google "cycle timer" that is more or less what you are after.
But remember that is actually a fairly high duty cycle for a submersible pump and may shorten it's life.
Why do you want it to run so often?

To be honest I'm just following what I read in a book. What frequency would you recommend instead, please?

Hi, google Apollo 2 repeat cycle timer, or Apollo 12 repeat cycle timer and you'll get one company's quality looking product ... which seem to be in the the retail range of $70-$90 for these types of devices ... that is great for short interval repeats, with the important detail (in my view), of these also having a daylight sensor to not be operating in the dark when the plant is trying to get some sleep.

But I think griz knows what he's talking about and unless you are forced by a specific need like in real aeroponics misting, try to avoid subjecting your pump to repeat startup surges so frequently. It is not uncommon for a pump to require quadruple its rated power to get moving before it can operate normally. It's a good bet the economical pumps windings (and capacitors if any) aren't designed to last as long with such frequent surge demands...

RDWC is a somewhat generic description that can be assembled in a number of ways. Would it be possible to run the system continually with a water fall the aerate the solution? another alternative would be to run it over night to aerate the water and leave it off the bulk of the day. this would be somewhat dependent on how the volume of water to root ratio, growth cycle, and water temperature but would likely keep your plants growing.
I used to use a watering cycle of, I believe :30 on and 1:45 off, with less frequency during the night time. the timer I used was digital, cast about $30, and have 14 on and off cycles available each day. I basically set my timings around what was available.
If you could post a pic of describe how you system will/does operate, that would be most helpful.

$25 shipped. i bought one, but havent installed it, but looks well built. ive had other cycle timers that could control more finitely, but this one seems fine.

http://www.ebay.com/itm/221197850993?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

Here is a link that might be useful: timer

For lower power applications (taking into consideration initial surge requirements) this Chinese relay looks like it could be adapted. @ $13.50 shipped to USA if you like to tinker I'd check it out if I had more free time. It is hard to understand the specification which gets confused in translaton. The seller will give you any ranges you want on the "on" and "off" cycles up to 30 minutes if you just tell him your choice.

http://www.ebay.com/itm/281103870225

you might need a vacuum tube plug, so if anyone wants to investigate this, ask him if this $2.45 (shipped & tracked) plug fits:

http://www.ebay.com/itm/270724124019

Not sure I would trust my garden to it until checking it out better, and it would probably need to be kept dry to be sure nothing blows up ;-). Not recommending it to anyone who isn't willing to fool with wiring this sort of thing, but on the other hand if it can be made to work it would be good for DIYers to know about such an economical option.

(Note, the total repeated cycle is the sum of "on" plus "off" when comparing to a mechanical dial timer so e.g., 10m on plus 30m delay would be a 40 min cycle.)

This post was edited by PupillaCharites on Thu, Jul 4, 13 at 12:50

Many thanks for taking the time to help me. I have uploaded an image of the 6 oxypot bubbler system which I am trying to convert to recycling. Any recommendations as to what the time cycle should be will be most welcome.

I'm still trying to understand what you are exactly doing which looks very intersting btw, is it that before the rez-only bucket somehow regulates the level of everyone else by just worrying about the level in it? But before you had no way to recover or mix nutrients to balance heavy and light users? But once you shoot the load of nutrient in, it is stuck downstream until you toss it out?

If your project is to back-circulate and take advantage of mixing in the level controlling bucket, what would you do, just put another rez below everything and pump into the level control bucket and get the return from the end of the line somewhere, dumped either in the new rez or simplify everything and just connect downstream directly to the control bucket with the pump? Looks like it has airhoses independently and they'll stay the same.

If I get this system mod (I don't mind saying dumb things if I'm totally wrong about it since I'm inexperienced), what is the purpose of such frequent cycling? Is there some super aeration going on in the control bucket? I can't see any possible reason not to run it continuously and just stop it a few times a day maybe to have an opportunity to add in a way that the movement doesn't fool you into putting too much in and maybe having an accident. Or is the running very vigorous or causing too much heat with the double intent to super aerate too?

Heck if I owned that baby I'd drive her without stopping (not sure about night- and just manually stop it when I felt like checking rest levels easily) and turn the control leveler bucket into a tower by stacking a couple more buckets on it to enclose waterfall with a cheap laptop fan off eBay on it all for something like 10-20 watts including the fan and water pump!

Hope someone experienced can correct any bad ideas I have, but that would be my newbie suggestion.

EDIT: OK, I now get the reason for the cycling since there is only a one way bridge into each bucket. So it goes in and drains out...so what needs to be done is pump X liters in and rest for X liters to drain out. If X= say 4 liters for each bucket, that's 24 liters. A pump operating at 80 gph , call it 320 l/h will fill in around 4-5 minutes, and then it will drain in less time likely and can rest while the new water is used, while the removed water mixes with the control bucket. So your times make a lot of sense for that setup. Sounds to me like you were in the ballpark, though doubt half your frequency would make much difference.

This setup doesn't seem as good as it could be IMO. It woould be more interesting to me to swap out the control bucket for twin larger rez's in place of the original and opposite at the end of the stream. Why not grow stuff in the downstream rez while you are at it... That way you could double or triple the cycle time, have more tolerance in the tide levels and my thinking is get much better mixing.

This post was...

Pupilla,
I believe the rez in the center is the "control" bucket. since the system is not airtight, the water level of all buckets connected by the drain line will be the same. in the control bucket is a water pump that pushes water to each of the grow buckets through the 1/4" feeder lines entering into the top of each grow bucket. That is how the system get recirculated.
Andy,
If your outlet lines are larger than your input lines(and your valves are fully open), you can run the water pump continuously. It will always drain faster than it will fill. well assuming the pump isn't very powerful but even then the system can only pump as much water into the grow buckets as is available in the control bucket.
If I explained it correctly to pupilla, that system will probably not aerate correctly. the flow of nutrient entering each grow bucket will probably not be enough. you might consider putting a 'T' in your water pump in your control bucket with one leg "watering" the grow buckets and the other creating a waterfall inside the control bucket for aeration.
Just run the pump 24/7. If in doing so, the pump pushes out water faster than in comes back into the return line, simply make the return lines larger. 1/2" PVC is hard to overcome with 1/4" feeders.

Thanks, I understand the need to ensure the drainage exceeds the input. I am told that the nutrient/solution only needs to be moved around normally during daylight. Does the air pump need to oxygenate 24/7 or can it too be reduced during the night hours?

Sorry to ask basic questions but these sort of issues don't get covered in the hydroponics books!

This post was edited by andysollitt on Tue, Jul 9, 13 at 11:42

I've re-read the above and found it answered my question. Thanks to all who helped.