Summary

I built this motorized valve to automaticaly water some plants every day. It was made from parts i had laying around...
It is now working for about a year without failing once. Im pretty satisfied with it.

Instructions

The valve is a standard 3/4" part with 2 Gardena conectors.

The connector between the motor and the valve I made out of a normal screw cutte to the right lenght.
One hole goes through the center for the shafts from the motor and the valve. Another two threaded holes are used to fix the shafts with screws. One of the screws is longer so it can push the end switches.

I used these parts as end switches:
SSCTL10600:
http://www.alps.com/prod/info/E/HTML/Switch/Detector/SSCT/SSCTL10600.html

and i used this motor:
http://www.pollin.de/shop/dt/NTY2OTg2OTk-/Motoren/DC_Getriebemotoren/Gleichstrom_Getriebemotor_CBxx.html

Unfortunately the motor is no longer available in this shop and also i don't know if you can get these switches. Therfore you can't build this straight forward, but you can change the design or use it just as inspiration.

Motorized Valve