Length of flood-drain cycle

[jaybee]

I have been digging about (superficially!) and can't find a definitive (maybe there isn't one) answer on optimum FD cycle length.

er, is there one?

My system seems to be happy with anywhere between 5 and 45 mins so far. I may well ask 'her who does the planting' to plant symetrically in both beds and try them on different rates.

[Murray]

There isn't one, within reason.
Auto siphons sort themselves out and the length of time is determined by the volume of the bed.
Smaller bed fills more quickly and therefore the auto siphon will trigger sooner than the auto siphon in an adjoining larger bed.

The actual litres per minute being pumped into any bed is governed by the auto siphon.
If there is not enough water coming in, it will not start,
If there is too much water coming in, it will start but will not stop.

If you are employing a timer together with a fast fill slow drain system then , obviously the length of the cycle is determined by the timer.
Fill time is dependant on your pump capacity but is typically 15 minutes or less.
Drain time is dependant on the total volume of the grow bed and the size of the outlet hole and is typically between 30 to 50 minutes.

[Jens UK]

hello everybody, just the thread i am looking for....

Jens here from the UK, building my first system (3 IBC CHOP)

got my syphons running well from the start (affnan style with breather pipe)

i made the GB exit pipes from 21mm overflow pipe as the next size up here is 32mm and am concerned about the flood/drain times.

at the moment flood is 20 mins. and drain 15mins.
if i supply more water to bring down the flood time, the drain time increases dramatically as the exit pipe is strugling to put out much more water than is coming in.

should i bring the flood time down?
would a syphon with 32mm piping work?


thanks

jens

[Murray]

Hi Jens and welcome.

A 32mm overflow pipe will work better and help it to drain quickly. Pity you cannot get 25mm PVC pipe. We find it is ideal.
How have you got the breather pipe set up ?

Those flood and drain times you have are ok

[Jens UK]

hello Murray,

thanks for the quick reply, great forum!

plumbing supplies in the UK are a bit limited unfortunately, i am always jealous when i see the kind of fittings people use in the US etc. on you tube

the breather pipe is like the ones you have on the outside of your syphons, i found that it breaks the syphon much better with it. probably not necessary if i swap to 32mm pipe and faster drain time.
i ll do a thread with pics. soon.

cheers

jens