Hello. if i decided to build a compressed air engine based on rotary vane pump, it would have to withstand very high pressures and have as little friction as possible. i'm talking about a cylinder, 4" in diameter and 1/2" long. this thing should work on pressure difference of cca. 150 bar (450 in - 300 out). the problems i see, are: 1. bending stresses on vanes this is not really a problem, i guess. vanes could be ridiculously thick and short (with making the inner rotating cylinder large enough compared to the housing thus reducing the bending moment). increasing the number of vanes would also reduce it. 2. friction i guess the greatest losses would be caused by friction between the vanes and the rotor. i'm thinking of putting the vanes "on wheels" - see sketch. 3. sealing that's a topic i'm not familiar with at all. how are modern vane pumps made? what about rubber seals (hydraulic/pneumatic)? i've also heard of metal-on-metal seals that are nothing but two smooth and flat surfaces touching each other. they have a little leak, but that's just what keeps them "sealed". there could be just two touching metals and grease between. how good would that be? i could also glue an elastic bag into every compartment and put it on a metal plate with rollers where it would have glided otherwise. this would greatly reduce the number of spots where leaks could have occured. keep in mind there's never a full 150 bar difference on one seal since pressure drops gradually through a number of vanes.