These shut-off (or on/off) valves from Blumat brand are the quarter-turn valves you've been looking for! These valves are ideal for blumat watering systems. They can be installed in-line in any 8mm tubing, but we recommend super-flex. Simply remove the collar, and place the collar over the 8mm tubing. Then slide the tubing over the 8mm barb, screw on the threaded collar, and you are in a perfect position to irrigate your plants!
These can be used to turn on/off water supply to your entire garden, or just branches of your garden (or even individual plants, plant rows, etc.--your imagination is the limit!).
PLOT TWIST: These blumat fittings can also be used as purge valves. A purge valve is used to remove air, particulate matter, or other debris from a water supply line. This can be accomplished in two different ways. One is simply by concluding an 8mm tubing or line with one of these valves. The valve will remain closed 99% of the time, but should be opened if air/debris is suspected in the tubing. The air and/or debris will flow out of the tubing when the valve is opened.
The second way to install a purge valve in a blumat watering system is by cutting in the middle of a "loop" design, installing a 3-way 8mm Tee fitting, and installing one of these valves on the open-end of the tee. Simply open the valve to "purge" or clear your lines.