Solenoid valves are an essential part of any timed electronic water system. It allows water to pass through a particular tube, and it is therefore essential to the correct functioning of the system. If you find that there is no water being sent to a particular area of your garden, or if you find that the plants in your greenhouse are not being watered, then a quick test of the valve should show you whether or not this is the cause of your problems.
Step 1 - Locate the Solenoid Valve
Remove the electronic water timer from the tap, and take off the back using a screwdriver. The solenoid valve will be inside, connected to both the timing mechanism and the inlet flow device. It is made up of two parts: a coil of copper wire (which forms the solenoid), and a plastic plunger which is used to limit the flow of water (which forms the valve). You can leave this part in the timer, but you may need to remove the battery or power supply from the latter before you perform any kind of test.
Step 2 - Test With a Multimeter
The quickest way to test the solenoid valve is to apply a charge directly to it. There are two wires which cross directly above the valve as it lays in the timer that you will touch with a multimeter. This should send a charge onto the valve, and if it is functioning normally, it will open. If you want to make sure that you are applying enough power to the valve, then you can take a lamp or torch bulb and hold it to the wires while the multimeter is supplying the power. A sufficient charge will light the bulb. In the event that the voltage is correct but the valve does not open, you will need to remove the whole solenoid valve and replace it.
Step 3 - Perform a Homemade Test
For those not lucky enough to possess a multimeter, there is another simple test you can perform using the bulb and a battery. Press the battery onto the wires which surround the solenoid valve, and then use the torch or lamp bulb to test that there is enough power going through. The bulb should light up, just as with the multimeter, and if the valve is working then it should also open.
You may also perform this test with an ohmmeter, checking for anything below 3.4 ohms or so.