I just bought a replacement jet pump for a house well. It is
supposedly self priming. The definition of self priming isn't what I
thought. It is self priming after the intake pipes and volute are
filled with water.
Self priming to me would mean that the pump could literally prime
itself after all the plumbing was hooked up. There would be no need to
fill the intake with water.
Am I wrong or is the manufacturer stretching the truth?
I thought they use to give a certain amount of "feet of head" that it would
self prime. Today manufacturers seem to spend an awful lot of time coming up
with deceptive terms to describe the power of the device
A jet pump will never be self priming. It uses part of the water to
provide the lift. No pump can lift very far. If you want a pump that
will work even when the lines have drained then get a submersible and
put it down the well.
Not being familiar with your particular pump ....is it deep or
shallow?.... and jet pumps in general, but according to what I see on
wiki, a jet pump is a velocity type pump, NOT a positive displacement
pump. You need a positive displacement pump to pull a vacuum,
therefore a prime. It appears a deep jet pump sits right in the water
source, and therefore needs no prime. Perhaps that's what your
supplier is calling "self priming". Either way, sounds like you've
been conned, sorry to say.
Someone educated me on positive displacement pumps and how much they
can lift a while back. A perfect vacuum is about 32 feet of water at
sea level so that is the absolute max that you can lift with any
pump. No water pump can get anywhere close to a perfect vacuum. In
practice lifting 20 feet would be amazing.
i.e. USS Cole attack.
Portable pumps could not siphon the floodwaters out of the engine room.
"The ship's small portable pumps could not boost the water out of the
three-story-high engine room. Grasping for a crude solution,
Peterschmidt suggested cutting a hole lower down--in the side of the
ship just above the waterline. No commander relishes punching a hole in
a wounded ship, and slicing steel was dangerous. With fuel thick on the
surface of the water in the engine room, the risk of fire from a stray
spark was grave. Reluctantly, Lippold agreed to cut the hole. The
alternative, said Peterschmidt, was to "lose the ship."
An enlisted man cut the hole; the ship did not burn; the pumps were able
to get ahead of the flooding".
Bill - Former US Navy Metalsmith and Damage Controlman USS Salem Ca-139
In Hamptonburgh, NY
A deep jet pump has the jet at the bottom at the water intake. I don't
know how you make it work without pumping water through the down pipe to
the jet. Must be a check valve at the intake.
A shallow well jet pump has the jet attached to the pump. When the
jet/pump are primed (just at the pump, not much water) it will lift the
water out of a shallow well where the lift pipe is not full of water
(limited lift as in james' post). It might be reasonable to call this
self-priming. There is a check valve at the intake to normally keep the
lift pipe full of water.
That makes sense. The check valve keeps the pump immersed and also
provides a enough of a seal in the pipe to pull a vacuum. I can see
how a bad check valve (or flapper valve) could put the kibosh on the
whole system. Perhaps the OP has neglected this issue. We didn't get
much info from the OP other than, it don't work.
I haven't actually tried it yet. Self priming to me meant no need
to fill the volute and supply lines with water before starting the pump.
The directions with the jet pump said I need to do that. So I was
wondering what "self priming" was supposed to mean.
The set up we have is similar to the one on this page:
The well is only 25' deep. The pump and pressure tank are in the
There used to be artesian wells on this farm long ago. No need to
pump water for livestock. The irrigation wells gradually took the water
levels down so the artesian wells are history.
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