Compressed Air Water Pump
COTS Commercial Off The Shelf timers
Arduino timer by Ralf
Do it yourself el-cheapo timer
This is my first attempt at the wiki so I hope I will do this right.
If you are really looking for an el-cheapo solution and all you need to do is to turn a solenoid on and off at adjustable intervals, take a look at the 555 IC.
It is about $1.69 at Radioshack, then you need two potentiometers (turning knobs), and a handful of passive components, getting away with the uC and laptop altogether.
With the values in the schematics, we would get 2 seconds on and 6 seconds off when putting the knobs in the middle.
I don't know enough about triacs so I would probably go for an old-fashioned relay and a transistor to amplify the current for the coil and isolate galvanically.
The relay could then in turn be used to control the air-solenoid.
Always be careful both with high currents, high voltages and pressurized air!
I took most of the construction from:
Another timer circuit design by Earthling
- 2' x 2" PVC pipe
- 2" flat PVC cap
- 2" Spigot x 3/4" Fips 
- 3/4" male thread coupling
- 3/4" brass check valve
- 2 x 3/4" male threaded PVC plugs
- 2' x 3/4" PVC pipe
- 2 x 3/4" hoses long enough to go down the well
- Ream out one 3/4" male threaded PVC plug with a 3/4" hole for the 2' x 3/4" pipe and attach them.
- Drill two 5/8" holes in the flat PVC cap and tap them to 3/4" for the air in and water out 3/4" male threaded PVC plugs. Use plumbers tape and attach the plugs. Glue the PVC cap to the 2' x 2" pipe.
- Remove the spring of the metal check valve like in the hydromissions slapshot instructions.
- Glue the 2" to 3/4" plug to the other end of the 2' x 2" pipe, attach the 3/4" male threaded coupler and the 3/4" check valve.
- Attach the hoses to the plugs with plumbers tape and clamps and test the pump.