Hydrostatic cylinder drive???

[oughtsix]

I have seen these little hydrostatic pumps at surplus center:

https://www.surpluscenter.com/item.asp?UID=2324022401522920&item=9-7686&catname=hydraulic

at .43 cu inch they don't seem like they would be of much use in driving a wheel motor of any decent size/power. But at $129 for a dual pump they seem like they should be good for something...

Could you use one of these pumps to control a couple cylinders for something like a front end loader. Or maybe use a pair of these to control a small backhoe? With a mechanical linkage to control the swash plates could you not only have directional control but also speed control over the cylinders? No valves, minimal plumping, pretty easy to drive with a vertical mower motor????

Just a thought????

 

[jda1961]

whats the flow rate and operating pressure?

 

[oldnslo]

A couple of things to consider.


I could not view the specs sheet but in reading through the description they where talking about a charge pump and filtration requirements so it makes me believe you would need a remote reservoir. Not sure what the flow rate is on the charge pump.

Since these are designed to run motors you would have to use double rod cylinders to get equal flow rates and not exceed charge pump capabilities.

Pressure rating is 1450 PSI with peaks of 3,500 PSI intermitant. Not sure what the duty cycle is so they could do some work.

talked about vertical mounting so I don't know if this means shaft up or shaft down position.

For $129 plus shipping they could be a handy little unit if applied properly.

May want to consider installing a fan like most small HST's have.

My two cents worth, should I ask for change??

Roy

 

[mmurphy]

Oughtsix, I would say no, hydro systems are typical for a closed system. They will have a charge pump ahead of them supplying oil back to them to keep up with internal leakage like Oldnslo said. The hydro pump and hydro motor kinda like keeps a balance in the way the oil will make a loop. (for a lack of a better description)

 

[dfkrug]

Could you use one of these pumps to control a couple cylinders for something like a front end loader. Or maybe use a pair of these to control a small backhoe?

I have seen those for sale at SurpCntr.

If you can use 6GPM at 1500psi, you have separate pumps, so you can
use them for 2 different open center circuits. I would set the swash
plates at max and use OC valves. For a hoe, you could run the swing
circuit separate from the other valves for more control. That price is
about what you would pay for a simple shaft-driven gear pump, like
a Prince 0.164ci. As stated, you will need a reservoir/filter setup.

The vertical shaft is nice, so you could use a recycled lawn more engine,
like a B&S 16hp.

 

[oughtsix]

SPECIFICATIONS

* Disp. 0.43 cu. in. / rev.
* Pump Type Variable piston
* Rotation CCW
* Pressure:
1425 PSI cont.
3500 PSI int.
* Speed:
600 RPM min.
3600 RPM max.
* Flow per Pump(fully stroked):
6 GPM @ max. speed
* Mount 4 bolt 108mm X 145.5mm c.c.
* Shaft 15mm tapered w/keyway and
10mm-1.5 LH threaded end
* Control Shafts 12mm dia. x 15mm
w/dual flats and pin holes
* Rqd. Filtration Input to charge pump
* Oil 10W-30 or 15W-40 engine type
* Inlet Port SAE 8
* Work Ports SAE 8
* Drain Port SAE 6
* Size 7-1/2" x 5-1/4" x 7"
* Shpg. 17 lbs.

A couple of things to consider.


I could not view the specs sheet but in reading through the description they where talking about a charge pump and filtration requirements so it makes me believe you would need a remote reservoir. Not sure what the flow rate is on the charge pump.

Since these are designed to run motors you would have to use double rod cylinders to get equal flow rates and not exceed charge pump capabilities.

Good points from everyone... thanks for the replies. This was my thinking on some of the points you guys made:

1) The description says "Rqd. Filtration: Input to charge pump". I read this as the pump has an integrated charge pump that requires a filter in front of it. Considering the original intended use of the pumps (really cheap zero turn mower... It would have to be a really cheap mower to use wheel motors with a matching small displacement to the pump). I can't imagine a cheap mower requiring a separate external charge pump. That wouldn't fit with the economics of the pump. The pump inspires a mental picture of a 18hp Craftsman ZTR with a 30" deck for $2000.

2) Double rod cylinders - Yes this makes a lot of sense. A single rod cylinder would have different displacements on each side causing different flow rates. Interesting thought on how much displacement/flow differential you could get away with? How much the charge pump could make up and still operate with some kind of life expectancy?

3) Set the swash plate and use it as a fixed displacement pump. This could definitely be done but is kind of counter to what I was hypothesizing about. I was envisioning a trailer hitch back hoe with an old lawn mower engine and a couple of these pumps. Plumb the pumps directly to the cylinders... no valves... very simple. I was imagining a bypass valve between the two sides of the pistons to short the flow at the end of the cylinder cycle. I really liked the idea of making the variable displacement a feature. Move the swash plate a little to move the bucket slowly... move the swash plate a lot to move the bucket quickly.

4) The biggest concern I had was about heating of the hydraulic fluid. But the pumps are probably really designed for closed loop operation anyway. Some sort of inline cooling would probably be a good idea though for any kind of life expectancy.

5) Hydraulic reservoir: I hadn't considered there would be any way to get around having some sort of reservoir. Something to supply the charge inlet and a place for the overflow to drain. Considering the closed loop operation the tank wouldn't have to be very big.

6) May want to consider installing a fan like most small HST's have. Yep! Definitely! Another great idea I hadn't thought about!

7) Would there be leakage between the two sides of the pump when the swash plate is in the neutral position causing the bucket to slowly lower instead of keep its position?


I am not ready to run out and build a mini back hoe using these pumps. I just saw these and saw the price and it got my wheels turning. I needed some input / reality check of my idea. I knew this was the place to come for some intelligent input. The volume differential of a single rod cylinder makes sense... but I still wonder if it would be a show stopper?

 

[J_J]

I believe those pumps are used on walk behind hydrostatic mowers. They use small to med size wheel motors. That pump takes about 14 HP to run it. It also uses motor oil as the hyd fluid. The input filter should be about a 10 micron. I believe the hex bolt in the first picture, on the right side top is used to open the bypass valve

Here is the other side.

 

[oughtsix]

Very interesting. I don't know how you got to the back side of the surplus center website so you could see the back side of the pump but the picture is very informative.

Walk behind mower makes a lot of sense for this pump size. I haven't stumbled over wheel motors under 7 cu but I would guess they exist. I guess you also would not want a walk behind to go very fast.

5 Ports. I am guessing 1 charge port. 2 x 2 ports for 2 X wheel motors.

This refines the view in my head of how a system would be plumbed. Reservoir to Pump. 4 X lines from pump to (motor). Normally I would guess a drain from the motor back to the reservoir.

This brings up a mental picture of all the hydraulic fluid (motor oil) constantly circulating through the pump and motors with very little returning to the reservoir. That sounds like a lot of heat build up in the hydraulic circuit... but I guess this is really the definition of a closed loop hydraulic drive system.


I see ~2000 of these pumps available online. That gives my spine the feeling that the original application for the pump didn't pan out... maybe because of poor lifespan of the original mower???? 7lbs blew me away as a very very lite hydraulic component of any kind.

 

[J_J]

With a closed loop system, the fluid is sent to each wheel motor, and then back to pump. A lot of wheel motors have case drains to help lubricate and cool the motors, and the extra fluid from the case drains are sent back to the pump case, and then to cooler/radiator, and then to tank. The charge pump adds fluid as necessary to maintain a full supply of fluid in the closed loop circuit. The charge pump, usually pump about 10 % of the hydro pump.

 

[J_J]

oughtsix,

If you go to your link, and in the middle of the page, you will see a link MORE PHOTOS. That will show more pictures.