HIGH PRESSURE KUBOTA BX23S

   #1  

Dockside

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BX23S, IH 1450
My BX23S is a 2019 with 135 hours. I had ordered it with what Kubota calls a 3rd function valve and the mechanical thumb options. I converted the thumb to hydraulic & use that valve to power the thumb cylinder. I began reading forum posts regarding PSI & ordered the BXpanded gauge kit. Tested today & I’m getting a 2700 PSI reading at high idle connected to the output from the 3rd function valve—it was a lot simpler to connect there rather than the recommended output to the loader.

I would understand that overall hydro pressure should be constant through-out the system & should never get a “boost” regardless of where it was connected--or am I understanding wrong?

Machine has been running flawless—no leaks or operating issues.
Thanks for any input here.

PS: Other than my mod to the thumb all hydraulics are Kubota original issue.
 
   #2  

Dave M7040

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By converting a mechanical thumb to a hydraulic one you may have created a situation wherein, one hydraulic cylinder can be pushing against a smaller hydraulic cylinder and in doing so amplifying the pressure in a circuit.

This is similar to the situation where owners destroy bucket cylinders by back dragging especially with forks installed.

The pressure relief valve cannot control or protect a circuit once the circuit's control lever is in the neutral position.

Imaging picking up a bucket of gravel with a FEL. You can barely get the bucket off the ground as the relief valve is limiting the pressure in the cylinders. Now you take a shovel and, with the bucket slightly elevated above the ground, you add more material to the bucket. The pressure in the cylinders and hoses has to increase to support the added weight. The relief valve can do nothing. To the extreme, the cylinders or hoses will fail from excess pressure.

Find somewhere else on your machine to measure the pressure before starting to make adjustments.

Dave M7040
 
  
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#3  
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Dockside

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Dave,

Thanks for your reply & your detail which makes for a clearer understanding of the operating sequence. My local hydro shop owner (I did the installation & modification to the thumb cylinder--they made up the hoses) commented on that when I explained what I was doing--he was concerned about the increased pressure of the opposing forces. But said it would not be a problem when I stated factory specs were 1840 psi maximum (this was prior to me testing). Factory hoses & cylinders are rated 3000 psi, new thumb hoses are rated 4000 psi & thumb cylinder is rated 3000 psi.

What’s confusing to me (I’m a novice here) is that when I took the reading I split the hose coupling leading to the thumb which connected the gauge directly to the bypass valve. So the thumb & opposing bucket along with the rest of the tractor implements were idle, no other implements are in that circuit to the bypass valve--it controls only the thumb cylinder. I imagine that if the bucket were in operation & opposing the thumb then there would be an increase in overall system pressure but not when idle. Am I reading that correct?

Did not think photos were necessary but will send along if you think it would help.

Thanks again,
John
 
   #4  

Dave M7040

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This response is a quick one without much research.

I am seeing spec'd hydraulic pressures for a BX23S around 3,000 psi

forum BX23S hydraulics 1.jpg


forum BX23S hydraulics 2.jpg


Are these pressures the ones you felt may be too high?

Dave
 
  
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Dockside

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Well, how ‘bout that…… Could not find it in my owner’s manual. But doing some Google search found it in the Kubota Workshop Manual WSM (free download www.kubotabooks.com). I responded to your first reply here since TractorByNet sends an email notice for replies. I now see your reply in the other forum, which is where I was getting the 1840 psi rating & where I originally posted.

So now appears all is well and I’m actually low by about 300 psi—I think I’ll not mess with it. That thumb has been amazing to work with compared to the factory manual unit--here are some pics.

The WSM has all the good stuff in it!

Thanks again,

John
 

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   #6  

check

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2009 Kubota BX25
This response is a quick one without much research.

I am seeing spec'd hydraulic pressures for a BX23S around 3,000 psi

View attachment 693450

View attachment 693451

Are these pressures the ones you felt may be too high?

Dave

Wow, that is so weird. The hydraulic pressure spec for my 2009 BX25 is only 1750! Surely they did not almost double it for the BX23s.
 
  
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Dockside

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I know, strange, hardware is most likely identical or almost so. What are the ratings for your hoses & cylinders? Where are you getting the ratings for your BX25?

I downloaded the WSM & it is there on the noted page

Thanks
 
   #8  

Dave M7040

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Wow, that is so weird. The hydraulic pressure spec for my 2009 BX25 is only 1750! Surely they did not almost double it for the BX23s.
The high WSM pressures are the HST pressures.

What concerns me is that it is most unusual for Kubota to set up a new machine far above the stated relief setting.

I am left to wonder if, in installing the loader and third function, a plumbing mistake was made.

Dave M7040
 
  
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Dockside

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The Kubota BX2412 3rd function kit consists of factory made-up hydraulic hosing, pre-formed steel tubing & wire harness. It would take an installer some serious cutting, bending & patching to install these in other than the intended manner.

I need to split the loader from the tractor in order to release the quick coupler & get to that blue tagged fitting. Been involved in a good size yard project here & it’s been non-stop since Saturday morning. I hope to be done later today & soon as I get the machine cleaned up will split the loader, connect the gauge to that fitting & post the results.

Sorry if I caused any confusion here but as I posted earlier, I am a novice when it comes to hydraulics & I guess this is how we get educated.

John
 
  
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Dockside

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Late finish, 18” down & about 18” shy of where I needed to be for the last tree ball this poor boy arrived at the rock from hell. Anyway, I wanted to get this settled, so split loader & took a reading from the recommended fitting and, of course, gauge showed 1800 psi (hash marks are in 50’s & skinny spaced so +/- the usual).

Still don’t understand the 2700 psi reading from the 3rd function valve, but as I stated earlier, unit has been going strong for 135 hours. Based on Dave’s remarks glad I upped the hose psi to 4000. I do notice that when the BH bucket & the thumb are run independently they move faster than when they are run simultaneously—possibly could the pressure be split or shared at that point which is why I haven’t had any issues?

Thanks again all for your comments & sharing your knowledge.
 
 
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