Sealless Centrifugal Pumps

5.1.1 Scope

To develop the definitions and construction for sealless pumps that are driven by canned motors or magnetic couplings. These standards include types and nomenclature; design and application; installation, operation and maintenance; and test. Not included are submersible wastewater pumps which do not have external shaft seals and are therefore not susceptible to external shaft leakage.

5.1.1.1 Objective

To clearly outline the information necessary to define and describe the construction and use of sealless pumps.

5.1.1.2 Introduction

The sealless pump is used when there is a need to contain toxic, dangerous and/or valuable fluids. Application may be dictated by space, noise, environment, or safety regulations. This section outlines components of sealless centrifugal type pumps.

The driven shaft is completely contained in a pressurized vessel containing the pumped fluid. The pressurized vessel or primary containment device (chamber) is sealed by static seals such as gaskets or O-rings.

The power required by the driven shaft is transmitted through a containment barrier. Methods include (1) the “canned motor pump” with a liner (can) placed between an induction motor’s armature and stator; (2) the “magnetic drive pump” with a shell(s) located between an outer rotating element with permanent magnet(s) and a mating inner ring which follows the driving magnets. The inner rotor may have permanent magnets or it may be an induction device.

See Figure 5.1 for a diagrammatic breakdown of the types of sealless centrifugal pumps.

5.1.2 Canned motor pump (CMP)

5.1.2.1 Close coupled end suction

Figure 5.2 — In this group, the impeller(s) is mounted on the end of the shaft which is overhung from its motor bearing supports.

The impeller is mounted directly on the rotor assembly making one rotating assembly. The bearings are supported by housings at each end of the rotor assembly. The motor components are protected from the process liquid by non-magnetic liners (shells).

During operation, the motor section and bearings are cooled and lubricated by the process liquid by internal circulation, external circulation or by separate liquid flush.

5.1.2.2 Close coupled in-line

Figure 5.3 — In this group, the pump and motor are mounted vertically. A single stage overhung impeller is used in conjunction with a casing with in-line flange connections. Motor and bearings are cooled and lubricated by the process liquid.

5.1.2.3 Separated pump and motor

Figure 5.4 — This group has single or multistage overhung impellers; however, the pump and motor are separated by a thermal barrier, usually an air space. The impeller is mounted on the rotor assembly which is supported by bearings at each end. The rotor assembly contains an auxiliary impeller which circulates the process liquid in the motor section through a heat exchanger for control of the fluid temperature.

5.1.2.4 Vertical submerged canned motor pump

Figure 5.5 — This group of pumps is of the single stage overhung impeller design that is suspended from a coverplate. The complete pump and motor is immersed in the process fluid. This method of installation provides sealless pump application inside a sealed vessel.

5.1.3 Magnetic drive pump (MDP)

5.1.3.1 Separately coupled

Figure 5.6 — This group of pumps is end suction, single stage or multistage, overhung impeller design. The impeller is mounted on a rotor assembly which contains the inner magnet ring of a magnetic drive. The process fluid is retained by a containment shell which separates the inner magnet ring and the outer magnet ring. The outer magnet ring is mounted on the shaft of a frame which is coupled to a motor or power device. All of the above is mounted on a common baseplate.

5.1.3.2 Close coupled

Figure 5.7 — This group of pumps is of the same construction as described in Section 5.1.3.1, except the outer magnet ring is mounted directly on the driver shaft.

5.1.3.3 Vertical submerged

Figure 5.8 — In this group of pumps, the impeller is mounted on the end of a shaft which is overhung from its drive bearing supports. The drive section utilizes permanent magnets or an eddy current drive system to transmit power to the pump. This type of sealless pump uses a standard motor to drive the outer magnet ring, which in turn drives an inner magnet ring. A containment shell that contains the process fluid separates the magnet components.

The containment shell in the drive permits sealless pumping from a sealed vessel using a submergible pump.

5.1.3.4 Part names

Table 5.1 lists the names of most parts that go into the construction of sealless centrifugal pumps. The reference numbers are the same as those shown in Figures 5.2 through 5.8.

Part name	Number	Definition
Adapter	71	A machined piece used to permit assembly of two other parts, or for a spacer, or for a heat barrier on a high-temperature sealless motor pump.
Assembly, rotor	222	The rotating assembly of an electrical machine containing lamina-tions and conductors, which, when interacting with stator core assembly, produces torque.
Assembly, stator	223	The stationary portion of the electric machine containing laminations and conductors. Energizing these conductors creates an interaction with the rotor assembly, producing torque.
Bearing, inboard	16	Rolling element bearing in the frame nearest the pump.
Bearing, outboard	18	Rolling element bearing closest to the motor.
Box, electrical connection	243	Electrical box in which the motor leads are joined with the power source.
Bushing, bearing, inboard	235	Sleeve type bearing in the drive section, which is lubricated by the pumpage.
Bushing, bearing, outboard	237	Same as 235
Can, rotor	221	Liner over the rotor assembly (driven components) that protects against corrosion.
Collar, thrust, inboard	72	A circular collar mounted on a shaft to absorb the unbalanced axial thrust in the pump.
Collar, thrust, outboard	74	A circular collar mounted on a shaft to absorb the unbalanced axial thrust in the pump.
Cover, casing	239	The portion of the magnetic drive that houses the driven magnet assembly, bearing, shaft and containment shell.
Cover, motor end	207	A piece which encloses the end(s) of a motor stator housing.
Exchanger, heat	250	Additional member including heat exchanger tubing for control of pro-cess and motor temperature.
Frame	19	A member of a pump to which are assembled the rotating outer mag-net ring and the drive motor or element.
Gasket	73	Resilient material of proper shape and characteristics for use in joint sealing between parts to prevent leakage.
Housing, bearing, inboard	31	A part in which the inboard bearing is mounted.
Housing, bearing, outboard	33	A part in which the outboard bearing is mounted.
Housing, stator	201	A housing in which a stator core assembly is mounted.
Indicator, bearing wear	304	Mechanical or electrical device which indicates bearing wear.
Inducer	246	A high specific speed impeller installed in the front of the first stage impeller of a centrifugal pump to reduce NPSHR.
Magnet assembly, inner	230	The permanent magnet or induction device assembly attached to the pump shaft, located within the containment shell and driven by the outer magnet assembly.
Magnet assembly, outer	232	The permanent magnet assembly attached to the power drive shaft, located outside of the containment shell and driven by a driver.
Pipe, column	101	A vertical pipe by which the pumping element is suspended.
Plate, terminal	301	An assembly which provides sealing of electrical feedthroughs as a part of the secondary containment system.
Ring, rub	252	A replaceable ring mounted in or on the bearing housing and/or outer magnet assembly. It is used to prevent the outer carrier from hitting the containment shell if the anti-friction bearings in the power end fail.
Shaft, drive	12	The cylindrical member which transmits power from the driver to the outer magnet assembly.
Shaft, pump	6	The cylindrical member on which the impeller is mounted and through which power is transmitted to the impeller.
Shell, containment	217	The member that separates the inner and outer magnet assemblies. It also forms the barrier between the pumpage and the secondary containment.
Sleeve, journal	306	A removable sleeve which provides a rotating journal-bearing sur-face.
Sleeve, backup	305	Sleeves used to provide structural support of the containment shell of a CMP.
Switch, thermal	300	Embedded in stator winding to sense motor temperature and actuate a control or signal when limits are reached.
Tube, circulation	251	A tube through which process fluid is piped from discharge of pump to outboard bearing housing for cooling of drive section.