fix overpressure, sag: check valves, accumulators?

[orangetree]

I have two problems where I've seen advice on TBN to solve with a "check valve":

1. a cylinder "sags" - eg, my snowblower chute deflector. Set it at the angle i need; a minute later the deflector has drooped down.
2. a grapple can experience very high pressures when, say, it's closed on a long tree, then the FEL is lifted. Or just bouncing along driving with a long/leveraged tree. Loads increase in the grapple cylinder substantially, with no relief valve in the (closed) circuit)

In #1, I do want to "check" "backward" flow ... unless I don't (I want it held from fluid moving in the direction it sags down - except when i open the valve that direction. I am not understanding how a check valve wouldn't prevent contracting the cylinder at all.

In #2, over on Alternative 3rd function? "check valves" are discussed to solve this problem. A user clarifies a hydraulic accumulator could be used here. But those do not seem to be in common use, and not what folks referencing "check valves" refer to. It seem like a dedicated, higher-pressure OP valve could be used(?)

 

[ericm979]

I think for #1 you want a pilot operated check valve. The valve stays closed unless there is pressure from the pump (through the rear remote valve) going to that side of the cylinder.

And for #2 a double relief valve. Maybe a single since the load you want to relieve is all in one direction (opening the grapple).

 

[orangetree]

I think for #1 you want a pilot operated check valve. The valve stays closed unless there is pressure from the pump (through the rear remote valve) going to that side of the cylinder.

And for #2 a double relief valve. Maybe a single since the load you want to relieve is all in one direction (opening the grapple).

Thanks! these make sense conceptually. Amazing how much variety of hydraulic (or air) control systems there are. Almost like whole factories were run before computers...

For #2, relief of grapple over pressure.

• My ck2610 spec says FEL OP valve is 2500psi (I plan to Tee in a gauge, haven't done anything yet). How much higher can/should I go on this relief valve?
• ? 1/2 NPT 30 GPM 1500-3000 PSI Hydraulic Cushion Valve Prince Mfg DRV-4HH | Relief & Cushion Valves | Hydraulic Valves | Hydraulics | www.surpluscenter.com

on #1 - keep chute deflector up.

• FYI - [seems like] these are often called "Lock Valves" (pilot-operated or not).
• ? is this a workable product for my small chute cylinder app?
  • $30 - Rexnord PCD-F1-2G Dual Pilot-Operated Lock Valve Gasket Mount | Check & Lock Valves | Hydraulic Valves | Hydraulics | www.surpluscenter.com while most PO-check valves I see are in the $150 range; that's a big discount for 'old inventory'
    • Edit: I suppose "gasket mount" means I"d need to machine a ported base ... not worth the $100
  • $150 - am I missing any significantly cheaper products? Lock Valve 1/2" NPT 25 GPM 3000 PSI Prince Mfg RD-1450 | Check & Lock Valves | Hydraulic Valves | Hydraulics | www.surpluscenter.com

 

[ericm979]

You don't need a 30gpm relief valve. Your tractor claims 11.7 gpm but I think that is adding the main and steering pumps together, which is done for marketing but is not applicable to the real world. The steering pump is around 4-5 gpm so figure 7.5 for the main pump. You can probably find the exact numbers somewhere, I did not look hard.
A smaller valve would be appropriate, if any are made.

I'm not convinced that a relief valve is needed here. You should try not to pick up heavy badly balanced loads in the grapple anyhow so you don't bend the loader frame. The same is true with pulling with the lids.

You can see some of the pressures that can be reached in this video

I'd argue that you should not do those things anyhow. And even being as bone headed as he was for demonstration purposes, nothing on the tractor was damaged.

 

[orangetree]

great video, thanks. I'm actually surprised it ONLY got up to 5-6000psi. I would have expected more given the leverage.

I didn't see any smaller relieve valves, but will keep looking. Any reason to think the large valve would be less effective here, or just 'overkill'?

Since I'm installing the 3rd function, I might as well add one since it seems relatively cheap piece of mind if i end up prying on something. <*cough*> I'm sure it will never be dusk after a long day just trying to get ONE more thing done NOW <*cough*>

 

[ericm979]

It'll work, it'll just be a little harder to package than a smaller one.

 

[Threepoint]

Here is an excellent video on how a double-piloted check valve works to lock the cylinder in position. I'd love to be able to add one to the sidelink cylinder on my CK3510SE's top 'n tilt. Unfortunately, with a cylinder that short, there isn't enough room to mount one. So I just live with the very gradual drift.

 

[LouNY]

They can be hose mounted they dont have to be ridge piped.

 

[orangetree]

I had a realization that concerns me about this app:

The cushion/double relief valve simply "short circuits" both sides of the cylinder, allowing an overload condition to resolve by the rod moving with the load. they are marketed for exactly this purpose afaict.

HOWEVER: isnt the area of the two sides of the plunger different? smaller on rod end due to rod's cross section? this would mean that the volume-per-inch-travel differs, and it does no good to only short circuit.

Eg, if i simply pipe a double-acting cylinder to itself - i cant compress it, the bottom is expelling more fluid per thou travel tham the top is making space to accept?