In the current domestic irrigation market, whether for agricultural, landscape , residential, golf course, or other irrigation projects, automated control technology is basically adopted, especially with the current applications of the Internet of Things and agricultural big data. Valves, particularly irrigation solenoid valves , are a crucial component for controlling water flow in pipelines, and are also a point of frequent use and prone to issues. For contractors and users, it is very necessary to understand some knowledge about solenoid valves.

       Perhaps a common trait among science majors, we prefer to first understand and clarify the working principle of products we use, which brings peace of mind and allows for mastery. According to different project requirements, solenoid valves used in irrigation have many different functions, including pipeline control valves, pressure reducing valves , pressure relief valves, pressure sustaining valves, and combined function valves like pressure reducing and sustaining valves, etc. These multi-functional valves all rely on a "basic valve" structure, which is the fundamental working principle of the valve. You can watch the video below, which is an anatomical diagram of a "basic valve".

The following discussion pertains to valves used in irrigation, specifically the working principle and troubleshooting of "normally closed solenoid valves". Solenoid valves for other uses are not covered here.

I. Explanation of Basic Valve Body Structure

Below, a simple schematic diagram of a valve body structure is used to illustrate the internal structure of the basic valve.

       We have extracted it and I have added simple annotations. In fact, this basic valve is very simple, consisting of only three parts: the upper valve body, the diaphragm, and the lower valve body. The chamber formed by the upper valve body and the diaphragm is called the "upper chamber"; the chamber formed by the diaphragm and the lower valve body is the "lower chamber". Don't underestimate these two chambers; all the principles lie within them.

                                                                                                                    Exploded view of basic valve parts

       By adding some auxiliary equipment to this basic valve body, many irrigation valves with special functions can be assembled, such as: pressure regulating valves, safety valves, pressure relief valves, pressure sustaining valves, and some combined pressure stabilizing and regulating valves, etc. Understanding the structure and working principle of this type of solenoid valve makes it easier to solve problems during on-site debugging, installation , and later management processes. Explanations for these valves, if needed, might require a separate article to introduce.

The upper image shows the valve in the closed state, the lower image shows the valve in the working state (arrows indicate water flow direction)

The valve body shown above is relatively simple. The structure of the valve body below is more reasonable, with these advantages:

1. The water flow direction is changed from hemispherical to straight-line, resulting in smaller head loss and greater flow capacity.

2. The diaphragm and sealing gasket are separated, with the diaphragm retracted to the top for protection, making it less prone to deformation and extending its lifespan.

3. Opening and closing are more sensitive.

Left image shows valve closed, right image shows valve open

II. Explanation of Valve Body Working Principle

After understanding the structure of the basic valve, let's discuss its operation, which involves simple physics concepts: pressure (P), force (F), area (S), etc., F=P*S. The pressure acting on a unit area equals the force on that object. Here, it's important to note: the diaphragm is designed such that the force-bearing areas in the upper and lower chambers are different. The force-bearing area in the upper chamber is larger, while in the lower chamber it is smaller. This is crucial information and the key point. Valve closing: When the water pressure in the upper and lower chambers is the same, due to the different force-bearing areas, the force on the diaphragm in the upper chamber (larger area) is greater than the force on the diaphragm in the lower chamber (smaller area), achieving the "closing action" of the valve. (The execution action is water from the inlet filling the control chamber, pressing the diaphragm down to close the valve.) Valve opening: When water is drained from the upper chamber (externally or downstream of the valve), the pressure in the upper chamber decreases, resulting in a force less than that on the diaphragm in the lower chamber. The diaphragm moves upward, achieving the "opening action" of the valve. (The execution action is draining the control chamber, allowing water pressure to lift the diaphragm and open the valve.)

III. Common Solenoid Valve Troubleshooting

Once the basic valve body and working principle are clear, troubleshooting during use becomes easier. In the entire automatic control system diagnosis process, there needs to be an order, i.e., a troubleshooting sequence.

1. Generally, before diagnosing solenoid valve issues, some preliminary work is needed: such as confirming if the water source is on, if the controller is connected and programmed correctly, if the flow adjustment handle on the solenoid valve is closed, and then trying manual operation. If the manual solenoid valve works normally, the problem might lie with the controller, solenoid coil, or cables.

2. Confirm if the upstream controller has normal output? (Typically, AC irrigation controllers output around 24V, pulse controllers around 12V). This avoids concluding the solenoid valve is faulty just because it doesn't open. This can be checked by measuring the voltage at the solenoid valve output port with a multimeter. If there's a problem, address it. If the output is fine, proceed to the next step. (For pulse solenoid valves, pay attention to the controller's pulse time setting. Solenoid coil types can open with a 50ms setting, while motorized types need 100ms to ensure complete opening.)

3. Check if the connecting cable between the solenoid valve and controller is continuous? If a wireless control system is used, skip this step. Also use the multimeter's resistance setting to measure the control signal cable. Infinite resistance indicates an open circuit, while a typical continuous path has resistance ranging from tens to hundreds of ohms, depending on the length and material of the laid cable.

4. The final step is troubleshooting the solenoid valve itself. Aside from physical damage to the valve body, which is easy to judge, the remaining solenoid valve issues boil down to two common problems: the solenoid valve fails to open, and the solenoid valve fails to close.

Solenoid Valve Fails to Close:

There are two possible reasons for this.

First: Physical obstruction, such as small stones, dead leaves, or twigs, preventing the diaphragm from sealing completely. After clearing such obstructions, check if the diaphragm and its attachments are damaged.

Second: Insufficient pressure acting on the upper diaphragm, which may be due to the following reasons:

1. The inlet filter of the upper diaphragm chamber is clogged. This prevents water from entering the upper diaphragm chamber, failing to generate sufficient water pressure to close the diaphragm.

2. The seal between the upper and lower valve bodies is not tight, or the pilot tube fitting is not tightened. Water can easily leak from these points, also hindering the generation of sufficient pressure to close the diaphragm. The solution here is to tighten the valve body fixing screws.