Blackmer E-Series Pump Shaft Support

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Multiple support points address deflection

Shaft Deflection

While pump technology is designed with longevity in mind, there are common problems that can disrupt operation. One is the deflection of components in and around the pumping chamber. Deflection occurs when the effects of pumping forces on the rotor causes the shaft to bend.

Pumps are designed to deal with some level of deflection during rotation, but uncertainty arises when the shaft does not have adequate support. Shaft deflection can create larger problems, such as bearing damage and failure, mechanical seal leaks and failure, excessive vibrations, premature and excessive component wear and failure, and even broken shafts.

So long as the pump apparatus provides proper support across the shaft, deflection isn’t a pressing concern. This article looks at Blackmer’s E Series patented between-the-bearing support system as part of their seal-less mag-drive internal gear pump. Specifically, how it minimizes deflection to keep the pump and its critical components running longer.


Strong Support System

Blackmer’s between-the-bearing support system uses an eccentric spindle supported at three points – the head, the crescent location and the back of the containment canister. In addition to the three main points of contact, the spindle system includes two radial bushings and a thrust bushing. Once installed, it sits stationary in the pump while the rotor turns around it.

The eccentric spindle features a shorter shaft, larger diameter and three bushings. This means hydraulic forces are supported across the spindle rather than centered on weak points. Working together, this spindle system is designed to curtail deflection issues typical of cantilevered load designs.

Standard cantilever design on internal gear pumps has support shortcomings across the shaft. The typical bushing placement is near the rotor, with a single bearing on the other end of the shaft. This leaves the remaining segments of the shaft poorly supported, allowing those areas to suffer deflection during operation. With Blackmer’s between-the-bearing support system, extended radial bushings support the entire length of the rotating element spread out across three spots, minimizing deflections.

With this support system and the 2 in. (50.8 mm) spindle design (on Blackmer’s 3" 69 size pump), deflection is minimal to the tune of 0.005 in. (0.13 mm). Comparatively, using the same pump size, deflection in one 0.44 in. (11.1 mm) shaft deflects 0.056 in. (1.4 mm). That amount of deflection promotes rotor, casing, and head wear, which can lead to early shaft seal failure. Premature wear becomes less of a concern with the between-the-bearing support system.


Pumps are limited by design and the performance parameters. Without proper shaft support, internal gear pumps coul suffer from deflection and rotor or shaft failure. The E-Series between-the-bearing support system acts as a preventive maintenance tool in this case.

About the author:

Michael Coburn is the Product Manager for Blackmer Gear. He can be reached at