How to Spec a Hydraulic Motor System

Most hydraulics manufactures websites have a power conversion chart and formulas table that will tell you exactly what converts to what when changing from one power source to another.

Depending on what type of pump and what type of hydraulic motors there are several factors that would have to be added in to get the right information you would need.

If each motor only ever run by itself then the electric pump motor will only be a few Hp bigger at most. But if multiple motors with maximum loads are being ran at the same time then you will need a proportionally larger pump and motor to run them.

To add to the preceding GA, the type of hydraulic motors for this is commonly called "pressure compensated," and the pumps (which can supply a multitude of motors) are described as "constant-pressure, variable-volume." Such systems are frequently used to power a number of conveyors if electric motors might be awkward. Also, they are quite compact and usually direct drive, eliminating gearboxes or chain/sprocket drives. An offsetting disadvantage would be the possibility of oil leaks.

To spec such a system, you would want to assess the speed/torque/flow of each motor; determine the pressure(s) required; add up all the flows; and spec a pump (or combination of pumps) that can handle this flow at the highest pressure involved. There are many manufacturers of such motors and pumps; you might want to declare one or more acceptable brands or their equivalents.

Short answer NO! Hydarulic motors are typically rated in torque per unit of pressure ie: in-lbs/xxpsi, ft-lbs/100psi etc, speed of the motor is determined by the motors displacement cubic inch per rev, cubic cm per rev etc. maximum pressures and maximum speeds are determined by the manufacture (watch out for the 10% duty rating of some manufactures at max -max).

In order to convert electric motor power to hydraulic motor power you must convert the electric motor torque. This will give the equivelent torque at the equivelent rpm.

At different rpms the hydraulic motor will "show" torque as pressure This torque is the required torque to do the job applied which is limited by the system pressure (note: some hydraulic motors can develope full torque at 0 rpm with no damage!)(Note: output can be limited by pressure and can be lowered by lowering system pressure)

There may or may not be readily available software to do this, but it can be done pretty easily anyway with basic equations relating torque, rpm, and horsepower to each other (in whatever units you need). This is just a matter of fundamentals.

Thank you all for your comments. I am going to put togather maybe a spreadsheet with the basic equations and see how it works out.

Thanks you all again

-ashraf