A solenoid valve is a small but important component in a hydraulic lifting system. Although its structure is relatively simple, it plays a key role in controlling the movement of hydraulic oil.
In hydraulic lift power units, solenoid valves are commonly used to control the oil circuit for lowering the platform. When the solenoid valve receives an electrical signal, it changes the position of its internal valve spool, opening the hydraulic oil passage. This allows the lift to descend smoothly.
This article explains how a solenoid valve works, how it is commonly wired, and how it controls the lowering function of a hydraulic lift.
1. How Does a Solenoid Valve Work?
A solenoid valve uses an electromagnetic coil to control a valve mechanically.
The basic working process is simple:
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The control system supplies electrical power to the solenoid coil.
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The coil generates a magnetic field.
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The magnetic force moves the internal valve spool.
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The position of the spool changes the hydraulic oil passage.
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Hydraulic oil can then flow through the corresponding circuit.
For example, a commonly used solenoid valve in our hydraulic lifting equipment uses a 24V DC coil.
When the control system supplies 24V DC to the coil, the solenoid is energized and the valve changes position. When the electrical signal is removed, the coil is de-energized and the valve returns to its normal position.
Therefore, the solenoid valve essentially acts as an electrically controlled switch for the hydraulic oil circuit.
2. How Does a Solenoid Valve Control Lift Descent?
In many hydraulic lift power units, the solenoid valve is used to control the lowering circuit.
When the lift is stationary, the hydraulic oil circuit remains closed, preventing the oil from returning to the tank through the lowering passage.
When the operator presses the DOWN button, the electrical control system sends a signal to the solenoid valve.
For example:
DOWN command → 24V signal → solenoid coil energized → valve opens the lowering oil passage → hydraulic oil returns to the tank → lift descends
Once the oil return passage is opened, the hydraulic oil can flow back to the hydraulic tank. Under the force of gravity and the load on the platform, the lift moves downward.
When the DOWN signal is removed, the solenoid coil is de-energized. The valve returns to its normal position, closing the corresponding oil passage and stopping the lowering movement.
This is why the solenoid valve is an important part of the descent control system on a hydraulic lift. For a deeper look at how the full control system is structured, see our article on building a reliable hydraulic goods lift PLC program.
3. Solenoid Valve Wiring
The wiring of a typical solenoid valve is relatively simple.
For a commonly used 24V DC solenoid valve with an indicator light, the electrical connection normally consists of the two coil terminals and, depending on the connector design, a protective earth/ground connection.
The two coil terminals are connected to the control circuit from the electrical control box.
When the control box outputs 24V to the solenoid coil:
24V ON → Solenoid energized → Indicator light ON → Valve operates
When the 24V signal is removed:
24V OFF → Solenoid de-energized → Indicator light OFF → Valve returns to its normal position
The indicator light is useful during commissioning and troubleshooting because it provides a quick visual indication of whether the solenoid coil is receiving power.
For example, if the lift does not descend and the indicator light on the solenoid connector does not turn on when the DOWN command is given, the problem may be related to the control signal, wiring, fuse, relay, PLC output, or power supply.
If the indicator light turns on but the valve does not operate, the problem may instead be related to the solenoid coil, valve spool, hydraulic pressure, or the valve itself.
4. What About the Ground/Earth Connection?
Some solenoid valve connectors have an additional terminal for protective earth/ground.
This connection is intended to provide electrical protection and help reduce the risk associated with leakage currents, electrical faults, or unwanted electrical interference.
However, whether the earth/ground terminal should be connected depends on the specific solenoid valve, connector design, electrical system, and applicable electrical safety requirements.
For this reason, the wiring should always follow the manufacturer's wiring diagram and the applicable electrical standards.
The two coil terminals and the protective earth connection should not be confused with each other. The coil terminals are responsible for energizing the solenoid, while the protective earth connection serves an electrical safety function.
5. Why Is 24V DC Commonly Used?
24V DC is widely used for control circuits in industrial hydraulic equipment.
One reason is that 24V DC is well suited to control systems containing PLCs, relays, sensors, switches, and solenoid valves.
Using a low-voltage control circuit also helps separate the control signals from higher-voltage power circuits such as the hydraulic pump motor.
A typical hydraulic lift control system may therefore contain:
AC power → control power supply → 24V DC control circuit → PLC/relay → solenoid valve
This allows the electrical control system to send a relatively simple ON/OFF signal to operate the hydraulic valve.
6. Troubleshooting a Solenoid Valve on a Hydraulic Lift
When a hydraulic lift does not descend, the solenoid valve is one of the components that should be checked.
A basic troubleshooting sequence can include:
Step 1: Check the DOWN command
Confirm that the DOWN button or control signal is actually being received by the control system.
Step 2: Check the 24V output
Use a multimeter to check whether the control box is providing the expected voltage to the solenoid coil when the DOWN command is active.
Step 3: Check the indicator light
If the solenoid connector has an indicator light, check whether it turns on when the DOWN command is given.
Step 4: Check the solenoid coil
If the correct voltage is present but the solenoid does not operate, the coil may be damaged or the valve may have a mechanical problem.
Step 5: Check the hydraulic circuit
If the solenoid operates normally but the lift still does not descend, check the hydraulic oil circuit, valve spool, return passage, hydraulic pressure, and other related components.
This step-by-step approach can help distinguish an electrical problem from a hydraulic or mechanical problem.
Conclusion
The solenoid valve is a simple but essential component in many hydraulic lifting systems.
Its basic function is to use an electrical signal to control the position of a valve spool and therefore control the flow of hydraulic oil.
In a typical hydraulic lift, the process is straightforward:
Electrical signal → Solenoid valve operates → Hydraulic oil passage opens → Oil returns to the tank → Lift descends
With a commonly used 24V DC solenoid valve, the control box can easily control the lowering function of the hydraulic lift through a simple electrical signal.
Understanding the solenoid valve's working principle and wiring is also useful for installation, commissioning, and troubleshooting of hydraulic lifting equipment.
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