Pressure relief valve to ease quick couplings

[PTWannaHave]

Hello all,

I've been reading the forums a lot lately regarding the challenges of using the quick couplers when under pressure.

Some good suggestions came up, such as stopping the engine and cycling the aux. PTO handle. However, I don't recall a good solution for the snow blower that happens to have been sitting outside in full sun... It would annoy me to no end to drive up to it to use it, and not be able to make the hydraulic connection because of the built up pressure in the attachment's hoses/circuit.

I thought there must be a better way than a hammer and pin...??!! (Btw, I have zero experience with hydraulics.) I thought that there must be a device/fitting that can be plumbed in the circuit to relieve pressure (without spilling) before using the QDs...

I imagined an inline T-type fitting mounted between the hyd. motor and one of the hoses, where a screw (that can never come out) is backed out 1/4-3/4 of a turn to relieve pressure. Go attach your hoses, and then come back to turn screw back in.

An employee at a store that sells hydraulic components tells me he's never seen such a thing... I found the following online that are representative of a possible solution?:

Pressure Relief Valve: RECTUS GmbH: Quick Coupling Division Europe

Holmatro - Mastering Power - Products - System components - Couplers - Pressure relief valve

For now, I've made a mental note that if I ever own hydraulic-powered attachments, store them in the shade...!! In my search for a solution, I came across the following that appear to be better couplers than standard AG couplers:

hydraulic high pressure non spill quick coupling SBA-high pressure hydraulic coupling for mold circuits-Quick Coupling for all your mold lines, heating, hydraulic core pull circuits and sequential valve gated hot runners-Quick Mold Change Syste

Attachments - Toolcat 5600 and 5610 Utility Work Machines - Bobcat Company

I would have a hard time explaining to friends, family, and wife that it is 'normal' that it is sometimes so hard to make the hydraulic connections...

A lot has been written on this subject matter, so I am not trying to exasperate... If you've heard of an adequate fitting as described for the PT, I would most likely pick some up at the same time I buy a machine and/or implement.

Cheers,

 

[6sunset6]

Just put a male QD on one hose and a female on the other and hook them together when not using. Pressure will equalize. OF course the tractor end has to match. A little more costly as you need a pair of M and F for each implement but then you can never mix up which one to plug in where.

 

[Gravy]

Just put a male QD on one hose and a female on the other and hook them together when not using. Pressure will equalize. OF course the tractor end has to match. A little more costly as you need a pair of M and F for each implement but then you can never mix up which one to plug in where.

I have done this, but it doesn't completely solve the problem. The pressure still rises with temperature increases, sometimes to the point where the couplers will not uncouple.

PTWannaHave's idea of a relief screw sounds good to me. I'll have to think about it some more, but it might be doable.

 

[J_J]

I have mentioned this many times before. You only need one QD fitting. a short hose, and a plug in the end of the hose.

When you remove the attachment from the PT, plug the adapter in to the matching QD. This will let any fluid that may expanded, seep into the adapter hose. This may cause only a few psi of air in the adapter. If the hot attachment ever cools down, it will suck in a little air. No biggie.

Could also use a needle valve on a tee before the QD to release pressure.

 

[American Bulldog]

Just take the coupler off if the pressure is too high. A couple wrenches and a couple minutes. That will definitely relieve the pressure. Yes it is a PITA, but git-er-dun. So far I have always been able to get the couplers on, but that is what I would do if they were stuck.

 

[MossRoad]

We have had our PT for 10 years now and I have only had this problem 4 times that I can recall. The first two times I just used a wrench and loosened a hose fitting until a couple drops came out. The next two times I put a rag in the connector and put either a screwdriver or bolt in on the rag and gave it one good whack with a hammer. It took about 5 seconds to do it.

Has this become that big of a problem that folks are going to add $$ worth of hardware to each of their powered attachments?

 

[Johnbro]

Well here's one less thing to worry about: sitting in the sun won't increase the pressure in your hydraulic system. Unlike gases, fluids don't expand or contract with temperature.

 

[J_J]

Well here's one less thing to worry about: sitting in the sun won't increase the pressure in your hydraulic system. Unlike gases, fluids don't expand or contract with temperature.

Are you sure about that? Then, why do we check the level of the oil when the engine is cold?

Also can you explain why a hyd attachment with QD's , will be hard to connect. but when the fluid is released, it connected OK.

 

[J_J]

In reference to fluid expansion.

An excerpt from one of Brendan Casey articles:

The cylinders were extended to the internal stop and pressurized to 250 bar. The ball valve was closed and the rod-end port connection was removed. As the hydraulic oil and cylinder body started cooling down, pressure decreased slowly to zero, although no leaking could be detected at the rod-end port.

I explained to the engineers on site that the cause of their 'apparent' problem was the heating and subsequent cooling of the oil being supplied to the hydraulic cylinders during testing.

But they still didn't believe me and remained of the view that the problem was a result of leaking seals.

So to prove the point, I got a hot-air gun - normally used for packaging wrap and started to gently heat the hydraulic cylinder. As I expected, cylinder pressure started to increase.

 

[westbrooklawn]

Solids, gasses, liquids, all expand and contract with temperature change - Physics 101 basic....