Operating Instructions for
Electric Pressure-Building Systems

To avoid damaging container and/or heating element, turn power off immediately after transfer is complete. Never operate the electric pressure-building system in any empty dewar or in open air.

Single Set Point Models

Prepare the dewar for normal withdrawal as described in Operating Instructions for Model CMSH Multishielded Liquid Helium Containers. Plug power cord into an appropriate outlet and turn power switch on. Pressure in dewar will start to rise shortly. If the transfer line has no shutoff valve then liquid will start to flow as soon as the pressure in the dewar rises to a sufficient value. The pressure will continue to rise until it reaches the nominal set point. A built-in pressure switch will automatically maintain the pressure at the set point for the remainder of the transfer. When the dewar is empty, turn off the power and unplug the power cord.

NOTE

When the electric pressure-building system is operated in a full dewar the pressure may build very rapidly upon initial turn-on. Even though the heating element is automatically switched off at the set pressure, there may be a pressure overshoot. This is normal. As transfer continues, the pressure should drop down near the nominal set point and oscillate slightly for the remainder of the withdrawal.

Dual Set Point Models

Operation of the dual set point model is similar to the single set point model, except that an extension cord must be plugged into the power inlet on the left side of the control box in order to power the unit. In addition, the transfer pressure can be selected via the selector switch. The middle position of the selector switch is the “off” position.

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