[DennisCNC]

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 :tired: of researching.

Thanks

[Runner4404spd]

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?

[DennisCNC]

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

[Geof]

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.

[DennisCNC]

^ 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

[Geof]

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.

[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.

[Geof]

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.

[Gerald_D]

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)

[DennisCNC]

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?

[Gerald_D]

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.

[StealthDumpKits]

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.

[Geof]

Dennis are you open to out-of-the-box thinking? I assumed earlier that you want a variable speed drive that is immune to water splash. Hydraulics will give you that as has been discussed so far but it does have complexity with reservoir tanks, filters, coolers, etc(?) and it needs two lines for pressure and return flow.

How about a water based system using a Pelton Wheel turbine on the spindle. These can run much faster than your 4500 rpm so a gearbox would be needed but they can have awesome power in a small package. The pump would be a multistage centrifugal producing around 300 psi and the whole system might have an overall efficiency of close to 80%. You would only need one pressure line going to the turbine because your return flow could be dumped into the drain system for the water used on the cutter. You will already have a pump for the coolant water flow which will most likely have to be filtered so you just increase the capacity of this and take a tapping off to feed your turbine drive pump.

One advantage I can think of is that a leak in a water based system is no problem; a leak in the hydraulic system makes a real mess with oil everywhere. But I have no idea whether Pelton turbines are readily available in small sizes.

[DennisCNC]

^ That would be the perfect solution as the return water will be used for the tool cooling and washing away sand! I didn't even know there was such a thing. Thanks for great tip! Woulder how much water it will need.

[Geof]

^ That would be the perfect solution as the return water will be used for the tool cooling and washing away sand! I didn't even know there was such a thing. Thanks for great tip! Woulder how much water it will need.

I think this calculation still applies; HP = psi * gpm / 1714 so you just rearrange it to get gpm = 1714 * HP/psi so if you want 5 HP at the spindle at 300 psi you need 29 gpm at 100% efficiency so if my guess of 80% efficiency is close you need 36 gpm and your pump motor needs to be about 7 or 8 hp.

This is not exactly an original idea on my part; Pelton wheel turbines as drive motors in an industrial setting go back well over a hundred years. I do not know if any U.S. cities ever had very high pressure piped water but many English cities did. It was supplied at around 700 psi and the purpose was to drive small Pelton turbines to run industrial machinery; this was before electric motors. Before the Pelton turbines machinery had to be run from overhead lineshafts that were driven from a steam engine located outside the building. I have seen the turbines in a museum display but I am darned if I can remember whether it was in Washington D.C. or in London.

[DennisCNC]

So far search results a pretty bleck on the small Pelton tubines. For now I will stick with the hydraulic system and latter try to make a small turbine myself. I found a some good sites with details on the construction of a turbine. Pretty cool how a lot of invetions come about by mistake.

[Geof]

So far search results a pretty bleck on the small Pelton tubines. For now I will stick with the hydraulic system and latter try to make a small turbine myself. I found a some good sites with details on the construction of a turbine. Pretty cool how a lot of invetions come about by mistake.

You probably found stuff related to making run-of-the-river hydro electric installations. Not too applicable in Florida, you are a bit short of many hundreds of feet fall in a river over a short distance.