How to convert bh77 from power beyond to open center

[bobburke]

I’m adding a pto pump to run my bh77 backhoe. It’s currently tapped into the circuit between the 3 point lift and front loader.
The new circuit will run from the pto pump, though a relief valve, thought backhoe vale and return to the tank.
Do I need to do something to backhoe control valve to make it more efficient running on new circuit and pump?

 

[TheOldHokie]

I’m adding a pto pump to run my bh77 backhoe. It’s currently tapped into the circuit between the 3 point lift and front loader.
The new circuit will run from the pto pump, though a relief valve, thought backhoe vale and return to the tank.
Do I need to do something to backhoe control valve to make it more efficient running on new circuit and pump?

It is already plain open center. No need to change anything except where it hooks up.

Dan

 

[torch]

I’m adding a pto pump to run my bh77 backhoe. It’s currently tapped into the circuit between the 3 point lift and front loader.
The new circuit will run from the pto pump, though a relief valve, thought backhoe vale and return to the tank.
Do I need to do something to backhoe control valve to make it more efficient running on new circuit and pump?

Make sure to route the existing supply back to the rear 3ph -- don't just plug the lines or you will damage your tractor's pump. Some models have a diverter valve in the hydraulic block you can open, other models require a different cover or require that you simply connect a hose between the two ports.

 

[Donystoy]

I have been considering doing this myself after the warranty is over on mine. The bh77 seems enemic in speed compared to the woods 650 that I had on the b7200. I always ran it on the higher pto speed that the lx2610 does not have. Even the bucket curl on the bh77 seems weaker with the smaller cylinder.

 

[bobburke]

Make sure to route the existing supply back to the rear 3ph -- don't just plug the lines or you will damage your tractor's pump. Some models have a diverter valve in the hydraulic block you can open, other models require a different cover or require that you simply connect a hose between the two ports.

When I remove the backhoe from the tractor now I couple the quick connect feed and return to complete the hydraulic circuit.

 

[bobburke]

I have been considering doing this myself after the warranty is over on mine. The bh77 seems enemic in speed compared to the woods 650 that I had on the b7200. I always ran it on the higher pto speed that the lx2610 does not have. Even the bucket curl on the bh77 seems weaker with the smaller cylinder.

I agree.. it’s a shame with the cost of the backhoe it should be so slow and dim witted. The main boom lift on mine gets so hot you can barely touch it after it’s been run.

 

[bobburke]

It is already plain open center. No need to change anything except where it hooks up.

Dan

Thank you Dan

 

[TheOldHokie]

I agree.. it’s a shame with the cost of the backhoe it should be so slow and dim witted. The main boom lift on mine gets so hot you can barely touch it after it’s been run.

So how big of a reservoir and what size pump are you planning to use in your conversion? Do you expect the boom temperature will be lower?

Dan

 

[bobburke]

So how big of a reservoir and what size pump are you planning to use in your conversion? Do you expect the boom temperature will be lower?

Dan

I built a 8.25 gallon tank mounted under the floorboard.. I had a machinist turn the belly 2500 rpm pto shaft down to a 5/8” keyed shaft. I’m still debating the pump size but leaning toward a 6.5 gpm. Most tractor sized for a bh77 have a pump around this size. I figure with a pressure relief dumping fluid back to the tank before the control valve even if flow is to much pressure will dump before it can damage anything.

 

[PaulL]

I had a machinist turn the belly 2500 rpm pto shaft down to a 5/8” keyed shaft.

Why turn the shaft down rather than buying/making an adapter?

 

[PoTreeBoy]

I built a 8.25 gallon tank mounted under the floorboard.. I had a machinist turn the belly 2500 rpm pto shaft down to a 5/8” keyed shaft. I’m still debating the pump size but leaning toward a 6.5 gpm. Most tractor sized for a bh77 have a pump around this size. I figure with a pressure relief dumping fluid back to the tank before the control valve even if flow is to much pressure will dump before it can damage anything.

According to tractordata.com you have 6.4 gpm now.

 

[lugbolt]

the speed at which a cylinder extends or retracts is based on it's bore size, to an extent the rod size (pin bias effect), geometry of the cylinders/arms, and more importantly the flow of the oil going into/out of the cylinder/fittings/hoses.

On the little L series the pumps only flow so much-which is engineered into the tractor's overall design. If there were a pump installed with more volume, it would certainly speed the system up, but would also make the loader mostly unusable because it'd be "TOO" fast. Similarly, the 3 point hitch. This is, of course, if everything stayed the same as it already is, with only changing the pump volume. Remember, everything has to work together, both mechanically and also in the engineering/manufacturing phases. If we installed a higher volume pump, now we'd also have to address fittings, valves, hoses, lines, pipes, filter(s), screens, and a bunch of other stuff, which could add significant cost to the tractor, potentially putting it non-competitive with other brands. Or the other option, redesign the entire system so it uses more of a pilot-operated valving, similar to excavators and skid-steers. You guys wanna gripe about the cost of a loader valve now? Wait til you price a valve assembly for a mini-ex. Or a pump assembly. Some other brands of tractors (including my MF) use a different system which uses a flow control valve such that the systems have a ton of power (more than the tractor can handle) "AND" be somewhat faster operating. But again, more expensive to make, and of course to purchase. And much more expensive to fix.

There is no free lunch.

8 gpm flow at 2000 psi, the system works faster but still has the same "power" as the same system that has 4 gpm at 2000 psi.

So if you're adding a pto pump, hoses, lines, reservoir (and I might also suggest a cooler of some sort...), you want to size it properly, keeping in mind that the valve can only deal with so much flow. How much? That I don't know. Pull the covers off of the valve assembly, get the model off of it and maybe do some digging to see what they're rated for.

 

[TheOldHokie]

I built a 8.25 gallon tank mounted under the floorboard.. I had a machinist turn the belly 2500 rpm pto shaft down to a 5/8” keyed shaft. I’m still debating the pump size but leaning toward a 6.5 gpm. Most tractor sized for a bh77 have a pump around this size. I figure with a pressure relief dumping fluid back to the tank before the control valve even if flow is to much pressure will dump before it can damage anything.

You are looking at the same flow rate as the tractor pump so its not going to be any faster and its going to generate the same amount of heat passing through the backhoe.

Your reservoir is a 2X larger so you will get additional cooling. You may also eliminate a little heat generated by the tractor side plumbing. Probably minimal.

The relief valve pressure srtting will determine digging force. If you set it higher than the tractor you will have more digging force bit also generate more heat.

To get more force you need higher pressure. You have not told us what your relief will be set at.

To get faster response you need a pump larger than the 6.8 GPM produced by the tractor

To get better cooling you need a significantly larger reservoir. You have added capacity there.

It looks like what you have in mind will give you better cooling but not much else.

Dan

 

[bobburke]

Why turn the shaft down rather than buying/making an adapter?

I looked for anything that would fit the original splined shaft for two years. New or used driveshafts were over $300 and then need to be modified to fit the pump side. Turning the shaft was $50 and new seal was $10. There is just enough room to direct couple the pump with a 5/8-5/8 lovejoy coupling.

 

[TheOldHokie]

I looked for anything that would fit the original splined shaft for two years. New or used driveshafts were over $300 and then need to be modified to fit the pump side. Turning the shaft was $50 and new seal was $10. There is just enough room to direct couple the pump with a 5/8-5/8 lovejoy coupling.

I am not trying to rain on your parade but have you considered the HP (torque) that Lovejoy coupling has to transmit?

Dan

 

[bobburke]

I am not trying to rain on your parade but have you considered the HP (torque) that Lovejoy coupling has to transmit?

Dan

I did. I bought the largest coupling that still had a 5/8” bore. I’m sure the pump won’t need the full tractor hp before the 2100 psi relief valve is opened.

 

[bobburke]

You are looking at the same flow rate as the tractor pump so its not going to be any faster and its going to generate the same amount of heat passing through the backhoe.

Your reservoir is a 2X larger so you will get additional cooling. You may also eliminate a little heat generated by the tractor side plumbing. Probably minimal.

The relief valve pressure srtting will determine digging force. If you set it higher than the tractor you will have more digging force bit also generate more heat.

To get more force you need higher pressure. You have not told us what your relief will be set at.

To get faster response you need a pump larger than the 6.8 GPM produced by the tractor

To get better cooling you need a significantly larger reservoir. You have added capacity there.

It looks like what you have in mind will give you better cooling but not much else.

Dan

The one problem with the b7800 was the fact it only had one hydraulic output. When I only had the loader mounted it was fine, once the backhoe was mounted everything slowed down. There is simply to much restriction in the system. Not only feeding the backhoe with flow but what’s worse is exhausting the extra fluid when cylinders are retracted. Yes the tractor pump is over 6gpm but I know I’m not getting it through the control valve.
I wasn’t entirely sure until I tried a friends l3901 with the his bh77 fed from a rear hydraulic output. It’s twice as fast and the cylinders run much cooler.
I’ve put a lot of thought and research into my plan of have a separate system just for the backhoe and then returning the loader circuit back to the stock plumbing.
Thank to everyone for the advise.

 

[TheOldHokie]

I did. I bought the largest coupling that still had a 5/8” bore. I’m sure the pump won’t need the full tractor hp before the 2100 psi relief valve is opened.

7gpm@2100 PSI will be sinking roughly 10+ HP. Assuming you are using a 3 piece jaw type coupler you can find the rating of your coupler here.

https://www.lovejoy-inc.com/wp-content/uploads/2017/11/Jaw2010catalog.pdf

Like I said not trying to rain on your parade but I have built quite a few pump drives of this sort and the HP requirements are significant. I have snapped low HP toming belts with pumps that size. Lovejoy couplers of this type are low even fractional HP. My personal preference is chain couplers but you may not have enough room for one.

Dan

 

[TheOldHokie]

The one problem with the b7800 was the fact it only had one hydraulic output. When I only had the loader mounted it was fine, once the backhoe was mounted everything slowed down. There is simply to much restriction in the system. Not only feeding the backhoe with flow but what’s worse is exhausting the extra fluid when cylinders are retracted. Yes the tractor pump is over 6gpm but I know I’m not getting it through the control valve.
I wasn’t entirely sure until I tried a friends l3901 with the his bh77 fed from a rear hydraulic output. It’s twice as fast and the cylinders run much cooler.
I’ve put a lot of thought and research into my plan of have a separate system just for the backhoe and then returning the loader circuit back to the stock plumbing.
Thank to everyone for the advise.

It's a fixed displacement pump - you are either getting it through the backhoe or you are unloading through the relief.

Dan

 

[TheOldHokie]

I’ve put a lot of thought and research into my plan of have a separate system just for the backhoe and then returning the loader circuit back to the stock plumbing.
Thank to everyone for the advise.

i have no problem with the idea of converting the hoe to standalone and when I first read your post I assumed you were going to use the rear PTO and a larger pump. That's easy and field proven. Your mid PTO solution comes with a lot of new and untested issues. I can attest from personal experience there are unexpected bumps in new roads.

Dan