Danfoss Electronics MP 54, MP 55 Data Sheet

Data sheet

Differential pressure switch / Lube oil protection control

MP 54 and MP 55

MP 54 and MP 55 oil dierential pressure switches are used as safety switches to protect refrigeration compressors against low lubricating oil pressure.

If the oil pressure fails, the switch will stop the compressor after a predetermined time period has elapsed.

MP 54 and MP 55 are used in refrigerating systems using HCFC and non-ammable HFC refrigerants.

MP 54 has a xed dierential pressure setting. It also incorporates a thermal time relay with a xed release time setting.

MP 55 have adjustable dierential pressure and are available with thermal time relay.

Features

Approvals

• Fixed and adjustable dierentials available

• Extremely narrow switch dierential accuracy

• Reliable, long life stainless steel bellows

• Sturdy metal cover and universal mounting hole patterns

• Integral ½ NPSM swivel cable connector allows direct attachment of ½ in. male pipe thread connector

UL listed for USA and Canada, le E31024

• Simple manual trip, electrical test function eliminates need of tools and test “jumper” wires

• Standard four-wire hook-up

• Can be used for HCFC and non-ammable HFC refrigerants

Data sheet | Dierential pressure switch / Lube oil protection control, MP 54 and MP 55

Materials in contact with the medium

Technical data

Unit type Material

MP 54 MP 55

MP with capillary tube

Ambient temperature

Stainless steel 19/11, no. 1.4306 to EN 10088 Deep-drawn steel plate, no. 1.0338 to EN 10130 Free cutting steel, no. 1.0718 to EN 10277

Copper Cu-DHP, no. CW024A acc. to EN 12450

The time relay is temperature-compensated in the range - 40 – 140 °F

Switch dierential Maximum 2.8 psi

Maximum working pressure MWP = 245 psig

Maximum test pressure Pe = 320 psig

Control voltage 240 or 120 V AC or DC

Permissible voltage variation -15 – 10%

Contact load of time relay output contacts M-S

240 V AC: 2 FLA

240 V DC: 0.2 FLA

Electrical connection NPSM

Max. bellows temperature

Cable entry

212 °F

Integral ½ in. female NPSM swiwel cable connector allows direct attachment of ½ in. male pipe thread connector.

Ordering

Enclosure ~NEMA 1

For R22, R134a, R404A, R407A, R407C, R407F, R422B, R422D, R448A, R449A, R450A, R452A, R507A, R513A

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.

Connection

Code no.

¼ in are nut

with 36 in

capillary tube

¼in are nut

with 88 in

capillary tube

–

Typ e

Control

dierential

∆p

Regulation

range

LP side

[psi] [inHg] – [psi] [s]

6.0 29 inHg – 175 psi 45 060B200866 – –

6.0 29 inHg – 175 psi 45 – 060B205066 –

MP 54

9.0 29 inHg – 175 psi 90 060B200266 – –

9.0 29 inHg – 175 psi 120 060B200366 2) – –

9.0 29 inHg – 175 psi 120 – 060B205366 2)

4.3 – 65 29 inHg – 175 psi 45 – 060B205466 –

4.3 – 65 29 inHg – 175 psi 60 060B201266 1) – –

MP 55

4.3 – 65 29 inHg – 175 psi 90 060B200666 – –

4.3 – 65 29 inHg – 175 psi 120 060B200766 – –

4.3 – 65 29 inHg – 175 psi 120 – 060B205766 –

) With glow lamp that remains on during normal

operation of compressor.

) Three-wire hook-up

Time relay delay time

¼ in are

Note:

When time delay is energized which also means that min. permisible oil pressure (dierential ∆p) is reached, light goes out.

Data sheet | Dierential pressure switch / Lube oil protection control, MP 54 and MP 55

Design

1. Connection to pressure side of lubrication system, OIL

2. Connection to suction side of refrigeration plant, LP

3. Setting disc (MP 55)

4. Reset button

5. Test device

The operation of the pressure switch is based only on the dierential pressure, i.e. the dierence in pressure between the two counteracting bellows, whereas it is independent of the absolute pressure acting on both bellows.

The MP 55 can be set for dierent dierential pressures by the setting disc (3). The set dierential pressure can be read from the internal scale.

The MP 54 has a xed dierential and has no pressure setting disc. The factory-set dierential pressure is stamped on the front plate of the switch.

Terminology

Dierential range

The pressure dierence between LP and OIL connections within which the control can be set to operate.

Scale reading

The dierential 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 dierential

The pressure rise above the set dierential pressure (scale reading) necessary to cut o current to the time relay.

Release time

The period for which the dierential pressure control allows the compressor to run with too low an oil pressure during start-up and operation.

Data sheet | Dierential pressure switch / Lube oil protection control, MP 54 and MP 55

Electrical diagram

Function

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 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.

[bar]

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

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.

On start-up

[s]

Data sheet | Dierential pressure switch / Lube oil protection control, MP 54 and MP 55

[bar]

During operation 1 bar = 14.5 psi

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.

Pos. C: The lubricating oil pressure falls during operation to a value lower than the set/xed dierential. At point C, safety circuit T1-T2 cuts in and the timer is activated.

Pos. D:

The lubricating oil pressure reaches the set/xed dierential plus the contact dierential 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.

[s]

Pos. E:

The lubricating oil pressure falls to a value lower than the set/xed dierential 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 dierential. 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 dierential pressure switch 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.

Dimensions [in] and weights [lb]

MP 54, MP 55

Net weight: approx. 1.8 lbs

Danfoss Electronics MP 54, MP 55 Data Sheet

Specifications and Main Features

Frequently Asked Questions

User Manual