Chamber FAQ

What is an expansion valve?

ESPEC’s new Platinous chambers have a lot more going for them than a cool touch-screen programmer.  They have an electronic expansion valve—the first in the U.S. to do so.  Let me explain what it does and why it makes a better chamber.

An expansion valve is used in a refrigeration circuit to change the refrigerant from a compressed liquid to an expanded gas.  As it expands to a gas, it draws energy, causing a cooling effect.  For more about how refrigeration works, see: http://www.howstuffworks.com/refrig.htm

Environmental chambers typically use a solenoid valve for the expansion valve.  It is “clicked” open and closed depending on the cooling demand, as judged by the system controller.  Because it can only be open or closed, the controller must cycle the valve in order to maintain the temperature. This is hard on the rest of the circuit.  Electric heaters, whose output can be varied, rather than cycled, are simultaneously used to control the temperature.

ESPEC had used a capillary tube instead of a solenoid valve for our Platinous models.  The diameter of the capillary tube is selected to optimize cooling for that specific circuit.  Heating is then solely used to control the temperature.  This provides for fine control tolerances, since there are no sudden blasts of cooling.  It can limit performance, however, and is not especially efficient.

An electronic expansion valve is the best of both worlds.  The opening of the valve can be adjusted, via an integrated stepper motor.  This allows 440 increments of adjustment for the refrigerant flow.  Now we have the ability to adjust the cooling without stressing the refrigeration system, plus less heating is needed.  The result is a more reliable and efficient test chamber.

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