Hydraulic motor and pump help

Metalburner · Nov 29, 2016

So I'm reading a model off of Parker wheel motor and pump set up. It appears to me that each wheel motor requires it's own pump. So if the wheel motor is 10cir, it needs a pump of about .62cir. So in total, unless I wanted to run a line from the pumps to my hydraulic loader, I'd need a third pump dedicated. I know the loader needs about 5.5-6gpm or a .32-.36cir pump.

I can see why zturn mowers use 26hp+, need about 1/2-3/4 dedicated to the hydraulics, then the rest for a mower deck.

I am hoping my math is correct based off of what I'm reading from Parker from their specs
HTJ Medium Duty Integrated Hydrostatic Transmission for vehicles up to 18 lb GVW | Parker NA

I'm not using this combination, just using it as a reference point for how large of pump to motor. The motor setup is way faster than what I'd ever what to go.

MossRoad · Nov 29, 2016

Don't know if this will help you any or not, but my Power Trac is an articulated machine with 4 wheel motors. I have three pumps.

One pump is a variable volume pump. This provided directional control of the wheel motors.

Then there is a second pump that provided 8gpm at 2500psi for the main PTO. This PTO powers implements, like mowers, brush cutters, tillers, etc...

Then there is a third pump. This 3rd pump provides about 4gpm at 2500 psi. It feeds a steering valve. The steering valve drives two steering rams. The steering valve has a power beyond port that provides power to a valve bank that controls the loader up/down, dump/curl and a 3rd function for the quick attach valve, which is also use for power angle of implements like plows and brooms, grapple, etc...

It appears you need independent directional and speed control of two wheel motors, plus power to implements. You're gonna need more than one pump, I'd think, or you're gonna have problems with drive priority when using implements.

Good luck with your project. Sounds fun. :thumbsup:

oldnslo · Nov 29, 2016

Metalburner said:
So I'm reading a model off of Parker wheel motor and pump set up. It appears to me that each wheel motor requires it's own pump. So if the wheel motor is 10cir, it needs a pump of about .62cir. So in total, unless I wanted to run a line from the pumps to my hydraulic loader, I'd need a third pump dedicated. I know the loader needs about 5.5-6gpm or a .32-.36cir pump.

I can see why zturn mowers use 26hp+, need about 1/2-3/4 dedicated to the hydraulics, then the rest for a mower deck.

I am hoping my math is correct based off of what I'm reading from Parker from their specs
HTJ Medium Duty Integrated Hydrostatic Transmission for vehicles up to 18 lb GVW | Parker NA

I'm not using this combination, just using it as a reference point for how large of pump to motor. The motor setup is way faster than what I'd ever what to go.

A true hydrostatic drive uses variable volume pumps feeding a motor in a closed loop environment. The variable volume pump allows adjustment of travel speed to match HP available. Skid steers typically have two variable pumps and either two or four drive motors. They also have a 3rd pump for implements.

The Struck unit used a fixed displacement gear pump so it has to be sized based on available HP to drive it. Two totally different designs doing similar jobs. Each of the variable pumps probably probably cost about 3 times as much as the gear pump which is why they are used for "hobby" type equipment but less frequently used for serious use equipment.

Metalburner · Nov 29, 2016

So am I better off spending the money for two variable pumps plus a third gear pump?

Metalburner · Nov 29, 2016

MossRoad said:
Don't know if this will help you any or not, but my Power Trac is an articulated machine with 4 wheel motors. I have three pumps.

One pump is a variable volume pump. This provided directional control of the wheel motors.

Then there is a second pump that provided 8gpm at 2500psi for the main PTO. This PTO powers implements, like mowers, brush cutters, tillers, etc...

Then there is a third pump. This 3rd pump provides about 4gpm at 2500 psi. It feeds a steering valve. The steering valve drives two steering rams. The steering valve has a power beyond port that provides power to a valve bank that controls the loader up/down, dump/curl and a 3rd function for the quick attach valve, which is also use for power angle of implements like plows and brooms, grapple, etc...

It appears you need independent directional and speed control of two wheel motors, plus power to implements. You're gonna need more than one pump, I'd think, or you're gonna have problems with drive priority when using implements.

Good luck with your project. Sounds fun.

Exactly. At first I wanted to use one large pump to power everything, but the more I look into it, the harder it would be to implement that into it. Cause then I'd need one large pump and a large engine to run it. Even on a mini skidsteer like a Ditch Witch SK750, they have 2 pumps, one for the wheel motors and another for the loader arm and implement(s).

I'd have no problem running 3 pumps if it came down to it, because I can design the mini dozer around it. I'm not planning on using it to build a house foundation...maybe to do a shed foundation, but that wouldn't be any larger than a 20'x30' or there abouts. Trying to build it like a glorified garden tractor.

MossRoad · Nov 29, 2016

It would seem that if you used two drive pumps and two drive motors, you'd have lots of trouble syncing them to go in a straight line. They'll never turn at the same speed ever. You'd be constantly on the controls. Sounds awful. :laughing:

So how does a crawler work if you use only one drive pump to drive two hydraulic motors? Again, I think you'd have sync issues between right and left. It would seem like the path of least resistance would be fluid going around a valve when its not open (in neutral). If you opened either directional valve, there'd still be a path of least resistance around the other valve and you'd build no pressure to turn a motor.

Don't crawlers use one pump, driving one motor, driving one differential, and they use brakes to slow or stop a track? It would seem that would be the simplest. One variable volume pump that drives one motor that turns one differential. You'd have a forward and reverse pedals (or a lever) and a left and right brake.

I don't know. I'm just talking out loud. Time for me to go read how tracked vehicles propel themselves.

Metalburner · Nov 29, 2016

I was looking into using a hydrostatic transaxle and putting 10" disc brakes on the axles to turn, rather independent control, the Struck MT1800/2000 did this with a Peerless 2338...however that has been long discontinued. All of our zturn mowers and our Ditch Witch has two wheel motors and two variable displacement pumps. I like the idea of independent control of the tracks to make right turns in the same spot, especially in tight areas.

Trying to find a suitable transaxle to do this is not easy. I'd have to find an older garden tractor like a John Deere 318 and pull that out.

I wouldn't think synching up two pumps and motors wouldn't be that hard. I'd mount the pumps side by side with the same size pulley (unless they came with one) and run a V-belt to the engine to them. This is how all zturn mowers are setup I believe.

Another way I could do it, is how Struck has been doing it with their smaller crawlers (RS1000, RS196k, MD series) is an intricate series of pulleys and belts to a drive chain to the track sprockets. They claim with all the gear reduction on the RS1000 that at the tracks it has 1500ft/lbs of torque. It's pretty complicated to do that in my mind, than it would be to run wheel motors and pumps.

oldnslo · Nov 29, 2016

two variable pumps and two motors is exactly what a majority of skid steers have. The operator running the levers controls direction and speed by changing the variable pump displacement. Same principle as what most zero turn mowers have. Best maneuverability and performance and probably most money

Single fixed or variable pump driving a motor driving a differential with brakes to steer is also common. My guess would second best on performance and ease of operation.

Two fixed pumps trying to drive two motors could prove a challenge since feathering them would require a very good metering control valve and creates heat

One fixed pump feeding two track drive motors. On similar footing would probably track reasonably well turning or varying the speed or driving at less than full speed again requires a good control valve and creates heat.

fixed pump potentially more difficult to control and change direction depending on quality of the control valves. least cost of all.

Metal burner,
It comes down to your fabricating capabilities, what do you want this machine to do and at what cost. Several different options that provide different levels of performance and cost.

With My abilities I would be to buy a used piece of equipment that meets my needs.

Metalburner · Nov 29, 2016

oldnslo said:
two variable pumps and two motors is exactly what a majority of skid steers have. The operator running the levers controls direction and speed by changing the variable pump displacement. Same principle as what most zero turn mowers have. Best maneuverability and performance and probably most money

Single fixed or variable pump driving a motor driving a differential with brakes to steer is also common. My guess would second best on performance and ease of operation.

Two fixed pumps trying to drive two motors could prove a challenge since feathering them would require a very good metering control valve and creates heat

One fixed pump feeding two track drive motors. On similar footing would probably track reasonably well turning or varying the speed or driving at less than full speed again requires a good control valve and creates heat.

fixed pump potentially more difficult to control and change direction depending on quality of the control valves. least cost of all.

Metal burner,
It comes down to your fabricating capabilities, what do you want this machine to do and at what cost. Several different options that provide different levels of performance and cost.

With My abilities I would be to buy a used piece of equipment that meets my needs.

If I could buy a used machine I would, however most want a lot more than what I'm willing to pay. My fabrication skills are good. I don't have much machining skills nor much for tooling to do that. Any parts I can't make, I'd ever find a machine shop nearby and pay for a part, or buy what I need in store or online.

Most of my fab skills is welding (went to college for it), so I have no issues there. My goals for this machine is to be able to pull a plow for gardening, tow a smallish trailer with wood or rock, dirt or whatever, move a 1000-1500lb fiberglass bass boat around in the yard when need be, and has the ability to move snow in the winter. I had thought about a simple hydraulic blade for snow removal, however a front loader would be a lot more useful.

Like I've stated before, think of it as a garden tractor with a front loader and a cat 0 3pt hitch. It'll be maybe slightly longer and wider than a JD X series garden tractors, but not by much. I figured if I buy parts over time, I can spread out the cost a lot easier than dropping several thousand dollars in one sitting. Excluding the cost of a brand new engine and steel, budget for the hydraulics is $3500, that's brand new or slightly used.