In hydraulic systems, precise and fast fluid control is key to achieving efficient operation. Have you ever encountered sluggish valve movements, delayed response, or frequent equipment downtime? Such issues often stem not from the hydraulic pump or cylinder itself, but from a commonly overlooked component — the solenoid coil. Although small in size, it plays a core role in converting electrical signals into mechanical action. Whether you are designing a hydraulic control system or troubleshooting malfunctioning equipment, understanding the solenoid coil's working principle is essential and valuable.
This article will take you through the solenoid coil’s role and operation within hydraulic systems — from energizing the coil to generating magnetic force and actuating the valve spool. Each step affects the system’s efficiency and reliability. We will also cover common faults, selection tips, and at the end, provide practical brand recommendations to help you make informed choices.
Table of Contents
- 1. What is an Electromagnetic Coil
- 2. How Solenoid Coils Work in Hydraulic Systems
- 3. What Kind of Solenoid Coil Is Suitable for Hydraulic Systems
- 4. Common Solenoid Coil Failures in Hydraulic Systems
- 5. Advantages of Using Solenoid Coils in Hydraulic Systems
- 6. Replace the Solenoid Coil
- 7. Tips of Choosing Replacement Solenoid Coil
- 8. FAQ
- 9. The Importance of Quality Electromagnetic Coil Manufacturer
What is an Electromagnetic Coil？
Solenoid Valve Coil is the most important electronic control component in the solenoid valve. It is composed of copper or aluminum wire wound into a hollow form. It converts AC or DC electrical energy into linear mechanical motion to drive the solenoid valve.
This is achieved by placing a ferromagnetic core inside the coil. In the solenoid valve, the ferromagnetic core is called the valve core. When the current flows through the coil, due to the magnetic effect of the current, a magnetic field is generated in the surrounding space, thereby magnetizing the valve core into an electromagnet, and then under the electromagnetic force, the electromagnet further slide upward into the coil, thereby opening the valve port or pilot hole to realize the on-state of the solenoid valve
How Solenoid Coils Work in Hydraulic Systems
1. Energizing to Generate Magnetic Field
In a hydraulic system, when the solenoid coil receives an electrical signal, it is energized. The current flowing through the coil generates a magnetic field inside it. This magnetic force is strong enough to attract or move the valve spool.
2. Valve Spool Movement Opens the Oil Circuit
Under the magnetic force, the valve spool (plunger) is pulled to move, changing the open or closed state of the oil passage inside the valve body. The spool’s position change directs hydraulic oil to actuators such as cylinders, causing them to extend or retract.
3. De-energizing Causes Reset and Closes the Oil Circuit
When the solenoid coil is de-energized, the magnetic field disappears, and the valve spool returns to its original position by the force of a spring, closing or restoring the oil circuit. This stops the hydraulic oil flow and halts actuator movement, completing one full control cycle.
What Kind of Solenoid Coil Is Suitable for Hydraulic Systems?
1. Suitable for High-Pressure Environments
Hydraulic systems often operate under high pressure (e.g., 16–35 MPa), so the coil must provide enough magnetic force to reliably drive the valve spool. High-power coils (such as 10–20W) are commonly used to ensure fast and strong response.
2. Good High-Temperature Resistance
Hydraulic systems may reach high temperatures during long operation. The coil should be made of high-temperature-resistant insulation materials, such as Class B (130°C) or Class F (155°C), to prevent overheating and failure.
3. High Protection Level (IP Rating)
Since hydraulic environments may involve dust, oil, and moisture, it is recommended to use coils with at least IP65 protection rating to prevent contamination and extend service life.
4. Matches DC or AC Power Supply
The coil type should match the control system’s power source:
- DC coils: smoother operation with low noise, suitable for precise control.
- AC coils: fast actuation but may generate heat and noise; coils with shading rings can reduce humming.
5. Compatible Interface Size
The coil’s inner diameter and mounting thread must match the valve body. Standard connectors like DIN 43650 (Type A/B/C) are commonly used for easy installation and maintenance.
Recommended Coil Specifications
- Voltage: DC 24V or AC 220V (depending on system design)
- Power: 10W–20W (for medium to high power systems)
- Insulation Class: Class F or higher
- Protection Level: IP65 or IP67
- Connector: DIN 43650 A/B/C or terminal type
If you need help selecting specific models or brands (e.g., Bosch Rexroth, Parker, Hydac, Yuken), feel free to ask!
Common Solenoid Coil Failures in Hydraulic Systems
| Failure Type | Symptom |
|---|---|
| Coil Burnout | Coil overheats, deforms, or emits a burnt smell; resistance test shows open circuit. |
| Coil Not Energized (No Actuation) | No movement when power is applied; valve spool does not respond. |
| Insufficient Magnetic Force | Spool movement is weak or incomplete, causing slow or unstable operation. |
| Continuous Power but No Response | Control signal is active but the valve does not move at all. |
| Frequent Switching Reduces Lifespan | Early coil failure or unstable operation. |
| Coil and Valve Body Mismatch | Coil cannot be properly installed, or experiences abnormal operation or overheating. |
1. Coil Burnout
Symptom: Coil overheats, deforms, or emits a burnt smell. Resistance test shows an open circuit.
Causes:
- Long continuous energizing causing overheating
- Overvoltage or unstable power supply
- Insulation aging or high ambient temperature
- Valve core is stuck, causing overload on the coil
2. Coil Not Energized (No Actuation)
Symptom: No movement when power is applied, valve spool does not respond.
Causes:
- Disconnected power or loose wiring
- Internal short or open circuit in the coil
- Fault in the control circuit (e.g., PLC or relay)
- Low voltage insufficient for actuation
3. Insufficient Magnetic Force
Symptom: Spool movement is weak or incomplete, resulting in slow or unstable system action.
Causes:
- Voltage drop due to long cables or low power
- Low-power or poor-quality coil
- Stuck valve spool or contaminants inside
- Excessive spring tension or mechanical resistanc
4. Continuous Power but No Response
Symptom: Control signal is active but no valve movement.
Causes:
- Valve spool jammed and magnetic force insufficient
- Coil internally damaged but no visual signs
- Incorrect control logic or signal output
- Improper installation causing coil-core gap
5. Frequent Switching Reduces Lifespan
Symptom: Early coil failure or unstable operation.
Causes:
- Frequent on-off switching by the control system
- No delay or buffer in control logic
- Using a standard coil in high-frequency applications (should use impact-resistant type)
6. Coil and Valve Body Mismatch
Symptom: Coil cannot be properly installed, abnormal operation, or overheating.
Causes:
- Voltage, size, or specifications do not match the valve
- Use of non-original or incompatible replacement parts
Recommendations
- Regularly check coil temperature, voltage, and insulation resistance
- Use branded, compatible coils matched to the valve model
- Avoid long energizing periods without actuation
- Keep installation areas clean to prevent contamination
If needed, a visual guide or downloadable checklist can be provided—just let me know!
Advantages of Using Solenoid Coils in Hydraulic Systems
1. Fast Response and Precise Control
When energized, solenoid coils generate a magnetic field almost instantly to actuate the valve spool. This allows for rapid switching of hydraulic fluid flow, offering much faster response compared to manual or mechanical controls. It's ideal for systems that demand high precision, such as CNC machines and injection molding equipment.
2. Compact Structure and Easy Integration
Solenoid coils are small and can be directly mounted on the valve body without the need for complex external actuators. This compactness makes them perfect for space-constrained hydraulic setups and supports easy modular integration and maintenance.
3. Remote Control and Automation Support
Solenoid coils can be controlled via electrical signals, enabling remote operation and improving convenience and safety. This makes it easy to integrate the hydraulic system with PLCs, sensors, and other automation components for intelligent and programmable control.
4. Energy Efficient (with Proper Design)
Modern high-efficiency solenoid coils are designed with energy management in mind. Many coils switch to a low-power holding mode after actuation, reducing continuous power consumption and lowering operational energy costs.
Replace the Solenoid Coil
When the solenoid coil used to control the hydraulic solenoid valve wears out or stops running, the solenoid coil needs to be replaced in the hydraulic system.
A solenoid is an electromagnet with a metal coil tightly wrapped around a solid metal core. They generate a controlled uniform magnetic field, and metal coils can be inserted or removed, thus providing a control method for various equipment, including hydraulic valves.
Tips of Choosing Replacement Solenoid Coil
From the apperance and sizes, sometimes, there is almost no difference between the different types of replacement solenoid coils, but they can have various supply voltages and power comsumption, which may affect which one you choose. They are also available from many different manufacturers, reprensent differenct quality.
Common Voltages Are:
- 12v dc solenoid coil
- 24v dc solenoid coil
- 110v ac solenoid coil
- 120v ac solenoid coil
- 220v ac solenoid coil
- 230v ac solenoid coil
- 240v ac solenoid coil
Learn more about how to choose a right quality solenoid coil, please visit:
https://www.valvecoil.com/how-to-choose-high-quality-solenoid-valve-coils/
Frequently Asked Questions: Solenoid Coils in Hydraulic Systems
Q1: Will the coil operate without power?
A1: No. When power is off, the magnetic field disappears, and the valve spool typically returns to its original position using a spring or hydraulic force.
Q2: What are the signs of solenoid coil failure?
A2: Common symptoms include valve not actuating, slow or erratic operation, coil overheating, or a burnt smell indicating a burnout.
Q3: Can a solenoid coil be energized continuously?
A3: It's generally not recommended to keep it continuously energized unless it's designed for that purpose, as prolonged operation can lead to overheating or coil damage.
Q4: Do I need to drain hydraulic oil to replace a coil?
A4: Usually not. As long as the system is powered off and pressure is safely released, the coil can be replaced without draining the hydraulic fluid.
The Importance of Quality Electromagnetic Coil Manufacturer
A qualified solenoid valve coil can promote the normal operation of the solenoid valve and reduce the occurrence of accidents. So you need a professional solenoid coil manufacturer to provide you with products and services.
Ningbo Beris Electronic (BRS) is a China top manufacturer specializing in the design, development and manufacturing of solenoid valve coils, armature assembly and connectors.
We offer global customers with standard or customized solenoid coil & accessories products, both we provide professional one-stop solutions.
Hydraulic System BRS Serviced:
- Water supply system
- Turbine system
- Fuel/gasoline supply system
- Wastewater treatment plants
- Process control in manufacturing plants
- Hydraulic motors, breaks, pumps in automotive industry
- Hydraulic machinery in aerospace and marine industries
- Heavy machinery in construction and landscaping
- Machinery in agricultural sectors
