Sandfilter Backwashing

[cdnvic]

Ok, you have one accident with a tank that was put together incorrectly. Can you now show me where someone was killed, or even hurt with a normally functioning sand filter? It's just if you want to give out advice you should be able to cite credible evidence. Making up fantastic stories about people killing themselves backwashing a pool is a little unnecessary don't you think?

we could go on splitting hairs but for me it's too boring as i find it boring to google for the incidences i have mentioned NOT "made up".

if it makes you happy then we can also agree that

quote: "...a fractured skull, fracture to the eye orbit, fracture of two front teeth, right temporal lobe brain injury, brain stem injury, trauma to the cervical vertebrae and facial lacerations"

is something to take lightly as it happens to each of us pool owners quite often.

as far advice is concerned... those i gave are well founded. i don't poke my nose, make and insist (even after receiving the facts) on irrational statements like "air in the pipes"

if the water level in 60 m² pool drops 1' (30.5cm) then we are talking of nearly 2,000 liters or 530 gallons. one should switch on brains, do a mathematical estimate what pipe length is needed to take that volume before making these kind of statements

to sum it up: you Honourable Sir have no idea as far as pools are concernded. but as far as "no idea" is concerned you possess a lot of it and the same goes for your maths.

You can try and dig your way out all you want after making a ridiculous statement but the fact remains that people are not killed backwashing pools. Making statements like that helps nobody, and did nothing to help the OP deal with the problem. As for a 60m2 pool, the volume of it is impossible to determine without knowing the depth so your calculations are useless.

As for my knowledge of pools I have not only the knowledge, but the training and certification to manage commercial pools to go along with it. I stand by my statements. Yours have proved to be rubbish.

[Naam]

"As for a 60m2 pool, the volume of it is impossible to determine without knowing the depth so your calculations are useless"

:D

hmmmm... if the water of a 60m² pool drops 30cm one needs the pool depth to calculate the volume of the missing water? even a fifth grader with a 'C' in maths would find that statement utmost ridiculous. please keep up the good job of making fun of yourself. saves me the hassle.

edited: bekos my vife allviss zays i shoodd not yewse to mutch tchermann krammar und tchermann vords vhen i talks to edyukated peeple who's natiff lankvich is der english.

Edited July 8, 2007 by Dr. Naam

[cdnvic]

I'm just happy so long as the killing stops

[tamsin]

it wouldn't take a 'professional' two minutes to have explained the backwashing process, let alone 2 hours, and try getting the pool equipment supplier out for some advice once he's already had your money.

the pool has 60 sqm of tiles, i know because i bought them, so the interior of the pool, sloping from a mere 1 to 1.5 metres, 6 metres long and 4.5 wide approx., is filled with that amount of water - when it hasn't gone down the drain, for whatever reason. the 1.5 hp pump and the sandfilter are located snugly side by side in a small pump room. so don't know how there could be an air lock. so far, no one's been blown up. what a way to go, blown up by your own swimming pool in your desert island villa, how the folks back home would laugh ...

[Naam]

6 metres long and 4.5 wide approx

that means the pool surface is not (as you stated first) 60m² but 27m². i don't understand the expression "airlock" but you might have some air accumulated in your filter. that can be easily checked (AND should be done periodically) by opening the little valve located on top the filter (combined with the pressure gauge) to bleed the filter from air but only when the pump is running. if you open the bleeder valve without the pump running you will suck IN air.

[cdnvic]

it wouldn't take a 'professional' two minutes to have explained the backwashing process, let alone 2 hours, and try getting the pool equipment supplier out for some advice once he's already had your money.

the pool has 60 sqm of tiles, i know because i bought them, so the interior of the pool, sloping from a mere 1 to 1.5 metres, 6 metres long and 4.5 wide approx., is filled with that amount of water - when it hasn't gone down the drain, for whatever reason. the 1.5 hp pump and the sandfilter are located snugly side by side in a small pump room. so don't know how there could be an air lock. so far, no one's been blown up. what a way to go, blown up by your own swimming pool in your desert island villa, how the folks back home would laugh ...

So approximately 33,750 litres in volume. That means about 270 litres for every cm of water level (using 1.25m as an average level). Let's be conservative and say your level is dropping 15cm, which would be just past the skimmer outlet if you were at the correct level to start. That's 4000 litres. How long was this initial backwash?

Now, with the level dropping again once the pool was topped up and the pump restarted, if this drop was very quick it leads me to think a void has been created somewhere and the new water is quickly displacing it. That's actually the only thing that makes sense if the drop stops without any further action on your part (it's unclear from the description if this is the case) but 4000L is more plumbing than I have between a pool twice that size and it's pump room, a sizable distance away.

The only way I can think of that much water exiting the system that quickly is by it going directly from the bottom drain to the sewer. The pressure of the weight from 33000L of water is all I can think of that would push out 4000L fast enough to be considered "dropping like a rock". Is it possible for water to route directly out from your bottom drain without passing through the multiport valve? if such a drain existed and your gardener opened it by accident then two things would happen;

During backwash, water would be leaving from two sources (pump and directly from the bottom drain) causing a much faster than normal drop in water level. You don't really need a valve between the sandfilter and drain as the multivalve does fine so I'm wondering if and valve has been opened, is it possibly direct from the bottom drain? If a direct drain existed it would have to have a valve for obvious reasons.

After the pump restarted the system would have a void from when the strainers ran dry. As this was being filled from water drawn from the bottom, the water level would drop some until the void in the system was filled and water began recirculating back into the pool. This would not have been near as long a drop in level as earlier but it would have been fairly quick, and a couple cm is feasible depending on the volume of your plumbing. Did the water drop sharply as it did during the backwash or did you see it begin dropping and shut everything down just to be safe?

[Jai Dee]

The only way I can think of that much water exiting the system that quickly is by it going directly from the bottom drain to the sewer.

Deja vu... Didn't I hear that somewhere before?

[Naam]

The only way I can think of that much water exiting the system that quickly is by it going directly from the bottom drain to the sewer.

Deja vu... Didn't I hear that somewhere before?

:D

[tamsin]

after specific instructions NOT to fiddle with the sandfilter, arrived home yesterday to find the filter handle firmly lodged between the settings 'closed' and 'drain' and it will not budge - what the hel_l has he done now?

[Naam]

after specific instructions NOT to fiddle with the sandfilter, arrived home yesterday to find the filter handle firmly lodged between the settings 'closed' and 'drain' and it will not budge - what the hel_l has he done now?

is the pump off?

[tamsin]

is is now. he told me he'd cleaned the pool 'but water not come from waterfoon' (sic). so whether he'd tried to move the handle on the sandfilter whilst the pump was still on or not, difficult to ascertain. memory span of a gnat.

[Naam]

is is now. he told me he'd cleaned the pool 'but water not come from waterfoon' (sic). so whether he'd tried to move the handle on the sandfilter whilst the pump was still on or not, difficult to ascertain. memory span of a gnat.

looks like he must have tried to move the lever when the pump was on. but you did not mention whether you can turn the lever now. can you?

[tamsin]

nope. as i said, the bloody thing's lodged, stuck solid, will not move at all and i now have a nice cloudy pool with no means of filtering it. the handle WILL push down, but it won't budge to left or right. well, not without the aid of a monkey wrench, which i think might just break the thing (handle) off.

has the nitwit tried to turn the thing whilst the pump was on? (can't get a coherent answer out of him) what to do?

[Naam]

has the nitwit tried to turn the thing whilst the pump was on? (can't get a coherent answer out of him) what to do?

looks like it. switch off pump (for safety reasons). unscrew the top of the multiport-valve. i suspect that the seal between bottom and top is destroyed and blocks any attempt to turn the lever. can't think of any other reason.

if possible get first new seal from pool shop and replace.

[tamsin]

grit. unscrewed lever and plastic mount to find grit inside. who'dve thought a little bit of grit'd completely stall the thing. thankyou dr naam for your help. until next time ...

[Naam]

until next time ...

[cdnvic]

You really need someone different to service your pool. I'd lock the gardener out before he does any more damage.