If your outflow pipe is larger than your inflow your going to end up with
cavitation unless you can reduce the outflow. If you have a piece of smaller
diameter on the inflow than what is on the outflow it would be easier and
cheaper to put a valve on the outflow . It does not hurt a pump to restrict
the outflow, you dont want to restrict the inflow however.

"SW" wrote in message
...
Would downsizing the pump be preferable to restricting outflow. Inflow
I will correct, but even then, if the pump was too high output it
would still cavitate. True?

On Thu, 08 May 2003 23:21:09 GMT, "Ted"
wrote:

On the Sequence pump website there is some troubleshooting guidelines and
I
remembered that it refers to cavitation problems and what to do. I have
copied that below.
Hope it helps.


With the pump running, slowly close down your valve on the discharge side
of
the pump. If the noise goes away, then you were hearing cavitation.
Cavitation is caused when the pump isn't getting water re-supplied
quickly
enough. To remedy this, you need to
1. Reduce the output by partially closing a valve on the discharge, until
you reach a point where the cavitation stops.
2. Increase the diameter of pipe on the suction of the pump.
3. Shorten the length of the pipe on the suction of the pump.
4. Reduce the numbers of elbows on the suction of the pump.
5. Lower the elevation of the pump.
Any one or combination of the above changes will help eliminate
cavitation.

"J. Douglas Mercer" wrote in message
news:Vnpua.774319$L1.218044@sccrnsc02...
Don't know.
Interesting topic though.
Cavitation refers to a "cavity" when the upstream pressure exceeds the
ability of the ambient pressure to fill the vacancy.
Mostly used in submarines, though, sometimes aircraft.
"Drag" might be a better word for it with aircraft.


"SW" wrote in message
news I have an inground pool. 2 inch plumbing throughout, except necked
down to 1 1/2 right before the intake to the pump. The output goes
through a filter system which has pressure gauges and then to the
pool
return line (2 inch) and the spa return (also 2 inch). The pump is
putting out 1 1/2 to 2 hp. When the pump runs, it sounds as if there
are bubbles in the intake line. NOT the pump itself, but the intake
line leading to it. I don't see any air in the pump or lines. When I
close off 1/2 of thr output by closing down the pool return, leaving
only the spa line open, the presssure in the filter line jumps from
15
psi to 22 psi and the noise in the intake instantly stops. Open the
pool return line again, and the noise instantly returns. Is this
cavitation? The motor seems to run hot, but has had no problem
putting
out flow or tripping breakers. What can I do? I can't reasonably
change the intake to 2 inch without spending big $$ as all the valves
will need to be changed.

Is this cavitation or an air leak. I've never seen cavitation before
,
and know little, but it sure seems like it to me.