I have learned along the way that the back flow of air through the pump IS definitely a problem, especially when working with air tight systems or relatively low height water columns. For this reason, I have added two mechanism to aid with the control of the fill and drain cycles. I have also added a central "manifold" through which all air flows, allowing for expansion/experimentation.
The air escaping through the planters, when the reservoir empties, was also a problem, so I added a separate bottle that I call a bubbler. The bubbler redirects the escaping air and reduces the bubble size, reducing splashing, vibrations and effectively extending the pump on time. I suppose it could be used as a planter as well. Don't know what you'd call the bubble method.
The MODULARITY has been expanded so that the "HUB" of the system is the Bubbler and the TEE below. Everything else is swappable. You can change reservoirs and/or reservoir types as well as "planter lines" and types of planters at your whim. This allows for experimentation and expansion without having to disturb that which does need to be disturbed.
I do plan on improving/screwing with stuff as time goes on and required a "productive" window sill garden that accommodates different designs and methods, without starting from scratch each time. This what I've come up with and hope to be adding "Modules" as time goes on.
Step 1: Modular Reservoir
1 ea 2L pop bottle with cap
Approx. 18 inch length of 3/8 inch OD Vinyl tubing (trim as required in final setup)
1 ea 7/8 inch length of 7/16 inch OD tubing
1 ea 5/8 inch length of 1/2 inch CPVC tubing
Hot melt glue (Silicone would probably be best)
WHAT I DID
1. Drill one each 5/16 inch and 13/64 inch holes in the cap as shown.
2. Cut both ends of the 2 ft length of tube on an angle as shown.
3. Thread the 2 ft length of tube through the 5/16 inch hole in the cap as shown.
4. On the end of the same tube, that will be outside of the bottle (cap orientation), slip the 7/16 and 1/2 inch pieces over each other as shown to form an adapter.
5. This adapter will leak without tension applied, so hot melt glue as shown to seal.
5.Place cap on bottle and adjust tube so it reaches the bottom of the inside of the bottle.
Step 2: Bubbler Assy
1 ea narrow and relatively tall soft drink bottle w/cap
Plastic mesh bag(s)
1 ea 1 inch length of 1/2 inch CPVC tubing
1 ea 1/2 inch CPVC TEE connector
WHAT I DID
1. Drill 13/64 inch "vent" hole in the bottom of the bottle as shown.
2. Strip mesh bag(s) of anything other than mess, such as labels or string.
3. Loosely stuff mesh into bottle as shown. Evenly distribute inside bottle to avoid channels where large bubbles can form and run.
4. Drill a 9/16 inch hole into cap and expand with a piece of 1/2 inch CPVC tubing as shown. Place cap on bottle.
5. Place the TEE on one end of the 1 inch piece of CPVC tubing and the bubbler bottle on the other as shown.
Step 3: DWC Module - Deep Water Culture
1 ea 2L pop bottle
1 ea small pop bottle w/cap
1 ea 13 inch piece of 7/16 inch Vinyl tubing (mine was a 12 inch scrap and was minimally long enough)
Hot melt glue
Approx. 4 inch piece of coat hanger wire
1 ea aquarium air stone
1/4 inch aquarium air tubing as required... at least 1 foot
WHAT I DID
1. Cut a 5/16 inch slot in one of the recessed groves on the bottom of the 2L bottle as shown.
2. Cut one end of the 7/16 inch tubing on an angle and insert same end just inside the slot. Put tension on the tube and glue in place as shown. I used two elastics to secure will glue cooled, which are in the rest of the pics and are not necessary, but could be used as min/max markers.
3. Bend wire as shown and use it as a clip, at the neck of the bottle, to secure other end of 7/16 inch tubing in a vertical position.
4. Cut a 1 inch hole near the top of the bottle, opposite the tube.
5. Using scizzors, cut the neck off of the small bottle and insert into 1 inch hole as shown. Use a small bottle as they are not "flared" like the 2L are and it makes for easier insertion into the 1 " hole.
6. Drill a 13/64 inch hole into the cap.
7. Insert air tube through through 13/64 inch hole and put the air stone on the end that will be inside the bottle (again, cap orientation).
8. Put cap on the "side" cap and adjust tube so that the air stone rests on the bottom.
NOTE : Stones, and any submerged hole for that matter, will clog over time changing the associated rates. Routine observations of the full cycle wouldn't hurt to keep wandering variants under control if necessary.
Step 4: Flood and Drain Module
1 ea 19 inch length of 1X4 pine (same length as a pop case)
3 ea 1 inch thread detergent bottle caps (convenient)
1 ea pop bottle lid
1 ea 1 inch length of 1/2 inch Vinyl tubing
3 ea 1/2 inch lengths of 1/2 inch Vinyl tubing
3 ea 1/2 inch CPVC TEE connectors
1 ea 1/2 inch CPVC 90 degree elbow
WHAT I DID
1. Drill four equally spaced 1.25 inch holes at 4.5 inch centers w.r.t. each other. (same spacing as a pop case)
2. Build "interface" from bottle cap to I/2 inch CPVC connectors. Please see pics below for details. I made 3 using detergent caps and 1 from a pop bottle cap.
3. Secure bottles and "interfaces" through holes as shown.
4. Interconnect the bottles using 1/2 inch CPVC or Vinyl tubing. I use Vinyl for this because of its' "flexibility", excuse the pun, but would probably use CPVC in a larger or permanent setup for its' rigidity.
Step 5: Manifold Assy
Please note that a gang valve, with it's individual line controls, would be preferred for multiple lines, but for those who do not require such controls................
WHAT I USED
1 ea several inch length of 1/2 inch CPVC tube
2 ea end caps for same
1 ea 13/64 inch drill bit
1 ea 1/64 inch drill bit
1 ea small, self tapping screw
Air tubing as required during assembly
WHAT I DID
2. Install end caps on each end.
1. Drill 1 ea 1/64 inch hole, near one end, into, but not through tube.
3. Tap 1/64 hole using small, self tapping screw and screw in fully when complete.
1. Drill 3 ea 13/64 inch holes into, but not through, tube as shown.
3. Insert aquarium air tubing securely into holes as required.(not shown)
PRESTO - A one input / two output (at least in this case) air pressure manifold with a passive, adjustable, pressure relief valve. Please excuse any incorrect terminology. Additional holes (ports) could be added as required until maximum air usage limit is reached or reservoir no longer empties completely.
Step 6: Modular Planters
4 ea 2L pop bottles
WHAT I DID
1. Cut the bottom off the bottles.
2. Drill several small drainage holes in the bottom piece.
3. Invert bottom piece and force into the top piece as shown. Trim if required, but it should be a snug fit.
In the photos, only one is complete, the other three are for demonstration purposes only.
Step 7: Assembly
Hopefully the pics speak for themselves.
Step 8: Operation and Operating Parameters
Pump comes on and pressurizes the manifold, initiating the emptying of the reservoir up the tube and into the Flood and Drain unit, as well as the bubbling of the air stone in the DWC unit. This continues until the reservoir completely empties or equilibrium is reached between the opposing forces. It can be "tuned", and will be discussed seperately. As the reservoir empties, the bubbles will be redirected, largely, up the tube and into the bubbler rather than the air stone.
The greater the resistance from the air stone, the faster and more completely the reservoir will empty.
Pump goes off and the water that has evacuated the reservoir returns under the force of gravity. The returning nutrient pushes the air up and out, into the manifold, and out through the DWC air stone as well as any other leak available. The bubbling of the air stone will reduce as the weight of the returning nutrient diminishes, until all of the nutrient returns or an equilibrium of the opposing forces is reached. This can be easily tuned as well.
Please see video for demo of unit w/DWC only as a vent -
Please see video for demo of reservoirs only-
Tuning is achieved by varying the opposing forces, such as gravity and air pressure. Generally speaking, gravity affects various "thresholds", while air pressure affects rates and the ability to reach the thresholds or a state of equilibrium. At least in my understanding and my ability to explain same. Lets just say, it's a balancing act.
The effects of gravity can easily be varied, and observed, by increasing or decreasing the height of the planters w.r.t. the reservoir or by varying the depth of the air stone in the DWC unit.
The effects of air pressure, acting against gravity, can be regulated by the porosity of the air stone in the DWC unit, by varying the depth of the "self tapping screw valve" in the manifold or reservoir lid, or any other method of controlling the "air tightness" between the air pump and the reservoir.
Using air tightness only, one can overcome the issues with the slow drain rates regardless of pump used, as long as it can supply enough air and pressure that is. With the DWC unit eliminated, the excess air will simply vent out the screw valve thingy.
NOTE: Only one complete system can go onto any one individual pump because of the pressure loss that will occur when/if the reservoir empties. Any slower systems will stop filling, and start draining, when the first one starts bubbling. One larger, shallow reservoir would be preferred over multiple reservoirs in larger systems.