What Is a Solenoid Valve? Operating Principles and 2-Way/3-Way Fluid Control
A solenoid valve uses electromagnetic force to move a sealing element, opening, closing or switching a fluid path. Changing the coil's energized state actuates the valve mechanism and changes the fluid connection. The pressure difference that actually moves the fluid is usually supplied by a pump, a pressurized vessel or a difference in liquid level.
In automated dispensing equipment, a 2-way solenoid valve opens or closes one branch; a 3-way valve switches a common port between two branches. To understand their roles, consider the electrical state, port connections and fluid direction together.
01What happens inside the valve when power is applied?
Energizing the coil creates a magnetic field that drives a moving mechanism, such as an armature, and changes contact between the seal and valve seat. How the valve returns after de-energization depends on its construction. Not every solenoid valve uses a linear plunger: the 6010 uses a rocker mechanism with a diaphragm to control the fluid path.
- ControllerOutputs an on/off command
- CoilApplies or removes magnetic force
- Valve mechanismChanges the sealing position
- Fluid pathOpens, closes or switches
An audible click therefore only suggests that the mechanism may have moved; it does not prove that fluid has passed through. During commissioning, also check tubing direction, pressure conditions, bubbles and blockages, and verify actual discharge at the outlet.
02How do normally open, normally closed and 3-way valves differ?
| Configuration | De-energized state | Energized state | Fluid-control role |
|---|---|---|---|
| 2-way normally closed (NC) | Connection between the two ports closed | Connection between the two ports open | Allows flow through the branch when energized |
| 2-way normally open (NO) | Connection between the two ports open | Connection between the two ports closed | Stops flow through the branch when energized |
| 6010 3-way | COM connected to NO | COM connected to NC | Switches the common port between two branches |
A normally closed valve can serve a branch intended to close on power loss; a normally open valve can serve one intended to remain open. However, the equipment's safe power-off state also depends on other valves, check-valve arrangements, residual pressure and liquid-level differences. One valve's name alone cannot define that state.
A 3-way valve is not a tee fitting that continuously connects all three ports. In the switching arrangement above, one side is closed when COM is connected to the other. Confirm port numbering and permitted flow directions for the specific product.
03Example: switching one pump between reagent and wash fluid
In the 6010 3-way configuration, port 1 is NC, port 2 is COM and port 3 is NO. Connect the reagent bottle to port 1, the wash-fluid bottle to port 3 and port 2 to the pump inlet; connect the pump outlet to the dispensing needle. In this example, de-energization selects the wash branch and energization selects the reagent branch.
Step 1: select reagent and dispense
The controller energizes the valve. After confirming that the 2—1 path is established, run the pump to draw fluid. Before the first dispense, discharge air and displaced fluid from the tubing at the waste position, then move the dispensing needle to the target vessel and perform the metered dispense.
- Reagent bottleConnected to port 1, NC
- 3-way valveEnergized: 1—2 connected
- PumpDraws fluid from port 2
- Dispensing needleDispenses into the target vessel
Step 2: select wash fluid and flush the shared path
After dispensing, first end the pump's metering action and put the fluid path in a condition that permits switching. Move the needle to the waste position, then de-energize the valve. Once 2—3 is connected, the pump draws wash fluid to flush the shared path through the pump and needle. Before the next reagent dispense, arrange reagent displacement to prevent wash fluid from diluting the first aliquot.
- Wash fluidConnected to port 3, NO
- 3-way valveDe-energized: 3—2 connected
- Pump and dispensing needleFlush the shared path
- Waste vesselCollects wash fluid
04Why does 1 second of energization not always dispense the same volume?
When a pressure difference drives flow downstream of the valve, volume can be estimated as flow rate multiplied by open time if flow is stable and opening/closing transients are negligible. Actual flow varies with liquid level, supply pressure, outlet backpressure, viscosity and tubing resistance, and transitions occur during switching.
For example, dispensing volume can change as the reservoir level falls even when the program uses the same open time each cycle. Short dispensing pulses are also affected by drive response, tubing deformation and residual droplets. For consistent small-volume dispensing, select a suitable metering method and measure mean volume and repeatability with the actual fluid.
If the system already uses a syringe pump or another metering mechanism, the pump normally executes the target-volume action while the solenoid valve establishes the path at the correct time. The program must prevent the pump from continuing against a closed path and avoid connecting an unintended branch.
05How should pressure, response time and power be interpreted during integration?
| Parameter | Product conditions | What to check in the equipment |
|---|---|---|
| Operating pressure | −75 kPa to 0.25 MPa | Whether suction pressure, outlet backpressure and switching transients remain within the permitted range |
| Power supply | DC 12 V or 24 V; permitted deviation from rated voltage: ±10% | Select the correct rated voltage and check actual voltage at the valve and wiring polarity |
| Response time | ≤15 ms under no-load conditions for the standard configuration | Do not treat this as the time for outlet flow to stabilize; check temperature, medium and pressure difference |
| Power consumption | Standard configuration: 2.5 W; energy-saving circuit configuration: 2.5 W at start-up and 1 W holding | Whether start-up and holding drive are matched, and heat dissipation is adequate during continuous energization |
The stated response-time test conditions include fluid and ambient temperature of 25°C, rated voltage, maximum operating pressure with air, and pressure applied to the common port. A no-load actuation specification does not replace fluid-response measurements after tubing installation. Also check seal material, temperature and drive method. Proof-test pressure is likewise not the permitted continuous operating pressure.
Wetted materials must suit both reagent and wash fluid, taking concentration, temperature and contact time into account. For manifold-mounted, threaded or barbed connections, also check installation sealing, tubing stress and service clearance. A suitable connection type does not automatically establish fluid compatibility.
06Related products and validation steps
- Draw the de-energized and energized fluid paths first, and verify how COM, NC and NO correspond to the actual ports.
- Run the actual drive circuit, fluids and pressure conditions. Observe switching response, external and internal leakage, and residual outlet droplets.
- Validate the first dispense, consecutive dispenses and the first dispense after washing in the equipment cycle. Record mean deviation and repeatability separately.
- Check handling of power loss, restart, a stuck valve and a pump that has not stopped. Confirm that fluid goes to the intended destination.
07Frequently asked questions
Can a solenoid valve be used as a pump?
A solenoid valve mainly changes fluid-path connections; it does not provide continuous pumping. A pump, pressurized vessel or liquid-level difference is still needed to provide the pressure difference.
Can a 3-way valve mix two reagents simultaneously?
The 6010 3-way arrangement described here selects between COM-to-NC and COM-to-NO branches. It is not a mixing valve that opens both inlets simultaneously. Mixing also requires control of each fluid's volume, addition sequence and mixing space.
Does faster valve actuation make dispensing more accurate?
Actuation response is only one factor. Dispensing accuracy also depends on the metering method, flow variation, bubbles, tubing elasticity and residual droplets. Measure performance at the target volume in the actual fluid path; response time alone cannot determine volume error.