Types of pneumatic solenoid valves, functions of pneumatic solenoid valves

Types of pneumatic solenoid valves, functions of pneumatic solenoid valves Solenoid valves are classified according to their normal state, type of operation and circuit function. All of this must be specified when selecting a new solenoid valve and integrating it into an existing system. Like any other type of self-starting valve, solenoid valves are usually classified according to their normal (de-energized) state. This feature also indicates its fail-safe position. When power is removed, a spring within the solenoid valve returns the plunger to its normal position. 1. Normally open solenoid valve: Normally open solenoid valve opens when the power is off. Activate the solenoid to close the valve. This is useful in applications where air or gas flow must be maintained in the system in the event of a power failure. 2. Normally closed solenoid valve: As opposed to normally open solenoid valve, normally closed means blocked in its unenergized state. Power is sent through the solenoid valve to open the valve. Normally closed solenoid valves are more common than normally open types. Most applications require system lines to be shut down or isolated during a system failure. 3. Bistable solenoid valve: Normally open and normally closed solenoid valves are considered monostable valves. A bistable solenoid valve, on the other hand, has a second solenoid valve instead of a spring return mechanism. They have no normal position. When powered on, they remain in the same position even when power is removed. Another classification of solenoid valves is the type of operation. They can be activated in two main ways. The first is direct action, which relies entirely on the electromagnetic force generated by the solenoid. Next is the indirect method, using pressure provided by the pilot line. These methods can also be combined to create a valve activated by electromagnetic force and line pressure. 4. Direct-acting solenoid valve: For this type of solenoid valve, the static pressure increases as the orifice size increases. An increase in static pressure requires stronger solenoid valve action;therefore, the magnetic field is stronger. This means that for a given amount of pneumatic pressure, greater flow requires a larger solenoid. Pressure and flow are then directly proportional to the required solenoid size. This type of solenoid valve is typically used in low flow and operating pressure applications. 5. Internal pilot solenoid valve: For high flow and high pressure applications, use an internal pilot solenoid valve. In this type of valve, pressure across the valve opens or closes the valve. To achieve this, an orifice or a balancing hole is installed. The usual design involves core blocking flow at the orifice. When the valve closes, air passes through the orifice and pressure builds up on both sides of the diaphragm. Whenever the airflow is blocked, a closing force is generated due to the larger effective area at the top of the diaphragm. When the valve opens, the spool opens the orifice, relieving the pressure at the top of the diaphragm. Line pressure then opens the valve. 6. External pilot solenoid valve: This type of valve uses the same concept as an internal pilot valve, but the pressure used to drive the valve comes from an external supply of air. A separate air circuit is integrated into the valve via an additional port. Both internal and external pilot solenoid valves are called indirect or servo-assisted valves, and their main driving force comes from the pressure difference between the upstream and downstream pipelines of the valve. 7. Semi-direct acting solenoid valve: Semi-direct acting combines the principles of direct and indirect acting valves. In addition to the magnetic force from the solenoid, the pressure difference across the valve helps open or close the valve. When the plunger is actuated, the diaphragm is lifted to open the valve. At the same time, an orifice opens, causing the pressure at the top of the diaphragm to release. Closing the hole with a plunger creates more pressure on the top of the diaphragm, closing the valve. Finally, solenoid valves are also classified based on their circuit function. They can function as a simple isolation valve, servicing a single flow path. Other applications require multiple flow directions. An example is a cylinder that requires pressurization and exhaust flow paths. 8. Two-way solenoid valve (2/2-way valve): These types of solenoid valves have an upstream and a downstream port. They are the most basic type and are used to prevent or allow airflow. Two-way solenoid valves are available in normally open and normally closed configurations. 9. Three-way solenoid valve (3/2-way valve): The three-way solenoid valve has three ports: inlet (pressure port), exhaust and outlet (actuator port). They have two states. These two states alternately apply and discharge pressure from the actuator or downstream equipment. The three-way solenoid valve can also be configured as normally open and normally closed, adding universal functionality. For a normally open three-way valve, when the valve is powered off, air flows from the air inlet to the air outlet, and the exhaust port is closed. When powered on, the air inlet is closed and the air outlet is connected to the exhaust port. The opposite is true for normally closed valves. On the other hand, the universal function is used to select the flow reversal from one port to another. 10. Four-way solenoid valve (4/2-way valve): The four-way solenoid valve has four ports: one inlet (pressure port), two outlets or actuator ports, and one exhaust port. The valve's two states allow flow from the pressure port to one of the outlet ports while venting pressure from the other port to