Data Sheet
Differential pressure switch
Type MP 54, 55 and 55A
MP 54 and MP 55 are used in refrigerating systems
using HCFC and non-ammable HFC refrigerants.
MP 54 and MP 55 oil dierential pressure
switches are used as safety switches to protect
refrigeration compressors against low
lubricating oil pressure.
If the oil pressure fails, the oil dierential
pressure switch stops the compressor after a
certain time period.
MP 54 and MP 55 are used in refrigerating
systems using HCFC and non-ammable HFC
refrigerants.
MP 55A is used in refrigerating systems with
R717. MP 55A can also be used in systems with
HCFC and non-ammable HFC refrigerants.
MP 54 has a xed dierential pressure setting. It
also incorporates a thermal time relay with a
xed release time setting.
MP 55 and MP 55A have adjustable dierential
pressure and are available both with and
without thermal time relay.
Features
• Wide regulating range
• Can be used for deep freeze, refrigeration and
air conditioning plant
• Can be used for HCFC and non-ammable
HFC refrigerants
• Electrical connection at the front of the unit
• Suitable for both alternating and direct
current (AC and DC)
• Screwed cable entry for cables from 6 – 14
mm diameter
• Small contact dierential
AI211986438834en-000901
Danfoss
60B55.13
Danfoss
60B59.13
On start-up
Dierential pressure switch, Type MP 54, 55 and 55A
Functions
Figure 1: Electrical diagram
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 eective lubricating oil pressure, the oil dierential pressure
(the dierence between the oil pump pressure and suction pressure), is lower than the set value.
The timer is deactivated when the oil dierential pressure is more than the set value plus the contact dierential.
Figure 2: Functions for During start
The two diagrams below explain the terms "oil dierential pressure" and "contact dierential". Both have to be
considered when using oil dierential pressure switches.
The rst diagram shows the function of the dierential 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 dierential plus the contact dierential, 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 dierential plus the contact dierential 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.
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Dierential pressure switch, Type MP 54, 55 and 55A
Figure 3: Functions for During operation
Pos. C: The lubricating oil pressure falls during operation to a value lower than the set/xed dierential. At point C,
safety circuit T1-T2 cuts in and the timer is activated.
Pos. D: The lubricating oil pressure reaches the set/xed dierential plus the contact dierential before the timer
period elapses. At point D, safety circuit T1-T2 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/xed dierential during operation. At point E,
safety circuit T1-T2 cuts in and the timer is activated.
Pos. F: The lubricating oil pressure remains lower than the set/xed dierential. 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 dierential 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.
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2
1
3
4
5
12345
Connection to pressure side of lubrication system, OIL
Connection to suction s ide of refrigeration plant, LP
Setting disk (MP 55 and MP 55A)
Reset button
Test device
Unit type
Material
MP 54
MP 55
Stainless steel 19/11, no. 1.4306 to EN 10088
Cold forming steel, no. 1.0338, EN 10139
Free cutting steel, no. 1.0718, EN 10277
MP 55A
Stainless steel 19/11, no. 1.4306 to EN 10088
Cold forming steel, no. 1.0338, EN 10139
Free cutting steel, no. 1.0401, EN 10277-2
Features
Specications
Control voltage
230 V or 115 V AC or DC
Permissible voltage variation
-15 – 10%
Max. working pressure
PS/MWP = 17 bar
Max. test pressure
P
e
= 22 bar
Ambient temperature
The time relay is temperature-compensated
in the range
-40 – 60 °C
Screwed cable entry
P
g
13.5
Cable diameter
6 – 14 mm
Max. bellows temperature
100 °C
Switch
dierential max. ∆p [bar]
0.2
Dierential pressure switch, Type MP 54, 55 and 55A
Product specication
Design and Materials
Figure 4: Design for MP 54, MP 55 and MP 55A
The operation of the pressure switch relies only on the dierential pressure, i.e. the dierence in pressure between
the two counteracting bellows, whereas it is independent of the absolute pressure acting on both bellows.
The MP 55 and 55A can be set for dierent dierential pressures by the setting disc (3).
The set dierential pressure can be read from the internal scale.
The MP 54 has a xed dierential and has no pressure setting disc.
The factory-set dierential pressure is stamped on the front plate of the switch.
Table 1: Materials in contact with the medium
Technical data
Table 2: Technical data for MP 54, MP 55 and MP 55A
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Features
Specications
Enclosure
IP20 to EN 60529 / IEC 60529
Contact loads
MP with time relay (contacts M-S)
AC15 = 2 A, 250 V
DC13 = 0.2 A, 250 V
MP without time relay
AC15 = 0.1 A, 250 V
DC13 = 12 W, 125 V
Wire dimensions
solid / stranded
0.2 – 1.5 mm
2
exible, without ferrules
0.2 – 1.5 mm
2
exible, with ferrules
0.2 – 1 mm
2
Tightening torque
max. 1.2 Nm
Rated impulse voltage
4 kV
Pollution degree
3
Short circuit protection, fuse
2 A
Insulation
250 V
Danfoss
60B109.12
Net weight:
approx. 0.8 kg
Dierential pressure switch, Type MP 54, 55 and 55A
Terminology
Dierential range
The pressure dierence between LP and OIL connections within which the switch can be set to operate.
Scale reading
The dierential between the oil pump pressure and the pressure in the crankcase that exists at the moment the
contact system cuts in current to the time relay on falling oil pressure.
Operating range
The pressure range on the LP connection within which the switch can operate.
Contact dierential
The pressure rise above the set dierential pressure (scale reading) necessary to cut o current to the time relay.
Release time
The period for which the dierential pressure switch allows the compressor to run with too low an oil pressure
during start-up and operation.
Dimensions and weight
Figure 5: Dimensions and weight for type MP 54, MP 55 and MP 55A
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Type
Dierential ∆p
Operation range,
LP side
Relay release time
Code no.
Connection
[bar]
[bar]
[s]
1
⁄4 in Flare
1 m cap.tube
1
⁄4 in
ODF solder
M12 x 1.5 with
6 mm cutting ring
MP 54
0.65
-1 – 12
0
(1)
060B029791--
0.65
-1 – 12
45
060B016691--
0.9
-1 – 12
60
060B016791--
0.65
-1 – 12
90
060B016891--
0.65
-1 – 12
120
060B016991--
MP 55
0.3 – 4.5
-1 – 12
45
060B017091
060B013391
-
0.3 – 4.5
-1 – 12
60
060B017191--
0.3 – 4.5
-1 – 12
60
060B017891
(2)
--0.3 – 4.5
-1 – 12
90
060B017291--
0.3 – 4.5
-1 – 12
120
060B017391--
0.3 – 4.5
-1 – 12
0
(1)
060B029991--
Type
Dierential ∆p
Operation range,
LP side
Relay release time
Code no.
Connection
[bar]
[bar]
[s]
G
3
⁄8 A supplied with
ø6.5 / ø10 mm w
eld nip‐
ple
M12 ×1.5 with 6 mm cut‐
ting ring
MP 55A
0.3 – 4.5
-1 – 12
45
060B017491
060B018291
0.3 – 4.5
-1 – 12
60
060B017591
060B018391
0.3 – 4.5
-1 – 12
60
060B017991
(3)
-
0.3 – 4.5
-1 – 12
90
060B017691
060B018491
0.3 – 4.5
-1 – 12
120
060B017791
060B018591
0.3 – 4.5
-1 – 12
0
(4)
060B029691
Dierential pr
essure switch, Type MP 54, 55 and 55A
Ordering
igure 6: MP 55E
F
Table 3: For R22, R134a, R404A, R407A, R407C, R407F, R422B, R422D, R448A, R449A, R450A, R452A, R507A, R513A
(1)
(1)
MP without time relay. Versions without time relay are for applications where an external time relay is required – perhaps with a dier
MP without time relay. Versions without time relay are for applications where an external time relay is required – perhaps with a dierent
release time than the one specied
release time than the one specied
(2)
(2)
With glow lamp that remains on during normal operation.
With glow lamp that remains on during normal operation.
ent
Table 4: For R22, R134a, R404A, R407A, R407C, R407F, R422B, R422D, R448A, R449A, R450A, R452A, R507A, R513A, R717*)
060B029891
(3) W
With gloith glow lamp that rw lamp that remains on duremains on during noring normal opermal operationation
(4) MP without time rMP without time relayelay. V. Versions without time rersions without time relay arelay are fe for applications wheror applications where an ee an exxtterernal time rnal time relay is relay is requirequired – pered – perhaps with a haps with a differdifferenentt
rrelease time than the one elease time than the one specifiedspecified
(4)
*) only for MP 55A
For complete list of approved refrigerants, visit www.products.danfoss.com and search for individual code numbers,
where refrigerants are listed as part of technical data.
NOTE:
If the operational light goes out, the compressor should not run longer than the release time
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Document type
Approval authority
UA declaration (EMCD/LVD)
LLC CDC EURO TYSK
EU declaration LVD
Danfoss
Manufacturer declaration for China ROHS
Danfoss
Electrical safety certicate
CCC
Marine safety certicate
DNV GL/RINA
Dierential pressure switch, Type MP 54, 55 and 55A
Certicates, declaration and approvals
The list contains all certicates, declarations, and approvals for this product type. Individual code number may have
some or all of these approvals, and certain local approvals may not appear on the list.
Some approvals may change over time. You can check the most current status at danfoss.com or contact your local
Danfoss representative if you have any questions.
Table 5: Certicates, declaration and approvals
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