24volt vs 9volt solenoid valves
The electric solenoid valve operates on 24 volt alternating current (vac) and is turned on and off by a timer called an “irrigation controller” or often just “controller”. All 24volt valves and controllers are compatible with each other. The exception to this rule is valves operated by controllers that are battery powered, that need 9volt solenoid valves.

Flow Control
The flow control is a separate handle in addition to the manual on/off control on the valve. The flow control bypasses the automatic valve features allowing the valve to be closed in an emergency by turning a handle just like a standard manual valve. More important is that it also allows the valve to be “throttled”, that is, the water flow may be adjusted to any rate desired.

Jar Top or Traditional Top Held on with Screws?
A jar top valve works as well as a top with screws holding it on, but it is faster to open for repairs.

Today’s valves are pretty maintenance free. Almost all automatic valve failures result from installation or design problems.
Dirt in the irrigation pipes. Inside the valve there are very small water passages that lead to and from the solenoid. Water must flow freely through these small passages. If a grain of sand or glob of algae gets into these passages it can block them and the valve will fail to open or (more likely) fail to close. It is critical to flush all the dirt out of the pipes before installing the valves. A 100 to 200 mesh filter installed at the water source connection can also help keep out contaminates that comes in with the water supply.
Almost all valve solenoid failures are caused by water getting into the solenoid. The water gets into them through the wires. The solenoid wires have multiple strands of wires twisted together with insulation around them. Because they are twisted there are very small gaps between the wires which form passages along the length of the wire. Water is sucked up through these small passages and deposited into the solenoid by capillary action. Thus it is critically important that the wire splices on the valves be completely water proof so that water can’t be sucked into the solenoid through the wires. You should water-proof the wire splices right after you test the valves!