Labconco Protector Controlled Atmosphere Glove Boxes 5080102 - Manual (Page 22)

NORMAL OPERATION
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C. The Labconco CA Glove Box is designed to operate in the range of +6 to –6 inches of
water pressure (gauge). With such a relatively small amount of pressure/vacuum setting,
outside factors can and will alter the working pressures in the box. To overcome these
factors, the Pressure Control Module will maintain the desired pressure differential with the
surrounding atmosphere. Those factors that cause change in the gauge pressure inside the
box are:
Inside temperature changes Atmosphere/Room pressure changes
Movements of the Gloves Leaks in the box
Temperature Changes in the Glove Box – The expected pressure changes due to
temperature fluctuations within the box will be in the order of 0.5 inches of water per
degree F temperature change, (at 70F). The difference from theoretical calculations can be
explained by the change in volume via moving walls and compression of the gloves. In
addition to ambient variations, any electrical equipment or endo/exothermic processes
present in the box will result in a change of gauge pressure.
Atmospheric or Room Pressure Changes – There is a direct correlation between the
atmospheric pressure and the gauge reading on the box. The indicator on the box is “gauge
pressure”, the difference from inside the box to atmospheric pressure. So, for each 1" of
mercury change in barometric pressure, there can be a change up to 13 inches of water
pressure. Pressures exerted by HVAC systems are usually small in comparison to the other
factors listed here.
Movement of the Gloves – It is readily apparent that whenever the gloves are moved, the
change in volume is sensed by the pressure gauge. Set the pressure High/Low limits at
sufficient range to accommodate normal movement within the box. You will hear the
solenoid valves energize as the pressure indicator moves beyond the limit set points.
D. Functional descriptions of the pressure control module switches and indicators are shown
on the following page.