Page 53 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

Change filters and strainers with more frequency.
Be sure all pipe gaskets and ring seals are perfectly centered
within the flange faces.

5. Lower the temperature of the fluid in the suction vessel. This
decreases the Hvp.
6. Pressurize the suction vessel. This increases the artificial Ha 23 ft
for every 10 psi.

To Reduce the pump's NPSHr
1. Use a pump ihth a larger suction flange. This lowers the Hi. An
example of this would be to change a 3 x 4 x 10 pump into a 4 x 6
x 10 pump. The 10-inch impeller needs to remain the same for
discharge pressure. However, by converting the 4-inch suction
flange into a 6-inch suction flange, the inlet losses would be
reduced.

2. Machine and polish the suction throat of the pump. This is
probably the worst casting, and roughest finish in the entire pump.
Center the suction flange on a lathe and ream-out the suction
throat. This reduces the Hi.
3. Machine open and increase the inside diameter of the eye of
enclosed impellers. This reduces the Hi.
4. Use a larger/slower pump. This reduces the Hi and Hf.
5. Use a small booster pump to feed the principle pump. This increases
the artificial head (Ha).
6. Use smaller capacity pumps in parallel. This reduces the Hi and Hf.
7. Use a double suction impeller. Convert an end suction centrihgal
pump into a split case horizontal design.
8. Use an impeller inducer.
As you can see by reading through some of these solutions to
cavitation, some of the changes are very practical, and others are not.

A few of the above-mentioned solutions to cavitation are almost comical and not
even cost effective. The idea is that they would work to reduce and stop cavitation
and the resulting seal, bearing and pump failure. Too many maintenance people
(engineers and mechanics) are running around in circles, wringing their hands, and
jumping up and down, trying to deal with cavitation. Who would have thought that
there are so many solutions, practical or not?

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