Laymans help on motors

[woodlandfarms]

I am struggling with a concept and wondered if someone could put it in simple terms.

I want a motor that goes 540 RPM. I have 3000 PSI and 18GPM.

I start to look at motors and there are a bunch that do this, but at various cubic inches.

So, now am so friggin confused. If a motor does the the RPM's I want, at the GPM I have and PSI I push, why do I care about the cubic inches? I know there is a reason, but I am struggling with this theory.. I assume it has to do with Torque, but it seems the torque numbers are the same as well...

 

[Eagleview]

The cubic inch capacity of a hydraulic motor per revolution is directly related to how many revolutions it will turn with the amount of oil your machine can deliver per minute . In simple to understand terms , if a motor has a 10oz per revolution capacity and your machine can deliver 1000oz's per minute at a given speed , the motor will turn 100 times .

 

[J_J]

The cu in of the hyd motor will determined the speed with a certain GPM. The pressure will determine the torque. You need so many HP to run the hyd driven implement. If you have 18 GPM, from the pump at 3000 rpm, the pump has a displacement of 1.4 cu in. It takes about 37 HP from the engine to do this work.

Now, the hydraulic motor, using this same 18 GPM at 3000 psi, will turn a hyd motor at 540 rpm if the motor displacement is 7.6 cu in. There is an efficiency loss from the force of the pump to the motor of about 85%, so therefore, the hyd motor on the implement will develop a force of about 31.45 HP

What you need is a hyd motor that runs at 540, with 18 GPM , displacement of 7.63 cu in, and will generate the torque you need to operate the implement. Something like this

https://www.surpluscenter.com/item.asp?UID=2009113007472532&item=9-7081-125&catname=hydraulic

 

[J_J]

Carl,

To add to the above post. I believe you have a solenoid on your machine for the PTO, that applies the full pump GPM. On the other hand, on my PT, I have a speed control, which is simply a lever type valve for varying the speed of the hyd motor, by allowing only so much fluid to the hyd motor. The rest of the supply fluid is routed back to tank. If you look at these hyd motors about 5.3 cu in and above, they turn in a certain rpm range. As you increase displacement, the rpm decreases. If you want a fast rpm motor with the same 18 GPM, the displacement will be lower, like 1 to 3 cu in. A 2 cu hyd motor, using 18 GPM will turn at 2,079 rpm. Higher pressure, higher torque.