Why not check valves in FEL?

[MtnViewRanch]

Just wanted to give you something to think about. I don't think that many guys even think about using float with their side link, and if you don't have the right circumstances, it is no big deal, bit if you do, it is a very big deal.

 

[Mace Canute]

Good question. beenthere has nailed it pretty well but the question made me wonder....how long will it be before piloted check valves are mandatory on all agricultural and industrial equipment when an object is lifted with a hydraulic cylinder and has no mechanical safety catch?

 

[AKKAMAAN]

Good question. beenthere has nailed it pretty well but the question made me wonder....how long will it be before piloted check valves are mandatory on all agricultural and industrial equipment when an object is lifted with a hydraulic cylinder and has no mechanical safety catch?

There is a distinction between "falling" and "drifting" here...slow drifting is usually not a big safety issue...
Pilot check valves will not protect load from falling when a pressure line breaks...for that needs mechanical stop or flow "fuse"....and it is still not 100% safe, but protects for line failure.....

Pilot check valve is more a drift protection, for support legs on backhoes, cranes etc....pilot check valves only works both ways on a double action cylinder if piston seal is 100% sealed. Of course no external leaks allowed either.

Pilot check valves should make it easier to connect/disconnect QD's on pressurized hoses...

See this article about flow or velocity fuse
and
other hydraulic fuses

 

[Mace Canute]

Not quite AKKAMAANI. I operated large digger trucks and large bucket trucks for many years when I was a Lineman for the provincial electrical utility. They had pilot operated check valves on ALL the hydraulic cylinders. It was required to do a daily check on them to ensure they were working as designed. It was a simple test, just put pressure on a cylinder (both sides of the piston on certain cylinders), shut the pump off, and operate the hand controls. If there was movement in the cylinder, it failed and if there was cylinder creep, that was a failure too (which may or may not have been related to the pilot operated valve). Your statement "Pilot check valves will not protect load from falling when a pressure line breaks" is absolutely wrong! That is exactly why they are used and they are mounted on the cylinder to ensure there is minimum opportunity for anything to fail (think less parts). Having a pressure line between them and the cylinder defeats their purpose. Your statement "pilot check valves only works both ways on a double action cylinder if piston seal is 100% sealed." is only partially true, they have to be mounted directly on the cylinder. If you put them anywhere else, you may as well not have them.

 

[wdchyd]

Not quite AKKAMAANI. I operated large digger trucks and large bucket trucks for many years when I was a Lineman for the provincial electrical utility. They had pilot operated check valves on ALL the hydraulic cylinders. It was required to do a daily check on them to ensure they were working as designed. It was a simple test, just put pressure on a cylinder (both sides of the piston on certain cylinders), shut the pump off, and operate the hand controls. If there was movement in the cylinder, it failed and if there was cylinder creep, that was a failure too (which may or may not have been related to the pilot operated valve). Your statement "Pilot check valves will not protect load from falling when a pressure line breaks" is absolutely wrong! That is exactly why they are used and they are mounted on the cylinder to ensure there is minimum opportunity for anything to fail (think less parts). Having a pressure line between them and the cylinder defeats their purpose. Your statement "pilot check valves only works both ways on a double action cylinder if piston seal is 100% sealed." is only partially true, they have to be mounted directly on the cylinder. If you put them anywhere else, you may as well not have them.

True, I see many on Cranes, Bucket Trucks,Aerial Fire Apparatus, Drill Rigs.....virtually anything used for hose break protection and unauthorized use while equipment not running......all have built-in cartridge valves and/or hard piped/tubed direct to cyl barrel.......

Hardly ever see hoses between POCV and cyl....(usually a makeshift add-on)

 

[radman1]

It is mainly a function of cost for most. My compact wheel loader has optional check valves on the tilt and lift cylinders. Check valve sits on the cylinder. Break a hose and the load won't come crashing down. The loader can sit for days and get no down drift if the loader is left up. However, I suspect the float function probably no longer works with the check valve but have not tried it.

 

[picker77]

I can see how a check valve would disable float, but since "float" only applies (at least on tractor FEL's) to the loader arms and not the dump/curl cylinder, I suppose a DPOCV on just the dump/curl cylinder would be ok?

 

[mmurphy]

I may have missed something but, I think we were talking about check valves in the valve its self. Were we not?

 

[wdchyd]

But in reading the CCM website this question popped into my mind about double pilot operated check valves like those that come on the CCM cylinders: Why don't the curl and lift cylinders on FEL's have these from the factory? Seems like it would cure a lot of the minor and sometimes major FEL drift/leakdown problems

The OP mentions external DPOCV (double pilot operated check valve)....I think you are referring to the load check valve that's incorporated internally in the FEL controls.....

 

[mmurphy]

The OP mentions external DPOCV (double pilot operated check valve)....I think you are referring to the load check valve that's incorporated internally in the FEL controls.....

Now I see. I was thinking the whole time about load checks. Thanks.