A pressure switch is a device that is used to detect and monitor the pressure in a variety of applications. On this page, we will show you how to use a pressure switch in three different ways: by detecting an active pressure circuit, detecting a loss of flow, and monitoring upstream air pressure. We have videos that demonstrate how each of these switches is plumbed into the circuit and how they work. Pressure switches are versatile devices that can be used in a variety of applications! Check out Air Logic’s Pressure Switch Catalog.
How a mechanical pressure switch works
Pressure switches rely on changes in pressure to actuate. When pressure on the switch’s diaphragm increases, it starts to compress a spring. That spring is calibrated to compress only beyond a certain pressure rating, or the setpoint. Once the spring compresses beyond that point, the switch will trip. Pressure switches can either close normally open (NO) electric contacts or open normally closed (NC) contacts. Learn more: https://air-logic.com/pressure-vacuum-switches/
Example 1: Detecting an active pressure circuit
The way it works and how it is plumbed into the system
In this video, the red right is connected to the (NC) normally closed circuit. The green light is connected to the (NO) normally open circuit. The idea is to use the green light to indicate an activated pressure circuit.
For the pressure switch to actuate only when the intended circuit is energized, it must be plumbed into the correct spot. In the video, the correct spot is in between the 5-way valve and the check valve. As the 5-way valve energizes the pneumatic circuit, it pressurizes the switch and the system lights the green light. After the 5-way valve is flipped, the circuit loses pressure, the pressure switch resets and the red light is indicated.
The set point of the switch:
The pressure switch in this video is set at 18 psi, which is slightly lower than the system’s normal operating range of 20 psi. The reason for setting it that low? To avoid problems with leakage and tolerance stack-up or drift on the equipment.
Applications:
Industrial automation monitoring – Feedback on a pneumatic circuit can monitor critical operations of equipment by creating a closed-loop. Knowing if a pneumatic circuit that should have been activated was actually activated is achievable in this way.
Safety circuits – A pressure switch can indicate if circuits are energized before maintenance. The pressure switch could indicate if the equipment is in a “ready” or “not ready” status for maintenance.
Maintenance schedule – a PLC can alert a technician to perform a preventative maintenance action after a circuit has been activated so many times.
Example 2: Detecting a loss of flow
The way it works and how it is plumbed into the system:
The pressure switch in this video is plumbed in between the orifice restrictor and the device that is using the airflow. The orifice restrictor is providing flow control and dropping the pressure of the incoming air. So, when the engine is running and consuming air, the pressure is low. But, if the consumption of the engine is interrupted, the pressure spikes and the pressure switch detects the rise.
The set point of the switch:
The pressure switch in this video is set at 15 psi, which is slightly higher than the normal operating pressure of this circuit under normal conditions. The differential of the switch is important in this application because the switch must reset to indicate a normal flow condition.
Applications:
Equipment monitoring – Loss of flow may indicate an equipment failure. A pressure switch can alert the system or operator of the failure.
Filtration monitoring – An increase in pressure may indicate a blocked filter. As a filter becomes blocked, the restriction in the system will increase. After enough of an increase, the pressure switch can indicate a filter that needs to be replaced.
System tampering – A pressure switch in this application will be monitoring if an unauthorized increase in pressure has occurred.
Cylinder end of stroke – As a pneumatic cylinder finishes the stroke or is impeded, there will be an increase in pressure. A pressure switch can detect that increase and provide feedback to a system.
Example 3: Monitoring upstream air pressure
The way it works and how it is plumbed into the system:
The pressure switch in this video is detecting if the incoming air pressure is on. The Air compressor in the factory is in another room, so this application is to detect if the compressor is running, connected, and up to pressure. This way, it is clear the engine should run if the valve is opened. With a switch, this can be integrated into a controller and automatically monitored.
The set point of the switch:
The set point of the switch is 95psi in this application. The shop Air Pressure varies from 100-120psi during normal pressure control operations.
Applications:
Tanked gas applications – If the tank drops below the operating pressure of the equipment, the system can safely shut down.
Process control – Detect inlet pressure drops to determine if the system should be enabled or not. Inlet pressure drops may indicate a pump system failure. Compressed air systems are complicated and may have a valve turned off after the pressure tank.
Pressure Switches from Air Logic:
Air Logic has many types of pressure switches and they are highly configurable for your application. Our Mechanical pressure switch design is time-tested and reliable. We can customize the set point (operating points), spring pressure, maximum pressure, pressure port, and more. Check out our catalog!
Customer-specific specifications.
The pressure switches from Air Logic are made to order and can be shipped quickly. We can also preset the set pressure for customer applications. That way, customers can specify their product to always have the same pressure set point. Some customers specify the cut-in or cut-out pressure( ie. cut-in or cut-out point). A customer-specific test plan is made when the cut-out point or reset point is required for a pressure switch. This may also include the system pressure, a custom range spring, specific pressure, or pressure gauge usage. There can be many critical factors for your application – Please reach out if you have specific questions.
Electrical circuit specifications
There is a range of electrical ratings to match the power supply and electrical output required. Each F5100 series switch is made with a single pole double throw (SPDT) micro switch. The micro switch determines the electrical rating and performs the actual switching function. All of the electrical components are contained within the switch case. The pressure switch may be wired as a normally closed switch or as a normally open switch.
Operating principle
Air Logic’s product is a mechanical pressure switch. The air pressure from the pressure port pushes against the diaphragm (sensing element). The diaphragm (pressure-sensing element) pushes against both the spring and switch contacts. The spring force determines the set point. Adjust the spring force by turning the adjustment screw in or out. Mechanical pressure switches are straightforward and easy to implement in many system designs. Diaphragm switches are another way to describe Air Logic’s pressure switches.
Pressure range
The pressure range of a pressure switch may be important for pressure control or process control in your application. The fluid pressure setpoint must be lower than the maximum setpoint to make the switch work.
Low-pressure switches
Low pressure is a relative term that applies differently depending on the industry. A typical pressure switch from Air Logic will have an operating pressure range from 1-100psi. We can also make switches that work at lower pressures or even at negative pressure.
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