8/14/2019 How a Self-Priming Pump Works _ PumpStoreUSA
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but they can move much more slowly. The propeller blades on a
cruise shipturn at around 100RPM, while a jet turbofan engineturns
at 10,000 RPM or more.
What's Different About a Self-Priming Pump?
A "self-priming" centrifugal pump overcomes the problem of air
binding by mixing air withwater to create a fluid with pumping
properties much like those of regular water. The pumpthen gets rid
of the air and moves water only, just like a standard centrifugal
pump.
It is important to understand that self-priming pumps cannot
operate without water inthe casing.
Here's how it works:
During the priming cycle, air enters the pump and mixes with
water at the impeller. Water andair are discharged together by
centrifugal action of the impeller into the water reservoir. The
airnaturally tends to rise, while the water tends to sink.
Air-free water, now heavier than air-laden water, flows by
gravity back down into the impellerchamber, ready to mix with more
air coming in the suction line. Once all air has beenevacuated and
a vacuum created in the suction line, atmospheric pressure forces
water up intothe suction linetowards the impeller, and pumping
begins.
Recirculation of water within the pump stops when pumping
begins. The next time the pump isstarted, it will "self-prime" --
that is, it will be able to once again mix the water and air in
thecasing to create a pumpable fluid until the pump is fully primed
again.
This type of pump differs from a standard centrifugal pump in
that it has a water reservoir builtinto the unit which enables it
to rid pump and suction line of air by recirculating water
withinthe pump on priming cycle. This water reservoir may be above
the impeller or in front of theimpeller. In either case, the
"self-priming" capability of the pump comes from the pump's
ability to retain water after the very first prime.
So Can I Just Start a Self-Priming Pump Any Time, Even If It's
Dry Inside?
No. A self-priming centrifugal pump must have water in the
casingin order to operate. Youcannot pull any self-priming pump
right out of the box, turn it on, and expect it to pump. If
it'sfull of air, it won't prime. "Self-priming" refers to the
pump's ability to repeatedly turn anair/water mixture into a
pumpable fluid -- NOT the ability to create a vacuum (literally)
out ofthin air. In fact, you should never try to run a self-priming
pump without water in thecasing. It's dangerous and will often lead
to seal failure.
Nothing here is intended to replace or stand-in for proper
training and/or the use ofyour pump's owner's and safety manuals.
ALWAYS READ THE SAFETY ANDOPERATION MANUALS BEFORE OPERATING ANY
PIECE OF MACHINERY,
http://www.pumpstoreusa.com/knowledgebase/suctionlift/http://www.honeywellaerospace.com/pdf/CFE738DA.pdfhttp://www.nps.gov/glba/InDepth/learn/preserve/projects/whale/documents/Kipple_CoralPrincessUWAcousticRpt.pdf
