"Tom Bahama" wrote in message
ink.net...
For my in-ground swimming pool, I recently had installed a new 48 sq. ft.
DE
filter system with a new 1 hp pump. Suction piping from pool is 1.5 inch
swaged up to 2 inch at pump inlet. When operating on the first day, air
bubbles were in the pump strainer basket and a loud rumbling noise was
coming from the diverter valve. No air bubbles were visible in the pool
however.

I think you have way too big of a pump, but it depends on your head
pressure. The 1.5" suction line will limit your max water flow to about 60
GPM (assuming it is PVC). Usually a 1/2 to 3/4 hp pump will easily get you
to 50 - 70 GPM. If your pump is trying to pull more than this through that
pipe, you may deteriorate it prematurely or even worse cause cavitation in
the pump. That could be the noise you're hearing and may be the source of
bubbles. The bubbles could also be from a suction side leak, so check the
pipe and pump fittings carefully, and strainer basket lid too.

I had the repair guy come back out. His diagnosis - the pump was too
close
to the pool (it's about 15 ft. away) such that too much water was being
sucked in by the pump. His remedy - downsize the pump impeller. I told
him
that according to the pump ooperating manual, the pump should be located
as
close as possible to the pool to cut down on resistance and friction.
But
that clearly fell on deaf ears.

The distance shouldn't matter too much, but you will pump less water with a
longer line. I think you may want to be pumping less water, however, this is
better done by adding a restriction to the output and not the input. An
inlet restriction will make cavitation worse. A smaller impeller would help
if the pump is oversized, but the proper size pump would be a better
solution.

He also said that I should keep the vacuum plate cover off the strainer
basket and only use the cover when vacuuming the pool. Is this guy
feeding
me a line or what?

I can see how you'd get slightly greater flow through the inlet pipe with
that plate removed, but the problem is the 1.5" inlet pipe itself and not
the 1.25" or 1.5" hole in the skimmer plate.

Could what I think are air bubbles be turbulence instead?? I did notice
after the downsizing and after a couple of days air bubbles still swirl in
the strainer; like before, no bubbles are getting back to the pool. The
noise at the valve isn't as noticeable and sometimes is nonexistent, and
the
pump does not lose prime when not operating. Since new system cost me
$1,500, I want to make sure it works right and I get my money's worth!

How big is your pool and how much water do you need to pump to circulate it
all in 6 to 8 hours? What is the max flow rate through your filter? What is
your operating head pressure at the flow rate you need -- do you have a
pressure gauge on the top of your filter? Without knowing all of this, you
cannot choose a proper pump.

I have a 3/4 HP pump on my pool, and I bought a flow meter to see what was
really going on. If I pump directly to waste, I get 75 GPM through my 1.5"
pipes and the pump cavitates terribly. Under normal operation, I get 50 to
60 GPM. As the filter gets dirty, it goes to 40 and even 30 GPM. If you look
at most pump curves, their flow rate is severely affected by head pressure.
If you don't spec it close, you could have greatly increased or decreased
flow rates.

You can test this excessive flow theory by closing off some of your pool
water inlets with rubber stoppers (or a few kids with hands). If you have a
gauge on your filter, close off water inlets one at a time and check the
gauge. If things quiet down and bubbles disappear as the pressure goes up,
you probably have found your problem. Do not exceed 35 PSI on your gauge
though, or you may damage things.

I'm considering a high head 1/2 HP pump as a replacement for my existing 3/4
HP pump. This pump will flow between 50 and 60 GPM under just about all
conditions of operation, from dumping directly to waste to a really dirty
filter. My filter pressure gauge currently reads 12 PSI when clean, and 20
PSI when really dirty.

--
Mark
Kent, WA