"Mark or Sue" wrote in message
news:1iPwb.306614$Fm2.324871@attbi_s04...
"Brandon" wrote in message
news:dTNwb.21475$m24.21096@fed1read02...

Ok, so, lets say the pool is 14K gallons.
According to the link that Travis provided...
I could circulate the entire pool in...
3 hours at a flow rate of 77.78 GPM
4 hours at a flow rate of 58.33
5 hours at a flow rate of 46.67
6 hours at a flow rate of 38.89

So I need to find a filter that will handle the capacity that I want.
If
I
want the whole thing circulated in 3 hours, then I need a filter AND a
pump
that will move that much water correct ?

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?

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?
Thanks for all the information you have offered. It is much appreciated.
Brandon

Now what happens if I have a filter that will handle 60 GPM and a pump
pushing 85 gallons per minute?
In other words, can you oversize the pump to the filter, and what
happens?( or doesn't happen)?

Good question. The head pressure caused by the filter will increase as
flow
increases, but this isn't necessarily bad. If you pump more water through
the filter than it is rated for, I believe filter performance (quality)
will
diminish. Another problem I have is that when backwashing, the pressure is
really low so the pump flows even more than when filtering. I'm just on
the
edge of cavitating my pump when backwashing. If I bypass the filter
directly
to waste, the pump does cavitate so I can't do that. It is better to have
a
filter that slightly exceeds your pump capacity than the other way around.

Personally, I think it is better to have a pump running longer at low flow
than a huge one that filters the whole pool in two hours. There are times
when you want to run the pump all of the time (freezing conditions, algae
blooms), and a giant one will cost you more to run during those times. It
also takes time for the water to mix well and the things in it to
stratify.
This again makes long and slow better than short and fast.

Finally, realize that there is a speed limit in water pipes. If the pump
intake from the pool skimmer is 1.5" PVC pipe, you shouldn't flow more
than
60 GPM through that pipe. Otherwise, it will deteriorate faster due to
water
friction. For some reason, pressure pipes have a slightly higher speed
limit
than suction pipes, but for pools the suction pipe is usually the limiting
factor.

--
Mark
Kent, WA