Cylinders, valves and outlet fittings for air are generally made from brass for corrosion resistance in the marine environment.

[4][3] Flow of air through the helmet could be controlled by manually adjusting the back-pressure on the helmet exhaust valve, usually on the lower right side of the bonnet, and by manually adjusting the inlet supply valve on the airline, usually fastened to the front lower left of the corselet.

Manual pumps would be operated at the speed necessary for sufficient air supply, which could be judged by delivery pressure and feedback from the diver.

[6] Vertical lever pumps with bell-crank operation were also made, usually for shallow water work.

The Anthony and Yvonne Pardoe Collection of Diving Helmets and Equipment – illustrated catalogue (PDF).