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23. While the cell is heating up to the desired temperature, open the inlet ball
valve and apply the amount of pressure indicated in the “Recommended
Minimum Back Pressure” table.
Recommended Minimum Back Pressure
Test Temperature Vapor Pressure Minimum Back Pressure
°F °C PSI kPa PSI kPa
212 100 14.7 101 100 690
250 121 30 207 100 690
300 149 67 462 100 690
350 177 135 932 160 1,104
400* 204 247 1,704 275 1,898
450* 232 422 2,912 450 3,105
500* 260 680 4,692 700 4,830
*For tests above 400°F, use Teon o-rings.
While the cell is heating, the pressure inside will rise due to the thermal
expansion. Use the pump to release hydraulic oil and prevent over-
pressurization. Maintain the pressure on the uid until the desired tem-
perature is stabilized, as indicated by the thermometer. Use the hydraulic
pump’s pressure release valve to regulate and maintain the pressure.
The heating time of the sample should never exceed one hour.
When working with heated pressurized vessels, always wear protec-
tive safety glasses.
Excessive pressure puts stress on four main areas of the cell:
1. End cap bending - may be observed either by eye or by measure-
ment
2. End cap compression - may be observed as deformed or bent
threads
3. Cylinder shear - elevated areas along the end of the cell bodies
4. Cylinder stress - stress cracking or severe pitting will appear on
the cell body
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