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Multi-Vane Air Motor Occasionally Won't Start

Multi-Vane Air Motor Occasionally Won't Start

Multi-Vane Air Motor Occasionally Won't Start

Hi All

I need some outside expertise diagnosing an odd issue.  We have designed a tool that uses a multi-vane compressed air motor.  (http://www.irtechpubs.com/ir_pdfs/Air%20Motors/Air%20Motors/Vane%20Motors/04562716_ed3.pdf)

We have started this motor hundreds of times, but twice this year (with two different motors), the motor failed to start when we pressurized the inlet (under little load).  Both times, air could be seen to be blowing out the muffler, so presumably the vanes were being bypassed, and both times the motor was able to restart after we manually rotated the shaft a little.

Unfortunately our tool may not be accessible during startup, and the risk of failure to start is worrisome.  Is this common to this type of motor, and if not, should I be specifying another option or type?

RE: Multi-Vane Air Motor Occasionally Won't Start

It's a plague with that type of motor; for various reasons, the vanes stick in the inboard position, and the air goes around them.

Preventive measures that work long enough to say they work, and not long enough to make the motor reliable, include:

- carbon vanes
- vanes coated with dry nonstick lubricating material
- lubrication, applied internally or externally, or atomized in the air
- springs pushing the vanes out
- intentionally coarse finishes on the vanes or the rotor in the hope that air will get into the cavity at the vane root

and probably some other features that I haven't noticed.

For metal vanes in a metal rotor, the best I've been able to do is an occasional drop of Marvel Mystery Oil in the air supply.  ... and that still doesn't always work.


Mike Halloran
Pembroke Pines, FL, USA

RE: Multi-Vane Air Motor Occasionally Won't Start

That's a great answer Mike, but it's bad news for me.  

My air supply is furnished with a filter/lubricator, so I'm not sure I can do any more that way.  Maybe I should look for a vane motor with springs.   Do you know of any in the 1 HP range?

RE: Multi-Vane Air Motor Occasionally Won't Start

I notice a requirement for a flush with solvent and spindle oil every 40 hours.  If there are no warranty issues, consider using MMO in the FRL instead of spindle oil; it already contains a solvent.

I don't know if any motors with spring vanes are available in that size.

Can you arrange for the motor to be cycled regularly so that it stays lubricated and the lube doesn't get a chance to gum up?


Mike Halloran
Pembroke Pines, FL, USA

RE: Multi-Vane Air Motor Occasionally Won't Start

in addition to Mike's excellent list, add pressurization through the spindle, and into the vane cavities.  While this method worked for us in ensuring a start, it will also cause more rapid vane tip wear.

RE: Multi-Vane Air Motor Occasionally Won't Start

I'm still learning and trying new things.

I had some issues with the veins rusting or sticking on some air motors for me recently.

What if..

There was a valve on the exhaust side, and you just close the valve when the motor isn't running.    On the inlet side, I'm using there's some FRL system there, so it'll keep that side dry too..

Or perhaps, setting the regulator to 1-2 psi, so that the inside of the motor/veins were always under positive pressure.

RE: Multi-Vane Air Motor Occasionally Won't Start

It would take more than pressurizing the motor to force the vanes out - you need some pressure difference between the root of the vane cavities and the cylinder.  Your idea might work if there were no valve on the exhaust and  you keep the inlet air above some minimum pressure (I've heard 40 psi from one manufacturer as a minimum for pushing out the vanes).  In this case, you would need some sort of brake to stop the motor, and you would be always consuming some air.

My current plan is to go with the Deprag "advanced line" motors which include vane springs.  (These are more expensive, and they might introduce their own problems down the road with fatigue - we'll see).

RE: Multi-Vane Air Motor Occasionally Won't Start

Vane-type airmotors need to spin to throw the vanes out to keep running.  It may help if you could orient the motor so that the housing eccentricity was down; gravity down, shaft horizontal.  Then the vanes would come to rest extended and better catch the incoming starting air and get the rotor spinning.


RE: Multi-Vane Air Motor Occasionally Won't Start

"It may help if you could orient the motor so that the housing eccentricity was down"

We looked at this.  The vanes are so light, and the surface area between the vanes and their slots is so large that the shear force from the lubricant is more than enough to keep the vanes from falling out under their own weight, even when shaking vigorously.  It wouldn't matter what orientation the cylinder was in with respect to gravity - the vanes tend to stay bottomed out after they pass the narrow part of the cylinder unless pushed out by air pressure, springs or centrifugal force.

(Plus, in our motor, the cylinder is assembled inside the motor body without any kind of angular locating feature, so we can't know which orientation the eccentric is in).

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