"Brandon" wrote in message
news:240xb.22208$m24.2187@fed1read02...
"Mark or Sue" wrote in message
news:1iPwb.306614$Fm2.324871@attbi_s04...
Yes. And its a circultar solution because the filter head pressure
affects
how much water your pump can pump. Most pumps have appalingly flat
curves,
which means a slight change in head pressure can have a dramatic effect
on
flow rates.

I am still at a bit of a loss on what head pressure is, and what changes
it. I am assuming it is directly affected by flow rate through the
filter.
I.E when the sand is dirty, you head pressure increases, correct? So,
when
you backwash and the sand is clean, that is "normal" as read on the
pressure
gauge?

Head pressure is caused by the resistance to flow and is measured in feet of
water or PSI. This is the pressure that must be overcome to move the water.
Pipe length and water flow rate increase head pressure as they increase.
Pipe diameter lowers head pressure as it increases. A filter has a given
head pressure and the manufacturer will state what it is. This is the
"clean" head loss. As the filter becomes dirty, head pressure will increase.
For a sand filter, at 10 PSI more head than normal, it is time to backflush
(so you want a pressure gauge on your filter).


I ordered a Hayward 310T( I got it for 355 delivered, a heck of a deal
considering everyone else I found was 400 plus freight), just because it
is
rated at 92 GPM. I am leaning towards a 1 hp Pentair whisperflo pump
which
will push at about 82GPM at 20 feet of head( I have 2" plumbing).

Any thoughts?

Glad you have 2" pipes, so you should be able to flow this much water. As I
said before, I think a smaller pump run longer is better than a large one
run faster. My pool is slightly larger than yours (17,000 gal) and I run a
3/4 HP pump at around 50 GPM (actually 30 to 60 GPM depending on head
pressure). When the pump dies, I'll replace it with a 1/2 HP pump that has a
better flow curve (almost always 50 GPM instead of only 50 GPM when the
filter is clean).

That being said, what you propose should work, it will just cost more when
you have a water problem to remedy because you'll need to run it 24 hours a
day for up to a week.

--
Mark
Kent, WA