Debem KM 70 Magnetic Drive Centrifugal Pump

A sealless magnetic-drive chemical pump for flows up to 65 m3/h

The KM 70 is the large model in Debem's KM series of magnetic-drive centrifugal pumps, built in polypropylene or PVDF. Debem describes the KM range as developed in collaboration with CDR Pompe, retaining the characteristics of the DM pumps while offering higher flow rates and better energy efficiency for heavier duties. With no dynamic shaft seal and no metal wetted parts, it is applied to acids, alkalis and other corrosive liquids in chemical, galvanic and water-treatment plants.

Technical specifications

How the magnetic coupling works

An outer magnet on the motor shaft turns an inner magnet built into the closed impeller, which is hermetically enclosed inside the pump casing. Because the impeller is not physically fixed to the motor shaft, no mechanical seal can leak through wear. The trade-off, which every magnetic-drive pump shares, is that the liquid should be clean and the pump must not run dry. Debem's DM manual states the pump must never be used without liquid in the casing, never with a closed suction valve and with only small amounts of fine solids; apply the same caution to the KM unless the manufacturer confirms otherwise for your duty.

Selection and ordering

Select the impeller trim so that the duty point sits on the curve for the flow and head required, because the four diameters shift head at a given flow. The datasheet provides the flow-head, NPSH and power curves for each trim at 2900 rpm. Choose polypropylene up to 70 C or PVDF where temperature reaches 100 C or the chemical requires it, check the density of the liquid against the motor power, and specify the motor voltage and any ATEX requirement at the time of the order. Related Debem sealless sizes are the DM 06, 10, 15 and 30.

Plan the piping so that the pump always starts flooded, keep pipe weight off the casing, and fit a shut-off valve on both sides for maintenance. The KM 70 weighs 33 kg or 34.5 kg without motor, so allow for lifting equipment and a rigid baseplate under the B5 motor flange. Give the fluid specific gravity and solids content in the enquiry, because both determine whether the magnetic coupling and motor power are suitable.

Getting the duty point right

Magnetic-drive pumps are less tolerant of operation far from their design point than many sealed pumps, because the inner magnet assembly runs on bearings lubricated by the pumped liquid. Size the KM 70 so that the normal operating point sits comfortably within the curve for the chosen impeller rather than at the extreme of maximum flow or near shut-off. Calculate the system curve from the real pipework, including fittings, filters and elevation, and compare it with the 145, 139, 129 and 119 mm impeller curves in the datasheet. Check NPSH available at the suction against the NPSH curve, particularly for warm liquids or tanks with low liquid levels. For liquids heavier than water, the motor power needs to be confirmed, since a denser fluid demands more power at the same flow and head; a viscosity approaching the 150 cps limit also affects performance.

Installation and first start

• Mount the pump below the minimum liquid level of the feed tank so the casing stays flooded.
• Keep the suction line short and straight, sized at least to the 3 inch or DN 80 connection, with no air pockets.
• Support suction and delivery piping independently, as the plastic casing should not carry pipe loads.
• Fill the pump and the suction line with liquid and vent the casing before the motor is switched on.
• Check motor rotation briefly with the pump full, never dry.
• Open the delivery valve gradually after start-up and check the operating pressure and motor current against the selected point.

Maintenance and problem solving

Because there is no shaft seal, routine maintenance centres on the internal bearings, the impeller and the casing. Dry running, cavitation and solids are the most common causes of damage. Fit dry-running or low-level protection where the tank can empty, and a strainer where solids may enter. Low flow often comes from a blocked suction, air ingress or a decoupled magnet drive caused by a sudden overload; stop the pump, find the cause, and restart only once the casing is full again. Noise and vibration point to cavitation or worn bearings. Always flush and neutralise the pump before opening it, as it may contain hazardous chemicals.

Chemical service in Omani conditions

In Oman’s chemical dosing stations, desalination pre-treatment and metal finishing lines, pumps are often installed outdoors or in hot plant rooms. Polypropylene pumps are limited to 70 °C, and a liquid stored in an unshaded tank in summer may approach that limit, so check summer fluid temperatures before choosing the polypropylene version over PVDF. UV exposure degrades many plastics, so shade the pump and plastic piping. Motors installed outdoors should be protected from dust and from salt-laden coastal air, and motor cooling fans kept clean so the motor does not overheat in high ambient temperatures.

Documents and quotation

The KM 70 technical sheet includes the curves, motor options and dimensions. Send the fluid, concentration, temperature, density, flow and head for a quotation. Compare with the Grundfos NK end-suction pump for a metal long-coupled alternative, or browse other chemical and process pumps.