help? filter pressure issue!

[badutahboy]

I'm just curious if someone can tell me what my filter pressure should be... this is a brand new pool, above ground 18x33x52" deep... I have a 1 hp dual speed pentair pump, and a 150 pound sand filter...

On low speed, the filter pressure needle barely moves... when I kick it to high, the pressure jumps to about 12 PSI..

Anyone got any input? Is this normal?

[Sumo1]

I've got no experience with 2speed pump but I'd be thrilled if the highest my gauge ever went was 12! That means you've got very little restriction in your system. When I replumbed our church pool, I added 2 new returns and replaced all the skimmers, feeding new 2" lines. That pump (2hp) has the least restriction of the 4 and flows a steady 140gpm. The other pumps have at least a little bit of 1 1/2" in them and their flow rates are a bit lower. Three of the pumps run at 18-20psi but the 140gpm pump runs at 12psi.

I hope to get a 2speed pump next year for my pool. Enjoy!
Hal

[mas985]

Usually, low speed will be about 1/4 the pressure of high speed. So I would expect it to be about 3 PSI on low which may be too low for the guage to read depending on the guage. Filter guages start to lose accuracy after some time and especially if they have to weather the winter.

[badutahboy]

Usually, low speed will be about 1/4 the pressure of high speed. So I would expect it to be about 3 PSI on low which may be too low for the guage to read depending on the guage. Filter guages start to lose accuracy after some time and especially if they have to weather the winter.



Thanks for that... like I said, this is a brand new system, and the gauge works when it's on high, so I suspect that it's just a matter of the gauge not being able to read reliably at such a low pressure.


Given that fact, any advice about how I should handle backwashing (in terms of knowing when to do it)... should I just follow a schedule, or should I stick to the normal logic of waiting for pressure to rise, even if it means not backwashing all season?

[Sumo1]

A pool service friend of mine backwashes all his customers' filters every week, regardless whether they're sand or DE filters. I think that's ridiculous and wasteful. If I were in your situation, I'd wait for a noticeable rise in pressure.

Hal

[mas985]

The pressure rise for a dirty filter will be different on low speed vs high speed so given your situation, you are probably better off picking a high speed pressure rise to backwash. For backwashing, I probably wouldn't do a backwash before a 4 PSI rise on high speed although some people go much higher than that but then the flow rates can start to be impacted by quite a bit.

[badutahboy]

Awesome.. thanks for your help folks

[waste]

As aylad can tell you, she doesn't use a pressure gauge, you can use the flow from the returns to 'gauge' when the filter needs to be cleaned. When the filter needs cleaning, the flow out of the returns is a lot lower than when the filter is clean. But, as Mark said, you can use the pressure rise on high speed to determine when you need to backwash.

[Poolsean]

Most people in the industry will use a 7-10 psi rise as a guage, regardless of the type of filter. I have a cartridge filter and go by a 7 psi rise.
It's best to use your starting pressure on high speed.

[mas985]

Most people in the industry will use a 7-10 psi rise as a guage, regardless of the type of filter. I have a cartridge filter and go by a 7 psi rise.
It's best to use your starting pressure on high speed.

I never quite understood why the industry recommends such a high PSI increase. 7 PSI is over 15 feet of head increase and I bet if you look on your pump head curve, you will be decreasing flow rates by over 25%. A 10 PSI increase is close to 23 FEET OF HEAD. Way too high for my comfort.

I clean my filter when it is not more than 1 PSI increase. Of course this is still only twice a year but even if I had to clean it once a month, I don't think I would let it get much above 3 PSI.