sand filter "filter to pool" high pressure no flow.

[rayna]

hi I have a conventional sand filter for my 48,000 litre free form pool. I have recently (beginning of our season) cleaned up the pool which required flocking with a "Polyaluminium chloride" product. Once it had settled overnight I vacuumed direct to waste. did this two days in a row then on third day decided to clean up the few spots very small patches of flocked debris using the filter back to the pool in the normal way. Then backwashed all ok. On resetting after backwash and restarting filter to pool the backpressure went straight up to 1.1bar and I had no flow. Checked out recirculate option, backwash option both worked fine. Have since had pump and pipework apart and top off filter no obvious blocks. Filter takes two bags course and one of fine sand and water flow is to bottom gallery then rising up through bed to top discharge back to pool. What has caused this ??? Only thing I can suggest is that fine debris remains in filter sand bed in spite of normal cloudy backwash sighted and when I try forward flow to pool it binds up in some way. Water is absolutely crystal clear now. Any help appreciated.
Raynor J

 

[JohnT]

Welcome to TFP.

Since it works on recirculate, that pretty well eliminates a plumbing problem. When you backwash, how long do you let the pump run?

 

[Bama Rambler]

As said, Welcome to TFP. I agree with JohnT if recirc and backwash work normally it's most likely not a plumbing problem. I have a couple of questions.

1) What does your pressure normally run? You said that the pressure went to 1.1 bar (~16 psi) which to me isn't very high unless it normally runs much lower than that.

2) You said that you get no flow back to the pool. Is it truely no flow or is it just reduced flow? The reason I ask is that with absolutely no flow I'd expect to see higher pressures than 1.1 bar.

3) Do you have a filter top or side mount multiport valve?

It sounds like there's something blocking the flow through the filter. Maybe in the multiport valve or internal filter piping.

 

[PoolGuyNJ]

If the filter top is easily or still removed, scrape off the top 2" of the sand bed. Re-assemble and rinse, then filter.

Scott
PoolGuyNJ

 

[rayna]

Hi Answers are
Backwash runs for about 3-4 minutes till visually clean discharge.
I backwash whenever BP gets to about 1 bar
Normal running pressure to pool is about 0.2 to 0.4 bar.
No flow to pool at all.
Top mount valve.
Will do a sand scrape as suggested .
thanks all.
Raynor

 

[PoolGuyNJ]

May sound dumb, but check the returns in the pool and the any return side valve operation.

Scott
PoolGuyNJ

 

[Bama Rambler]

May sound dumb, but check the returns in the pool and the any return side valve operation.

I thought the same thing but they said that recirc works. If that's correct then the piping has to be ok.

.2 to .4 bar (3-6 psi) is pretty low for a normal running sand filter. Of course that's a non-issue as it normally runs that way.

If the backwash works correctly, it's leaning toward something in the multiport clogged up.

I'll be very interested in knowing what it turns out to be.

 

[rayna]

Hi again and thanks for interest. Have removed about 2" of sand and started up again. Did a short backwash first then "recirc" and then "filter to pool". I have some flow but pressure is only back to about 0.9bar.
Small quantity of sand particles out through the two pool eyeball return jets. Wouldn,t be 1/4 cup in total. I'm thinking that the fine debris has effectively blocked the sand and maybe I should go for a replacement charge. Seems odd because charge was new last year and swimming activity is only a couple of oldies three times a day during summer.
Filter chamber is 18" diam. 2' high with sand depth about 1'.
Top valve is absolutely clear and is fine except for a bit of bypass leakage.
Currently will leave it running for a while then do another backwash.
Anyone know the source of a simple venturi nozzle that I can fit on a hose to pick up the debris independantly from the pool bottom....McMaster-Carr?
Raynor J

 

[Bama Rambler]

Since backwash works, you should have a "waste" setting on the valve. Set it to that and hook up your vacuum to the skimmer and just vacuum to waste. That'll get rid of it.

 

[rayna]

Right. I think we need to put it down to inexperience..... what I have just done is to do a long ....backwash (~6-7 minutes) and though the discharge looked clear through most of that time maybe real fine stuff was being taken out, as I am now "filtering to pool" on about 0.4bar which is about the old normal.
many thanks all will comment again later.
Raynor J