Failure Modes of Solenoid Valves and Solution

1. Introduction to Solenoid Valves

A solenoid valve is an electrically controlled industrial device and an automated basic component for fluid control. As an actuator, it is not limited to hydraulic and pneumatic systems and is widely used in daily life.

Essentially, a solenoid valve consists of an electromagnetic coil and a magnetic core, with a valve body containing one or more ports. When the coil is energized or de-energized, the movement of the magnetic core allows fluid to pass through the valve body or be shut off, thereby changing the fluid direction.

2. Working Principle of Solenoid Valves

A solenoid valve features a closed chamber with through-holes at different positions, each connecting to a different oil pipe. A valve core is located in the middle of the chamber, flanked by two electromagnets. The valve core is attracted to the side whose electromagnet coil is energized. By controlling the movement of the valve core, different oil discharge ports are blocked or opened.

The oil inlet port remains normally open, allowing hydraulic oil to enter different oil discharge pipes. The oil pressure then drives the piston of the oil cylinder, which in turn drives the piston rod, and the piston rod actuates the mechanical device. In this way, mechanical movement is controlled by regulating the current of the electromagnet.

3. Classification of Solenoid Valves

3.1 By Working Principle

• Direct-acting type

• Semi-direct acting type

• Pilot-operated type

3.2 By Structure

• Diaphragm solenoid valve

• Piston solenoid valve

4. HVAC Control Valves

HVAC control valves, also known as locking valves or special valves for civil heating, facilitate property management and allow residents to independently adjust heating temperature and duration.

Typically composed of an electric actuator connected to a valve body, HVAC control valves are put into service after installation and commissioning. They use electrical energy to power the electric actuator, driving the valve to open, close, or regulate, thereby controlling or adjusting the pipeline medium.

Key features include reversing and locking functions: each household or group in the heating and water supply system can control on/off, and non-destructive opening is impossible, ensuring effective management.

5. Common Faults & Troubleshooting of Solenoid Valves

Solenoid valve faults directly affect the operation of switching valves and control valves. The most common fault is failure to actuate, which can be diagnosed and resolved through the following four aspects:

(1) Air Leakage

• Cause: Insufficient air pressure due to air leakage makes it difficult to open/close the forced valve. This is usually caused by damaged gaskets or worn slide valves leading to air leakage between chambers.

• Solution: Handle the fault when the solenoid valve is de-energized. If the repair cannot be completed within one switching cycle, pause the switching system for unhurried maintenance.

(2) Solenoid Valve Jammed

• Cause: The fit clearance between the slide valve sleeve and valve core is extremely small (less than 0.008mm), and they are usually assembled as a single unit. Jamming easily occurs when mechanical impurities enter or lubrication is insufficient.

• Solution:

• Temporary fix: Insert a steel wire through the small hole at the top to reset the valve core.

• Permanent solution: Remove the solenoid valve, take out the valve core and sleeve, clean them with carbon tetrachloride (CCl₄) to ensure smooth movement.

• Notes: Record the assembly sequence of components and external wiring positions for correct reassembly. Check if the oil mist spray hole is blocked and if lubricating oil is sufficient.

(3) Loose or Disconnected Wiring

• Cause: Loose or disconnected wiring terminals prevent the solenoid valve from being energized.

• Solution: Tighten the wiring terminals securely.

(4) Burned Coil

• Cause: Coil burnout is often due to moisture-induced poor insulation (causing magnetic leakage and excessive current), overly stiff springs (excessive reaction force), insufficient coil turns (inadequate suction), or rainwater ingress.

• Solution:

• Diagnosis: Disconnect the wiring and measure with a multimeter; an open circuit indicates a burned coil.

• Emergency measure: Switch the manual button on the coil from "0" (normal operation) to "1" to open the valve temporarily.

• Prevention: Protect the solenoid valve from rainwater and ensure proper lubrication and coil specifications.