Boekel Scientific 25515016 Cement Autoclave - Manual (Page 7)

4.3 Heating Period
1) Note the time and read the temperature indicated by the thermometer.
2) Turn on the heating current by snapping all three switches to the ON position (right).
The heater has two separate sections, each controlled by a snap switch. A pilot lamp
adjacent to each switch indicates which section of the heater is operating.
3) There will be very little evidence of a temperature rise during the first five minutes.
Thereafter, the thermometer at the top of the autoclave will show a rapid temperature
rise, indicating approximately 200° F after approximately 20 minutes. During this
period air will be forced out of the cylinder through the open vent valve. After the air
has been expelled, steam will begin to appear and finally to escape as a fine jet.
When this occurs, perform the following operations:
a) Close the vent valve firmly by hand. (Do not use wrench or pliers for closing). If
foreign matter gets on the valve seat it may cause the valve to leak. The matter
can usually be blown out by opening and closing the valve several times. The
packaging nut on the valve stem should be moderately tight to prevent excessive
stem wear.
b) Remove the thermometer and insulated cover. Tighten the bolts gradually and
evenly for the second time, proceeding around the bolt circle three or more times
to achieve uniform clamping pressure of each bolt against the cylinder head and
gasket.
c) Replace the cover and the thermometer, and continue to check the temperature
and pressure at five minutes or shorter intervals, as desired.
4) Soon after the vent valve is closed, the gage will indicate the development of steam
pressure, first slowly, then more and more rapidly until it indicates a pressure of
about160 PSIG. During this period the temperature of the steam, indicated by the
thermometer will also rise, reaching approximately 370° F (at a pressure of 160
PSIG). When this condition is attained, perform the following operations:
a) Turn off heater #2 by snapping its switch to the OFF position. LEAVE THE MAIN
SWITCH ON.
This lowers the heating rate and brings the autoclave temperature to the desired
pressure of 295 PSIG without an overshoot of more than 10 PSIG. Without this
reduction in heat input at the proper time, it is possible to overshoot 10° to 15° F in
temperature and 30-50 PSIG in steam pressure, even though the regulator cuts off
all current at 295 PSIG. The overshoot would be unavoidable due to the heat
capacity of the apparatus. With switch #2 in the OFF position, only one of the two
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