Adjustment on spool valve

[Forest View]

The photos are of the hydraulic controls on a BH77 backhoe.

Please notice that some of the valves have an adjustment on the topside of the valve. It has a slotted screw in the top and is adjustable after loosening the nut.

I'm interested to know what this adjustment does and any advice on how to set it?

Many thanks.

 

[TheOldHokie]

The photos are of the hydraulic controls on a BH77 backhoe.

Please notice that some of the valves have an adjustment on the topside of the valve. It has a slotted screw in the top and is adjustable after loosening the nut.

I'm interested to know what this adjustment does and any advice on how to set it?

Many thanks.

WAG - port relief pressure setting.

Dan

 

[Forest View]

WAG - port relief pressure setting.

Dan

Ok - will search information on 'port relief pressure setting' - Hoping someone can advise the proper setting & method of setting? Wondering if this was the issue all along - would this cause the dipper stick to kick-out and lose power?

 

[TheOldHokie]

Ok - will search information on 'port relief pressure setting' - Hoping someone can advise the proper setting & method of setting? Wondering if this was the issue all along - would this cause the dipper stick to kick-out and lose power?

All a port relief is is an adjustable pressure setting that only effects the one cylinder. Can't say if it is related to your problem.

Dan

 

[whitetiger]

Here are a couple of pages from the BH77 WSM.

 

[lugbolt]

whitetiger beat me to it

in a nutshell it's like a fuse in a hydraulic system.

On backhoes particularly, it's entirely possible to "use" the functions such that the hoe itself can generate far more pressure in the lines/hoses/valve section than the hoses/lines/valve can take without failure. Thus, they installed "safety valves" in them, to keep the spike from busting parts. It's also possible to generate some negative pressure, and the passage in the safety valve is opened in this condition to "tank" (return) side of the valve, so that it doesn't pull air. "Anti-cavitation" as Kubota calls it.

I don't recall how to adjust them, I want to say there's a special set of tools to do it. I say this because we were always directed to replace them if they were suspected to be problematic, and not to try to repair them or even take them apart. Only time I ever was really "allowed" to take them apart was for pictures that Kubota wanted for warranty purposes, to prove that the valve itself was defective.

 

[TheOldHokie]

whitetiger beat me to it

in a nutshell it's like a fuse in a hydraulic system.

On backhoes particularly, it's entirely possible to "use" the functions such that the hoe itself can generate far more pressure in the lines/hoses/valve section than the hoses/lines/valve can take without failure. Thus, they installed "safety valves" in them, to keep the spike from busting parts. It's also possible to generate some negative pressure, and the passage in the safety valve is opened in this condition to "tank" (return) side of the valve, so that it doesn't pull air. "Anti-cavitation" as Kubota calls it.

I don't recall how to adjust them, I want to say there's a special set of tools to do it. I say this because we were always directed to replace them if they were suspected to be problematic, and not to try to repair them or even take them apart. Only time I ever was really "allowed" to take them apart was for pictures that Kubota wanted for warranty purposes, to prove that the valve itself was defective.

The most common form of multi-spool directional control valves have the spools arranged in parallel. When multiple spools ate shifted together the oil supply flows to the actuator with the lowest load and the more heavily loaded actuator stalls and hydraulic pressure is equal in all actuators.

An alternative arrangement puts the actuators in series. In this arrangement exhaust oil from the first actuator feeds the second which then feeds the third, etc. This allows all loads to be moved simultaneously which is handy on something like a backhoe but the downside is the cylinder pressures become additive. In a three cylinder circuit the first cylinder sees the sum of all three loads. Because cylinders are pressure multipliers this can cause a situation where the upstream cylinder pressure actually exceeds the valves inlet pressure relief setting. To prevent this load multiplication from causing an individual cylinder pressure to exceed the working pressure limit of the cylinder additional pressure reliefs are installed on each series work section - e.g. port reliefs.

I would not expect anything special is needed to adjust the port relief pressures. You install a pressure gauge in the work circuit and generate a load on that circuit sufficient to raise pressure above the working limit and adjust the spring pressure with the screw to prevent the overload.

The anti-cavitation poppet operates at any negative pressure differential so i would think the adjustment mechanism has no effect on its operation.

 

[ayak]

Not sure if this is relevant to your particular problem or not, but a very good video regarding a BH77 problem (and its resolution), nonetheless:

 

[TheOldHokie]

Not sure if this is relevant to your particular problem or not, but a very good video regarding a BH77 problem (and its resolution), nonetheless:

I can't believe a professional hydraulic shop could not diagnose and fix that problem. The leak down was obvious and the port relief should have been near the top of their suspects list. Put them on the Do Not Call list.

Dan

 

[ayak]

I can't believe a professional hydraulic shop could not diagnose and fix that problem. The leak down was obvious and the port relief should have been near the top of their suspects list. Put them on the Do Not Call list.

Dan

I believe it was Dolly Parton (among others) who said “God helps those who help themselves…”

 

[whitetiger]

I can't believe a professional hydraulic shop could not diagnose and fix that problem. The leak down was obvious and the port relief should have been near the top of their suspects list. Put them on the Do Not Call list.

Dan

A very simple and quick test is to swap the circuit relief valve with one in another function. If the malfunction follows the relief valve, the relief valve is the culprit.
It only takes a few minutes, no parts, and is a definitive test.

 

[Forest View]

Here are a couple of pages from the BH77 WSM.

Big help - thank you whitetiger!

 

[ruger1980]

The most common form of multi-spool directional control valves have the spools arranged in parallel. When multiple spools ate shifted together the oil supply flows to the actuator with the lowest load and the more heavily loaded actuator stalls and hydraulic pressure is equal in all actuators.

An alternative arrangement puts the actuators in series. In this arrangement exhaust oil from the first actuator feeds the second which then feeds the third, etc. This allows all loads to be moved simultaneously which is handy on something like a backhoe but the downside is the cylinder pressures become additive. In a three cylinder circuit the first cylinder sees the sum of all three loads. Because cylinders are pressure multipliers this can cause a situation where the upstream cylinder pressure actually exceeds the valves inlet pressure relief setting. To prevent this load multiplication from causing an individual cylinder pressure to exceed the working pressure limit of the cylinder additional pressure reliefs are installed on each series work section - e.g. port reliefs.

I would not expect anything special is needed to adjust the port relief pressures. You install a pressure gauge in the work circuit and generate a load on that circuit sufficient to raise pressure above the working limit and adjust the spring pressure with the screw to prevent the overload.

The anti-cavitation poppet operates at any negative pressure differential so i would think the adjustment mechanism has no effect on its operation.

What you are describing is the way the bower beyond function works in the loader valve. The control valve on the BH77 is more like a series/parallel set up. In neutral position with no spools actuated oil flows through the center passage of each spool and out the tank port but oil is also available in the parallel passage. When a spool is actuated it blocks the center passage and directs oil through the parallel passage to that function. Oil is still available to all the other spools so that if more than one function is actuated it will receive oil as well.
None of the cylinders return flow supply another function, they all return through the tank port. If one were to use the 3 point function or remote valves (if equipped and situated after the backhoe valve) while using the backhoe then it could function as a power beyond circuit.

The port relief is designed to protect the circuit from outward forces. Say someone pushes the tractor using the bucket as a push point. If the load becomes great enough it will exceed the rating of the port relief and it will open allowing the stick to move. At this time the opposite side of the cylinder experiences a negative pressure and the ant-cavitation valve opens allowing oil from the tank port to be pushed into the negative pressure are filling the cylinder.

 

[Henro]

What you are describing is the way the bower beyond function works in the loader valve. The control valve on the BH77 is more like a series/parallel set up. In neutral position with no spools actuated oil flows through the center passage of each spool and out the tank port but oil is also available in the parallel passage. When a spool is actuated it blocks the center passage and directs oil through the parallel passage to that function. Oil is still available to all the other spools so that if more than one function is actuated it will receive oil as well.
None of the cylinders return flow supply another function, they all return through the tank port. If one were to use the 3 point function or remote valves (if equipped and situated after the backhoe valve) while using the backhoe then it could function as a power beyond circuit.

The port relief is designed to protect the circuit from outward forces. Say someone pushes the tractor using the bucket as a push point. If the load becomes great enough it will exceed the rating of the port relief and it will open allowing the stick to move. At this time the opposite side of the cylinder experiences a negative pressure and the ant-cavitation valve opens allowing oil from the tank port to be pushed into the negative pressure are filling the cylinder.

Your reply is interesting to me as TheOldHokie's post had me thinking and a bit confused.

I was trying to visualize how cylinders could be hooked in series, and how they would work in that configuration. Not sure I see it yet...LOL...but cylinders are sometimes hooked in series, like with a snow plow on a truck, but in that case they are reversed, so that displacement of the cylinders internally are equal...

 

[TheOldHokie]

What you are describing is the way the bower beyond function works in the loader valve. The control valve on the BH77 is more like a series/parallel set up. In neutral position with no spools actuated oil flows through the center passage of each spool and out the tank port but oil is also available in the parallel passage. When a spool is actuated it blocks the center passage and directs oil through the parallel passage to that function. Oil is still available to all the other spools so that if more than one function is actuated it will receive oil as well.
None of the cylinders return flow supply another function, they all return through the tank port. If one were to use the 3 point function or remote valves (if equipped and situated after the backhoe valve) while using the backhoe then it could function as a power beyond circuit.

The port relief is designed to protect the circuit from outward forces. Say someone pushes the tractor using the bucket as a push point. If the load becomes great enough it will exceed the rating of the port relief and it will open allowing the stick to move. At this time the opposite side of the cylinder experiences a negative pressure and the ant-cavitation valve opens allowing oil from the tank port to be pushed into the negative pressure are filling the cylinder.

No, you are describing the typical parallel setup. As soon as any spool is shifted the center is blocked and flow is diverted to the parallel core were where it is available to all spools and all loads are in parallel. Hence the name. Power beyond will also be blocked and all exhaust oil and or overpressure relief flow goes direct to tank.

In a series spool the exhaust oil is routed back to the center core where it is available to all down stream spools with the caveat that their loads are now in series rather than parallel. Hence the name.

On the L01s you will find that the 3 pt will operate with the lift spool shifted but not with the bucket spool shifted so that valve is some sort of hybrid.

I do agree that the port reliefs on the hoe are more likely designed to function as cushion valves to guard against spikes from impacts and sudden changes of direction.

Dan

 

[Henro]

No, you are describing the typical parallel setup. As soon as any spool is shifted the center is blocked and flow is diverted to the parallel core were where it is available to all spools and all loads are in parallel. Hence the name. Power beyond will also be blocked and all exhaust oil and or overpressure relief flow goes direct to tank.

In a series spool the exhaust oil is routed back to the center core where it is available to all down stream spools with the caveat that their loads are now in series rather than parallel. Hence the name.

On the L01s you will find that the 3 pt will operate with the lift spool shifted but not with the bucket spool shifted so that valve is some sort of hybrid.

I do agree that the port reliefs on the hoe are more likely designed to function as cushion valves to guard against spikes from impacts and sudden changes of direction.

Dan

Just a dumb question probably, but isn’t that only true if the spool is shifted fully? What about a partial shift?

Seems like if a spool is not shifted fully, some flow would go to whatever route it was following before the spool was shifted.

Are we sure the BH77 has a series setup like you describe? If so, what is the advantage over a parallel setup?

 

[TheOldHokie]

Just a dumb question probably, but isn’t that only true if the spool is shifted fully? What about a partial shift?
P pl
Seems like if a spool is not shifted fully, some flow would go to whatever route it was following before the spool was shifted.

Are we sure the BH77 has a series setup like you describe? If so, what is the advantage over a parallel setup?

There are no dumb questions.

There are also no hard and fast rules when it comes to directional control valves. I am not an expert but I have purchased and installed dozens so this is my understanding based on extensive reading/research and hands on use.

For a typical commodity parallel control valve the shift from the center core to the parallel (what Prince calls power) core cannot be feathered and occurs before the shift to the work circuit. The power core shift is immediate and blocks the center core and all partial shifts occur between the power core and work circuits. That description is consistent with the dozens of valves I have purchased and installed. Manufacturers can and will provide OEMs with custom grinds on the lands of the spools to facilitate other behavior. Like I said - there are no hard and fast rules.

Without a hydraulic schematic I can only speculate about the backhoe valve. It would be nice if the WSM contained one but they usually dont. I have however seen schematics of other hoes and those valves did contain a mix of parallel and series spools so it is quite possible the Kubota valve is as well. Its also possible it isn't. The advantage of a series circuit is all loads move positively regardless of their relative magnitude. In a parallel setup the larger loads can stall until the smaller load completes.

None of this has anything to do with the OPs problem which was as simple as a defective port relief that was bleeding of flow to the actuator.

Dan

 

[ruger1980]

No, you are describing the typical parallel setup. As soon as any spool is shifted the center is blocked and flow is diverted to the parallel core were where it is available to all spools and all loads are in parallel. Hence the name. Power beyond will also be blocked and all exhaust oil and or overpressure relief flow goes direct to tank.

In a series spool the exhaust oil is routed back to the center core where it is available to all down stream spools with the caveat that their loads are now in series rather than parallel. Hence the name.

On the L01s you will find that the 3 pt will operate with the lift spool shifted but not with the bucket spool shifted so that valve is some sort of hybrid.

I do agree that the port reliefs on the hoe are more likely designed to function as cushion valves to guard against spikes from impacts and sudden changes of direction.

Dan

Please take a look at the hyd. diagram for the BH77 control valve and report back. Hint it is a parallel circuit.
I have drawn up how oil would flow using stick and bucket in at the same time.

 

[TheOldHokie]

Please take a look at the hyd. diagram for the BH77 control valve and report back. Hint it is a parallel circuit.
I have drawn up how oil would flow using stick and bucket in at the same time. View attachment 63009

Thank you for the schematic. All spools are parallel with port reliefs on boom, dipperstick and swing cylinders. There is no inlet relief or separate high pressure carry over (PB) circuit. Downstream valves if any are fed by tank core which you have highlighted in green. Agreed?

Dan

 

[ruger1980]

Yes