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# Help me I'm lost and looking for my pump!

## Help me I'm lost and looking for my pump!

(OP)
I'm a mechanical engineer but I have no hydraulic experience.  I'm trying to find the right pump to design into a machine I'm working on.   The machine would be powered by a variable displacement pump directly coupled to a 28 hp Kohler (or similar) engine.  After wading through an endless assortment of online info over the last 6 weeks or so I'm dazed and glazed but I've still not found what I need.  My wish list is shown below.  The closest I've found to matching my needs is a Sauer-Danfoss "L" or Sauer-Danfoss series 45 pump, but these still don't do it all for my application.  Can someone please get me pointed toward the right pump?
* 1-1.5 in^3/rev (16-25 cc/rev).
* ~600 - 3600 RPM
* SAE "A" or "B" mounting to motor.
* 3000 psi continuous rating.
* No charge pump needed (open circuit).
* Capable of pumping both directions  (fixed shaft rotation direction)
* Swash plate control by stepper motor or external mechanical connection which I can add my control to.
* Prefer if all porting is on back plate (I'll be taking off the back and directly connecting to a custom manifold)
* Available individually (non-oem).
* Reasonably priced (I see mowing machine pumps at  ~$300 and industrial stuff$1500 & up.  My comfortable budget is $800/ea. in small quantities) Pumps that I've found that are close to what I'm looking for (but not quite): Sauer-Danfoss Series L (size 15 or 23) http://domweb.sauer-danfoss.com/domdb/SauerLit.nsf/1526f939eb2e202286256c5b0062ff21/9EA4C6F1B289135A86256CC700740E24/$file/BLN-9825_L%20Series%20OCP_TI_REV%20-.pdf

Sauer-Danfoss Series 45 (L25C): http://domweb.sauer-danfoss.com/domdb/SauerLit.nsf/1526f939eb2e202286256c5b0062ff21/217A829DEB872189C1256C94002EA39C/\$file/520L0571_Series%2045%20OCP_PB_Jun-2005_REV%20C.pdf

Thanks

Mark

### RE: Help me I'm lost and looking for my pump!

(OP)
Bud,

Thanks for responding.  The White KP pump has been on my radar screen for a long while.  it is nice (especially the price) but it only goes to 1500 psi continuous and it is for closed loop use requiring a charge pump (built in) which won't work for my application.

The Hydraulicspneumatics.com link didn't work for me.  Can you tell me what to search for or which links to use within that site to navigate to that document?

I've only known about hydraulicspneumatics.com for ~2 hours since reading the FAQ on this forum and I've been slowly marching through the manufacturers and their products (only to "C" now) since then.  Slow going.

Keep the suggestions coming.

Mark

### RE: Help me I'm lost and looking for my pump!

Mark:
Go to the "Designers Guide" on the H&P site and there are pumps and Hydrostatic links that will get you general info. Then you have to start digging.

Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

### RE: Help me I'm lost and looking for my pump!

* No charge pump needed (open circuit).
* Capable of pumping both directions  (fixed shaft rotation direction)

I am confused on that statement: meaning suck from tank, push to circuit, but then with shaft still turning in same direction to stroke swash plate the opposite way and suck back from circuit and push to tank?
This would seem to be a very high inlet vacuum in one direction?

kcj

### RE: Help me I'm lost and looking for my pump!

kevin;

Sounds like another Gas Saving Hydrostatic Drive setup to fill an Accumulator and use decelerating/braking energy.

In 1985 I was on a Mercedes tour bus in Germany that used a Hydraulic Pump/Motor to store and reuse energy. It was obvious when the pump was filling the Accumulators while decending the mountain roads. The added energy of getting moving was not apparent though. The driver controlled the pbraking by changing SwashPlate angle from a lever next to his seat. I don't recall if I ever found out how the energy add circuit functioned.

Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

### RE: Help me I'm lost and looking for my pump!

(OP)
<<I am confused on that statement: meaning suck from tank, push to circuit, but then with shaft still turning in same direction to stroke swash plate the opposite way and suck back from circuit and push to tank?
This would seem to be a very high inlet vacuum in one direction?>>

I see what you're thinking, but my circuit / thinking is in a different direction. It would be used on a constant force winch setup which is counterbalancing a load which is influenced by other controls (easiest to think of it as a counterbalance to an elevator). The primary flow would be from the pump to the motor and back to the tank. The constant force (aka, drum torque, hydraulic pressure) would come from always having some flow past a relief valve.  With the load moving in one direction (elevator up) the pump would be the source of high pressure fluid.  With the load moving the other direction the motor would draw fluid from the tank (through checkvalves to get the filtering correct) and pump it to the high pressure portion of the circuit. When working in this mode I'd like to reduce flow past the relief valve (but always maintain some for control) and have the majority of the high pressure fluid run backward through the pump so that the pump would act as a motor and spin the gasoline engine that its attached to.  The reason for doing that is to reduce the quantity of energy being dissipated from the system into heating the hydraulic fluid by having much of the waste energy spin the gasoline motor which would have its fuel temporarily switched off.  Make sense?

Mark

### RE: Help me I'm lost and looking for my pump!

So you are going to use the Kohler engine as a brake to absorb the energy being delivered by the load motor, now acting as a pump, to the primary hydraulic pump.  Doesn't sound like a good idea.

You should either recover the energy or just plan on rejecting it from the hydraulic system as heat.

Ted

### RE: Help me I'm lost and looking for my pump!

EngMark how do you intend to limit your engine speed while motoring the pump? In my experience engine overspeed is likely unless you have some sort of braking on the engine (like a jake brake on a diesel).

It would be a good idea to contact application engineers at Sauer Danfoss and/or the other manufacturers you are considering.  It is likely they have experience using their product in a similar application.

### RE: Help me I'm lost and looking for my pump!

Eaton has the Hydraulic Launch Assist (I think?) system for trucks and deleivry vehicles. that uses the accumulators, etc.

Seems like you really are describing a hydrostatic drive though, for drive, and braking and full control. Is this not similar to a normal constant tension winch drive system?

HST horsepower backwards is of course limited by the engine ability to absorb it. Noted by prior poster. IVT magazine Oct Nov 07 had an article on adding internal relief valves as braking inside the hst loop. I didn't read, just made a reference note to get back to it 'some day'. heat inside the loop could be a critical issue.

kcj

### RE: Help me I'm lost and looking for my pump!

(OP)
No, I don't plan on adding a Jake Brake or doing any significant mechanical modifications to the motor.  The engine I'm working with is fuel injected.  I'll be re-routing the signal from the engine's position sensor through my electronic controller and back to the engine.  My controller would know of any potential overspeed issues and would intervene by changing the swash plate angle appropriately.  This would have the mechanical fan on the engine providing some air flow to the hydraulic heat exchanger.   The engine wouldn't be able to absorb a large percentage of the waste energy but it would help.

Kcj:  It is sort of a hydrostatic drive, although in a normal hydrostatic drive all of the energy put into the fluid by the pump is (at least ideally) taken out of the system by the motor.  In the type of system I'm contemplating there are long periods (up to 10 minutes) where the hydraulic motor would be generating significant fluid power (20 hp?) (think of the elevator going all the way down in my previous analogy) which would go nowhere productive - past the relief valve to the tank and / or spinning the engine.  Heat!  The hydraulic pump would also generate excess flow which would cause heat, but with a variable displacement pump and control of engine speed that volume of fluid could be controlled and would be much smaller.  A heat exchanger is definitely in my future but I'm just trying to keep it as small and neatly packaged as possible.

Hydtools <"You should either recover the energy or just plan on rejecting it from the hydraulic system as heat. ">  Recovery of the waste energy is a fabulous goal that I aspire to and which I've done a lot of thinking about, but I think it would add (on a percentage of the small system I'm envisioning) a huge cost, weight, safety penalty (to be operated by casual consumer users).  The thought that my scheme to cut heat exchanger size by adding all of the complexity of having the hydraulic power spin the engine is less an advantage than a needless complexity is always in my mind, something that I'm always struggling to justify to myself.  I'll probably build my first prototype with no ability to adjust the swash plate angle on the fly, no motor cutout, etc., but when I get to that point I'd like to be working with a pump which was thoughtfully chosen to have that capability if it makes sense to pursue it, rather than having to start with a new type of pump and re-design / fabricate the cast and machined manifold it mates to.

jbwick: <"It would be a good idea to contact application engineers at Sauer Danfoss and/or the other manufacturers you are considering.  It is likely they have experience using their product in a similar application. ">  Would A little guy like me that is only guaranteed to buy one part and 30 at the most optimistic be able to get significant technical advice from one of the manufacturers engineers?  That would be fabulous if that's the case in this area of industry.  I've assumed that is dreamland.  Is that reasonably possible?

I'm still working my way through the directory that Budt suggested and it really is full of knowledge.  I'm down to the "R"s now and I'm seeing a reasonably qualified pump from Rexroth (Bosch).   I'll keep wading through as time permits.

Thanks for the info, thoughts and suggestions to date.

Mark

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