Horizontal Split-Case Pump Product

Overview

The horizontal split-case pump is the workhorse of large clean-water pumping: municipal distribution, cooling water, fire protection under NFPA 20, irrigation headworks, and HVAC plant rooms. Its defining feature is in the name — the casing splits along a horizontal plane through the shaft axis. Unbolt the parting flange, lift the Upper Casing Half, and the entire Rotating Element lies exposed in the Lower Casing Half like an engine on a stand, with suction and discharge piping still connected. No other pump configuration offers that maintenance access. In API 610 terms it is the BB1 type: between-bearings, axially split, single stage.

Casing and hydraulic design

The Lower Casing Half carries both nozzles — suction and discharge flanges sit side by side, usually horizontally opposed — plus the mounting feet, so the top half comes off without touching pipework or alignment. A die-cut Split Gasket seals the parting flange, and fitted Dowel Pin pins register the halves so the internal waterways line up to machining tolerance. Most casings are double-volute: two cutwaters 180° apart cancel the radial hydraulic load that a single volute puts on the shaft at off-design flow.

The hydraulic heart is the Double-Suction Impeller, a double-suction design fed from both sides simultaneously. This buys two things. Axial thrust cancels hydraulically, because the two suction eyes pull in opposite directions, so the bearings carry little more than rotor weight. And each eye swallows only half the flow, which roughly halves the NPSH required compared with an equivalent single-suction impeller — the reason split-case pumps tolerate marginal suction conditions in big water installations. Leakage back from discharge to suction is controlled at renewable rings: a Casing Wear Ring in each casing half running against an Impeller Wear Ring at 0.3–0.5 mm diametral clearance. When efficiency drops after years of service, replacing these rings restores it.

Rotating element

The Pump Shaft spans between bearings with the impeller keyed at mid-span by the Impeller Key and clamped by Sleeve Nut pairs. Renewable bronze Shaft Sleeve journals protect the shaft through the sealing boxes. The whole element — shaft, impeller, sleeves, and bearings — lifts out as one balanced unit, and plants commonly keep a complete spare element so an overhaul is a swap measured in hours.

Each end of the shaft runs in a Bearing Assembly: a Ball Bearing in a cast Bearing Housing doweled to the lower casing, closed by a Bearing End Cover, sealed with Oil Seal lips, and on oil-lubricated builds fed by a Constant-Level Oiler holding the bath at centreline. The outboard bearing is usually a duplex pair fixing axial position; the inboard floats to absorb thermal growth. A Shaft Deflector slinger keeps gland leakage out of the housing.

Sealing

Where the shaft passes through the casing, each side has a Shaft Sealing System. The traditional arrangement is a packed Stuffing Box: five graphited Packing Ring turns with a Lantern Ring two rings deep, fed discharge-pressure water through the Seal Flush Line, compressed by a two-bolt Packing Gland adjusted for 20–60 drips a minute — packing must leak slightly or it burns. Because suction pressure sits at both boxes (a by-product of the double-suction layout), sealing duty is mild, and conversion to cartridge mechanical seals is straightforward where drips are unacceptable.

Drive train and installation

A Flexible Coupling with two keyed Coupling Hub halves and a replaceable Coupling Element connects to the Drive Motor, typically a 4-pole TEFC motor from 15 kW to several hundred; an OSHA-compliant Coupling Guard encloses it. Pump and motor mount on a common Baseplate whose welded Base Frame is grouted onto Anchor Bolt foundations; laminated Shim Pack stacks under the motor feet bring shaft alignment within 0.05 mm TIR, and a Drip Rim collects gland leakage.

Application notes

Split-case pumps reach efficiencies above 90% at best efficiency point and hold high efficiency across a broad flow range, which matters at municipal scale where a point of efficiency is real money. Their limits are equally clear: the axially split joint restricts them to moderate temperatures and pressures (the gasketed flange cannot match a radially split barrel at high energy), and the double-suction impeller wants straight, symmetric suction piping — an elbow close to the suction nozzle in the wrong plane starves one eye and causes noise, vibration, and premature bearing wear. Five diameters of straight pipe, or a properly oriented elbow, is the standard rule.