Market Forge Industries STM-EX Service Manual download pdf (Page 6)

SEPTEMBER 26, 2014 6 STM-E, STM-EL, STM-EX & STM-ELX STERILIZERS

PRESSURE ACTUATED TEMPERATURE CONTROL

STM-E AND STM-EL

The pressure actuated temperature control, located be-

hind the control panel assembly, governs the manufac-

ture of steam by controlling the input of electric current to

the heating elements.

HOW IT WORKS

When the Timer is set, rear and front contactors will be-

come energized allowing input of current to the tempera-

ture control, thus closing the contacts completing the

current to the heating elements. Steam will then be gen-

erated within the sterilizing chamber.

The steam pressure within the sterilizing chamber is

transmitted by means of a tube to the bellows of the tem-

perature control; as the steam pressure increases, its

compression action on the bellows is set to cause the

Switch #1 on the control to cut out on rising pressure at

13.5 PSI and to cut in on falling pressure at 13 PSI (con-

trolling the two outer banks of heating elements). Switch

#2 is set to cut out on rising pressure at 15.5 PSI and cut

in on falling pressure at approximately 15 PSI (controlling

center heater element only).

Thus, a balancing effect of steam pressure build-up and

heater element current is constantly maintained during

the sterilizing cycle. When the Timer signies the end of

the cycle, the electric current to the contactors will auto-

matically be broken; the temperature control contacts will

be broken; and steam generation will stop.

ADJUSTING THE RANGE OF OPERATION, STM-E

NOTE: These instructions should be performed by

qualied service personnel only.

The operational range of the temperature control is fac-

tory set as follows: Outer bank of elements OFF at 13.0-

13.5 PSI; Center bank of elements OFF at 15.5- 15.0 PSI;

minor compensating adjustments can be made by turning

the adjusting screws counter-clockwise to increase pres-

sure and clockwise to decrease pressure. Both screws

should be turned the same amount when making an ad-

justment.

NOte: When resetting this control for elevations above

sea level a correction of 6/10 Ib. per thousand

feet is necessary.

1. Before making adjustments, shut all electrical current

to the sterilizer OFF to eliminate shock hazard.

2. Remove the Flue Cover.

3. Make sure that all exposed wires are not in a hazard-

ous position, and then turn on electrical power.

4. Run unit through cycle, observing pressure and tem-

perature gauges, turn adjusting screws as required.

Figure 5

CHECKING THE 230° SETTING, STM-EL

The Unit should be completely evacuated then tempera-

ture selector dial should be turned on 230° Fahrenheit.

Observe the current until it takes a sharp drop to ap-

proximately one-third of the full load; at this instant, there

should be a corresponding chamber pressure of 2 PSI

Observing the current further will show another sharp

drop to approximately 2 Amps; at this instant, there should

be a corresponding chamber pressure of 6.1 PSI and a

temperature reading of 228° to 232° Fahrenheit, on the

temperature gauge.

ADJUSTING THE RANGE OF OPERATION

STM-EL

The range of operation of Model STM-EL is adjusted by

simply turning the adjusting knob on the outside of the

Control Panel. A counter-clockwise turn decreases the

pressure while a clockwise turn increases the pressure.

Observe pressure and temperature gauges and adjust

knob as required.

NOTE: When resetting this control for elevations above

sea level, a correction of 6/10 Ibs. per thousand

feet is necessary.

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Market Forge Industries STM-EX Service Manual Page 6

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