Having bought a compressor, a bloke soon gets fed-up with just pumping air and builds a nitrox stick. But this also starts to get a bit dull after a while. So, I built an 'omnibooster'. I first read about this on The Deco Stop forum many years ago and decided to have a crack at my own. Basically, it's a device to move gas from one cylinder to another, completely scavenging the contents of the source vessel. This is particularly valuable with helium and trimix. The compressor is fed by a first and second stage attached to the source cylinder and the partial vacuum at the intake operates the second stage in more or less the same way as a diver would with his/her gob. The exhaust of the 2nd stage is blocked-off and the regulator is set to gently free flow in order to help the compressor breathe properly and avoid it working too hard. A buffer chamber is included downstream of the second stage, in order to prevent the diaphragm getting trashed by the compressor's rapid 'breathing'. Mk1 of this used a balloon but I now use a piece of 4" PVC pipe with some cuttings from a car inner-tube at either end and a t-piece cemented in the middle. Coincidentally, the intake of the Bauer PE100 is the same size as the tapping drill for ½" BSP So I cut a thread in it for an adaptor that can hold the nitrox stick and the new device: Behold: This works a treat and, to make sure I wasn't stressing the compressor, I built a manometer which I hooked-up to the small intake tube that the compressor's overpressure scavenging tube (visible in the second & third photos) feeds back into. This confirmed that the compressor wasn't sucking too hard and was breathing freely. I can now move any gas up to 40% O2 around without wasting any. Happy days!