# oil hydraulics questions

Discussion in 'Propulsion' started by Guest62110524, Jun 16, 2009.

1. ### Guest62110524Previous Member

I am building some new wheels and rolls
the power is hydraulic
I have a motor, Vs is 110 cm3, but is not Vs litres a sec?
cm3 is 110, torque is 1.5 nm bar, speed is 5-750 rpm
I only need 10 rpm or wheel travel 3.---4 feet min, torque required for 8mm plate is very little, I cant work out how much even though I have done 100,s plates
question is, how should I size the pump, should I just aim for say 3kw3ph motor and pump to suit, before I used a 1.5 at 1500rpm, and it was idling with 8mm, even on things like bow nose plates
how best to change flow rate? the other day in De. I saw a frequency converter, 45--90 Hz, tiny thing worked well
thanks
and is this motor suitable? rather thaN 4 POLE 1450
3 phase 5.5 HP x 2850 rpm 2 pole

2. ### Guest625101138Previous Member

I expect the 110cm^3 is the volumetric displacement. At 10rpm you will require the pump to deliver 1100cm^3/min. That is 1.1lpm.

If you assume the motor will give ample torque at 100bar then the power required is:

Power = Flow x Pressure (kW)

Where flow is in m^3/s
Pressure is in kPa

Power = 1.1/1000/60 x 100 x 100 = 0.183kW

A rough and ready hydraulic system will give at least 50% efficiency so say 50%. Motor power is therefore 360W or say 0.5HP.

Your observations on your previous 1.5kW motor support this. You really do not need any bigger.

Been ages since I have done any hydraulic component selection. For such a small amount of power you will do OK with a constant displacement pump (say little gear pump), relief valve set to limit the motor torque and a control valve to feed the motor.

The variable speed using variable frequency would be nice. However you may need a wider speed control than 2:1 range. Are you sure the 45 - 90Hz is not the speed limit setting rather than the actual range. You can certainly get full speed control.

You can also get variable volume pumps but they are expensive.

I would walk into a Rexroth dealer and ask them for a system that will do the job. Would help if you know the wheel torque required or the likely maximum motor pressure.

Rick W

3. ### Guest62110524Previous Member

thankee sorrr

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### gonzoSenior Member

Most hydraulic systems are regulated by a valve. The pump produces more flow than necessary, and the surplus fluid returns to the tank. If you need a lot of precission, there are flow and pressure regulators.

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