Danfoss 9/96
The two diagrams below explain the terms "oil
differential pressure" and "contact differential",
both have to be considered when using oil
differential pressure controls.
Function
(continued)
The first diagram shows the function of the
differential control during start; the second shows
the function of the control during operation.
Pos. A: Normal start-up
The lubricating oil pressure is built up during start to the set/
fixed differential plus the contact differential, before the
timer cuts out (in this example, after 45 seconds). At point A
contacts T
1
-T
2
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/
fixed differential plus the contact differential 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.
Pos. C: The lubricating oil pressure falls during operation
to a value lower than the set/fixed differential.
At point C, safety circuit T
1
-T
2
cuts in and the timer is
activated.
Pos. D: The lubricating oil pressure reaches the set/fixed
differential plus the contact differential before the timer
period elapses.
At point D, safety circuit T
1
-T
2
cuts out and the timer is
stopped, i.e. normal lubricating oil conditions for the
compressor have been established.
Pos. E: The lubricating oil pressure falls to a value lower
than the set/fixed differential during operation.
At point E, safety circuit T
1
-T
2
cuts in and the timer is
activated.
Pos. F: The lubricating oil pressure remains lower than the
set/fixed differential. At point F 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.
After start-up
It is important that a function check should be made to
ensure that the differential pressure control is operating as
it should. This check can be made by pressing the test
device (inside the unit on the left hand side).
When the test device is pressed down and held in this
position the compressor motor should stop after the release
time determined by the time relay has elapsed.
During operation
On start-up
Differential pressure controls, type MP 54, 55 and 55A
Catalogue RK.00.H5.02 - Page 315
