[olddog]

Yes. Another difference is that a lobed blower moves air from one side of the case to the other side. The screw compressor pulls air in at the end of the case, them moves the air longitudinally down the screws, and the air exits the opposite end of the case.

The picture you provided is perfect to see that there is a leak path back through where the two rotors inter-mesh. The air is pulled around the outside in the open void in the rotor. Some air slips by between the case and rotor too. This is what limits the pressure capability of the lobed blower. The slippage also adds heat to the air.

Straight lobes are much simple (cheaper) to make, but the air output pulses. They sound similar to a engine running. The twisted rotor gives a much smoother steady flow of air. I was told by an old time racer that they used to time the straight lobe blowers (the twist didn't exist yet) to the engine to get the pulse to hit (I think) just before the intake valve closed to pack more air into the cylinder. I have no idea if that is true.

I have seen Teflon strips added to the rotor tips, in engine applications. This is supposed to seal to the case. Not sure if it is claimed to seal where the rotor inter-mesh. No doubt it makes a big improvement, but I doubt it is a perfect seal. It reduces air temp and increases pressure capability. For industrial use where things tend to run 24/7/365 they wear out too quick. We have none of those.

As for your use of sucking the bullets, we do that on short runs for resin pellets. I'm not sure what the maximum vacuum is, but I'm certain it is way less than 1 atmosphere or no one would bother with water vein vacuum pumps. I would guess 1/3 to 1/2 an atmosphere.

Anyway congratulations on the Toyota. I'm sure it works well for you.