How To Install And Maintain A Split Case Pump

Apr 24, 2026

The split case pump (split case circulation), also known as a single-stage double-suction centrifugal pump, is characterized by its large flow capacity for conveying media. The working principle of the split case pump is as follows: The impeller is installed inside the pump casing and fastened onto the pump shaft, which is directly driven by an electric motor. A liquid suction port is located at the center of the pump casing and is connected to the suction pipe. The liquid enters the pump through the foot valve and suction pipe. The liquid discharge port on the pump casing is connected to the discharge pipe. When the pump speed is constant, its head and flow rate are related to the impeller diameter.

The suction and discharge nozzles of the split case pump are both located below the pump shaft centerline, horizontally positioned perpendicular to the shaft axis. The pump casing is split horizontally (split case design). During maintenance, there is no need to disconnect the suction pipe, discharge pipe, or the motor (or other prime mover). When viewed from the coupling toward the pump, the pump rotates counterclockwise. If required by special customer order, the rotation direction can also be changed to clockwise.

The main components of the split case pump include: pump casing, pump cover, impeller, shaft, double-suction sealing rings, shaft sleeves, bearings, etc. Except for the shaft, which is made of high-quality carbon steel, most other parts are made of cast iron.

The pump casing and pump cover form the working chamber for the impeller. On the suction and discharge flanges, tapped holes are provided for installing a vacuum gauge and a pressure gauge. At the bottom of the suction and discharge flanges, tapped drain holes are provided.

 

 

The impeller is statically balanced and is secured by shaft sleeves and shaft sleeve nuts on both sides. Its axial position can be adjusted using the shaft sleeve nuts. The axial thrust of the impeller is balanced by the symmetrical arrangement of its vanes. Any remaining axial thrust is taken up by the bearings at the shaft ends.

The pump shaft is supported by two single-row radial ball bearings. The bearings are housed in bearing housings at both ends of the pump casing and are lubricated with grease. The double-suction sealing rings reduce leakage of water from the pump's pressure chamber back to the suction chamber.

The pump is directly driven by an electric motor via a coupling.

The shaft seal is a soft packing seal. To cool and lubricate the sealing chamber and prevent air from leaking into the pump, a water seal ring is provided between the packing layers. During pump operation, a small amount of high-pressure water flows through the water seal pipe into the packing chamber, creating a water seal.

Since the assembly and disassembly of the split case pump are relatively simple and similar, and the installation and operation manual provides detailed instructions, this document takes the grease-lubricated structure with bearing inner sleeve as an example to illustrate its assembly and disassembly. The assembly and disassembly of other configurations of the split case pump will not be described in detail. For specific details, please refer to the corresponding installation and operation manual.

 

I. Assembly and Disassembly of the Split Case Pump

 

1. Assembly and Disassembly of the Rotor Assembly

 

(1) Place the shaft horizontally on a platform or other suitable support.

(2) Insert the impeller key into the keyway at the center of the shaft, then mount the impeller.

(3) Fit the sealing ring onto the impeller.

(4) On both sides of the impeller, install in sequence: O-rings or gaskets, impeller spacer sleeves, shaft sleeves, packing bushings, bearing spacer sleeves, packing rings, packing glands, and water deflector rings. If a mechanical seal is used, do not install the packing rings and packing glands; instead, install the mechanical seal and mechanical seal cover (or cartridge mechanical seal), and replace the packing-type shaft sleeve with the mechanical-seal-type shaft sleeve.

 

 

(5) On the non-drive end, install in sequence: inner bearing cover (with paper gasket and built-in skeleton oil seal), shaft shoulder spacer sleeve, bearing (with bearing inner sleeve already mounted), bearing retaining ring, lock washer, and round nut, then tighten slightly. Mount the bearing housing onto the bearing, tighten the connecting bolts between the bearing cover and the bearing housing, install the oil/grease cup, and then install the temperature measuring element.

(6) On the drive end, install in sequence: inner bearing cover (with paper gasket and built-in skeleton oil seal), shaft shoulder spacer sleeve, bearing (first mount the bearing onto the bearing inner sleeve; for a cylindrical roller bearing, first mount the bearing inner ring onto the bearing inner sleeve), bearing spacer sleeve, bearing housing (for a cylindrical roller bearing, first mount the bearing outer ring inside the bearing housing; when installing the bearing housing, align the end faces of the bearing inner and outer rings), outer bearing cover (with paper gasket and built-in skeleton oil seal), coupling, lock washer, and round nut, then tighten slightly. Tighten the connecting bolts between the bearing cover and the bearing housing, install the oil/grease cup, and then install the temperature measuring element.

Disassembly of the rotor assembly is the reverse of the above.

Special note: The quality of rotor assembly directly affects the installation of the rotor assembly with the pump casing and the pump's operation!

 

2. Assembly of the Rotor Assembly with the Pump Casing

 

(1) Clean the pump casing sealing rings and remove burrs.

(2) Apply sealant to the split casing flange faces of the pump body, or install a 0.3 mm thick kraft paper gasket shaped to match the flange (whether to use sealant or a paper gasket shall be determined according to the specific requirements of each pump).

Note: The edge of the gasket must be flush with the inner wall of the casing flow passage.

(3) Place the assembled rotor assembly onto the pump body, with the bearing housings resting on the supports at both ends of the pump body. Then hand-tighten the bolts connecting the bearing housings to the pump body until they cannot be turned by hand. According to the general assembly requirements, use a feeler gauge to check whether the clearance between the impeller and the sealing ring meets the requirements.

(4) Evenly tighten the connecting bolts between the bearing housings and the pump body.

(5) Adjust the lock nuts at both ends of the shaft to center the impeller with the pump body, then tighten the lock nuts.

(6) On the non-drive end, install the bearing end cover (with paper gasket) and tighten the connecting bolts between the bearing end cover and the bearing housing.

(7) Lift the pump cover and carefully lower it into the correct position.

(8) Install the dowel pins and the connecting nuts for the pump body and pump cover, then tighten the nuts symmetrically.

Note: Never lift the rotor assembly directly onto the pump body and tighten the bolts between the bearing housings and the pump body immediately.

 

 

(9) Manually rotate the pump rotor to check whether the rotor rotates freely inside the casing.

(10) After confirming compliance, add packing at the shaft seals on both ends of the pump (see later instructions for packing installation), paying attention to the position of the packing ring within the stuffing box.

(11) Press down the packing glands and tighten the connecting nuts until they cannot be turned by hand.

(12) Install pump piping and accessories (such as threaded plugs, cooling water system, etc.).

(13) Add bearing grease, filling 1/3 to 1/2 of the bearing internal space. The grease shall be molybdenum disulfide lithium-based grease (higher-grade greases, such as complex lithium-based grease, are acceptable).

At this point, the complete pump assembly is finished. Disassembly of the complete pump is the reverse of the above.