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hydraulic motor question...

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Topic: hydraulic motor question...

Posted By: Wes (VA)
Subject: hydraulic motor question...
Date Posted: 03 Jan 2011 at 11:23pm

Looking at getting a hydrostatic pump that is rated at 1425 psi and 6 GPM. I've found a motor that is rated at 1400psi and a GPM of 15. How will this setup perform? Will I still have the same amount of torque with just less speed? Thanks, -Wes

Replies:

Posted By: M Diesel
Date Posted: 06 Jan 2011 at 5:02pm

Basically yes. Pressure = force, flow = speed. You will get a max of 6/15 or 40%, barring any non linearity of the pump or motor.

Posted By: dadsdozerhd5b
Date Posted: 06 Jan 2011 at 8:27pm

are you looking for a pump or motor? in your post you listed both. what are you trying to do with it? most hydrostatic pumps are variable flow pumps, not putting out flow in neutral and max flow at full speed. motors require needed rpm to size correctly. pressure and flow are also parts of the equation. basically, the slower the motor turns, the more torque it has but also the more pressure to turn it. higher rpm motors require less pressure to turn. hope this helps

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HD5B, HD5G, (2) FARMALL A's, CUB. DO IT RIGHT THE FIRST TIME, IGNORE THE LAUGHTER. FLANNEL IS ALWAYS IN STYLE.

Posted By: Wes (VA)
Date Posted: 07 Jan 2011 at 9:06am

I'm wanting to match a motor up to the hydrostat pump I found with the above specs. Then I found the motor with the above specs and wondered how they would perform together. Sounds like with that combination I'd have to run a sprocket big enough for 'top end' but then I wouldn't have any grunt power. Guess I need a motor thats a little better match. All I'm saying is that its going in a fun machine..lol -Wes

Posted By: Coke-in-MN
Date Posted: 07 Jan 2011 at 9:41am

A variable speed hydro-stat uses a movable swash plate on the piston pump to control the volume and the direction of fluid. Cu. in. of oil per rev. also they have torque rating at a certain PSI.

I uses a piston pump (Vickers) with set swash plate as a brake on industrial feed rollers where payout of material had to be tensioned. By using a variable relief valve I could set pressure on the output of pump giving brake effect with only small amount of heat generated as a by-product. Ran that unit and several others for 15 years with only yearly oil Change as maintenance needed.

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Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."

Posted By: Brian Jasper co. Ia
Date Posted: 07 Jan 2011 at 11:21am

Seems like I read somewhere that the hyd motor's life would be extended greatly if it wasn't operating near it's max pressure. I think it maybe was on Northern Hydraulics web site.

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"Any man who thinks he can be happy and prosperous by letting the government take care of him better take a closer look at the American Indian." Henry Ford

Posted By: Butch(OH)
Date Posted: 07 Jan 2011 at 12:12pm

When it comes to hydraulic design and trouble shooting so much BS is posted as gospel I normaly just keep my trap shut and go on but you seem to have a handle on things by the way you asked the question so here it goes.

Taking away losses and assuming 100% eff your motor shaft is going to run at 40% of the pump input speed. This is simply figured by dividing your pump GPM (6) by the motor GPM (15) as Mdiesel stated. Not one bit differant than a chain drive with 6 teeth on the drive sprocket and 15 on the driven or a gear drive same number of teeth or a v-belt drive with 6" and 15" pulleys, figuring approxamate speed is dead easy. With hydraulics your loss changes with loading, fluid viscosity, wear etc. Standard tables exist for calculating or use Mfgs spec sheets when critical. Torque multiplication is the same, GPMs, number of gear teeth or sheeve size all the same type calculation. Again figuring zero losses for sake of simplicity your torque gain will be the driver torque x (15x6) or 2.5. As an axample if your driver runs 2000 RPM and has 10 ft lbs of torque your motor shaft is going to be running 800 RPM (2000 x .40) with a torque of 25 ft lbs (10 x 2.5) again hydraulic losses wil change these figures just a bit.

HP is a factor of the drivers capibilies and is NOT changed by the drive no matter how much you speed up or slow down the drive, man I get tired of reading that, LOL.

Posted By: Coke-in-MN
Date Posted: 07 Jan 2011 at 12:31pm

Heard or seen somewhere the hyd equation on a hydrostatic drive was 85% efficient at transmission of power from drive to driven.

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Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."