Pump Retaining Ring Selection

Centrifugal pumps are used in a variety of applications where fluid has to bedelivered from one point to another. Some applications require specialmaterials because some of the components of the pump come in contact withcorrosive mediums like acid, salt water, oil or mud.

A well-known application for acentrifugal pump is to deliver liquid gas into a gas turbine of a power plant.A
filter placed in front of the conveying units/impeller in these pumps preventsunwanted particles in the liquid gas from passing through the pump. This isimportant because these particles could cause damage if they find their wayinto the turbine. Because these pumps are designed to operate with the highestpossible efficiency, the pump needs a nearly 100-percent homogenous incomingflow with a minimum amount of turbulence. Requirements such as these are whythe positioning of the filter in the system design is so critical.

When deciding how to fix thefilter in the intake side of the pump, designers may initially consider atapered section internal retaining ring. However, there is the risk that thelugs of the ring could cause unwanted turbulence, since the incoming flow couldbe influenced by these barriers.

A constant section single-turnsnap ring can be considered as an alternative, but the gap created by this typeof ring can influence the incoming flow, as well.

One solution to these issues isto use a retaining ring that offers a 360-degree closed surface without radialdeformations which could influence the incoming flow negatively. A two-turnspiral-wound internal retaining ring will do the job. Another advantage tousing this type of ring is that it can be combined with a single-turn wavespring with overlapping ends to balance possible axial play in the application,which can result from an array of manufacturing tolerances as well as thermalexpansion during operation of the pump.

When it comes to materialselection for these rings, AISI 316 Stainless Steel is the standard forsalt-water contact. For other applications with high corrosive mediums andhigher temperatures, Inconel X-750 is the most common material. Both spiral andwave springs can be made out of any material that meets the demands of theapplication.

Using the combination ofspiral retaining ring and wave spring to fix the filter element allows for thering to be easily disassembled using the standard removal notches on the ringand a screw driver to service or change the filter element.

Henry Yates, is technical sales engineer of Rotor Clip Co. Inc.,Somerset, NJ. For more information,go to http://www.rotorclip.com.