Hydraulic Pump GPM Question

[Tx Jim]

Valves are rated for flow through the valve. Valve ratings will determine port sizes among other characteristics. Choosing an open center valve with a lower capacity than the pump opens the door for overheating whether the valve work ports are being used or not.
TXjim has vast experience with closed center systems where valves can be sized more in accordance to the function's requirements than the pump capacity.

You can argue, debate, ignore. But the above information is factual.

Rick
Thanks for reply. Yes the majority of my hyd experience is diagnosing closed-center hyd problems therefore my reason for asking.
Jim

 

[Tx Jim]

I agree with RickB about the flow rating in the valve core, but another thing to consider is the rating on the valve core is for the MAX gpm it will see. Although some remotes will only see momentary actuation, the excess return stroke displacement from a cylinder will be added to the pump flow returning back to tank, meaning total return flow should be considered to reduce the possibility of unwanted heat from pressure drop in the valve core.

I'm not arguing but rather asking so as to hopefully not to make incorrect future replies!!!

So if I'm understanding this correctly if the in/out/pby ports are identical size(1/2'') on a 8 & 12 GPM OC valve the inside of valve is smaller on the 8 GPM vs the 12 GPM therefore restricting flow back to tank & possibly causing heat??
Thank you. Jim

 

[wdchyd]

Jim, my understanding of flow ratings would be more along the size of the oil galleys and spool diameter internally along with port sizes. The heat would accumulate from back pressure measured before the control valve if undersized through pressure drop. Any pressure building beyond the OC valve would blow out the spool seals prematurely if no PB is used.
My understanding of heat generated is from hydraulic pressure going from high to low without doing any work.

 

[wdchyd]

Rick
Thanks for reply. Yes the majority of my hyd experience is diagnosing closed-center hyd problems therefore my reason for asking.
Jim

I would love to have your valued experience in working on these J/D closed systems. My guys have had a few J/D OEM piston pumps apart over the years doing reseals but we now have a new (to us) 100hp test stand in our shop. It has a supercharge feature for putting a positive charge on pump inlets where needed. Testing these pumps has been on my bucket list for years.

 

[Tx Jim]

Thanks for your reply. When I stated utilizing lower GPM(8 vs maybe 20 gpm) for controlling 3 pt functions(centerlink & side links) I was thinking very seldom required infinite cylinder movement requiring more precise control not flow through valve body when spool is in neutral. But it sounds as if that idea would cause unnecessary heating of oil. Thanks again.

I have many hrs experience diagnosing closed center hyd problems & I can still get STUMPED. I attended JD service/sales meetings where the speaker bragged about the advantages of saved fuel/hp & advantages of CC hyd's. Yes the 8 piston hyd pump is very complicated as are some of the JD control valves for steering,scv & 3 pt are very complicated & difficult to adjust individual internal valve clearances. Now today as you're probably aware most new/newer JD tractors have OPEN center hyd's.

There's a self employed JD technician in Ohio that's a member of another tractor discussion forum I'm a member that has constructed a hyd testing bench complete with a JD piston pump so he can test repaired CC hyd valves before he reinstalls the assembles.

 

[wdchyd]

Most of the J/D piston pumps we see are from early models skidders and const TLB´ in the 80s 90s vintage.

john deere 3b pump - Google Search

 

[Tx Jim]

Below is a photo of a portion of the hyd test bench I previously mentioned plus some of the hyd components he has received for repair.

 

[wdchyd]

Below is a photo of a portion of the hyd test bench I previously mentioned plus some of the hyd components he has received for repair.

:thumbsup: