# Thread: Hydraulic pump and motor?

1. ## Hydraulic pump and motor?

I'm thinking of using this hydraulic motor for a spindle drive motor:
http://surpluscenter.com/item.asp?UI...name=hydraulic

It is 0.372 cu in displacement, so counting leakage in motor and pump how big of a pump will I need to get ~4.5K rpm from this motor? What aprox. HP A/C motor will I need?
My head is getting of researching.

Thanks

2. you will nee about 10 gallons per minute. alot depends on how much leakage gets through the case drain. in order to figure your HP you will need to know how much pressure you can run. what is the pressure limit on the motor?

3. It is 2000 PSI cont. and 2500 intermittent. Is there are average number for leakage?

4. Just a comment. From your questions I would guess you have not worked with hydraulics before so maybe you don't know how noisy a machine might be with a 10 gpm pump running at up to 2500 psi driving a hydraulic motor at 4500 rpm. Particularly if you plan on varying the speed on the hydraulic motor that drives the spindle by using a proportioning valve. This might be noisy enough to be above OSHA limits.

Hydraulic drive can give you variable speed but it is better to use a swash plate pump and motor. This is the type used in hydrostatic transmissions but even these are noisy. Another thing with hydraulic drives is the low efficiency; a quick calculation tells me you will need a 10 hp motor (I hope someone comes on and either confirms or corrects this because it seems high) but you will probably only get half this power at the motor, maybe less. The rest goes into making things hot.

5. ^ You are right, there will be a lot of waisted power. I didn't even think of the noise!

These guys run a setup like I want:
http://www.ghines.com/systar.html

I wounder why the hydraulic pumps on water jet pumps are pretty quiet? They run around 3K psi.

Thanks

6. I clicked on the link and maybe now I understand why you want to go with hydraulics; possibly fewer problems with water splashing everywhere.

Regarding the water jet hydraulic pumps are these running exposed or in a housing; this can make quite a difference. But the main reason I suggest you consider the noise is because you will be throttling the flow from your main pump for speed control at your motor and this can create more noise than the pump just running against a constant load at a constant pressure. Possibly that is the difference in the water jet systems; those pumps are just running pistons at a constant speed or they are idling with the pistons stationary.

One suggestion I have is that you look into the swash plate type pump. You are in Florida, lots of lawn tractors around. The hydrostatic drive ones have a swash plate pump/motor system in the transmission. Perhaps you can get something from a scrap yard and modify it; pump end on your electric motor, drive end on your spindle. If everything is in a one piece housing that might be a challenge.

7. I was thinking of using a VFD on the drive motor for speed control or I might even not have any speed control if it is problem, just have on and off.

8. Originally Posted by DennisCNC
I was thinking of using a VFD on the drive motor for speed control or I might even not have any speed control if it is problem, just have on and off.
Your plan is to vary the hydraulic pump speed to vary the hydraulic motor speed. This will work and will probably reduce the noise levels immensely because you are reducing the hydraulic flow at its source not throttling it. The only disadvantage to this will be related to leakage; both the pump and motor have some bypass leakage which is more or less constant with pressure but independent of pump or motor speed. This means that leakage as a proportion of total flow increases as the flow decreases and if you slowed your pump motor down low enough your hydraulic motor might stall because the leakage is consuming everything. I have no idea how likely this is and at what speed you might expect to see it.

I think doing it this way is an unconventional way of doing hydraulics but it will probably work quite effectively. You might be able to do away with any hydraulic valves and if you used reversible pump and motor you might even be able to reverse the drive motor to reverse the spindle. Probably not necessary for you.

9. 0.372 cu in/rev @ 4500 rpm = 1674 cu in / minute = 7.2 gal / min (gpm)

At the very worst, the leakage in that motor, to drain or otherwise, should be less than 10%. An 8 gpm pump should be adequate.

To get the peak torque out of the motor, you want to be able to reach its peak pressure of 2500 psi. So, at the most you need an 8 gpm / 2500 psi pump, and at minimum, a 7.2 gpm 2000 psi pump.

HP = psi * gpm / 1714 = around about 12 HP worst case.

Motors are quiet enough, the pumps are normally the culprits. Cast iron bodied pumps are slightly quieter than alu. Vane pumps are much quieter than piston.

If you want to reduce the noise, turn the pump slower (4 pole motor or slower).
A 4-pole motor on 60Hz will turn around 1750 rpm, therefore the cu in /rev of the pump must be 4500/1750*0.372 = 0.96 cu in /rev.

So, find yourself a slow 12 HP motor and calculate (in terms of cu in /rev and psi) a pump to match.

But, having said all that, I would be nervous driving 12 HP through a puny 9/16" motor shaft......... (You might be willing to sacrifice torque (psi) to bring the electric motor size down, but it won't really reduce the pump size)

10. Thank you both for the input. I'll start searching for a vane pump and a ~8-10HP motor for starters.

Any one have a idea how many GPM car power steering pumps are?

11. Car pumps are much less than 12 HP - look at the size of belts driving them. (they are in the 1-2 gpm range). But they do have the advantage that they can be belt driven because their bearings can take side loads. Your spindle motor (mentioned right at the top) can't take side loads.

You can save the price of a VFD (and the electrical noise) by buying something like this:
http://hydraulics.eaton.com/products...VN-TM002-E.pdf
Variable displacement, vane, quiet.

12. Might want to recognize you'll need a filter and fluid cooling radiator for the system. As well as a relief valve and suitable reservoir tank.

Page 1 of 2 12 Last

#### Posting Permissions

We are the largest and most active discussion forum from DIY CNC Machines to the Cad/Cam software to run them. The site is 100% free to join and use, so join today!