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Associate

Join Date: Apr 2007
Posts: 45

# Torque and Hydraulic Motors

05/04/2007 2:08 AM

One of our customers want to change an existing (very old installation) hydraulic motor on a reactor with an electric motor. One of the key determinants is the torque that is generated at some stage of the reaction process must be available when the drive is changed to an electrical motor/gear box combo.

Is there a way we can determine the torque developed in the hydraulic motor by measuring the hydraulic pressure and knowing the rpm? Any good links on the operational characteristics of hydraulic motors?

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Ashok Pillai
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Guru

Join Date: Mar 2007
Location: City of Light
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Good Answers: 181
#1

### Re: Torque and Hydraulic Motors

05/05/2007 1:47 AM

You need as well the displacement of the motor in units of volume/revolution.

The theoretical torque is V/(2π)*p. The units must be coherent. Speed is not important for hydrostatic torque as for centrifugal pumps. Speed affects only the efficiency i.e. at higher speed the friction loses are more important.

If you know the motor type in the manufacturer's catalogue you find (normally) the displacement.

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Join Date: Nov 2006
Posts: 17
#2

### Re: Torque and Hydraulic Motors

05/05/2007 2:12 AM

M= ΔP .Vh/2.Π

Pump M= drive torque

Motor M=driven torque(with out η ).

ΔP = Pressure drop between outlet and inlet ,of the pump ,inlet and outlet of the motor

Vh =geometric stroke volume

I think the above equation is general for hydraulic pump and motor,and the effect of changing the R.P.M, is accompained by change in pressure,it means pressure changes accoredinly ,with speed change

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#3
In reply to #2

### Re: Torque and Hydraulic Motors

05/05/2007 3:12 AM

pressure does change as a function of resistance variation versus speed not the speed is the parameter but the way the process reacts to speed changes.

Anonymous Poster
#4

### Re: Torque and Hydraulic Motors

05/05/2007 5:22 AM

If to speak about drives to valves reactor, I do not advise this change.

Let's lose for the major advantages at failure:

-time closing-opening of the valve,

-reliability of a drive,

-independence of an electric line,

-manual management of the crane.

My experience is those.

Success to you.

Guru

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Posts: 3960
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#5
In reply to #4

### Re: Torque and Hydraulic Motors

05/05/2007 5:44 AM

I am sory but I do not understand your comment. Was it anywhere mentionned a valve? I did not see it, As you know in some reactors in order to have an uniform result there are mixers and during reaction the viscosity of the mass evoluates so that the torque capability is very important for the process efficiency. If the mixer does not woek properly yhen the charge is not uniform and can be a waste. For valves command hydraulics have the advantge of the accumulator which can be used in case of emegency shut down even if curent supply fails. It is the so called fail safe principle but as far as look at the question there is never mentionned such a situation

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Join Date: Jan 2007
Location: Israel
Posts: 18
#6
In reply to #5

### Re: Torque and Hydraulic Motors

05/05/2007 6:05 AM

Excuse, but I wrote only about drives to valves.

If to speak about drives to valves reactor, I do not advise this change.

Let's lose for the major advantages at failure:

-time closing-opening of the valve,

-reliability of a drive,

-independence of an electric line,

-manual management of the valve.

My experience is those.

Success to you

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Associate

Join Date: Dec 2006
Posts: 34
#7

### Re: Torque and Hydraulic Motors

05/07/2007 8:33 AM

If you know the torque with the hydraulic motor it will not change with the electric motor unless the speed is different. I am guessing they are either using a plotted curve for the hydraulic motor based on pressure and speed. That same pressure and speed curve would still apply. You can obtain a graph from the motor manufacturer that will give you speed, torque, current, and HP for the motor under load at a given voltage. Just convert it all to HP. The only difference will be actual efficiency. But if you are measuring actual pressure and flow and rpm you will be able to factor out the efficiency of the existing hydraulic motor installation.

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