Re: Centrifugal Pump Suction and Cavitation Problem
07/16/2009 12:55 AM
You give us absolutely no information on the type, size, head and capacity,
of your pump/system and the liquid pumped assuming it isn't water. That info is
almost always needed to answer a pump question in order to get a useful reply.
All we know at this time is that your vertical lift is more than can be
supported by atmospheric pressure, as has already been pointed out. Assuming
the pumping elements have to stay where they are you are going to have to
figure out some other way to add energy to the liquid to give it enough NPSHA
to meet the pump requirement.
Certainly a submersible pump, vertical turbine pump or a vertical sump pump
might be a better choice. But that is likely a more expensive solution than
modifying the system to use the existing pump.
The simplest way to do this may be with an eductor variant of an ejector
pump. Also known as a jet pump. These are frequently used for small domestic
well water systems where well levels can drop below 4-5 meters below the pump
inlet. In the USA when you buy a "Jet pump" you usually get a
conventional horizontal centrifugal pump with a suction chamber and two pipe
connections on the discharge close coupled to a fractional size electric motor.
Included would be an eductor and a foot valve to place at the inlet down in the
well casing. The installation would require two pipes. One from the discharge
to carry part of the flow back down the well to the eductor below. The other
larger pipe would carry the larger volume of water back up to the suction
Note another type of pump, a propulsion system for watercraft, is also
referred to as a Jet Pump". This is a source of confusion that you will
have to filter out as these devices for boat propulsion are becoming
This general approach can be applied to larger pumps. It's a cheap answer to
an immediate problem; but take note the eductor process added to the pump
system will decrease efficiency. This is not a big deal on a one or two KW
pump. It is on a 25 or 50kw pump, especially one running on a high duty cycle.
Anyhow, I've given you a couple of good search phrases: "eductor"
and "ejector pump". Follow them on your favorite search source and
you'll find out more about these things. A good written reference source is Karassik,
et. al., "Pump Handbook", Mcgraw Hill. Chapter 4, "Jet
Pumps" written by Alex M. Jumpeter.