Low-pressure Hydraulic Motor
Low-pressure Hydraulic Motor
(OP)
I have an application where I want to use a hydraulic motor to slowly turn a shaft forward until the clutch on the end of the shaft engages, and the hydraulic motor will then stall out. The torque to turn the shaft is only a couple of lb-ft. The available oil is about 20 psi. We don't need the motor to turn very fast....it's only for pre-engaging our clutch, not for achieving breakaway.
Anyone know where I can find a hydraulic motor that will turn (slowly..?) with only 20 psi inlet pressure?
Anyone know where I can find a hydraulic motor that will turn (slowly..?) with only 20 psi inlet pressure?





RE: Low-pressure Hydraulic Motor
Once you know flow rate you can determine motor size to get the motor speed you want. How slow is slowly?
Once the motor stalls what do you want to do with the oil flow? Stall the pump? Bypass oil through a relief valve? Bypass oil at low pressure through a valve?
Ted
RE: Low-pressure Hydraulic Motor
I am thinking an electric motor with a gear reduction might work better.
TN
Tom Nelson
Application Engineer (CFPS)
CATCO Parts and Service
St Paul,MN
RE: Low-pressure Hydraulic Motor
Mike Halloran
Pembroke Pines, FL, USA
RE: Low-pressure Hydraulic Motor
Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com
RE: Low-pressure Hydraulic Motor
Ted
RE: Low-pressure Hydraulic Motor
If the opposing torque is higher than T=PSID*VPR/(2*π) the motor isn't turning at all and there will be no flow except for leakage.
I think a constant flow source is required that will apply supply oil at what ever pressure is required to make the motor turn at the desired rate.
Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com
RE: Low-pressure Hydraulic Motor
peter, you just gave the definition of the flow makes it go scenario that bugs you so much.
That is the situation with a flow limited circuit, a fixed, constant displacement pump driving against a steady state load, that has valves and loads and conductors such that it is not pressure limited. The motor steady state speed is defined by the flow rate, the pressure defined by load and pressure drops. Pressures are a measurement of load as long as the pump has sufficient input energy (including rotational inertias) to turn it. The dynamic affects are small compared to the overall picture. Yes, accel, decel, fluid capacitance are there always, but small compared to the larger picture.
During accel, decell, dynamics, or pressure limited situation (pressure limited does not mean constant pressure), then of course summation of forces, capacitance, valve restrictions become the determining factors. I agree with you 100% in that situation.
But FLOW and PRESSURE limited are two different limitations that could be applying to a circuit. It is not 'either or', pressure or flow. It is like arguing if voltage is current across resistance, or if current is voltage divided by resistance.......
You see pressure limited circuits and assume that 'flow makes it go' is totally wrong. There is another world of flow limited exactly as you described above.
Any circuit must meet summations of forces, AND summations of flows. The circuit could be limited by EITHER pressure or flow. Most of your world is pressure limited, as it should be. But it is not the only explanation of the total fluid power physics world.
Anyway, back to original poster:
-If this is similar to a gearbox engaging shifter (that we have had many problems with many versions) it is an interesting and difficult challenge for such a seemingly simple task.
-could you use some sort of magnetic coupling like a seal less pump drive?
-A spring loaded drive like on a Bendix starter drive?
-20 psi delta is pretty low for any sort of fluid power component.
-How do you know when it is engaged? Is there some position indication that signals the next step.
-What happens once the cluch is engaged? does this device get removed from the circuit, or does it have to free spin when the main clutch/drive begins turning at higher speeds?
-How often does it get used?
kcj
RE: Low-pressure Hydraulic Motor
RE: Low-pressure Hydraulic Motor
Ted
RE: Low-pressure Hydraulic Motor
A current supply will supply the same amount of current regardless of the output voltage. What this application requires is a constant flow source but the pressure need to be what ever it takes to make the motor rotate. It is still force/torque that makes it go.
Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com
RE: Low-pressure Hydraulic Motor
Both flow and pressure drop through a circuit are required to do work, flow volume will limit speed and pressure drop will limit output force.
Ed Danzer
www.danzcoinc.com
www.dehyds.com