What Is A Latching Solenoid Valve?
Figure 1: Latching solenoid valve
Solenoid valves are critical components of fluid flow control. Conventional solenoid valves use an electric current to produce a magnetic force that moves the actuator and works the plungers and coils that operate the opening and closing of valves. This means that a constant flow of electricity is required to keep a standard solenoid working. However, not all solenoid valves require a constant flow of electricity; a latching solenoid device uses a small permanent magnet fitted at the top of the valve to operate. Because of this, they require less power to operate than standard solenoid valves, leading to immense power savings from their operation.
Table of contents
- What latching solenoid valves do
- Latching solenoid valve components & design
- How latching solenoid valves operate
- Types of latching solenoid valves
- Application examples
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What latching solenoid valves do
As a bistable solenoid valve, the latching solenoid valve uses an electric current and a permanent magnet set up to open valves and keep them open. It works similar to the standard linear solenoid valve but relies on the polarity of the current to increase or decrease the power of the permanent magnet. Some latching solenoid valves will use a spring or other load to provide the returning force that closes the valve.
When the latching solenoid valve is fully open or closed, it does not consume power; therefore, it is suitable for battery-operated and limited power operations. A latching solenoid valve can remain open until an electrical charge of the opposite polarity is applied. It closes within milliseconds by canceling the magnetic force stored by the semi-permanent magnet. The momentary excitation pulse used can also be increased or reduced to affect the opening speed.
The solenoid stroke can be optimized to improve efficiency. Latching solenoid valves are most effective where the holding time in the open position is longer than the moving time. Essentially, the valve must hold the fully open/closed status for a long time.
Latching solenoid valve components & design
Pulse latching solenoid valves are operated mainly by reversing the polarity of the current. This happens in two ways:
- Two-way coil design: A two-way solenoid has one winding wire and another from the electrical source from which the current's polarity changes.
- Three-way coil design: A three-way latching solenoid valve is a three-wire solenoid with two windings in opposite directions.
Power is selectively applied to one of the coils, achieving current flow in one direction. Applying current to the other coil on a three-way latching solenoid valve applies the reverse polarity effect. The latching solenoid valve can operate with either DC or AC by adding valve coils to change AC to DC.
How latching solenoid valves operate
A standard DC latching solenoid valve comprises a coil, plunger, and stop—usually a magnetic material. When an electric current is applied to the coil, it forms an electromagnet, attracting the plunger to the stop. This action puts the plunger in an open position and allows for the flow of fluids.
There must be a constant supply of electricity to the coils to keep the valve in an open position. It takes more energy first to raise the plunger and open the valve than maintain it in the open position.
Types of latching solenoid valves
Latching solenoids are classified by their magnetic properties. There are two main types: Permanent Magnet Solenoids and Residual Magnet Solenoids.
Permanent magnet latching solenoid valve
Permanent magnet latching solenoid valves use permanent magnets (Figure 2 labeled D). These magnets help the solenoids (Figure 2 labeled E) to maintain the solenoid in the extended on or off positions. The permanent magnet generates a small magnetic flux to attract the armature (Figure 2 labeled A) to the fixed pole (Figure 2 labeled F) when no current is applied. We can modulate the action of this permanent magnet by changing the strength of the electromagnetic flux from the solenoid coil primarily by changing the polarity of the current.
The bistable solenoid valve can maintain on or off positions without significant power consumption. In some scenarios, like when there is no load action on the armature, the hold and return functions can be done with a spring (Figure 2 labeled C), thus further reducing energy consumption. The polarity and size of the current affect the magnitude of electromagnetic flux and its effect on the solenoid. The magnet holds the armature in permanent contact when the current flow ceases, and reversing the polarity cancels the flux and returns the armature to the extended position.
Figure 2: Latched (left) and de-latched (right) positions of a latching solenoid valve: armature (A), housing (B), spring (C), permanent magnet (D), coil (E), and pole (F).
Residual magnet latching solenoid valve
Residual magnet latching solenoids operate on the basic principle of the permanent magnet latching solenoids, albeit with a few design differences. It still maintains the extended on or off positions with zero current but without the use of permanent magnets. There is no heat production or electrical noise in the latched position.
Residual magnet solenoids leverage the residual magnetism property of most DC actuators enhanced by special internal design features. This provides all the magnetic force required to hold either position. An excitation pulse with reversed polarity opens and closes the valve. Their fundamental difference with permanent magnet solenoids is that you cannot latch a residual magnet solenoid once unlatched like you would with a permanent magnet solenoid. Someone can only latch it through the application of an electric current.
Today's magnetic latching solenoid valves qualify after extensive testing and specific industry and environmental standards. But so do other types of solenoids. Here's what you stand to benefit from using Latching Solenoid Valves.
Since pulse latching solenoid valves can maintain positions with zero power input, they are less prone to electrical noise. They also offer fast response times since it only needs a momentary impulse to open or close the valve. These are critical attributes when the solenoid measures or calibration scenarios.
In generating electromagnetic flux, solenoid coils often suffer heat buildup. With permanent and residual magnets, Latching Solenoids get around heat dissipation. This makes them excellent for temperature-sensitive applications, e.g., photochemical, chemical reagents, or blood products.
Low power consumption
The low energy demands of latching solenoids make them ideal for remote applications where the power supply is inconsistent or limited. This also makes them great for battery-operated setups, where having control of power used without affecting efficiency is critical in conserving battery life.
Compact size and versatility
Latching solenoids are inherently smaller than Standard solenoids by having fewer components, making it easy to package them for different applications.
Latching Solenoids are unsuitable for operations requiring them to be failsafe devices/safety valves in cases like blackouts. They would be useless unless with the help of complex drive circuits with backup power.
Latching solenoid valve operation is universal, and anyone wanting to control their fluid flow uses them somehow. Typical use cases include:
- Door locks
- Industrial instrumentation equipment
- Battey operated fluid flow systems
- Air conditioning systems
- Industrial cleaning equipment
What is the purpose of a latching solenoid valve?
A latching solenoid valve is present in systems that require minimal supervision or remote control since they can maintain a set position without the constant application of power.
How can you know if your magnetic latching solenoid valve is malfunctioning?
Troubleshoot the bistable solenoid valve if they fail to open or close, are partially open, generate a buzzing noise, or have a leakage problem. Refer to the manufacturers' guide for further details.
What factors should I consider before operating a DC latching solenoid valve?
When operating latching solenoid valves, it is essential to apply the correct current. A low current may prevent the valve from opening or closing entirely, and operating it at excessive voltages will produce extreme heat, leading to premature wear.