Kubota Pressure Relief Valve

[drivadesl]

I installed an aftermarket hydraulic thumb on my Kubota U35 Mini Excavator. I plumbed the cylinder thru the auxiliary hydraulic circuit that came with the machine, but the circuit does not come plumbed with a relief valve so I went to the Kubota dealer who will sell me a relief valve for $500 each! That seems way to pricey to me, so does anyone know a way around this with maybe an aftermarket valve that will work in place of the OEM?

Thanks for any suggestions.

 

[Tractor Seabee]

Surplus Center one of our tBN advertiser/sponsors has them for around $75.00. Are you sure you need one? That circuit may already be behind a relief that is not obvious. Talk to your dealer shop foreman? If they offer one get the Workshop Manual and trace out the circuits yourself. Thats what I did in planning some adds to my BX. OEM parts are usually pretty spendy even when they are an off the shelf item. You can bet the K one is not special made for them. That's how the dealer makes their parts dept a profit center.

Ron

 

[J_J]

Your hyd system probably already has a relief valve to protect the pump.

Anything you add in that circuit will be protected by the main relief.

They also make an external relief valve for a particular hyd component such as a cyl or motor.

Surplus Center

 

[J_J]

If you have one pump, then you will have a relief valve for everything.

If you have two pumps, each pump circuit will have a relief valve.

It would be stupid for a manufacturer not to do this.

If you have a manual, trace the aux line back and see where it gets it's flow.

You might also have one pump with two to three outlets. P1, P2, P3. Maybe steering, attachments, drive, etc

I have three pumps on my Power-Trac, and each pump circuit has a relief valve.

 

[drivadesl]

I spoke with the shop foreman. The relief valve for the thumb must be set to a pressure below the bucket curl so an independent valve is needed. Yes I knew this.

I could install one inline with the thumb extension, but would need a separate return hose. Last thing I want is another hose! I am going to price one with Messicks, might be a better price.

I find the pricing on Kubota spares to be more outrageous than any of my other equipment.

Thanks for your replies.

 

[J_J]

Would a cushion valve work for you on the thumb cyl? No tank hose.

1/2 NPT 30 GPM 1500-3000 PSI HYD CUSHION VALVE

http://www.surpluscenter.com/_MoreSpecs/dr9-4019-50-h.pdf

 

[J_J]

If you had a larger hyd cyl on the thumb, and the mechanical s were right, you probably would not over power the thumb cyl, and the BH relief would protect the bucket.

 

[skyhook]

If you had a larger hyd cyl on the thumb, and the mechanical s were right, you probably would not over power the thumb cyl, and the BH relief would protect the bucket.

As usual, you are very knowledgeable JJ, may i ask,...
When you say a larger cylinder, do you mean, one that handles "more" pressure than the set relief?

 

[tomcat7359]

Drivadesl, does the aux circuit that your thumb is plumbed into, have "line reliefs" or "port reliefs". Not sure what Kubota calls them but they are usually in the aux hyd valve section. If your aux hyd valve has them, you only need to adjust the piston end circuit, as that is what the bucket curl will be pushing against when the bucket contacts the thumb. Thumb cyls usually have much smaller diameter rods and bend fairly easy when the stronger bucket cyl pushes against it.

On Caterpillar aux hyds, the aux line reliefs are set at full PSI. about 4000, I set mine down to 3000. Thumb is still very powerful, but now protected from me getting carried away putting to much force against it with the bucket curl. Just my 2 cents from previous experience.

 

[J_J]

As usual, you are very knowledgeable JJ, may i ask,...
When you say a larger cylinder, do you mean, one that handles "more" pressure than the set relief?

Your bucket cyl may try and make a ram cyl pump out of the thumb cyl and the cyl should be able to with stand 3000 psi. A relief valve across the cyl will protect the cyl.

However, some cyl are rated to only 2500 psi.

Depending on the mechanical relationship, you may generate more, or less force. A cyl pushing at 90 degrees will develop the most force.

 

[varmint]

I installed one of those cushion valves like the one J J linked to on my snow blade, and it is easy to adjust the relief pressure, based on the info I got from one of the techs at Surplus Center- when on side of the 78" blade hits something immovable, I can see the blade give before there's any damage.

 

[Stonehaller]

I installed one of those cushion valves like the one J J linked to on my snow blade, and it is easy to adjust the relief pressure, based on the info I got from one of the techs at Surplus Center- when on side of the 78" blade hits something immovable, I can see the blade give before there's any damage.

I don't think the cushion valve is what you want for a thumb cylinder. Cushion or cross over relief valves will let oil from one side of the cylinder flow to the other side when it exceeds the relief setting. Ok for hydraulic motors or dual angle cylinders on a plow but not for a single rod cylinder on a thumb where the volumes on each side are not equal. The cushion valve would work while the valve for the thumb is activated which would protect the bucket cylinder from being over powered by the thumb, but typically you need protection the other way, to prevent the bucket from over powering the thumb and that is where the cushion valve would not help. He needs work port reliefs with cavitation makeup that will dump pressure to tank on the side exceeding the port relief setting and draw oil from tank on the low pressure side. That is probably what the Kubota valve is.

 

[J_J]

You could add a work port relief, but he said he did not want a third line which is the tank line.

 

[drivadesl]

Hey guys thanks for the good info! The Kubota mechanic conceded there are aftermarket parts that will work, but ended it there. I could operate the thumb if careful, but if not, could end up damaging something serious so I do want to set it up correctly Interestingly he commented $520 for a dinky valve like this seemed even high to him.

Based on what I'm reading from you experts, the cushion valve is not the way to go. I'm more inclined to want to use the OEM parts, or at least the OEM concept for the OP relief, but was looking for a less expensive option. Adding another hose onto the boom is not what I want. I was out of town since yesterday so didn;t get a chance to contact Messicks but will try when I get a chance.