how does electric sprinkler valve work?

[hj]

The diaphragm in the valve has a small "equalizing" port. When the solenoid is closed water passes through that port into the area above the diaphragm and allows the diaphragm to close with some assistance from a spring. When the solenoid is activated, it opens a port between the upper chamber and the downstream piping allowing water pressure to raise the diaphragm and the system begins to water the lawn. When the solenoid closes, the water no longer can exit the upper chamber and the equalizer port allows the process to start over again. IF the equalizer port were larger than the bypass port, OR the diaphragm has a tear so that more water can enter the upper chamber than the bypass port can "drain" then the valve will either only partially open, or not open at all. But whether you consider the valve normally open or closed, depends on your definition. They are "trying" to be open but the solenoid is keeping them closed as long as there is no power to the solenoid.

[jimbo]

Good explanation, hj.

I used to have a good cutaway pic of a solenoid operated valve, showinf all the ports. but I can't find it. Keep looking.



Here is the wiki version: http://en.wikipedia.org/wiki/Solenoid_valve

By the way, we should expand this discussion to include the fluidmaster fill valve! Figure that one out, with the little pin in the middle of the diaphragm!

[BRD]

Maybe I can explain this in a different way. Irrigation valves are electrically activated ( that is the solinoid is opened and allows water to exit the upper chamber and exit to the downstream side of the valve) and hydraulically operated. The hydraulic part of why a valve stays closed at a given static pressure is because the surface area on the top side of the diaphragm is larger then on the bottom, therefore the force exerted on the top of the diaphragm at a give pressure is greater. When the solinoid opens it allows this water in the upper chamber to begin to evacuate downstream thereby allowing the force at the bottom side of the diaphragm to push open the valve diaphragm. If you take this formula, Pressure (psi) = Force(lb) / Area (in2) you can get an idea of what is occuring. For example, If the house static water pressure is 60psi and the lower area of the diaphragm is 2 sq. in., the force would be 120lb. If the upper area is 3 sq. in. then that force would be 180 lb. that is what is holding the valve closed until something changes those dynamics. Hope this helps.