LEAK DETECTION :

1) ELECTRONIC LEAK DETECTOR - Most sensitive and accurate. Most commonly employed principles are the semi conductor, ionisation or corona formation and infra red detection.

The detector contains an internal pump that draws air into a probe or tube. If refrigerant gas is present in the sample, the electrodes in the sensing element generate a current, and an output signal is obtained.

High pressure cut out

Danfoss type LP controller

ELECTRICAL CONTROL SWITCH

In modern refrigerated cargo installation, leak detection sensors fitted in the hold and machinery spaces activate audible and visual alarms located in the control room in the event of a refrigerant leak.

2)  LEAK DETECTION TORCH - This method is based on the colour of a flame that
surrounds a glowing copper element. The flame turns blue - green ; if the air being consumed
contains the refrigerant. These torches should only be used in well ventilated spaces and
must not be used to search for combustible gas leaks.

3)  SULPHUR CANDLES - The lit candles, indicate the presence of ammonia gas by
giving off a cloud of dense white smoke.

4)  LITMUS PAPER - The paper when wet, indicates the presence of ammonia gas
by change in colour, e.g. red litmus turns blue.

The flexible bellow is connected to the Lub Oil Pressure line. A pressure increase tends to empand the belloow which tries to push the lever up but opposed by the range adjustment spring. The motion of the bellow due to changes in pressure is transmitted through the lever to open or close electrical contacts. A small permanent magnet ensures that the contacts open or close with a snap action so that damage by arcing is minimised:

When the Lub. Oil Pressure is normal, the upper contacts are closed and engine runs without any alarm. When the Lub. Oil Pressure falls below a predetermined value, the upper contact opens and an alarm sounds after a small time gap. When the Lub. Oil Pressure falls below minimum limit, then the bellow collapses and the lower contact closes which in turn shuts off the fuel oil solenoid valve stopping the engine.

LUB OIL LOW PRESSURE ALARM & FUEL TRIP RELAY CIRCUIT

Electrical control circuit for refrigeration systems :-

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