Centrifugal pumps are used in a variety of applications where fluid has to be
delivered from one point to another. Some applications require special
materials because some of the components of the pump come in contact with
corrosive mediums like acid, salt water, oil or mud.
A well-known application for a
centrifugal 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 prevents
unwanted particles in the liquid gas from passing through the pump. This is
important because these particles could cause damage if they find their way
into the turbine. Because these pumps are designed to operate with the highest
possible efficiency, the pump needs a nearly 100-percent homogenous incoming
flow with a minimum amount of turbulence. Requirements such as these are why
the positioning of the filter in the system design is so critical.
When deciding how to fix the
filter in the intake side of the pump, designers may initially consider a
tapered section internal retaining ring. However, there is the risk that the
lugs of the ring could cause unwanted turbulence, since the incoming flow could
be influenced by these barriers.
A constant section single-turn
snap ring can be considered as an alternative, but the gap created by this type
of ring can influence the incoming flow, as well.
One solution to these issues is
to use a retaining ring that offers a 360-degree closed surface without radial
deformations which could influence the incoming flow negatively. A two-turn
spiral-wound internal retaining ring will do the job. Another advantage to
using this type of ring is that it can be combined with a single-turn wave
spring with overlapping ends to balance possible axial play in the application,
which can result from an array of manufacturing tolerances as well as thermal
expansion during operation of the pump.
When it comes to material
selection for these rings, AISI 316 Stainless Steel is the standard for
salt-water contact. For other applications with high corrosive mediums and
higher temperatures, Inconel X-750 is the most common material. Both spiral and
wave springs can be made out of any material that meets the demands of the
application.
Using the combination of
spiral retaining ring and wave spring to fix the filter element allows for the
ring to be easily disassembled using the standard removal notches on the ring
and 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.
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