towards buying valves and time consuming modifications. if you just work the function of the hoses repeatitly you are going to dissconnect right before you dissconnect them, you HEAT up the fluid. that hot fluid is already expanded when you dissconnect. cools off then super easy to reconnect later. even if the outside temps warm up, there is room for the expansion and still easy to reconnect. this has worked for me 100% of the time since i started doing it lately. i see jj reason of drawing in air=can be purged through normal operation or an easy procedure. as for water getting in, just don't let the couplers near water or expose it to it. wrap a plastic bag around it. i am not saying the valve ideas are silly to releave pressure, just seems like it would be easier to work the fluid until warm, and then shut the engine/pump off, move valve in all directions to releave all pressure or potential gravity leak down that can lead to pressure build up and then dissconnect. doesn't cost anything either. just my 2 cents.

well, last winter i was using my snow plow up to the time i disconnected it and hooked up the blower. a few hours later i went to re-hook up the plow and the lines wouldn't engage without using a piece of wood to relieve the pressure. this does get old. In the summer i generally leave the implement or the loader under a shaded area so there isn't as much of a problem..... yet sometimes there is. Its never as cut and dry for me.