Oscillation saves lives

How pneumatic logic is being applied to helping wounded people breathe without electric power.

A gas-powered ventilator uses only the energy available in a compressed gas bottle to keep injured patients alive in emergency situations where electric power and major medical facilities are not available. Fully controllable by turning valve knobs, it also an example of how automation functions can be achieved and controlled purely by using pneumatic logic. It has been developed by Parker's KV Division and has a base made of moulded, aluminium filled polyurethane, with surface-mounted or embedded valves depending on exact requirements. Its sole power source is a bottle of compressed air. Air from the bottle is admitted to a reservoir, where it builds up until the pressure causes a valve to switch, initiating inspiration (breathing in). The rate of pressure build up is controlled and adjustable. The system has a downstream flow control valve that delivers gas at low pressure to the patient. This is calibrated along with the inspiration time to control the tidal volume of delivered gas. A patient pressure relief valve limits any over pressure if the patient's airways are blocked. Expiration is initiated when air from the gas bottle fills a second reservoir until a second valve opens. No pneumatic suction is applied. Expiration depends only on the natural compliance of the lungs. This phase is typically 1.6 to 2 times longer than the inspiration phase. Breaths per minute and tidal volume are adjusted by turning valve knobs. The modules are designed to give a constant inspiration to expiration ratio over a range of breathing rates and airflows. When asked whether this was relevant to more traditional automation problems, Clive Schofield, country manager and market development manager life science for Parker's KV Division responded: "Historically, many different applications can use pneumatic logic, but it is now generally integrated with electrical solenoid control. Pure pneumatic logic is now generally confined to systems where there is either only a gas supply such as emergency ventilators or aircraft safety systems; or systems that need to be intrinsically safe, with no electrical switching. "We currently supply this type of system to customers in the aerospace maintenance market, for portable fall arrest safety systems, and the bulk tanker delivery market. These systems rely upon having no electrical supply either available or permitted for safety reasons. The applications require pneumatic logic and timing functions to switch valves at pre determined intervals".