View Full Version : how does electric sprinkler valve work?

07-03-2006, 03:22 PM
I am having a problem with what I believe to be a leak in my irrigation system. I called a professional to get an estimate for finding and fixing a leak. He proceeds to tell me how they check out all the wiring and solenoids and valves etc. "That's good" I think to myself, but the sprinklers work, I think one of the underground pipes is leaking when (whichever of the 8) the station is turned on.

Then this guy starts telling me that the valves/solenoids don't work the way that I think they work. IE, when power is applied the solenoid is activated and opens the valve. He said it works just the opposite, the valve is normally open allowing water to pass and it closes when power is applied. :confused:

Seems to me that this guy may not be snapping on all of his synapsis.

Can anyone on here give me the staight scoop?


Bob NH
07-03-2006, 06:07 PM
Valves are closed when the solenoid in not activated. Otherwise, all of your valves would open if the power failed.

Most electric irrigation valve are "pilot operated". The design is made so that water pressure and a spring work together to keep the valve closed. The solenoid opens a small "pilot" passage to relieve the water pressure in an area that is keeping the valve closed, allowing the pressure on the supply side to open the valve.

By using the pilot operation, the solenoid doesn't have to be strong enough to keep the valve closed against the pressure. That reduces the cost of the valve.

Pilot operated valves require a certain minimum pressure to actuate the valve.

07-04-2006, 07:12 AM
Some hydraulic, i.e., water operated, valves are normally open with the water pressure keeping them closed, but since the only way they could open accidently would be if the water pressure was shut off, the system would not have any water to flood the area. All others are normally closed, and if the spriinkler guy tells you otherwise get a different sprinkler guy.

07-05-2006, 11:17 AM
and I appreciate the detailed replies.

Thanks :D

Gary Swart
07-05-2006, 01:06 PM
Seems to me that it would be a wise move to install a backflow preventer on the main sprinkler line rather than relying on each electric valve to work individually.

05-16-2009, 07:54 PM
Your lawn professional person was correct. It is slightly more complicated than the other posters stated.
Major components to the irrigation valve.
1 The valve body
2 The lower camber
3 The upper camber
4 The diaphram separating the two chambers
5 The spring above the diaphram
6 The 24 volt solnoid

When you are starting your system in the Spring water will flow and fill the lower chamber in the valve body first. A small tube or passage way will allow the upper chamber to fill with water next equalizing pressure on both sides of the diaphram. The spring on the top side of the diaphram exerts pressure causing the forces to be un-equal keeping the valve closed.
When electric current activates the solnoid, the small tube or passage way is closed. (The electricity is CLOSING the previously open...) The water pressure is lessened on the top side of the valve allowing the water source to force the diaphram up....opening the valve. The reverse happens when the valve is closed.

05-17-2009, 03:47 AM
(The electricity is CLOSING the previously open...) quote]

You had a good explanation up to this point. But then it is wrong. When the solenoid is activated, it does not CLOSE a port, it OPENS another port which allows water from the top chamber to flow into the outlet, thus lowering the pressure in the top chamber, and then water supply pressure overcomes the spring, and the valve opens. The manual bleed screw which many valves have does the same thing.

This is the way every valve I know works.

05-17-2009, 04:15 AM
My valves have no power available to them in the winter since I unplug the transformer. And they stay closed.
Like others said. If it was the opposite, then whenever the power went out everybodys lawn sprinklers system would turn on.
I only need mine 6 months out of the year so I disconnect power to save the eqipment and a tiny bit of power.

05-17-2009, 04:19 AM
First answer - How does the water get into the upper chamber in the first place?
The solenoid stops the flow from the lower chamber lowering the pressure, the manual bleed releases water from the upper chamber thereby lowering the pressure.

05-17-2009, 04:24 AM
To rayh 78,
Do you leave your water turned on?
If you turn your water off, how do you know if the valve is open or closed??

05-17-2009, 04:49 AM
My entire response to rayh 78 did not appear in the post.
Water pressure is required to open and close a valve. Electricity is just the automated way.
Turning off the electricity will NOT open the valves.
Note- Valves under water pressure will stay shut and (not to confuse things here) valves without pressure will stay shut. The slight pressure from the diaphram spring is the deciding factor. Take the spring out and the valve will not work no matter what.
Lowering the water pressure in the upper chamber is what opens the valve.
I think we have beat this topic to death.

05-17-2009, 05:08 AM
To jimbo,
You are right because an activated solenoid retracts.

05-17-2009, 07:03 AM
To rayh 78,
Do you leave your water turned on?
If you turn your water off, how do you know if the valve is open or closed??

Yes always leave water turned on going to valves.
Dont even blow out line. Just use automatic drain valves under each head.
Not much freezeing here. In winter all I do is unplug transformer, so no power to system.

05-20-2009, 08:19 PM
As the proud owner my first sprinkler system (inherited from previous home owner), I find this really informative, if I may…

- How does the manual flow adjustment/shut-off part on these eletric solenoid valves work? Is it OK to use this part of the valve to throttle the flow down a little?

I lowered the flow on some of mine using this, probably no more than a turn, because in a few a zones water was going too far (i.e. watering the street, my neighbors house, etc). I also noticed that the supply line, which runs in the crawlspace, doesn’t rattle upon shutoff as noticeably as when the stems were fully open (lower flow = less water hammer?). Just want to make sure I'm not hurting the valve, or reducing its lifespan.


05-21-2009, 05:27 AM
Keep on adjusting. Turn it down, then back off a bit. Valves will close more reliably, and probably last longer.

05-21-2009, 06:49 AM
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.

05-21-2009, 06:53 AM
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!

06-22-2009, 06:48 PM
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.