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| Solenoids Used in Medical Electronic Sterilizing System |
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There has always been a need for sterilization of medical instruments, but never more so than now. With the increasing danger of life - threatening viruses such as HIV there is a need for guaranteed sterilization - time after time.
Sterilization in major hospitals and clinics has always been efficient and well controlled using large and small static sterilization stations which guarantee inactivation of all bacteria and viruses. However, this has not always been the case in small private medical and dental practices and in the developing countries of the world where the cost of such equipment has been prohibitive. Traditionally in these situations sterilization employs liquid disinfectants or the boiling of instruments in water at 100 degrees C for 20-30 minutes.
A few years ago, a need emerged for efficient equipment which was simple, portable and cost effective. In order to meet this need, a major manufacturer introduced a portable steam sterilizer. This was in fact a domestic pressure cooker fitted out internally with racks for medical syringes. This unit unlike the normal water boilers was able to operate under pressure and could achieve 121degrees C -123 degrees C which on a 20-minute cycle guaranteed inactivation of all bacteria. This was successful but relied on an external heat source from gas, electric or kerosene stoves and upon manual timing.
With this unit as a basis for forward progress, the medical division of the company was funded to develop a portable automatic autoclave which had a built-in electric heater, a timer and a pressure relief valve to give a capability of sterilization at 126 degrees C in 11 minutes under a pressure of 1.6 bar.
This was achieved and was a major improvement on the first model. However, this unit did not guarantee sterilization as the temperature and pressure were not monitored or displayed and also the unit could be opened before the sterilization period was complete thus contaminating the instruments.
The development was then further funded to produce an electronic bench-top automatic portable autoclave. This latest unit incorporates a 6-position light sequence display which begins when the cycle start button is pressed. The visual display shows -begin cycle, heat up, reach sterilization temperature, sterilization confirmed, end of cycle, safe to remove lid. Two independent safety pressure relief valves provide a greater level of safety. Integral temperature and pressure gages provide visual reference of the operating conditions. A cycle counter provides the recording of individual sterilization cycles. An electromechanical lid interlock ensures the sterilization sequence cannot commence unless the lid is fitted correctly and ensures that once the sequence has commenced, the lid cannot be removed until the sterilization cycle has been completed or deliberately canceled.
In order to achieve the lid interlock, development was done in conjunction with Saia-Burgess using a tubular linear solenoid. It was necessary to develop a solenoid design to accommodate a very limited space availability, a high ambient temperature, a critical spring to solenoid force stroke ratio and suitable mechanical interface.
From a standard pull type tubular solenoid with a clevis plunger, the design evolved to include high temperature PTFE leads terminating in a 2-way connector and with a custom designed plunger fitted with a stainless steel pin to interface with a plate catch. This design is currently fitted to the existing production portable sterilization unit
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