Abstract: A disc for use in a pneumatic valve includes a stiffening insert encased in a flexible body. The stiffening insert acts to protect a central actuation region of the disc against radial compression, which may arise if the disc is used to seal against a bore hole, and against material flow towards the actuation region away from a clamped periphery. The behavior of the disc in a valve assembly is therefore more predictable and reproducible. The flexible body may further be tensioned across the stiffening insert.

Abstract: A demand valve for gas mixing comprises two or more flow control valves that are connected to separate gas supplies. The demand valve includes a common actuation mechanism, such as a diaphragm arranged to displace levers, each of which, in turn, opens and closes proportionally in a substantially constant ratio a respective flow control valve. Inhalation flow drawn through an outlet causes displacement of the diaphragm and hence opening of the flow control valves. Gas from the separate supplies is therefore mixed in a main chamber to a substantially constant composition, regardless of the flow rate demanded, before being dispensed via the outlet.

Abstract: A demand valve for gas mixing comprises two or more flow control valves that are connected to separate gas supplies. The demand valve includes a common actuation mechanism, such as a diaphragm arranged to displace levers, each of which, in turn, opens and closes proportionally in a substantially constant ratio a respective flow control valve. Inhalation flow drawn through an outlet causes displacement of the diaphragm and hence opening of the flow control valves. Gas from the separate supplies is therefore mixed in a main chamber to a substantially constant composition, regardless of the flow rate demanded, before being dispensed via the outlet.