Attachment Hydraulic Hose Pressure Relief

[retiree-urgency abandoned]

It's nice & hot which means the hoses on attachments are pressurized and tough to connect to the tractor. In other threads, it seems that if you connect the 2 hoses on the implement to each other when you take it off the tractor, the pressure is less or not a problem.

My attachments are plumbed with male fittings - female fittings on the tractor, so I was thinking of assembling some female-to-female fittings to connect the attachment hoses when not in use. After more thought, would it make more sense to connect 2 female fittings to a T pipe-nipple and add a valve to the 3rd leg to drain pressure?

Just trying to make life a little easier when switching attachments.

 

[MapleLeafFarmer]

or .... when you unhook a hydraulic attachment just push the plunger/poppet of both fitting with a ragged hand.
A small amount of fluid may come out.
This helps prevent problems when re connecting in hotter weather.
Quick, easy, and cheap.

 

[WI_Hedgehog]

There's this thing:

Buy Hydraulic Quick Coupler Relief Tools

Tractor Relief Tool™ buy page

www.tractorrelieftool.com

 

[North Idaho Wolfman]

If you connect the two hoses together, they can't build pressure so no need for a tee, but if
it makes you feel better have at it!

 

[Runs With Scissors]

If you connect the two hoses together, they can't build pressure so no need for a tee, but if
it makes you feel better have at it!

+1 on this.

It also has the benefit of keeping dirt out of the connections.

 

[mdhughes]

If you connect the two hoses together, they can't build pressure so no need for a tee, but if
it makes you feel better have at it!

I'm not following the logic on this Wolfman, if they are connected you still have a close loop and the fluid is still going to warmup and expand.

 

[Old Machinist]

I only have one implement with a connection being my grapple. My hoses are zip tied together so I can't connect them to each other. I have thought about switching to the connect under pressure flat face but then realized I don't have any need. I just push the male poppet against the frame of the grapple to relieve the pressure before connecting. I use the rubber caps and plugs to keep the dirt out but I still have to clean them with paper towels before and after. I keep a roll in the ammo box I mounted on the tractor.

 

[nbryan]

I now have handy now a hammer, round-faced drift (sized to be a snug fit in fitting), and a rag, for when those connectors refuse to snap together. Increased temperatures after the removal from the tractor has had these things really tightly sprung sometimes. Wrapping the fitting with a rag as a safety and cleanliness thing, the released oil can spurt rather forcefully everywhere.

 

[Russell King]

If you connect the two hoses together, they can't build pressure so no need for a tee, but if
it makes you feel better have at it!

A sealed system can build pressure if the fluid temperature increases due to thermal expansion. A pressure cooker is an extreme example of that.

Connecting the two lines together will ensure the pressure equalizes through the system but it can increase.

If there was a short empty hose between them that would allow the fluid to compress air in the short hose which may help but eventually that short hose would be full of compressed air and hydraulic fluid unless it is drained out occasionally.

 

[JonM]

if your hydraulic fluid is at a good operating temp before you disconnect it will be easier to reconnect when it cools.

for example if you have a grapple attached but didnt really use it cycle it a few times so the fluid has a chance to changeover before disconnecting it. the warmer fluid will contract a little as it cools making a later connection easier even if the ambient is warmer.

 

[edritchey]

It's nice & hot which means the hoses on attachments are pressurized and tough to connect to the tractor. In other threads, it seems that if you connect the 2 hoses on the implement to each other when you take it off the tractor, the pressure is less or not a problem.

My attachments are plumbed with male fittings - female fittings on the tractor, so I was thinking of assembling some female-to-female fittings to connect the attachment hoses when not in use. After more thought, would it make more sense to connect 2 female fittings to a T pipe-nipple and add a valve to the 3rd leg to drain pressure?

Just trying to make life a little easier when switching attachments.

If you put a 3 way valve on one of the lines on your grapple you can crack it open to relieve the pressure prior to connecting the lines to your tractor. I also like to connect them together like Wolfman already mentioned pressure will still build up especially if the attachment is sitting out in the sun but the 3 way valve will take care of that problem. Here is a link to a good one. Click Here

 

[Schmitty]

If you put a 3 way valve on one of the lines on your grapple you can crack it open to relieve the pressure prior to connecting the lines to your tractor. I also like to connect them together like Wolfman already mentioned pressure will still build up especially if the attachment is sitting out in the sun but the 3 way valve will take care of that problem. Here is a link to a good one. Click Here

This is what I did, but I put it on the tractor side, as that's where the pressure comes from. Then the grapple gets connected together...if I can muscle them together when I take the grapple off.

 

[PoTreeBoy]

A sealed system can build pressure if the fluid temperature increases due to thermal expansion. A pressure cooker is an extreme example of that.

Connecting the two lines together will ensure the pressure equalizes through the system but it can increase.

If there was a short empty hose between them that would allow the fluid to compress air in the short hose which may help but eventually that short hose would be full of compressed air and hydraulic fluid unless it is drained out occasionally.

In theory, IF the cylinder is not fully extended to start with, the total volume of the cylinder can expand by extending slightly. This will allow the fluid to expand without building pressure.

But the two hoses have to be coupled together, otherwise you have two closed systems and the piston can't move. The pressure on the rod end would be higher than the other end But by coupling them together the pressure equalizes and the rod extends slightly.

 

[WI_Hedgehog]

Fluid is in both hoses on both sides of the cylinder, so equal and opposite pressure; I don't see how hooking the houses together solves anything (but again, I'm new at tractoring).

The 3-way valves are expensive, I'm just going to buy two pressure relief kits, 1/4" for front & rear implements, 1/2" for the third function grapple (higher volume couplings).

 

[John T]

It's nice & hot which means the hoses on attachments are pressurized and tough to connect to the tractor. In other threads, it seems that if you connect the 2 hoses on the implement to each other when you take it off the tractor, the pressure is less or not a problem.

My attachments are plumbed with male fittings - female fittings on the tractor, so I was thinking of assembling some female-to-female fittings to connect the attachment hoses when not in use. After more thought, would it make more sense to connect 2 female fittings to a T pipe-nipple and add a valve to the 3rd leg to drain pressure?

Just trying to make life a little easier when switching attachments.

I've never had a problem with building extra pressure from Heat alone......

Usually the only time pressure will happen is if you don't block the implement and it starts to bleed down/sag...... always block them when off the tractor..... to prevent this.

And also Yes, I would swap the fittings M/F or make an adapter to connect the hoses when not in use.

Worse case, grab a couple metric adjustable wrenches and crack the fitting to relieve the pressure.

 

[PoTreeBoy]

Fluid is in both hoses on both sides of the cylinder, so equal and opposite pressure; I don't see how hooking the houses together solves anything (but again, I'm new at tractoring).

If they're not connected together, they may not be at the same pressure.

I'm a lousy artist, so I'll try to explain with words. The forces on the two sides of the piston are equal (but opposite). The force on the cylinder end is the area of the piston Ap times the pressure P. The force on the rod end is 1) the annular area between the piston and the rod Aa times the pressure P, plus 2) the force on the rod Fr. Assuming we relaxed the implement so that Fr=0, then Ap*P=Aa*P. Since Ap<>Aa, the only solution is P=0, which is what we want. The cylinder has to be free to extend slightly to accommodate the slight increase in volume. If it hits the end cap, that exerts a force Fr and changes things.

As @John T wrote (post #15), if the implement is allowed to exert force on the rod, that's going to increase the pressure in the hoses whether they're coupled together or not.

 

[WI_Hedgehog]

That

If they're not connected together, they may not be at the same pressure.

I'm a lousy artist, so I'll try to explain with words. The forces on the two sides of the piston are equal (but opposite). The force on the cylinder end is the area of the piston Ap times the pressure P. The force on the rod end is 1) the annular area between the piston and the rod Aa times the pressure P, plus 2) the force on the rod Fr. Assuming we relaxed the implement so that Fr=0, then Ap*P=Aa*P. Since Ap<>Aa, the only solution is P=0, which is what we want. The cylinder has to be free to extend slightly to accommodate the slight increase in volume. If it hits the end cap, that exerts a force Fr and changes things.

As @John T wrote (post #15), if the implement is allowed to exert force on the rod, that's going to increase the pressure in the hoses whether they're coupled together or not.

Makes sense. You're saying because the rod occupies volume the pressure increase due to heat could be mitigated by the implement cylinder moving slightly and offsetting the pressure buildup.

 

[WI_Hedgehog]

@PoTreeBoy : I read your explanation again today...very well written and well thought, thank you again for the education.

 

[retiree-urgency abandoned]

Sorry for the delayed update - got sidetracked on some other things. Had some parts in my parts jar and picked up the rest from the local hydraulic shop. Hardware store just had pvc valves - if they blow out, I'll upgrade to metal ball valves. Photo 1 shows components, photo 2 shows assembled components and photo 3 shows the assembly hooked up to the grapple hoses - just did that this afternoon.

I'll report back when I put on one of the attachments that has hydraulics. Currently working with bucket/toothbar, so the hoses will have time to build some pressure and test this out.

 

[WI_Hedgehog]

The PVC valve Tee needs to point toward the cab to protect the fitting from damage.