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Cleanable In-Line Components 229
equipment. While it is possible to use gas overpressure to transfer fluids from a
vessel, the ability to use speed controls to alter flow rates, pressures, and levels
make the use of pumps very common in process systems.
Installation of pumps needs to consider accessibility for maintenance such
as seal replacements, lubrication, and general housekeeping. It is also important
to consider physical location as the prime movers for pumps include electric
motors or hydraulic motors, both of which require attention to cooling as well
as the fact that they often contain many crevices and openings that are not
desirable from a clean process environment perspective. Electric motors with
fan cooling are often considered to be sources of particulates not desired in
clean process spaces. These issues are sometimes addressed by placing pumps
in service or “gray” space and allowing the piping to penetrate walls to/from
the process. It is also important to consider the needs for system drainage, line
pitch, and vibration potential. In many process systems, pumps are equipped
with low-point casing drains to enable complete evacuation of fluids from
the system.
The hygienic aspects of pumps need to include appropriate materials of
construction for the main pump chambers and, perhaps more important, all
sealing points. With the exceptions of air-operated double diaphragm (AODD)
and peristaltic type pumps, all other pump types include some sealing method
on arotating shaft. The complex nature ofrotating seals is inherently difficult to
flush and clean. Often the best design option is to place the seal mechanism
outside of the product contact zone, relying on aminimal elastomer exposure to
product and cleaning solutions. Another design method utilizes double mechanical
seals, with two rotating seal surfaces, and the option to use a flushing
liquid in the area between these sealing faces. In all cases, the rotating seal faces
rely on either a flush liquid or the process liquid to lubricate the rotating
mating surfaces. Although this lubrication uses extremely small quantities, it
nevertheless presents aneed for cleaning solutions to also be utilized to clean
these surfaces.
Centrifugal Pumps
Centrifugal pumps designed for hygienic applications often include impeller
retention methods that completely isolate the driving shaft from the liquid being
pumped (Fig. 13). Static seals are used to prevent fluids from touching threaded
fasteners such as impeller retaining bolts or the impeller includes an integral shaft
that can extend beyond the fluid chamber (Fig. 14). The result is that process
residues can be easily rinsed and cleaning solutions effectively cover all product
contact surfaces. Similar construction and impeller retention methods are used for
rotary lobe pumps. In fact, whereitwas once necessary to remove the lobes or rotors
from rotary lobe pumps to assure access of cleaning solutions, there is now
available, positive rotary lobe pumps that do not require disassembly prior to
using CIP procedures.
Progressive Cavity Pumps
Progressive cavity pumps are also available for CIP applications. It should be noted
that extreme care must be taken to prevent dry running of the rotor inside of the
stator as this can cause rapid destruction of the mating surfaces of the stator.