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Centrifugal Pump Bearings
- As one of the parts that is manufactured to the most exacting
of tolerances, the ball bearing does not deserve it¹s reputation
in the process pump market as being one of the two parts of a
pump that is constantly failing. Yet that is the reality. To
alleviate this situation, we need some understanding of what
bearings do and what we need to do in order to let that happen.
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Multiple Pump Operation
- One of the challenges that face pump users quite frequently,
comes into play when more than one pump is required to operate
at the same time on the same system. With such multiple pump
systems, there are two arrangements where the operating
characteristics of the different pumps can be considered to
provide a single combined performance curve.
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Slurry Pumping
- "One Size Fits All” most definitely does not apply in
this area of pumping. Even when we define a Slurry as a
mixture of solid particles in a liquid that is usually
water, we are still concealing a multitude of
applications behind a simple sounding phrase. The
variety of solids that are handled in slurry form covers
an extraordinary wide range of products and waste
material.
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Can't Find the Forest for the Trees
- To one degree or another, we’ve all done it! We’ve
found ourselves so far into the trees, we can’t find the forest. In
other words, we get too close the problem to identify a logical
solution. On one occasion, I overheard a discussion on the merits of
having a new pump supplied with a stainless steel bearing housing.
The logic offered was that an acid was leaking from a valve above
the proposed location of the pump. The leak would land directly on
the pump bearing housing and cause considerable corrosion damage.
This discussion ranged back and forth for quite a while before
someone inquired, “Why don’t we stop the leak!”.
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Making the Most of Mechanical Seals
- Any practical discussion of mechanical seal
operation starts with the acceptance that it takes more than just a
good seal to secure the leakage in a centrifugal pump. The seal must
be properly installed and protected in a strong pump that is
properly designed to accommodate a mechanical seal.
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Mechanical Seal Selection Basics
- Once referred to as the “black box” inside a pump that
no-one really understands, the mechanical seal is that
other part of the process pump that is constantly
failing. To help alleviate that unworthy accolade we
must understand the most important aspects of the
mechanical seal.
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Some Dangers of Batch Processes
- At the end of every batch, the
pump was vibrating so badly, it would shear the hold-down bolts and
move off the baseplate. The pump in question was used to empty the raw
wort (essentially unprocessed beer) from a large tank. The line to the
pump suction came from a bottom connection in the tank, through a 90
degree elbow and a short section of line to the suction flange of the
pump.
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The Pitfalls of Pump Piping
- There are three major problems
associated with poor pump piping.
1. There is a scarcity of accessible information available on the
topic.
2. No one pays any attention to it when installing a pump.
3. It can remain undetected and cause repetitive pump failures for
many years.
As a consequence of 1 and 2 above, most pumps are piped up
incorrectly. In fact when we look at the way many pumps have been
installed, it resembles a “plumbers nightmare.”
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Cavitation or Not?
- Is this really
cavitation I am dealing with, or is it air entrainment or
recirculation? The reason for that question is that all three
conditions have almost identical symptoms. Air entrainment and
recirculation will also cause the same rumbling/rattling noise and
high vibration as cavitation, as well as the recognizable impeller
pitting damage. The major difference is that cavitation is an NPSH
problem, while the other conditions have nothing to do with the
suction pressure or NPSH.
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What the Pump was Designed to Do
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Contrary to popular opinion, a centrifugal pump is not
designed to develop one head at a single capacity as
requested by the pump purchaser. In fact, a pump is
designed and produced to supply a whole range of
head-capacity conditions as identified on it’s
performance curve. The pump will operate on that curve
only if it is driven at the particular speed for which
the curve is drawn. However, the actual conditions on
that curve at which the pump will run, will be
determined by the system in which it operates.
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- Centrifugal Pump Specific
Speed Primer -
There is a multitude of pump designs
that are available for any given task. Pump
designers have needed a way to compare the efficiency of
their designs across a large range of pump models and
types. Pump users also would like to know what
efficiency can be expected from a particular pump
design. For that purpose, pumps have been tested and
compared using a number called the specific
speed (NS) which helps with these
comparisons.
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- How to Avoid Cavitation
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Cavitation can be avoided if the NPSH Available is
larger than the NPSH Required.
Article presents clear explanation of cavitation.
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- More on
Cavitation -
Article deals with the relationship between N.P.S.H. required and
cavitation.
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- Stable and
Unstable Curves
- What can be done to avoid or minimize
unstable curves? API 610 frowns on pumps with unstable
curves, and in fact prohibits them from situations where
pumps operate in parallel. When is this a problem and
why?
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How Does Pump Suction Limit the
Flow? -
One of the claimed advantages of the centrifugal
pumps over positive
displacement pumps is their ability to operate
over a wide range of flow. Since a centrifugal pump operates at the
intersection of a pump curve and a system curve, by varying the system curve the
operating point of the pump is easily changed.
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- Looking for Standards in Pump
Selection Software
- One of the more perplexing
issues that pump users, buyers and specifiers face is
how to effectively size and select a pump. It seems,
despite internal efforts by manufacturers to
streamline the pump selection process, that pump users are
calling out for a standard software platform to select
pumps.
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How
Does a Siphon Work?
- A siphon is a length of tubing that
allows you to transfer fluid from an upper location to a
lower one. The key feature of a siphon is that the fluid
is moved upwards from its start point before it turns
down towards its exit point. It seems
as if the fluid is being magically raised upwards
without the use of a pump.
A
siphon is just like a typical pump system.
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