Function / Advantages
The MAG-SAFE is developed and designed for monitoring DICKOW sealless pumps and preventing serious pump failures. The MAG-SAFE system is patented, Pat.No. 0610562. The Ni-thermocouple wire is spot-welded to the containment shell surface and forms a thermocouple.
Contrary to the PT100, the MAG-SAFE reads the temperature in the center of the magnets between shell and magnets direct at the heat source. Temperature changes in the thermocouple generate voltage changes. The transmitter converts these changes into a linear output signal of 4 to 20 mA. This gives the possibility to preadjust through a trip amplifier any shut-off temperature within the range of -50 to + 250°C (-60 to + 480°F).
Compared with the common PT100 monitoring, the following features of the MAG-SAFE are highlighted:
  • Fast and reliable detection of all temperature rises in the magnet area. Switch off in time, also at dry running and decoupled magnets. Combined with the coated SiC-bearings which can tolerate dry running until the MAG- SAFE is activated, this system offers reliable dry running protection.
  • Since the containment shell is the real heat source because of the eddy currents generated in it, any temperature rise will be monitored before the liquid temperature is remarkably affected. Thus, flashing of liquid can be prevented through a correctly set trip temperature.
  • Inadmissible containment shell surface temperatures in hazardous areas are prevented.
  • The direction of the internal cooling flow has no influence on the temperature reading.
  • Worn out ball bearings cause eccentric run of the outer magnets and will lead, if not detected, through wear at the protection device to a containment shell rupture. In this case, the MAG-SAFE will trip the motor by cutting the thermocouple wire. Leakage of pumped liquid due to containment shell failure is excluded.
Unit of Measure

Thermoelectric voltage

N/A 28 nV/K /Ni-NiCr Element)

Power supply, clamp 3 and 4

N/A 15-28 V DC, (intrinsically safe, potential free) Umax = 28V, lmax = 93mA, Pmax = 660mW

Output, clamp 3 and 4

N/A 4-20 mA

Burden (external resistance)

N/A <100Q

Protection, casing

N/A IP54

Ambient temperature

N/A - 40 °C to +70 °C (- 40 to +158°F)

Maximum trip temperature

N/A +250 °C (+480°F)

Casing material

N/A Al-alloy, coated

Sensor tip

N/A 1.4571,Ni, PTFE


N/A 0,5 kg (1,1 Ib)

Casing dimensions

N/A 123 x 80 x 57 mm (4,84 x 3,15 x 2,24 inch)

N/A Temperature rise in sealless magnetic driven pumps
In sealless pumps with magnetic couplings and metallic containment shells, eddy currents are generated which lead to heat and cause temperature rise of the pumped liquid in the containment shell. In order to prevent inadmissible temperature rise, this heat must be dissipated through an internal cooling flow.

The internal cooling flow causes a nearly constant temperature rise when operating the pump right of the thermal stable minimum flow. However, below minimum flow, the temperature will rise remarkably. Hence, these pumps cannot operate against closed discharge valve without an additional bypass, because heat cannot be removed properly. Dry running is the worst of these flow related conditions. The heat built up in the containment shell can cause temperature rise of more than 600°C (1110°F) which can also cause the magnets to demagnetize if the temperature is not reliably monitored.

Sleeve bearing, allowable temperature
Sealless pumps require sleeve bearings which work in the pumped liquid. The sleeve bearing material in DICKOW-pumps is Silicon Carbide with diamond layer, providing dry running capability. The widely used term "process lubricated bearing" is not quite correct, since there are no lubrication grooves applied. There is no defined flow through these bearings and pumped liquids as LPG or Methylene Chloride provide no lubrication capability. Similar to the situation between the faces of mechanical seals, a stable fluid film is required between the slide faces. If temperature rise in the magnet end causes vaporization of the pumped liquid, this fluid film breaks down and the sleeve bearing runs dry and fails sooner or later. Although the diamond coating can accept dry running in an empty pump because no hydraulic loads are acting, it cannot save the bearings if dry running occurs under normal operating conditions. Only a reliable temperature monitor can avoid such upset conditions. When handling volatile liquids, the relation between temperature and pressure in the magnet end and the boiling point of the liquid should be considered in any case.

During operation, the containment shell is pressurized with pressure Pgp. The pressure rise A Pgp depends on the pump's differential pressure and on the pump design. The intersection point between containment shell pressure at rated conditions and the vapour pressure curve determines the boiling temperature TD of the liquid. With a certain safety margin ATg, we find the setting temperature of the temperature monitoring device to avoid vaporization in the magnet end.

Temperature monitoring
Sealless magnetic coupled pumps are not considered as electrical equipment. Level detectors or temperature monitoring devices are not required by any safety regulation or by the authorities, even if the pumps are installed with explosion proof motors in hazardous areas. Usually, if seal- less pumps are selected for a particular service, it's because the process fluid is toxic, flammable or both. Since the goal is to keep the liquid within the system, paying careful attention to the prevention and detection of failures is vital for a sound operation. Experiences in applying such pumps have proved that the main reason for pump failures - besides worn out ball bearings - was the flow-related increase in temperature. This has led several manufacturers and end users to incorporate temperature measurement into their designs.

PT100 - Temperature probes
The most common temperature monitoring systems are the PT100-elements. The disadvantage of these elements is the location outside of the magnets.

This is proved by the test results shown in the graph below. The graph shows the temperature rise (T2) at the PT100 and the temperature rise (T1) in the center of the magnets during dry running of a pump over a period of 4 minutes.
In the center of the magnets the temperature rises very fast and can reach, depending on the magnetic losses, 450 - 500°C (840 - 930°F) already after 30 seconds.
The temperature reading at the PT100 after 4 minutes is 40°C (105°F) only. These results prove that the PT100-probe cannot act as a dry running protection.
To obtain reliable readings from the PT100- probe, the pump must be vented respectively properly filled with pumped liquid and the internal circulation flow must transport the heat from the magnet center to the measuring spot of the PT100. This is provided in our NM-pumps with circulation from discharge to discharge by rotor back vanes and the PT100 located at the return of the internal cooling flow (after passing the magnet area).
Problems with temperature rise can also occur through unreliable temperature reading of the PT100 when handling volatile liquids in pumps with cooling flow circulation from discharge to suction, or in case of decoupled magnets and starved cooling flow.

N/A Ex-Proof
The MAG-Safe is a certified electrical equipment for hazardous areas.
Certification BVS.96.D.2044 is available. Classification "EEx ib II CT4 intrinsically safe".
If no distributed controlled system is available, the MAG-SAFE must be connected to the motor circuit through a required trip amplifier.
The components are preassembled on a DIN- power rail. All electrical connections between the components are carried out. On site, the power supply unit has to be connected to the power source, the transmitter unit with the MAG-SAFE and the trip amplifier to the motor circuit.

Wiring diagrams / Trip amplifier
If the MAG-SAFE is supplied with the required power, the output can be connected to the trip amplifier or to an available distributed controlled system connected to the motor circuit.
Additional to the MAG-SAFE, Dickow can deliver also the trip amplifier unit. The DICKOW-Trip amplifier consists of following components:

Power supply unit: Typ KFAG-STR-Y 3597
Transmitter supply unit: Typ KFD2-STC3-Ex 1 71826
Trip amplifier: Typ KFD2-GS-1 .DA-Y 35398

The trip amplifier can be set to any temperature between -50 and + 250°C (-60 and + 480°F). During adjusting procedure, the trip temperature is displayed, during operation, the monitored containment shell temperature is displayed.