Figure 4-10. Test of low pressure cut-out switch

TM 5-4120-356-14

TEST

REFER TO PARAGRAPH 4-13b FOR PRELIMINARY STEPS IN MAINTENANCE OF THE LOW

PRESSURE CUT-OUT SWITCH.

2. CONNECT A CIRCUIT TESTER ACROSS THE ELECTRICAL CONTACTS OF THE LOW PRESSURE

CUT-OUT SWITCH.

3. SET THE CIRCUIT TESTER UP FOR CONTINUITY TESTING.

4. CONNECT A SOURCE OF VAPORIZED NITROGEN TO THE CAPILLARY TUBE FITTING OF THE

SWITCH. NITROGEN SOURCE MUST BE EQUIPPED WITH A GAGE CALIBRATED FROM O TO 50

PSIG (0 TO 5 ks/cm2).

5. WHILE OBSERVING CIRCUIT TESTER, APPLY 20 PSIG (1.4 ks/cm2) NITROGEN PRESSURE

TO THE SWITCH. CIRCUIT TESTER SHOULD SHOW NO CONTINUITY.

6. WHILE OBSERVING CIRCUIT TESTER, SLOWLY DECREASE NITROGEN PRESSURE. SWITCH

SHOULD TRIP (CIRCUIT TESTER SHOW CONTINUITY)2 WHEN THE NITROGEN PRESSURE IS

DECREASED TO 12 TO 2 PSIG (0.14 TO 0.84 ks/cm ).

7. IF SWITCH DOES NOT TRIP, REPLACE SWITCH.

8. IF SWITCH TRIPS BETWEEN 12 AND 2 PSIG (0.14 AND 0.84 ks/cm2), INCREASE PRESSURE

TO 20 PSIG (1.4 ks/cm2) AND PUSH THE RESET BUTTON. CIRCUIT TESTER SHOULD AGAIN

SHOW NO CONTINUITY.

9. IF SWITCH TRIPS BELOW 2 PSIG (0.14 ks/cm ) OR ABOVE 12 PSIG (0. 84 ks/cm ), THE

SWITCH MUST BE CALIBRATED. TURNING THE CALIBRATION SCREW CLOCKWISE INCREASES THE

PRESSURE AT WHICH THE SWITCH WILL TRIP. TURNING THE CALIBRATION SCREW COUNTER-

CLOCKWISE DECREASES THE PRESSURE AT 2WHICH THE SWITCH WILL TRIP. CALIBRATE THE

SWITCH TO TRIP AT 7 PSIG (0.49 ks/cm ).

10. IF SWITCH CAN NOT BE CALIBRATED AS IN STEP 9, REPLACE THE SWITCH.

11. DISCONNECT THE CIRCUIT TESTER LEADS FROM THE SWITCH CONTACTS AND DISCONNECT THE

NITROGEN SOURCE FROM THE CAPILLARY TUBE FITTING.

12. REFER TO PARAGRAPH 4-13b FOR FINAL STEPS IN MAINTENANCE OF THE LOW PRESSURE CUT-

OUT SWITCH.

TS54120356-14/4-10

F i g u r e 4-10. Test of low pressure cut-out switch