I haven't been able to find a design manual for a vane motor online. I'm trying to evaluate one a friend built as to its torque, force, and power. I have all the dimension, input pressure, and rpm, and I know how to do all this stuff for piston motors, expansive, partially expansive, and full pressure. I thought vane motors would be easy too but not so.

I know the force is vane area x pressure. I know torque is from vane to shaft center (lever arm) x force. I know work is pressure x volume. But all that is vague, it doesn't really give me the numbers because I still have questions.

Force: vane area x pressure. What is meant by vane area? It can't be adding up the area of all the vanes or else you could double the force by adding twice the vanes. So it has to be all the exposed vane area added together divided by the number of vanes? That's all I can think of, average vane area?

Also, I know that what causes the rotor to spin is differential area, the larger area at front of a chamber that's defined by two vanes will have more force than the smaller one at the back, so it will turn toward the larger area. So it seems that for accuracy, any calculation involving vane area would have to have the smaller area subtracted from the larger? Or no?

One reference seemed to imply that torque is constant throughout the cycle, but that was about hydraulic motors. Would air motors have that same characteristic?

I assume that with a no frills vane motor like my friend made, there would be no expansion to speak of, just dumping air through and exhausting at the same pressure. But when it comes to vane motors, if there was a way for the air to expand, I don't understand what it might be.

Torque is lever arm x vane area x pressure, which is the same thing as lever arm x force. But what part of the vane do you use? Average vane area? As if the rotor were centered instead of eccentric? Area of a fully extended vane / 2? I really don't have a clue on how to do the calculations for a vane air motor, and I've been looking online all day.

I think I have figured out by drawing it and measuring the lines that the maximum extended width of a vane is a complementary sum, in other words, if a vane is only partly extended, a vane exactly across from it would have an extension distance that would add to it to equal the same quantity as the maximum extension.

Thanks.

## Comments rated to be Good Answers:

Re: Rotary Vane Air Motor - Torque, Force, Power" by Codemaster on 08/26/2012 10:08 AM (score 3)## Comments rated to be "almost" Good Answers:

Re: Rotary Vane Air Motor - Torque, Force, Power" by K_Fry on 08/27/2012 2:44 PM (score 1)