Greetings, I just purchased a 3rd function kit from Summit and am the process of mapping out the hydraulic circuit. The other day I watched one of Neil from Messick's videos and he was addressing the issue of check valves to protect the system from pressure overload that can arise from forces that might be encountered using a grapple. I'm wondering if any members have installed one and where in the circuit would be the best place for it. Cheers, Erik
Inline Hydraulic Check Valve?
- Thread starter Erik Graham
- Start date
GreensvilleJay
Well-known member
Equipment
BX23-S,57 A-C D-14,58 A-C D-14, 57 A-C D-14,tiller,cults,Millcreek 25G spreader,
re: he was addressing the issue of check valves to protect the system from pressure overload that can arise from forces that might be encountered using a grapple
really ?? that's a new one for me, and frankly doesn't make ANY sense.
grapple setup is same as any other double acting cylinder(bucket curl, loader lift, etc.) so WHERE would this 'pressure overload' come from ?
the hydraulic pump,valves, cylinders are all 'common,off the shelf, used everywhere' bits and pieces
so again WHERE would this 'pressure overload' come from ?
a 'check valve' allows flow ONE WAY, so HOW could you even plumb in a 'check valve' into the 'system'?
sounds more like BSBB to me....
really ?? that's a new one for me, and frankly doesn't make ANY sense.
grapple setup is same as any other double acting cylinder(bucket curl, loader lift, etc.) so WHERE would this 'pressure overload' come from ?
the hydraulic pump,valves, cylinders are all 'common,off the shelf, used everywhere' bits and pieces
so again WHERE would this 'pressure overload' come from ?
a 'check valve' allows flow ONE WAY, so HOW could you even plumb in a 'check valve' into the 'system'?
sounds more like BSBB to me....
je1279
Well-known member
Lifetime Member
Equipment
LX2610 w/ 60" MMM, LP 72" Snow Plow, EA Wicked 55" Grapple, and Woods 60" BB
I belive in the video you mentioned (below) he was purposely trying to remove a stump with the top part of the grapple to demonstrate how that can significantly increase hydraulic pressure. If you use the grapple as intended you should be fine. If you do choose to add a check valve, I would add it on the grapple hose.
I think what the video demonstrates is that in ideal circumstances you wouldn't overload the system. However, higher throttle, ideal traction and the "I'll just try this for a moment" sort of thinking that I personally have been guilty of, it's entirely possible to have the hydraulic cylinder on your grapple to act like a pump-forcing fluid back at a higher pressure than it might be designed for. I think near the end of the video he shows that he was able to generate 6250 lbs of pressure. My thought is that a check valve works like the rocker on top of your pressure cooker. In a perfect world none of us would be doing bonehead things on our tractors, however................Cheers, Erik
Seriously, Been on a couple tractor forums for just shy of 20 years and never heard anyone having back pressure issues or problems. If a tractor had a problem that needed a check valve installed, these forums would be the first place that kind of problem would pop up and be talked about.... {what no icon for my "2 cents"???}
I think he meant relief valves. Interestingly, my backhoe has some (they're built into the controls), but my loader doesn't have any.
I personally wouldn't worry about it.
I personally wouldn't worry about it.
je1279
Well-known member
Lifetime Member
Equipment
LX2610 w/ 60" MMM, LP 72" Snow Plow, EA Wicked 55" Grapple, and Woods 60" BB
I don't disagree and as mentioned, if used properly you should never have this issue with a grapple. However, if someone wants to add one to their grapple if they don't always use it as advertised, it seems like cheap insurance.
I would like to try and provide some info to you regarding hydraulic system over pressures.
The 3 pt hitch is a good place to start as most owners do not know its circuit has both a relief and a safety valve.
The relief valve limits the pressure the pump can put into the lift cylinder and thus is limiting the weight the 3 pt can lift.
Once the 3 pt control is back in its neutral position with the weight held up by the 3 pt arms, the relief valve is no longer in the circuit limiting pressures in the 3 pt lift cylinder.
When the implement on the 3 pt arms is raised and stationary, if the owner adds more weight while the implement is raised, the hydraulic pressure in the 3 pt cylinder will continue to increase and the relief valve can do nothing to limit the increasing pressure.
If you are driving with a heavy implement in the raised position and going over bumps and dips, the inertia of the raised load greatly increases the pressures in the lift cylinders.
Modern tractors provide a Safety Valve for these situations. It remains in the cylinder hydraulic circuit at all times unlike the relief valve.
The safety valve will bleed off pressure avoiding over pressure of the lift cylinders and plumbing. The implement will drop a little each time the safety valve operates but damaging spikes are prevented. The adjustment/calibration of the safety valve cannot be done using the tractor pump because the pressure the safety valve opens at is far too high for the tractor pump. Often a fuel injector tester is used because it can generate pressures in the safety valve range.
The safety valve settings are between 3,300 and 3,600 psi.
The important point in all the above is that hydraulic pressures can be increased even with the tractor off or running with the control valve in its neutral position.
Adding a hydraulic thumb to a backhoe or excavator can also produce over pressure situations. The hydraulics curling the bucket or moving the thumb can be fighting each other and damage can occur because of pressure spikes.
Loader valves are less sophisticated than 3 pt hitch valves in that they only have a relief valve and not a safety valve. Curling a bucket forward and using it for bull dozing is shown in Owners' manuals as a practice to avoid. The leverage of the bucket and its linkages can magnify the pressures in the bucket cylinders to the point of damage.
There have been many owners of tractor who found forks to be a great addition to their loader. Unfortunately, too many of these owners find out the hard way that tipping the forks forward and using them to either push or pull generates excessive hydraulic pressures leading to hose rupture and bent cylinder push rods.
Grapples like forks can generate hydraulic pressures back into the system. A common way is lifting a heavy log Off Center so that one end of the log is having to be held up against the unbalanced gravity forces.
Dave
Last edited:
GreensvilleJay
Well-known member
Equipment
BX23-S,57 A-C D-14,58 A-C D-14, 57 A-C D-14,tiller,cults,Millcreek 25G spreader,
My post was trying to explain how the use of a grapple could result in spiking hydraulic pressures much greater than the relief valve setting.
I did say: " Modern tractors provide a Safety Valve for these situations. "
The L4310, built from 1998 to 2002, has a hydraulic relief valve in the front hydraulic block which limits how much weight the 3 pt hitch can lift.
The L225 has this unusual valve name as part of the 3 pt hitch control valve assembly: Back Pressure Valve
I do not know what this valve does!
There definitely is a relief valve on the L225 limiting how much weight the 3 pt can lift
Often the issue is not the function but what a particular feature was called decades ago. For example HPCO (high pressure carry over) is another way of saying Power Beyond.
Dave
Sorry but you are very wrong. I have attached a copy of your attached drawing with highlights of the different circuits. Backpressure valve #3 is connected to the return circuit highlighted in blue. The cylinder circuit is highlighted in red and is not connected to any other item in the valve. It would be clearer if we had a true hyd. schematic but we have what we have.
As far as the video from Messick's the items that Neil is referring to as check valves are most likely circuit reliefs placed there by the attachment manufacturer because more often than not their components are not rated for the maximum pressures that many machines are capable of.
They could be possibly be cross pilot operated check valves but I doubt they are. I would need more detailed info to verify 100% which they were.
As far as the video from Messick's the items that Neil is referring to as check valves are most likely circuit reliefs placed there by the attachment manufacturer because more often than not their components are not rated for the maximum pressures that many machines are capable of.
They could be possibly be cross pilot operated check valves but I doubt they are. I would need more detailed info to verify 100% which they were.
You do realize the original picture from the WSM states that 1 is the "back pressure valve" and 3 is the relief valve before you cropped it out...
Moreover why should pressure be directed to the relief valve in the normal position? Pretty sure this is an open center configuration
When the spool is moved to the left, the return pressure port "R" is blocked, ram cylinder port "C" is unblocked and allows fluid to flow in from the pressure port "P" to make the hitch raise. In this state the fluid will escape over the relieve valve "3" in case of excess pressure.
Conversely when the spool is moved to the right the pressure in "P" is blocked and "C" and "R" are connected allowing fluid in the cylinder to escape and lowering the hitch.
The WSM goes on to talk about how to adjust the relief valve and the description matches 3 in this diagram.
At least that's my understanding after studying up on this crap trying to figure out why my hitch won't go down. I'm still not exactly clear on how the fluid actually escapes/through which hole..
If I'm wrong in my thinking please call it out, I'm just trying to learn. Don't have much experience with hydraulics.
(If you tell me to open the drop rate valve to make my hitch go down I may lose my shit
)One thing you have to realize that in a hydraulic system we are not directing pressure. It is flow that we are concerned with. Pressure is merely a measurement of resistance to flow or load on the circuit. Yes item 1 is the pressure relief valve and it is in the path to the center of the spool valve. The relief valve has no function until we hit max working pressure as its purpose is to limit max. pressure or the load on the circuit. The backpressure valve is in the return circuit and there to help maintain an acceptable amount of resistance to the reservoir in the return circuit.You do realize the original picture from the WSM states that 1 is the "back pressure valve" and 3 is the relief valve before you cropped it out...
Moreover why should pressure be directed to the relief valve in the normal position? Pretty sure this is an open center configuration
When the spool is moved to the left, the return pressure port "R" is blocked, ram cylinder port "C" is unblocked and allows fluid to flow in from the pressure port "P" to make the hitch raise. In this state the fluid will escape over the relieve valve "3" in case of excess pressure.
Conversely when the spool is moved to the right the pressure in "P" is blocked and "C" and "R" are connected allowing fluid in the cylinder to escape and lowering the hitch.
The WSM goes on to talk about how to adjust the relief valve and the description matches 3 in this diagram.
At least that's my understanding after studying up on this crap trying to figure out why my hitch won't go down. I'm still not exactly clear on how the fluid actually escapes/through which hole..
If I'm wrong in my thinking please call it out, I'm just trying to learn. Don't have much experience with hydraulics.
(If you tell me to open the drop rate valve to make my hitch go down I may lose my shit
The passage to the cylinder "C" does not contain a circuit relief which would protect the circuit in the event of an overload.
Basically your assessment of how the valve works is correct and how all open center systems work. In neutral oil flows through the center of the valve and in operation the center passage must be blocked to direct oil to the function you are using.
I installed a Kubota shockless ride hydraulic accumulator system on lift circuit of the FEL of my my M59. I added a 10,000psi gauge to be able to see the difference between the system valved in or out.
Max pressure of pump was 2750psi deadheaded. I could readily see how the accumulators really cushioned the pressure spikes when traveling with a load. Using the grapple, lift, curl, and wheel traction could reach over 5000psi. Grubbing brush. Pressure reliefs are for the pump not cylinders with external force. I’m sure pressure spikes would also be experienced on the curl and 3rd function circuits too.
If you really want to know, put a gauge on it.
Tried using the gauge as weighing scale. With known weights suspended by sling repeatable. Grappled loads too many variables to be accurate. Still interesting to see and monitor the lift pressure.
Max pressure of pump was 2750psi deadheaded. I could readily see how the accumulators really cushioned the pressure spikes when traveling with a load. Using the grapple, lift, curl, and wheel traction could reach over 5000psi. Grubbing brush. Pressure reliefs are for the pump not cylinders with external force. I’m sure pressure spikes would also be experienced on the curl and 3rd function circuits too.
If you really want to know, put a gauge on it.
Tried using the gauge as weighing scale. With known weights suspended by sling repeatable. Grappled loads too many variables to be accurate. Still interesting to see and monitor the lift pressure.