Core Summary
A pressure switch is a device that switches the state of an electrical contact when the measured pressure reaches a set value. It is commonly used in pump control, air compressors, hydraulic systems, and safety interlocks. Its core specifications include range, set point, reset differential pressure, contact type, and pressure resistance.
1. Basic Operating Principle
Pressure drives the deformation of the sensing element
The pressure switch contains sensing elements such as diaphragms, pistons, or Bourdon tubes. The measured pressure acts on these elements, causing them to undergo mechanical displacement. When the displacement reaches a preset position, the microswitch is triggered, and the circuit switches between on and off states.
The setpoint and reset point can be different
Many pressure switches come with adjustable differential pressure capabilities. For instance, in the control of pump start-stop operations, the start pressure and stop pressure do not need to be identical. By adjusting the reset differential pressure, one can prevent the pump from frequently starting and stopping near the critical pressure point.
II. Main Structural Forms
Diaphragm pressure switch
The diaphragm structure features high sensitivity and excellent repeatability, making it suitable for low and differential pressure measurements. Common diaphragm materials include stainless steel or special alloys, and the corrosion resistance of the diaphragm must be verified for corrosive media. The Bailey & Mackey Type 1381 series belongs to the diaphragm pressure switch category.
Piston-type pressure switch
The piston-type structure exhibits strong pressure-bearing capacity and superior shock resistance and contamination tolerance compared to the diaphragm type, making it commonly used in high-pressure hydraulic systems or applications involving particulate media. The Bailey & Mackey Type 1581 utilizes a piston-type structure, suitable for higher pressure ranges.
Bourdon tube pressure switch
The Bourdon tube type is commonly seen in integrated switches for pressure gauges, utilizing the deformation of a C-shaped tube that straightens under pressure to push the contact point. Its advantage is low cost, but its response speed and impact resistance are inferior to those of the diaphragm and piston types.
III. Key Selection Parameters
Measuring Range and Overpressure Capacity
The measurement range should cover the working pressure and allow for a certain margin. Overpressure capacity refers to the peak pressure that the switch can withstand for a short period of time. Transient overpressures such as pump start-stop and water hammer should not exceed this value [please verify].
Contact form
Common types include SPST, SPDT, DPDT, etc. SPDT can provide both normally open and normally closed logic, making it suitable for circuits that require both activation and alarming. When selecting a model, it is also important to confirm the voltage and current that the contacts can withstand.
Electrical Connection
DIN plugs, cable outlets, terminal blocks, and other forms each have their respective application scenarios. Sealed cable outlets are typically preferred for outdoor or humid environments, while terminal blocks or DIN plugs are more suitable for use inside control cabinets.
IV. Typical Application Scenarios
Pump and Air Compressor Control
When the pressure in the pipe network falls below the lower limit, the pump or air compressor is activated; when it exceeds the upper limit, it is shut down. The pressure switch directly drives the contactor or achieves automatic control through PLC input.
Filter clogging alarm
Install a differential pressure switch before and after the filter to trigger an alarm when the pressure difference exceeds the set value, indicating the need to replace the filter cartridge. Such applications demand high response speed and repeatability accuracy.
Safety Interlock
In the event of overpressure in pressure vessels and hydraulic systems, the power source should be cut off. When functioning as a safety interlocking component, the reliability and certification level of the switch require special attention.
Parameter Table (Terminology Comparison)
> The above content is organized based on Bailey & Mackey pressure switch products. Specific parameters are subject to the original manufacturer's datasheet. QN TECHNOLOGY provides selection support for models such as Type 1381 / Type 1581 / Type 3311.
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