Replacing PTO Hydraulic Pump for Backhoe

[caissem]

Hi All,

First time poster here.

I'm running a Kubota L2850 with a little BL4520 backhoe which has a cracked PTO pump which I need to replace. The existing pump is rated at 4.9 GPM and has 3/4" input, 1/2" output lines. I would like to replace it with a Dynamic PTO pump rated at 7.5GPM with 1" input, 3/4" output) lines The Kubota replacement pump is crazy expensive. My questions are: 1) Do I need a pressure regulator valve to get my new pump down to around 5 GPM or will the higher flow be tolerated? 2) Will the existing input hose need to be increased to 1" or can I simply put a reducer on the new pump? 3) If I stick with the 7.5 GPM flow I realize I will probably need to upgrade my reservoir to around 10 gals from the existing 5 gals to keep the oil from overheating. The problem is the existing reservoir is top mounted and all the replacement reservoirs I've seen are bottom mounted. Anyone know of top mounted replacement reservoirs or have ideas on installing a bottom mount in this situation?

Thanks in advance for your ideas!

 

[oldnslo]

Simple answer is run the engine RPM lower with the dynamic pump since RPM times displacement = flow.

Trying to change the fittings sounds like a lot of extra work and running a smaller hose to a pump inlet is not a very good idea in most cases.

Pressure regulator does not control flow. You would require a priority flow control or flow divider both of which will create excessive heat.

 

[caissem]

Thanks, I'll give that a try. Looks like if I set the engine to around 900 RPM I can get 5 GPMs.

 

[Rock knocker]

What is the downside of running a 7.5 GPM?

That the pressure relief in the BH is not big enough to accommodate the increased flow.

 

[oldnslo]

Caissim
I suspect that there is a speed increaser on the dynamic pump so you probably wouldn稚 have to drop the PTO as much as you believe.

Possible Down side of running at 7.5 GPM are:
Will the backhoe valve handle that flow without excessive pressure drop?
Will the hoe be usable with that much flow increase? With cylinders flow is travel velocity or speed?
Heat generation from the potential for increased pressure loss.
Reservoir size may have to increase.
Suction, pressure, & return line sizes may have to increase to avoid high oil velocity which can aerate the oil.

Filter size might have to change.

This is a list of some of the items to consider

 

[Rock knocker]

The claim is that the BH is a renamed Woods BH 750, which is rated to 6 GPM. So you're getting closer. There are also relief valves that you can put in prior to the valve box to shunt any excess acculated fluid to the tank.

There is a very knowledgable poster or two or eigth who will hopefully chime in.
https://www.woodsequipment.com/files/Products/Manuals/MAN0450.pdf

 

[caissem]

Thanks. I have the 6.5' version which is equivalent to the BH65/BH650 so I think I'm still around 5 GPM according to another poster who has the BH565 manual. I was thinking about the flow control valve with a built in prv as backup to the one on the backhoe but then I would have to put another opening in my reservoir which is another thing to deal with and would require taking the tank off and getting it welded (I think?).

Really appreciate all the helpful responses!

 

[dfkrug]

I have the 6.5' version which is equivalent to the BH65/BH650...

Why not toss your broken PTO pump system and use the tractor hydraulics? It
is more than adequate to supply your hoe.

I have owned several L2550DTs, which have the same hyd system, and they ran my Woods 7500 clone
hoes fine. You have a manual flow diverter valve on your main hyd manifold near the pump.

 

[caissem]

Why not toss your broken PTO pump system and use the tractor hydraulics? It
is more than adequate to supply your hoe.

I have owned several L2550DTs, which have the same hyd system, and they ran my Woods 7500 clone
hoes fine. You have a manual flow diverter valve on your main hyd manifold near the pump.

Yeah, I thought about doing that although I didn't know about the diverter valve you mentioned. Its is definitely an option but its something I would need to research more and I need to get the hoe back in action asap and using the PTO pump is more straight forward. Also, I have a hydraulic leak in the tractor that I need to fix and demanding more of the main hydraulics at this point didn't seem wise. Not to mention that I already bought the new PTO pump Thanks for bringing up that option though, it is definitely a good one.

 

[nyone]

I wouldnt jump the GPM up a whole lot. It makes for a really jumpy and jerky backhoe. Even if you can run your rpm lower you could be below the power band and you will need more power to run a bigger pump.