Plumbing Connection 1-2015

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PLUMBING CONNECTION AUTUMN 2015 63
vaporise the liquid provided there is at least some flow going
through the pump, but in a multistage pump, temperature
rise can be a real issue in the latter stages; particularly when
a pump has balance devices that bleed off warmer liquid
back to lower pressure areas. In these circumstances, the
bleed off liquid may vaporize and damage the internals.
MINIMUM FLOW?
The preceding discussion has focused on what happens
inside a centrifugal pump at low flows. The big question is
where do we draw the line to determine “minimum flow”? In
other words, when do the negative effects become a pump
reliability issue? This is a judgement call and there is no
simple answer to this question.
There are too many different types of pumps and pumping
environments to make a single generalised rule. Any decision
on a minimum flow values will always be a trade off between
convenience and pump reliability.
My recommendation is to be guided by the manufacturer
where possible.
An excellent clue is also normally provided by the
manufacturer’s published performance curves.
Where the manufacturer ceases to show information such
as efficiency or NPSHR, this is a strong hint that they do
not expect the pump to be operated in this region. When in
doubt, ask.
*This article originally appeared in Pump Industry
magazine. For a limited time, readers of Plumbing
Connection can subscribe for free to Pump Industry
magazine. Go to now to take
up this offer and get more information on pumps.
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„ Watermark Approved
All backflow devices are Watermark approved for
use with potable water.
„ Easy Maintenance
Self contained check modules for quick
disassembly with no special tools required.
„ TriforceTM Checks
Centre stem guided checks with replaceable seat
discs provide low head loss and easy servicing.
„ Compact design
Valves are much smaller and lighter compared to
the previous 40 series Conbraco/Apollo models.
For more information, please visit our website
or phone 02 8543 9811
Valves
manufactured in theUSA
WaterMark
AS2845.1WM-022183
ABOUT RON
Ron Astall is a Mechanical Engineer with extensive pump industry
experience including Engineering, Contract Management,
Applications, Sales, Marketing and Quality Assurance; particularly
in the Process and Petrochemical Industries in his role at United
Pumps Australia.
With his consultancy, Astech Pumping Services and through
Strategic Achievement, he has also been an active provider of pump
industry training. Ron is the current President of Pump Industry
Australia (PIA) and Contracts Manager at United Pumps Australia.