SPI Supplies

SPI Critical Point Drying Apparatus

Detailed Description of the Apparatus and Service Information: Thermometer and pressure gauge
Construction

The thermometer is of the bimetallic type and measures the temperature of the brass wall of the pressure vessel. The sensing head of the thermometer does not break through into the water jacket or the pressure vessel.

The pressure gauge is a 0-2000 psi bronze tube Bourdon type gauge. By special arrangement with the manufacturers, the gauges are calibrated using methyl alcohol rather than the usual mineral oil. Hence, your system is assured of an oil-free contamination environment from the very beginning.

The pressure gauge is fitted into a ¼" BSP port in the pressure vessel; the pressure seal is a fiber washer.

Servicing

To remove and refit thermometer:

  1. The thermometer is screwed into a plug which is a push fit in the wall of the pressure vessel. The thermometer and plug (with compression O-ring) are removed as an assembly by rotating and pulling.
  2. Before refitting, grease the O-ring slightly.
  3. Should the thermometer fail to operate, first check it in water against a mercury thermometer. If malfunctioning, return to factory for replacement.
Note: There is a slight thermal lag between the true temperature inside the vessel and the reading on the thermometer if the heating or cooling is carried out rapidly. Using a thermal transfer grease between the thermometer stem and the pressure vessel will decrease this lag.

To remove and refit pressure gauge:

  1. Find a well-fitting wrench (spanner in some countries) for the nut on the stem of the gauge. We have found this size to be somewhat variable but is approximately 15 mm. Do not use a loose wrench on this nut or attempt to rotate the head of the gauge if the fit it not tight.
  2. Unscrew the nut and remove pressure gauge.
  3. Replace fiber washer before replacing gauge.
  4. When tightening seal after refitting, use a torque of at least 20 ft.lb. It may be necessary to use different thicknesses of washer (or a number of washers) before getting the correct pressure on the seal and have the gauge facing the correct direction.
  5. In case of gauge failure, return to SPI Supplies for replacement.

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Sunday October 12, 2008
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