When troubleshooting any irrigation component, it is best to have a fundamental understanding of how the component operates. Electronic solenoid valves are no exception. The following is a quick lesson on how electronic solenoid valves operate.
When troubleshooting an electronic solenoid valve, it is important to quickly isolate the problem as either electrical or hydraulic. Since electrical problems are more quickly identifiable, you should start here when troubleshooting the valve. There are several easy steps that can be taken by utilizing a volt/ohm multimeter to accurately determine if the valve is functioning properly.
Electric solenoid valves are powered by 24 volts AC (VAC) from the irrigation controller. Whenever the controller turns a valve on, it sends 24 VAC to the solenoid. The solenoid is the electronic portion of the valve. It is essentially a coil of wires that when energized, become magnetized and lift a small plunger inside the solenoid. The solenoid has two wire leads extending from it. One of the wires attaches to the “hot wire” that receives the 24 VAC from the irrigation controller. The other wire attaches to a “common wire” that acts as a neutral or return wire. The “common wire” is run in series and is connected to all the valves in the system, whereas the “hot wires” are run from each zone at the irrigation controller to each valve in the field. This is how each zone is operated independently from the irrigation controller
The most common symptoms of electrical problems are valves failing to turn on. If a valve fails to turn on, first check to see if the valve is getting the proper voltage from the irrigation controller. To perform this test, you will need a volt/ohm or multimeter. These handy devices will help you diagnose any electrical problem and are mostly electronic these days so you can read the results on a screen. Start by turning on the voltmeter and selecting the VAC setting, turn the zone on at the controller and touch one lead to the common terminal (COM) and the other lead to the zone terminal that is in question. You should receive a reading in the 24-28VAC range. If you do not record any voltage output for the station, then you may have a controller problem. If you do record the proper voltage, then the next step will be checking the resistance or ohms of the circuit.
Checking the ohms or resistance of the zone is also referred to as checking for continuity. To do this you will again be using your voltmeter but will need to turn it to the ohms setting. Sometimes it is identified as the symbol on the voltmeter (Ω) or (~). This simple test will let you identify if there is a shorted solenoid or a cut wire going to the valve. In either case, the valve will fail to open when the proper voltage is sent to it from the irrigation controller. You will be able to perform this test at the irrigation controller with your voltmeter. First, turn off the controller! NEVER CHECK RESISTANCE THROUGH A LIVE CIRCUIT. Place one lead on the common terminal (COM) and one lead on the zone terminal in question. You should get a reading from 20-60 Ω; every manufacture’s valves will have a slightly different reading. Any reading that is lower than the acceptable range is indicative of a shorted solenoid. Conversely, any reading above 60 is indicative of a wiring problem. This usually occurs due to the age of the valve, electrical surge, or cut wire.
If you get a reading of zero or OL (offline), this usually indicates a wire has been cut between the irrigation controller and the valve. If you receive the same OL (offline) reading for all the valves, this may indicate the common wire has been cut, since all the valves share this wire. Not just cut anywhere by the way, but the common has been cut between the controller and the first valve! To make repairs in this situation you may need to run a new common or track down the break with a fault locator.
If you find the solenoid is defective follow these steps to replace it:
- To replace a solenoid, first turn off the main water supply then remove the wire nuts and unscrew the old solenoid. Replace with proper solenoid for the model valve you have and reattach wire with waterproof wire nuts. Please note that you may have to dig up the valve box to get closer to the work.
- If you are still having a problem with your electronic solenoid valve working properly and everything checks out electrically, then it is time to troubleshoot the hydraulic portion of the valve. As with electronic troubleshooting, it is important to have a fundamental understanding of how the valve operates hydraulically.
- Electronic irrigation solenoid valves are referred to as “normally closed”. This means that the valve should stay shut or closed when water pressure is applied to it. Water enters the valve on the inlet side (note flow arrows) to the lower chamber. There is a flexible rubber diaphragm that separates the lower and upper chambers. Water must pass through the diaphragm via a port through its center or a small screened port located near the outside edge to get to the upper chamber. Once the water gets to the upper chamber of the diaphragm, it builds enough pressure to force the diaphragm downward causing the valve to close. In order for the valve to open, water must be ported off of the top chamber to relieve the pressure so the diaphragm can flex upward. When the diaphragm flexes upward, water is allowed to flow through the valve.
- There are several ways to port water off the upper chamber of the valve to allow it to open. If your valve is equipped with a bleed screw, you can open it and water will be directly ported off the top of the diaphragm. In this case water will flow out from the threads of the bleed screw and onto the ground.
- Some manufactures also equip the valve with a solenoid body capable of being turned ¼ or so counter-clockwise which will port water directly downstream to manually operate it. On some models, a lever is flipped under the solenoid on the valve body.
- When the solenoid is turned, it is unseated from the valve body allowing the water to flow from the upper chamber through a small drain under the plunger. When this happens, pressure is released from the top of the diaphragm and it flexes upward unseating it from the valve body. When you unscrew the solenoid it physically unseats the plunger from the valve and the valve opens.
- The next way water is ported off the upper chamber of the valve is by applying voltage to the solenoid. To ensure the valve functions in this automatic mode, make sure the bleed screws and/or the solenoid body is screwed down. 24VAC is applied from the irrigation controller, the solenoid will become magnetized and lift the plunger inside the solenoid. When this happens, water is ported off the upper chamber of the valve as described above and the valve opens.
In summary, look for these problems in diagnosing valve failures:
Valve Fails to Open:
- Controller not sending 24VAC to valve
- Cut wire
- Shorted solenoid
- Ports clogged between upper chamber of diaphragm and solenoid or clogged port between solenoid to downstream drain*.
Valve Fails to Close
- Controller sending unwanted voltage to valve.
- Port or screen on underside of diaphragm clogged.
- Ruptured diaphragm.
- Leaks around diaphragm between top and bottom of valve body (visible/external).
- Valve is not in the automatic mode.
- Weeping valve caused by debris in solenoid or diaphragm or water pressure exceeding 80 psi.
* It should be noted that on glue-type valves, those that have no female threaded connections, it is possible to glue shut the port (drain), on the downstream (solenoid) side of the valve. In this situation, the port (located directly beneath the solenoid plunger) that drains to the downstream side of the valve becomes clogged from excess pipe cement. The exit for this port is visible directly behind the glue stops. When this happens, the valve may open slightly when energized but will only open fully when activated manually. To remedy this, first, find a large paperclip. Unfold it into the shape of an “L” with the long end being at least 2” in length. Turn off the water supply, unscrew the solenoid and lift it off the valve body. Insert the long end of the paperclip and push it into the CENTER drain in the valve body (directly under the plunger), in the cavity where the solenoid had been unscrewed. Work it up and down like a plumber- helper until the drain is clear. Reassemble the valve, turn on the water, and activate it electrically. Repeat if necessary.
