orangetree
Gold Member
<dup>
Last edited:
Alternative 3rd function?
- Thread starter LS Tractor Owner
- Start date
- Views: 20771
orangetree
Gold Member
Thanks for this - it's a great point. The grapple hydraulic circuit probably has it much worse, but the same leverage also works on the FEL.
Thankfully (or NOT) the FEL has a "relief valve" of sorts, even with the valves closed ....
tractor falls over if leverage(on FEL) is too high
although as you say, the impact/impulse into the system - on all parts bearing the load - is going to be much higher as you bounce around, when there is a cargo with a high leverage
orangetree
Gold Member
I created a dedicated thread for how to solve the "check valve" / accumulator / overpressure issue
www.tractorbynet.com
fix overpressure, sag: check valves, accumulators?
I have two problems where I've seen advice on TBN to solve with a "check valve": a cylinder "sags" - eg, my snowblower chute deflector. Set it at the angle i need; a minute later the deflector has drooped down. a grapple can experience very high pressures when, say, it's closed on a long tree...
www.tractorbynet.com
2manyrocks
Super Member
- Joined
- Jul 28, 2007
- Messages
- 9,520
I am only referring to a check valve as a potential solution because that's what the Messick's video mentioned as protection for the hydraulic system. Please understand that I know next to nothing about hydraulic systems and would like to learn more so I don't damage my tractor out of my own pure ignorance.Thanks for the name. Yes, that function sounds like it applies to the concern here - although in a ~month of reading about this I don't believe I've seen anyone else refer to it ... at a minimum it's highly uncommon on everyday TLB/grapple/etc (?)
@davedj1, @2manyrocks, @LouNY discuss "check valves" on several pages of this thread - and in the (few) other threads discussing this same overpressure risk, the phrase seems to be used the same way. I'm trying to understand what folks are proposing; those uses do not seem to be a reference to an "accumulator" type device.
Is this some sort of overpressure device that, rather than shunting the fluid to tank, just "short circuits" the cylinder, allowing it to open/close as necessary to avoid damage? As I am picturing it, if say the normal hydraulic OP valve is set for 2000psi, this "grapple saver" would be substantially higher, say 3000psi. Thus it would only ever open when the valve to the grapple circuit is closed and the grapple is isolated from the rest of the system.
View attachment 743091
Maybe I should start a new thread about this, don't want to completely hijack this one
npalen
Elite Member
Nice looking tuits there!
npalen
Elite Member
I'm afraid that "polar moment of inertia" is being used out of context above.Thanks for this - it's a great point. The grapple hydraulic circuit probably has it much worse, but the same leverage also works on the FEL.
Thankfully (or NOT) the FEL has a "relief valve" of sorts, even with the valves closed ....
tractor falls over if leverage(on FEL) is too high
although as you say, the impact/impulse into the system - on all parts bearing the load - is going to be much higher as you bounce around, when there is a cargo with a high leverage
Polar Moment of Inertia - Definition, Formula, Uses, Types
Polar Moment of Inertia - Click to learn the definition along with its types, uses, formulas, and the differences between moment of inertia.
byjus.com
orangetree
Gold Member
Wrong person quotedI'm afraid that "polar moment of inertia" is being used out of context above.
Polar Moment of Inertia - Definition, Formula, Uses, Types
Polar Moment of Inertia - Click to learn the definition along with its types, uses, formulas, and the differences between moment of inertia.
LD1
Epic Contributor
That would be a cross-over relief valveThanks for the name. Yes, that function sounds like it applies to the concern here - although in a ~month of reading about this I don't believe I've seen anyone else refer to it ... at a minimum it's highly uncommon on everyday TLB/grapple/etc (?)
@davedj1, @2manyrocks, @LouNY discuss "check valves" on several pages of this thread - and in the (few) other threads discussing this same overpressure risk, the phrase seems to be used the same way. I'm trying to understand what folks are proposing; those uses do not seem to be a reference to an "accumulator" type device.
Is this some sort of overpressure device that, rather than shunting the fluid to tank, just "short circuits" the cylinder, allowing it to open/close as necessary to avoid damage? As I am picturing it, if say the normal hydraulic OP valve is set for 2000psi, this "grapple saver" would be substantially higher, say 3000psi. Thus it would only ever open when the valve to the grapple circuit is closed and the grapple is isolated from the rest of the system.
View attachment 743091
Maybe I should start a new thread about this, don't want to completely hijack this one
EDIT: thread created check valves, accumulators, overpressure; oh my
They make them, and they are common. But it will only protect the pressure surge IF and only IF the external forces are trying to extend the cylinder. You would have no protection in compression without a relief back to tank
jigs_n_fixtures
Veteran Member
Just for clarity: If the diverter is running the grapple, and sharing the function of the bucket hydraulics, the hydraulics to the grapple are isolated from the relief valve in the FEL valve when the diverter is closed. That is where the overpressure issue arises.Thanks for this - it's a great point. The grapple hydraulic circuit probably has it much worse, but the same leverage also works on the FEL.
Thankfully (or NOT) the FEL has a "relief valve" of sorts, even with the valves closed ....
tractor falls over if leverage(on FEL) is too high
although as you say, the impact/impulse into the system - on all parts bearing the load - is going to be much higher as you bounce around, when there is a cargo with a high leverage
Last edited:
orangetree
Gold Member
for this thread, here is the relevant product type you want to solve this overpressure issue. Not normally included on budget grapples, but apparently common on some rentals, and larger/higher-end models
"double relief valve" == "cushion 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 (this model is larger than needed; i haven't found a lower GPM model. It will work fine, though, just physically larger than necessary)
thanks for ericm979 on the thread about those
"double relief valve" == "cushion 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 (this model is larger than needed; i haven't found a lower GPM model. It will work fine, though, just physically larger than necessary)
thanks for ericm979 on the thread about those
orangetree
Gold Member
see the "cushion valve" i linked above - I can't find a flow diagram, but my understanding is it works both ways. With no pressure on either control port (you're not using the lever; pressure drifts down to ~none), a high pressure on EITHER cylinder port will cross-over/short-circut, allowing the cyclinder to relax OR extend as needed to relieve the pressure.
jigs_n_fixtures
Veteran Member
The problem I see with that valve is that as the load exerts a pressure on the hydraulics of the clamping side, the fluid bleeds to the other side of the circuit. So as the load wiggles and exerts pressure, it will gradually relax enough to drop the load. It doesn’t maintain the pressure.
Where an accumulator with a flow control valve, would dampen return flow to limit damage from the pressure spikes. But, would regain the clamping pressure, while allowing the pressure wave to be dissipated.
Where an accumulator with a flow control valve, would dampen return flow to limit damage from the pressure spikes. But, would regain the clamping pressure, while allowing the pressure wave to be dissipated.
LD1
Epic Contributor
Nope. Still doesnt work.
It will work extending. But not compressing the cylinder. The only way those DPCV's work is if there somewhere for the fluid to go when they reach their set pressure. When compressing a cylinder....there is no where for the fluid coming out of the base end of the cylinder to go.
LD1
Epic Contributor
Thanks for this - it's a great point. The grapple hydraulic circuit probably has it much worse, but the same leverage also works on the FEL.
Thankfully (or NOT) the FEL has a "relief valve" of sorts, even with the valves closed ....
tractor falls over if leverage(on FEL) is too high
although as you say, the impact/impulse into the system - on all parts bearing the load - is going to be much higher as you bounce around, when there is a cargo with a high leverage
Most tractor loaders do not have any relief on the work ports when the loader valve is centered.
Sorry to burst your bubble. They just dont.
orangetree
Gold Member
Correct - i made a joke that the entire tractor tips over, as your 'relief' if overloaded
Last edited:
orangetree
Gold Member
Doesnt this valve connect both sides of the circuit to each other? so fluid moves either direction?
However, thinking more about this, i realized that these cylinders have different areas on each end (due to the rod) - and thus different volume-per-inch-moved. meaning this wouldnt work in EITHER direction:
- compressing the cylinder would just overpressure the rod end, not enough space for fluid from bottom
- extending the cylinder would ~cavitate the bottom, too little volume sent to the bottom side
Now I'm confused because while i don't see how LD1 could be correct - it seems NEITHER way works on common cylinders... and yet that's the cushion valve's stated purpose
Last edited:
orangetree
Gold Member
Yes, the grapple would open(close) with the overpressure (assuming this concept even works, see my comment about area of top/bottom of cylinder). my assumption was this cushion valve would have a "high" breaking pressure, higher than the FEL OPfor instance
But you raise a good point that the accumulator could do the same, without that drawback. maybe the accumulator isnt as often used because two are required, and they arent cheap or small?
jigs_n_fixtures
Veteran Member
You’re tying to relieve just the clamping pressure, I can’t really envision a circumstance where the grapple will want to close tighter in response to the load wiggling.
So you need one small accumulator, one valve and a Tee on the on the hydraulic line which extends the cylinder to clamp the grapple
If you have a 2-inch cylinder, you would move 3.14-in^3/in of travel. Which would be 0.05-liter/in of travel. So, on SCUTs and CUTs, you don’t really need a large accumulator. A 0.15 or 0.25-liter unit would be sufficient. I can find those for right around $150, on eBay or Amazon.
So you need one small accumulator, one valve and a Tee on the on the hydraulic line which extends the cylinder to clamp the grapple
If you have a 2-inch cylinder, you would move 3.14-in^3/in of travel. Which would be 0.05-liter/in of travel. So, on SCUTs and CUTs, you don’t really need a large accumulator. A 0.15 or 0.25-liter unit would be sufficient. I can find those for right around $150, on eBay or Amazon.
npalen
Elite Member
My understand that the cushion valve in question is designed for use on circuits such as for angling a snow plow blade. The two angling cylinders are one way cylinders with a hose plumbed only to a base port on each with the two hoses going to the same valve spool. The displacement on the base side of both cylinders is the same so oil can flow between the two cylinders when the valve is opened by over pressure as when striking an object with one end of the blade..
