This is my first proper post after my “Hello from Barcelona” so please let me know if I'm doing anything wrong.
The problem I'm having is that the pressure in my sand filter goes up too quickly. Before I go into what is happening I’d better give you a bit of background.
About 7 years ago the mother-in-law changed the pump and filter. The pool professionals doing the work said that the filter wasn't big enough so changed it to the one in my sig (along with the pump). They also recommended using glass instead of regular sand so she took their advice and went with the glass. 3 years ago I took over looking after the pool from the handy man (whose level of expertise was to throw a few chlorine tabs in the skimmer once a week and rake out the leaves) and in my ignorance I carried on where he left off.
Last year I managed to start the pump with the return valve closed and promptly blew up and broke the screw threaded connector to the sand filter. I emptied the sand, changed the broken part, checked the laterals, half filled the tank, slowly put the sand back in and all went back to normal. The handy man had shown me the pressure gauge on the sand filter and told me that when the needle hits 2 (bar) it’s time to backwash. For two years I followed this advice which translates as 'a post backwash setting of 15psi' and a ‘time to backwash’ setting of 29psi'. I placed my hand in front of the return jets and could feel the pressure was quite low at 29psi and was Ok but not blasting out at 15psi. I mention this because a friends’ jets used to really be blasting the water back into the pool but you’d be hard pushed to see if mine were doing anything at all.
The glass was 6 years old when I put it back in, it didn’t look too bad but I had a nagging feeling that I should probably change it because the pressure kept going up too quickly. After a backwash (for 2/3 minutes) and rinse (30 seconds) the psi would be 15. If the floor had a thin film of dirt I’d hoover and after a couple of hours the pressure would be back at 29psi. Sometimes I’d have to backwash twice a day. I knew this wasn’t right so 2 months ago I decided to change the glass to see if this fixed the pressure problem. I still hadn’t discovered this site yet so just bought the only glass media available from a local DIY store and repeated the process. This time I decided to be more thorough and took out the laterals, inspected them and picked out the tiny bits of seeds stuck in the grooves until they looked like new (no damage). Placed a bowl over the open valve at the top of the filter and slowly half-filled with water using the bowl to evenly distribute it and then did the same with the new glass. I spotted straight away that the level was now much lower than it was when I emptied it. I followed the instructions and only put 80kg of glass in as this represented 100kg of sand but I'm convinced the old glass was at least 100kg (excluding what had been washed away in the alley through backwashing). The new level was just about half full but it used to cover the top return pipe (see link to filter) which would make it nearer ¾ full. Once everything was secure, I started the pump for a backwash and it let out a high pitch whine which had me ducking for cover. This is the first time I had turned the pump on in 8 months and after about 20 seconds it shut up and has not done it again but I've read it’s not a good sign if it does that and something could be on the way out.
Now here is where we get to my point.
Having read here that I should be backwashing much sooner than 29psi I did one yesterday when it was around 23 and afterwards it settled back to its usual 15psi. There was quite a visible brown film on the floor at one end of the pool so I hoovered that up whilst keeping an eye on the pressure gauge. After 45 minutes the pressure had gone up to 18psi (hoovering very slowly so as not to kick up the dust). I then connected up two homemade/Ebay bought 1 micron slimebags (another story), ran the filter and proceeded to top up the pool whilst washing some surface debris towards the skimmer. After 30 minutes of this the pressure gauge had now gone to 20psi. At this point I'm thinking ‘this can’t be right, by all accounts I should do a backwash now but I only did it just over an hour ago!” I then decide to hoover the other end of the pool which looks pretty clean but I wanted to test the new slimebags to see if they would catch anything. I open the side wall valve for the hoover (pipe already connected) and close the bottom drain and skimmer valves and the pressure instantly drops from 20 to 15 psi. I hoovered slowly for another 30 minutes and when I'm done I see the pressure has gone back to 20psi. I open the bottom drain and skimmer valve, close the side wall valve and the pressure has now gone up to 23psi (after 30 minutes of very light hoovering). That was 3 hours ago, I've just checked the pressure gauge and it is now on 25psi (with the slimebags removed an hour ago). I' going to leave it running and check it every hour just to see when it stops going up.
Whenever I open the side wall valve to hoover, the pressure always goes down 4 or 5 psi. If I hoover after a backwash it goes down to 10/11psi and then slowly starts to rise as I'm hoovering. I’m not sure what to make of this but my main question is why after a few hours does my pressure go from 15psi to 25psi? Admittedly it does it this quickly if I hoover but I've read on here that some people backwash once every few months but I have to do it once every few days.
It's probably not relevant but I'm getting small bits plant seeds and ...stuff through the return valves so I have another problem there with either the sand filter (don't think so) or the spider valve (checked it and it seems fine). I'll continue this subject in another thread so I don't confuse things.
So in summary, changing the sand hasn't resolved the pressure issue. The sand filter and spider gasket look fine, there's no leaks that I can see so is there a mismatch between the pump and the filter? Here are the links to their info:
Any help greatly appreciated (sorry if it's a bit long but didn't want to miss anything out).