Educate me on adjusting hydraulic system pressure

[Teikas Dad]

I've read several threads about how Kubota routinely sets hydraulic pressure lower than what's claimed in the literature. I've always felt that my loader wasn't lifting what it was really capable of. Last fall I loaded my 5' brushhog onto a flatbed trailer. The cutter weighs about 500lbs. I couldn't lift it any more than about 30" from the ground so it was a struggle to get it over the sides of my landscape trailer. I've got a B3200 with a LA504 loader. From what I've read I need a pressure gauge which can be inserted in one of the front loader hose ports to check the pressure on the system. Once the pressure is determined there are shims or washers that can be inserted to raise the pressure on the system.

My questions are these -

When installing the pressure gauge (with the hydraulic system quick connect) I'm assuming the tractor must be shut down and all the pressure relieved on the system - correct?

Once the gauge is in the loader hydraulic block, I fire up the tractor to operating RPMs and read the gauge as I cycle the loader control handle. If the pressure is lower than what the literature claims it is how do I determine which shim/washer is needed to raise the pressure? Are multiple shims/washers added or are there different size shims/washers?

The shop manual doesn't have a really clear photo of where the shims/washers are added so any info on that would be helpful.

Thanks

 

[newbury]

First are you sure yours uses shims?

My B7610 use shims, my M4700 a screw.

 

[Teikas Dad]

First are you sure yours uses shims?

My B7610 use shims, my M4700 a screw.

I honestly don't know, I've only seen references to shims.

 

[CalG]

You need to understand the test mode.

Fitting a gauge should be done with all pressure relieved. You have that correctly

But the pressure testing is done with the hydraulic circuit to which the gauge is fitted is fully loaded. If the cylinder is being cycled with less than "over capacity loading", the gauge will show only that pressure required to move the cylinder.

You might try moving the cylinder to it's end limit and mechanically block the movement, and so overload the fluid system.

It's important to know what you are testing. If the circuit is open to tank, there can be little pressure. Draw yourself a diagram and make sense of it!

In general, removing shims or loosening screws against spring tension will lessen the hydraulic over pressure relief.
Also note that the tractor is likely fitted with an over pressure relief, but also any auxiliary valve, such as the loader control valve will contain it's own pressure relieve valve. The system can never see more pressure than the lowest of any relieve vale setting.

 

[Teikas Dad]

You need to understand the test mode.

Fitting a gauge should be done with all pressure relieved. You have that correctly

But the pressure testing is done with the hydraulic circuit to which the gauge is fitted is fully loaded. If the cylinder is being cycled with less than "over capacity loading", the gauge will show only that pressure required to move the cylinder.

You might try moving the cylinder to it's end limit and mechanically block the movement, and so overload the fluid system.

It's important to know what you are testing. If the circuit is open to tank, there can be little pressure. Draw yourself a diagram and make sense of it!

In general, removing shims or loosening screws against spring tension will lessen the hydraulic over pressure relief.
Also note that the tractor is likely fitted with an over pressure relief, but also any auxiliary valve, such as the loader control valve will contain it's own pressure relieve valve. The system can never see more pressure than the lowest of any relieve vale setting.

I understand about what you're talking about in having the system under full load pressure. You did educate me though as I didn't know the system had to be under load. I just figured cycling the loader control would do it but I see what you mean about it being an open circuit. I've got some huge boulders on my property that I can put the bucket under and try lifting to provide maximum pressure.

 

[ultrarunner]

I believe Kubota gives a range... most that I know seem to be on the low side of the range when tested.

Maybe the spring takes a set or relaxes with use?

On my BX adding one shim brought it spot on to the max and the difference was noticeable.

I know one owner that got carried away and bumped it up about 25% over and ended up bending things on the loader... his momentary satisfaction was short lived when the backhoe cylinder rod bowed out like a pretzel...

More pressure is the easy part but more pressure adds more stress to components.

I had a stainless steel washer that was from some medical equipment that happened to work for me.

 

[Teikas Dad]

OK so if I understand it correctly what the shim does is compress the overpressure relief valve spring a little bit for higher pressure?

 

[kennyd]

Most of the Kubota's sCUT and CUT's do indeed need the shims to adjust the pressure, others models just use a threaded stud and jamb nut configuration. BXPanded sells a kit that is targeted to smaller Kubota's and includes them.

Here is our video on testing, the procedure is the same no matter the color.

 

[diesel85]

There is something wrong with your B3200.

My BX2200 easily lifts my ~650lb flail mower...

 

[Tractor Seabee]

There is a similar post in todays list. As I stated there; get the WSM before you start. If you can afford the tractor and its maintenance you can afford the WSM. My BX was 600# low when new. I bumped it to 2000 PSI. What a difference. 1500 hours and I have not bent any thing yet. The WSM has all the details and the shim part #. 1mm =39PSI.

Ron

 

[JWR]

I am puzzled by this entire discussion. So far as I knew, the hydraulic pressure in a system was determined by the relief valve. Other things affect the pressure (especially DURING FLOW) at at some destination -- things like hose and fitting diameters, expansion strength or resistance in the hoses, length of hoses, etc. but I thought the relief valves set the ultimate pressure in a system. No ??

 

[Teikas Dad]

Most of the Kubota's sCUT and CUT's do indeed need the shims to adjust the pressure, others models just use a threaded stud and jamb nut configuration. BXPanded sells a kit that is targeted to smaller Kubota's and includes them.

Here is our video on testing, the procedure is the same no matter the color.

Thanks for posting that, it clearly shows how to check the pressure.

 

[Teikas Dad]

The WSM doesn't have a ton of information. Anyone know how many PSI each different shim thickness adds?

 

[kennyd]

I am puzzled by this entire discussion. So far as I knew, the hydraulic pressure in a system was determined by the relief valve. Other things affect the pressure (especially DURING FLOW) at at some destination -- things like hose and fitting diameters, expansion strength or resistance in the hoses, length of hoses, etc. but I thought the relief valves set the ultimate pressure in a system. No ??

I am puzzled by your post. The very thing that is being discussed is setting the max pressure by setting the pressure relief valve (PRV) and how to test it with a gauge. No??

 

[Tractor Seabee]

The WSM doesn't have a ton of information. Anyone know how many PSI each different shim thickness adds?
View attachment 545023

Your attachment does not open. The WSM does state the PSI/mm thickness. Page 5-S4. I stated the value in an earlier post on this thread.

Ron

 

[Blondie70]

I thought the PSV was the final step in protection of the system from overpressure. Is the working pressure not controlled by another device that regulates pressure (below the PSV setting)??? Wouldn't the working pressure be increased by shimming this device and not the PSV?
Confused and confounded in the Sunny South ...........(also puzzled)

 

[Tractor Seabee]

I am puzzled by this entire discussion. So far as I knew, the hydraulic pressure in a system was determined by the relief valve. Other things affect the pressure (especially DURING FLOW) at at some destination -- things like hose and fitting diameters, expansion strength or resistance in the hoses, length of hoses, etc. but I thought the relief valves set the ultimate pressure in a system. No ??

The procedure being discussed in this thread is adjusting the relief valve, to set the base operating pressure desired as established by the system relief valve. two methods. depending on OEM are shims under the spring or a screw adjusting pressure on the spring as previously stated. Location varies per OEM. Resistance to flow must be measured at the end of a specific circuit while operating. No flow the PSI does not change at that point. It should be minor difference unless something is awry. That's why WSMs are so valuable for those doing their own mechanic work.

Ron

 

[Teikas Dad]

Your attachment does not open. The WSM does state the PSI/mm thickness. Page 5-S4. I stated the value in an earlier post on this thread.

Ron

Thanks

 

[Ortimber]

Subscribed. I'm interested in learning more about this. Great discussion!

 

[Teikas Dad]

Your attachment does not open. The WSM does state the PSI/mm thickness. Page 5-S4. I stated the value in an earlier post on this thread.

Ron

My WSM for the B3200 has brake repair specifications on page 5-S4. Hydraulics are in section 8. I'll take a closer look and see if I can find the info.