Big leak due to Multipoint?

[hughR]

On an inherited inground concrete pool, perhaps 20 years old.
At random times after backwashing the Hayward sand filter with an old Multiport valve ('SFC' brand if that means anything) so the handle will have been revolved 360 degrees and put into two positions - 6 o'clock for 3 mins, then 10 o'clock for 1 min) the pool water level will decrease by about one and a half inches over 12 hours, regardless of pumping or not. This water loss only occurs maybe one time out of three after the filter has been backwashed. It's really a random thing and I don't think there's a leak in the pool itself, which was relined two years ago. Could an old multipoint valve be the cause of such a serious leak? There is no sign of water in the pumphouse.
I would like to have said the water loss is only when the pump is working but it appears not. This has been going on for about nine months now and over winter there was no problem as the pool didn't need backwashing!
Suggestions desperately needed - thanks.

 

[Bama Rambler]

If the discharge from the backwash line is below the water line and there's no vacuum relief then it would be possible for the water to syphon if the multiport didn't seal off after backwashing. However, if that were the case then it would leak a lot more with the pump running than with it off. I'd be inclined to believe the leak is somewhere else. Take some pics of the equipment and post them here.

 

[hughR]

Yes, actually think it does discharge more when running than when off. Waste pipe goes down to end of garden and empties into ground about a foot under the pool waterline - but difficult to see any water as pipe buried. Any ideas as to life of Multiports? Any suggestions as to new one? Also interesting to think it might not be the Multivalve syphoning - but what then?!. But it only happens after the backwash (again, not always) and it's a large amount of water to go down about 4" in 24 hours! :!:

 

[Bama Rambler]

Since you confirmed that the backwash line is below the pool water line and that it leaks more when the pump is running, I'd rebuild the multiport valve. That will be fairly easy and not very expensive to do. Be sure to lube everything up as you put it back together.

 

[hughR]

Thanks for your replies Rama - delay in responding has been due to pool shop not keeping appointments, as I feel rather too timid to do the work myself on the multipoint. Also just now the Hayward pump has sprung a leak underneath so perhaps both should be completely replaced, they must be 20+ years old - is this par for their life? Wish I could find good ideas for replacement models on these pages, is there anything like that?
Thanks again for your response.

 

[Bama Rambler]

If they are 20 years old they've had a good life. I wouldn't hesitate to replace the multiport valve with the same brand that's in there now. Hayward makes a model that directly replaces the one you have now so you wouldn't have to rework the plumbing. You might check with your local pool store and they might offer you a deal on a complete package, filter, valve, pump and all. The only thing I'd suggest changing would be the pump to a 2-speed model.

 

[waste]

Hi Hugh (Thanks for the Statue of Liberty! )

You may just have a couple of gasket or seal problems, which would be easier and less expensive to replace than the multiport or pump

Please let me/ us know a little more about where things are leaking (i.e. under the pump or out of the 'waste' port).

Also let us know what the 'pool dudes' say after they inspect the system - they may or may not be right