Deep Pit Vertical Long Shaft Pump

The Deep Pit Vertical Long Shaft Pump is purpose-engineered for pumping from deep pits, sumps, tanks, and wet wells where the pump must be located above the liquid level. Unlike submersible pumps that operate fully submerged, vertical long shaft pumps have the motor and upper bearings located at grade level, with a long shaft extending down into the liquid. The key innovation of our cantilever design is that the shaft is supported only at the top, with no bearings below the mounting plate. This means no bearings ever contact the pumped liquid, regardless of how deep the pit is. This design eliminates the single most common point of failure in deep pit pumping: bearings that are submerged in abrasive, corrosive, or solids-laden liquids.

The cantilever principle is elegantly simple yet highly effective. The pump shaft extends downward from the motor through a hollow column pipe, with the impeller mounted at the very end. The shaft is supported only at the top by heavy-duty bearings located above the mounting base, completely outside the liquid. The shaft is sufficiently rigid to operate without intermediate bearings. For extremely deep pits (over 8 meters), the shaft diameter is increased to maintain critical speed margins. The absence of submerged bearings eliminates the need for lubrication below grade, for bearing replacement in confined spaces, and for bearing contamination by the pumped fluid.

The hydraulic design is optimized for deep pit service. The impeller is of the semi-open or enclosed type, depending on the fluid. For clean liquids, enclosed impellers provide maximum efficiency. For liquids containing solids, the semi-open impeller with adjustable clearance maintains performance without clogging. The volute casing is attached to the bottom of the column pipe and is submerged in the liquid. The casing is manufactured from cast iron, ductile iron, bronze, or stainless steel, selected based on the fluid corrosivity and abrasiveness.

The column pipe connects the mounting plate to the pump casing. The column pipe is manufactured from steel tube with flanged ends. The shaft runs inside the column pipe, protected from the external environment. For deep pits, the column pipe is supplied in sections with flanged connections for easy assembly. The column pipe also serves as the discharge riser, with the discharge flange located at the top of the column pipe at grade level. This eliminates the need for discharge piping running down into the pit.

The bearing system is located entirely above grade, accessible from the surface. The bearing housing contains heavy-duty angular contact or spherical roller bearings that support the shaft and impeller weight. For deep pits with long shafts, the thrust bearing must support the weight of the shaft and impeller plus the hydraulic thrust. Bearings are oil-lubricated with a constant level oiler. Bearing temperature monitoring (RTD) is standard. For extremely deep pits (over 12 meters), we offer forced oil circulation to the bearings.

The shaft material is selected for strength and corrosion resistance. Standard shaft material is stainless steel SS420 or SS630. For corrosive service, SS316 or duplex stainless steel is used. The shaft diameter is calculated to ensure that the first critical speed is at least 25 percent above the operating speed. For long shafts, the critical speed analysis is critical to avoid vibration.

The drive motor is mounted vertically above the bearing housing. The motor is typically a vertical hollow-shaft motor with a thrust bearing that carries the weight of the rotating element. For smaller pumps, a C-face motor with a solid shaft can be used. Motors are TEFC (Totally Enclosed Fan Cooled) for outdoor installation. For variable flow applications, we offer VFDs with inverter-duty motors.

In summary, the Deep Pit Vertical Long Shaft Pump delivers reliable service in deep pit applications with no submerged bearings, eliminating a major maintenance issue.