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....

 

[BobRip]

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.

Heat with a hot air gun, good technique. I have done that with erratic electronic components to isolated the component.

 

[woodlandfarms]

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.

Here is a calculator to help with your theory

Thermal Expansion - Volumetric or Cubic

 

[oldnslo]

If hooking under pressure is a constant problem you buy QD's that connect under pressure. Depending on the size up to around 10,000 PSI. I won't lie and say they are inexpensive, but they are still available.

Roy

 

[SpringHollow]

The world of digital thermometers is sapping knowledge from our yungins

Ken

 

[J_J]

If hooking under pressure is a constant problem you buy QD's that connect under pressure. Depending on the size up to around 10,000 PSI. I won't lie and say they are inexpensive, but they are still available.

Roy

Roy,

I haven't found to many QD's that will connect under full operating pressure. Some say up to 500 psi. Even the flat faced QD's.

 

[oldnslo]

Roy,

I haven't found to many QD's that will connect under full operating pressure. Some say up to 500 psi. Even the flat faced QD's.

JJ,
Here are two versions I found info on.

Snap tite version
The sun and the heat it generates is a source of life and energy for our planet. It's also the source of many headaches for the hydraulic engineer, one of them being thermal expansion.

While construction and utility equipment manufacturers experience the brunt of the sun's effects, manufacturers of skid-steer loaders may have the toughest challenge of all. Often, thermal expansion creates pressures of over 2000 psi, preventing standard quick connect couplings from connecting as designed. Compounding this issue was the decision made long ago to "key" the proper hose connections by using both a coupler and nipple on both the loader and attachment.

Herein lies the problem, to easily connect an attachment containing trapped pressure due to thermal expansion, both the nipple (male half) and the coupler (female half) would be required to connect while under pressure. Presently, users must remove or otherwise manipulate the coupling's valve to relieve the pressure, defeating the purpose of using a quick disconnect in the first place. Why should the user be forced to manually relieve the pressure and possibly damage the coupling, or endanger the environment with the subsequent spillage?

As if these demands weren't tough enough, the industry also mandated that they design a coupling that meets ISO-16028, an international specification for interchangeable, push-to-connect, dry break couplings.

Patented Design
Using the latest 3-D modeling software, Snap-tite's engineers designed and patented the Series CP74 coupling. While being able to connect to any manufacturers' ISO-16028 compatible design, either the nipple or coupler will connect to static pressures of up to 3625 psi.

The CP74 solution saves time, prevents damage and protects the environment while maintaining the interchangeable criterion of ISO-16028.



S70 Complete Coupler
SafeWay痴 S70 Series offers unique internal valving, combined with SafeWay痴 two-way sleeve feature, allowing one-hand connection under full system pressure. The body (coupling) half can be mated to either a ball valve or poppet valve ISO male tip (nipple). The S70 Series is used primarily with agricultural equipment. It is original equipment on full size tractors and front-end loaders. Use when connection and disconnection under pressure, without the use of tools, is desirable.

I suspect Parker/Pioneer & Eaton/Aeroquip also have models similar to these.

NOTE: I do not remember who makes or made the 10,000 PSI version but from memory I believe they where special for jack service.

Roy

 

[J_J]

I found this on DHH web site.

Connect Under Pressure Couplers
ISO 16028

These no-drip, skid-steer couplers connect by hand under pressure without releasing any fluid into the environment. Available in 1/2" male and 1/2" female, these couplers are fully compatible with our standard ISO 16028 couplers.

Applications: Mobile equipment and attachment tools where exposure to the sun or temperature change causes pressure to develop due to thermal expansion or trapped fluid. Any application where static pressure can get locked into the system.

* Male coupler will connect under residual pressure up to 3571 psi.
* Female coupler will connect under residual pressure up to 1595 psi.
* Mating coupler must be without residual pressure.
* Steel construction with anti-corrosive plating


It seems kind of hard to find a definitive answer on things like connect under pressure.

 

[oldnslo]

It seems kind of hard to find a definitive answer on things like connect under pressure.

Amen on that JJ,
different companies have different specs "connect Under Pressure"

I think Parker and possibly others have a model with a lever like a ball valve on the QD to aide in connecting under pressure.

From memory I think some models of IH tractors had this feature also. possibly the "86" series like 1486???

Roy

 

[MossRoad]

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.

I think we check the engine oil when it is cold so we don't burn our hands on the dipstick! :laughing:

Also, it gives the oil time to drain back down to the crank case.

I agree that something happens to the oil and it almost has to be expansion, when you leave an implement in the sun. Oil does expand and contract. However, it is not very much. But the pressures are tremendous in a closed vessel.

 

[MossRoad]

Heat with a hot air gun, good technique. I have done that with erratic electronic components to isolated the component.

I used to do that, too, and also use chiller spray to cool components. However, today's electronics are becoming less and less able to troubleshoot on a component level. We have become board swappers.