Third of 4-part article
Precautions for handling viscous liquids
Recommended precautions for centrifugal pumps in high viscous liquid service:
For pump designers
Precautions for handling viscous liquids
Recommended precautions for centrifugal pumps in high viscous liquid service:
For pump designers
- Ensure that there is adequate NPSH margin for the selected equipment.
This is one commonly overlooked area because the old traditional practice
of correcting a water performance into a viscous performance did not
include correcting the NPSHR. ANSI/HI Standard 9.6.7-2004 now includes
a method for correcting a known water NPSHR into a viscous NPSHR.
- Ensure that the shaft, key, and driver size are good for maximum viscous
horsepower. An upset condition where the liquid temperature falls below
the rated temperature will increase the liquid viscosity resulting in higher
than expected viscous horsepower.
- Consider the worst case scenario. For example, pumps exposed to severe
winter conditions may require insulating jackets with steam tracing at their
suction piping and part of their casings to heat the liquid and reduce its
start-up or initial viscosity to a more manageable level.
- For pumps with mechanical seal flush piping system that requires cyclone
separator, the cyclone separator may not function efficiently in high viscous
liquid service. Design changes may have to be made such as using an
over-sized orifice and cyclone separator to compensate for the effects of
high viscosity.
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For pump operators
In the context of this article, a high viscous liquid service is defined as one where
a viscous correction (correction factor) has to be applied to the capacity, head, or
efficiency of a water performance curve.
[ * ] Some information are excluded in this article. Read more.
R: 1111-PRFO - viscosity handling precautions
C: design, operation
Beta version
- To protect the mechanical seals from possible product solidification, and
to prevent the orifice in the seal flush piping from getting clogged, do not
operate a pump until the product temperature is within + or - [ * ] degrees
of its rated temperature.
- Every time a pump is shut-down its mechanical seal should be flushed
with a suitable flushing liquid, such as kerosene, to prevent residual
viscous liquid from solidifying in the mechanical seal.
- For installations in an environment that is subject to seasonal temperature
fluctuations, the pump should be monitored regularly for signs of unusual
temperature drop that will cause the liquid's viscosity to increase beyond
what had been anticipated for the service. Operating the pump under this
upset condition can damage the equipment or its driver. (In anticipation of
such possibility in extremely cold environment, some pumps are provided
with steam tracing, including at the suction piping, to warm up the liquid.)
In the context of this article, a high viscous liquid service is defined as one where
a viscous correction (correction factor) has to be applied to the capacity, head, or
efficiency of a water performance curve.
[ * ] Some information are excluded in this article. Read more.
R: 1111-PRFO - viscosity handling precautions
C: design, operation
Beta version