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Old 02-23-2010, 08:25 PM
GpsFrontier GpsFrontier is offline
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Join Date: Mar 2009
Location: Lake Havasu AZ.
Posts: 1,855

If I am understanding the ebb and flow process right the tube from the pump that fills the tray is also the drain tube back to the reservoir.
Yes, generally that's how a ebb & flow (flood & drain) system drains (but not to be confused with the overflow). Depending on your setup some more complicated setups might use a separate pump to drain the system. But as long as the reservoir is below the system itself, water (or any liquid) will always seak its own level. Meaning if one side is higher than the other, it will automatically equalize on both sides (seeking it's own level). So when the pump shuts off (stops pumping) the water in the high end will flow back to the bottom level until the top one is empty or the water level in both are equal.
Sounds simple but does this back flow cause problems with the pump over time?
I have never herd or seen any problems whatsoever. The only moving part in a typical pump is the propeller, witch is nothing more than a shaft with a magnet on it. When the electricity flows to the pump it creates an electromagnet spinning the shaft in one direction. When the electricity is shut off there is nothing stopping the shaft from being able to move in the other direction. You'll see how simple the design is when you disassemble it to clean it.
Would this action tend to back flush the pump filter and keep it clean?
Not really, it may a little but the water does not flow back with enough pressure to to do that. You will probably want to clean the filter once a week. I clean the reservoir and pump (including the filter) with every nutrient change. I would recommend cleaning the filters ever week regardless (even though I typically forget), because they can clog and stop the flow of nutrients to your plants. That's when I usually remember to do it myself, if not changing the nutrient solution weekly in that system.
How do you determine the size of pump that you need like for a 20 gal. tray or 4 five gallon buckets?
Most pumps have two ratings, gallons per hour and head height. Also some give the gallons per hour at different head height's. It really depends on your system. To me the most important is the head height. The head height tells you how high the pump will pump the water before the back pressure equalizes, stopping the flow of liquid. The higher it needs to go the more back pressure it needs to overcome before it can flow. So how much of a pump you need mostly depends on how your system is designed.

I generally try to get the most pump I can for the money (head height being the key factor). Because You can always lessen the flow, but you can't make it pump more than it's rated for. I never know what system I will want it for at a later date, so it's better if I can use a pump I already have instead of buying a new one. I attached a picture of a pump I got at Lowe's, it's my favorite pump of the ones I have (mostly because of head height witch is rated at 8.7 feet), and was about $45. I paid $30 for each of my other pumps (at a hydroponics store) and they are not even half the pump this one is.
How quick do you want to fill them to the point of overflow?
That's not really that important to me. My strawberry plants last summer took 40 min overflow (40-50 gallon in 4 different growing chambers), and my tomato's I have now only take 5 min to overflow (about a 8 gallon growing chamber). What is important is how you adjust your timer to make sure the roots don't become to dry, or drown/suffocate because of a lack of air/oxygen.
how long do you want it to soak before it drains? I read everything from a max. of 15 minutes to a quick fill and drain.
Their all right. It really depends on your system, growing medium, air temperature, humidity, type of plants, type of system you are using. So there is no real direct answer I can think of. Generally as long as there is moisture in the root zone that is enough. That's where the adjust-ability of the settings on your timer comes in handy. The roots need air/oxygen as well as water or they will suffocate and get root diseases, usually described as root rot. But you don't ever want to see wilting either.

Wilting will probably be either a lack of water, or result of heat or disease. You may also see wilting if the nutrient temperatures are too high, you want it to be below 72 degrees at all times. Depending on your system and amount of growing medium (or lack of), as well as type of growing medium, they will all be factors in how much moisture the root zone holds onto when the pump is off and the system is drained. You will probably need to do some trial and error with the timer to get the best fit of both (water & air) to the root zone of your plants.

The min on/off time for two of my timers is 30 min. These timers I usually have set for 30 on, 30 0ff all day during sunlight. At night the plants don't drink water, so I usually only have it run once (30 min) about every 3 hours until just before daylight. Then start the 30 on, 30 off, cycles again. If I had a 15 minute minimum on/off timer I would probably set it for 15 on, 15 off, all day. Or 15 on, and 30 off (or 30 on, and 15 off), depending on how hot it was and how long it took to flood the system. Observation is the best way to tell what's best for your plants.
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Last edited by GpsFrontier; 02-24-2010 at 02:47 AM.
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