Motor system set up help needed............

[info_man1]

Would like to use a hydraulic motor to drive/turn a shaft that will require up to 20 hp.
The hydro motor shaft must have a max rpm of 3,500 but I would like to be able to control the rpm.
The device I am trying to drive with this set up is belt driven and requires 15 hp to do it under full load.
A pulley on the hydro motor will connect the belt to the pulley on the drive device.
Not sure about the input/output spec..... please use/suggest what you believe is best.


Doug Hanson asked.......

In no particular order, here are a few questions for you:

What is your final desired output?
20 hp

Then, what drive belt ratios do you have?
Hydro motor pulley is 6.75", drive device pulley is 3.0"

Then what prime move do you have to run your pump?
I don't know what that means.

Then what pump do you have? Existing or must be purchased?
Must be purchased.

Then what system pressure do you want to design around?
The minimum required to accomplish this project.

There a many more questions, but most importantly, How much money do you want to spend?
The minimum amount of course.

[Doug Hanson]

20 HP and 3500 RPM = 30.011 ft/lbs of torque
with a starting design pressure of 2000 psi, a theoretical motor displacement of 1.1314 cui/rev is required
a theoretical flow of 17.14 gpm is then required, but to make up for flow losses and inefficiencies, bump that up to 19 gpm.
With a 2.25 to 1 ratio, that should give you a final drive speed of 1556 rpm.
Now to provide that flow, we need to know what you have in mind for a prime mover: engine or motor and what size and drive speed.
So far to accomplish 20 hp of work we need 22 HP, the inefficiencies of the pump are going to require more power yet.

[info_man1]

Doug......Thanks for your help.

You said:

"With a 2.25 to 1 ratio, that should give you a final drive speed of 1556 rpm."

I am looking for 3,500 shaft speed of hydro motor.......

You said:

"Now to provide that flow, we need to know what you have in mind for a prime mover: engine or motor and what size and drive speed."

A motor......whatever minimum size and speed is required.

[Doug Hanson]

You had written that you wanted a hydraulic motor speed of 3500 rpm and had a pulley on your Hydro motor that was 6.75" diamter, drive device pully is 3". That would put your final output speed at 1556 rpm.
I took that to mean Hydro motor is hydraulic motor and drive device pulley is the end output?

[info_man1]

I did give a pulley size, but I need the hydro motor shaft to have a max rpm of 3,500.

[Doug Hanson]

[info_man1]

[Doug Hanson]

OK, then back to the original arrangement, with the correction for me having the pully ratios backwards.

20 HP and 3500 RPM = 30.011 ft/lbs of torque
with a starting design pressure of 2000 psi, a theoretical motor displacement of 1.1314 cui/rev is required
a theoretical flow of 17.14 gpm is then required, but to make up for flow losses and inefficiencies, bump that up to 19 gpm.
With a 1 to 2.25 pulley ratio, that should give you a final drive speed of 7875 rpm.
Now to provide that flow, we need to know what you have in mind for a prime mover: engine or motor and what size and drive speed.
So far to accomplish 20 hp of work we need 22 HP, the inefficiencies of the pump are going to require more power yet.
So your going electric motor drive, what shaft speed on the electric motor 1750?
What controls do you need? Electrical control or manual control?
You want to vary speed from 0 to 3500, do you need directional change, do you need a nuetral?
How precise does the speed control need to be, do you need to provide feed back to stay within a margin of error?
Will there ever be an over running load? do you need to decelerate a load?
Many many more questions, I have no idea what your trying to accomplish.

[info_man1]

So your going electric motor drive, what shaft speed on the electric motor 1750?

I just need the minimum to for fill this requirement.....what do you suggest?

What controls do you need? Electrical control or manual control?

Manual control.

You want to vary speed from 0 to 3500, do you need directional change, do you need a nuetral?

No........neutral is not required.

How precise does the speed control need to be, do you need to provide feed back to stay within a margin of error?

Does not need to be precise........no feed back required.


Will there ever be an over running load? do you need to decelerate a load?

No over running load.......no need to decelerate.

Many many more questions, I have no idea what your trying to accomplish.[/quote]

I am trying to use hydraulic motor set up to turn a device using a belt on two pulleys.

The device I am trying to turn will require 15-20 hp to turn it under "test conditions".

Traditionally, a 20 hp electric variable speed motor is used to accomplish this task, but I would like to do it with a hydraulic motor set up.

[Doug Hanson]

1750 RPM is the most common shaft speed for 3 phase TEFC motors.
Pump size = 19 gpm / 1750 rpm * 231 = 2.5 cui/rev
You have two options here for control that determines what design of pump to use.
You could use a gear pump and a 3 port flow control, cheaper but will generate heat when throttled down.
or use a load sensing piston pump with a needle valve as a throttle and tie the load sense line in between the needle valve and the hydraulic motor, this makes a pressure compensated flow control that will generate as little heat as possible. The load sensing controller on the pump will also have a max pressure setting so a relief valve would not be required as it would be with the gear pump.

19 gpm * 2000 psi / 1714 *1.1 = 24.387 HP

You could either play it safe and use a 25 hp motor, or you can probably get away with a slight overload on a 20HP motor provided there is enough airflow availabe across the cooling fins of the motor. A steady 10% overload is common, a twenty percent overload should however be intermitant only.

Use a gear type unit for the hydraulic motor.