variable displacement hydraulic pump retrofit on JM354 Jinma

[bjr]

I'm considering retrofitting a variable displacement pump on the JM354. Anyone out there with any retrofitting pumps experience? It may have to be front crankshaft mounted. I'm wanting to get away from all the heat and wasted horsepower loss of the OEM constant displacement pump. I know Kinda spendy, but, I think it's doable. bjr

 

[RickB]

So you are changing from a positive displacement gear pump on an open center system to a variable displacement piston pump and closed center system with a high standby pressure?

 

[Bob Rooks]

I'm wanting to get away from all the heat and wasted horsepower loss of the OEM constant displacement pump. I know Kinda spendy, but, I think it's doable. bjr

I'm not sure you understand what you're saying. No hydraulic pump is 100% efficient, there will always be a HP loss, and there will never be a HP demand on a positive displacement pump in an open circuit when no functions are being used. What you're saying is that you want your hydraulics to act like a hydrostatic drive, and I really don't think you'd be happy with that. But sure, it's doable, go ahead. The current OEM pump turns at twice engine speed (look at the gearing), so I don't think you will mount anything off the crankshaft and expect it to be quick operating. Maybe give this project a little more consideration.

 

[Bob Rooks]

And consider this then: In order to perform one function, say raise the FEL, you will have to do two things instead of one. 1) Move the joystick lever. 2) Move the variable pump swashplate (which would require adding another pedal or hand lever).

 

[ptsg]

And consider this then: In order to perform one function, say raise the FEL, you will have to do two things instead of one. 1) Move the joystick lever. 2) Move the variable pump swashplate (which would require adding another pedal or hand lever).

I'm pretty sure the OP is looking for something like a pressure or flow compensated piston pump. It moves the swash-plate depending on the needs for the flow and pressure. Although, this requires close center valves, which the tractor won't have. The loader valve could be done but the 3 pt valve I'm not sure if it's possible.

On the pumps running twice the speed, that's not true. Hydraulic gear pumps usually run very close to crankshaft RPMs and most are rated for a max RPM of 3500.

This project might exceed the tractor's value just on the hydraulic components. That being said, it would still be very interesting to see.
Please, don't take me as a naysayer. I'm all in for these type of projects.

 

[MossRoad]

I'm considering retrofitting a variable displacement pump on the JM354. Anyone out there with any retrofitting pumps experience? It may have to be front crankshaft mounted. I'm wanting to get away from all the heat and wasted horsepower loss of the OEM constant displacement pump. I know Kinda spendy, but, I think it's doable. bjr

I don't think you'd like that. How are you going to control the speed of the flow to a cylinder with variable displacement? What's going to manipulate the swash plate in the variable volume pump to give you flow? You'll have NO flow to the loader cylinders, for example, unless something moves the swash plate AND moves the FEL valves at the same time. And then, it would be variable speed on the FEL, which would not be conducive to predictability in loader movement and speed, which would be really hard on the operator.

I have an all hydraulic machine. There's a variable volume pump that feeds the 4 wheel motors. Then there's a fixed displacement pump that feeds the steering, FEL, and quick attach system cylinder. Then there's another fixed displacement pump that powers hydraulic motors on mowers, tillers, etc....

 

[MossRoad]

I'm pretty sure the OP is looking for something like a pressure or flow compensated piston pump. It moves the swash-plate depending on the needs for the flow and pressure. Although, this requires close center valves, which the tractor won't have. The loader valve could be done but the 3 pt valve I'm not sure if it's possible.

On the pumps running twice the speed, that's not true. Hydraulic gear pumps usually run very close to crankshaft RPMs and most are rated for a max RPM of 3500.

This project might exceed the tractor's value just on the hydraulic components. That being said, it would still be very interesting to see.
Please, don't take me as a naysayer. I'm all in for these type of projects.

My two gear pumps are directly coupled to my engine's drive shaft. They turn at 3600rpm. My variable volume pump is also connected directly to the drive shaft. Same RPMs.

And I agree that there is load sensing equipment that can adjust the flow based on demand. There's some that also increase the engine speed to provide more pumping. But man, that would get expensive fast for little gain.

The OP's machine is made to run the way it runs. If he's concerned about excess heat buildup in the hydraulics, he'd be better off and money ahead by installing a hydraulic cooler system for a few hundred bucks.

 

[RickB]

Variable displacement piston pumps require a charge pump. Every valve or function on the tractor will need to be converted from open center to closed center or replaced with a closed center valve or device. The scope and expense of this proposed project is most likely well beyond the OPs understanding.

 

[LD1]

There is very little wasted HP and heat generated in a fixed displacement pump with open center hydraulics.

At least not any measurable difference between a variable displacement pump maintaining constant pressure across a closed center hydraulic system.

Variable displacement systems are by nature more complex, and more moving parts, and far more expensive. About the only benefit I can see on a tractor, is the ability to add functions with simple tee's into the system pressure rather than PB valves

 

[Bob Rooks]

Variable displacement piston pumps require a charge pump. Every valve or function on the tractor will need to be converted from open center to closed center or replaced with a closed center valve or device. The scope and expense of this proposed project is most likely well beyond the OPs understanding.

BINGO!