Product Overview

Table Of Contents

Functions

Figure 1: Electrical diagram

Danfoss

60B55.13

If there is no oil pressure on starting, or if the oil pressure falls below the set pressure during operation, the

compressor will stop after the release time has elapsed.

The electrical circuit is divided into two completely separate circuits: a safety circuit and an operational circuit.

The timer (e) in the safety circuit is activated when the eective lubricating oil pressure, the oil dierential pressure

(the dierence between the oil pump pressure and suction pressure), is lower than the set value.

The timer is deactivated when the oil dierential pressure is more than the set value plus the contact dierential.

Figure 2: Functions for During start

Danfoss

60B59.13

On start-up

The two diagrams below explain the terms "oil dierential pressure" and "contact dierential". Both have to be

considered when using oil dierential pressure switches.

The rst diagram shows the function of the dierential switch during start; the second shows the function of the

switch during operation.

Pos. A: Normal start-up

The lubricating oil pressure is built up during start to the set/xed dierential plus the contact dierential, before

the timer cuts out (in this example, after 45 seconds).

At point A contacts T1-T2 open and timer (e) is stopped, i.e. normal lubricating oil conditions for the compressor

have been established.

Pos. B: The lubricating oil pressure does not reach the set/xed dierential plus the contact dierential before the

timer period elapses. At point B the timer cuts out operational circuit L-M and the compressor stops. If a signal

source is connected to terminal S, it will be activated. Restart can only be performed after about 2 minutes by

activation of the reset button, provided the cause of the fault has been determined.

Dierential pressure switch, Type MP 54, 55 and 55A