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A literature search was conducted to find out more about the types of shaftless pumps that are being

used today in the industry. The advantage of the shaftless pump is that the impeller can be driven

without it being attached to an external motor shaft, and therefore without the need for seals (since

there is no shaft penetration into the impeller enclosure). This design eliminates the mechanical seal,

which is one of the largest components of pump maintenance costs, and assures that the pump is leak

free (unless the pump casing is broken). A drawback to this type of pump is the heat generated by the

magnetic flux as it passes through the metallic enclosure of the impeller. The liquid moved by the

pump is used to carry away the heat as well as lubricating the thrust surfaces and the sleeve bushings

used as the impeller mounting mechanism (since the pump shaft is not supported by bearings outside

of the pump's housing, support inside the pump is provided by bushings. The materials of

construction of these bushings and the required clearances of the parts restrict the kinds of fluids for

which this kind of pump may be used). This type of pump is generally used for moving clear liquids

that contain no solids (solids and more viscous type fluids would damage the bushings and/or the

thrust surfaces) and which can be dangerous to the environment such as acidic, caustic and abrasive

liquids. The following are the types of shaftless pumps or magnetic drive pumps or glandless pumps

that are available for use today:

1. MDP – Magnetic-drive pump (centrifugal pump with a magnetically coupled impeller to drive

shaft). The impeller of such a pump is magnetically coupled with the motor, across a separation

wall which is resistant to the fluid pumped. The motor drives a rotor carrying one or several pairs

of permanent magnets, and these drag around a second pair(s) of permanent magnets attached to

the pump impeller.

Figure 1. Magnetic-drive pump

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2. CMP – Canned-motor pump (centrifugal pump with a rotating magnetic field within the motor stator). The

canned motor combines the hydraulics of centrifugal pumps with the three-phase induction motor. The

hydraulic section is directly connected to the drive motor. A pipe-like sleeve or "can" is inserted in the

magnetically-bridged gap between rotor and stator. The "can" absolutely and hermetically separates the

rotor chamber from the pressurized fluid pumping environment. The torque required for shaft rotation is

transferred via the can, which consists of a non-magnetic material, by electromagnetic means. This type of

drive does not require a shaft aperture through the fluid-containing (usually pressurized) housing; therefore

there is no need for dynamic gaskets or mechanical seals. The necessary static gaskets are generally

problem-free but, in special cases, may be replaced by welded connections. Canned motor pumps,

therefore, are fully hermetic pump units. The pump section can be of single or multistage design. The

pump impeller (or impellers on multistage pumps) is mounted at the overhung end of a shared pump-and-

motor shaft.

Figure 2. Canned-motor pump

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3. Controlled-volume diaphragm pump. This pump is different from the other two pumps in that its fluid

contacting part (the diaphragm) is non-metallic (which helps provide chemical resistance if/when

chemicals are pumped through). The controlled-volume diaphragm pump has a flexible diaphragm that

directly contacts the process fluid. This diaphragm also acts as a seal between the drive mechanism and the

pumped liquid. The diaphragm can be driven mechanically, hydraulically, pneumatically or

electromagnetically. The pumps are available in single-, double- and multiple-diaphragm configurations.

All diaphragm pumps are seal-less and self-priming, and can be run dry without causing damage. Flow

rates of 200 gal/min and outlet pressures of 100 psig are common.

Figure 3. Controlled-volume diaphragm pump

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4. Flexible-tube pump. This pump design also has a non-metallic fluid contacting part (the fluid

flows through the tube away from the rotating element of the pump). The flexible-tube pump does

not use mechanical seals. Instead, the fluid is contained within the smooth walls of an

elastomeric, tubular structure and is moved forward as the tube is squeezed by a rotating element.

As the squeezed tube returns to it natural shape, the vacuum produced by the displaced fluid

draws more fluid into the tube. Pumping is achieved by a gentle, peristaltic action that allows for

a controllable flow of the fluid trapped between the two contact points on the inside of the tube.

This configuration requires no seals, glands or valves. Models are available with flow rates up to

200 gal/min and differential pressures to 200 psi.

Figure 4. Flexible-tube pump