A pressure switch for sensing fluid or air pressure contains a capsule, bellows, bourdon tube, and a diaphragm or piston element that deforms or displaces when pressure is applied. The resulting motion is applied directly or through amplifying levers (rod and float ball) to a set of switch contacts activating the controlled pump.
Pressure Switch Selection Specifications
Knowing the requirements for the pump you are controlling will help you to select a switch that will function properly. The specifications below are key to selecting the correct switch for your pump. Read each specification description to ensure you understand what the specification is and determine the correct range for your pump.
Understanding Pressure Switch Types
When selecting a pressure switch it’s important to check the specifications of the switch to ensure it will function properly for the intended application. There are many styles of pressure switches but all are either electromechanical or solid state. This information on pressure switch types and terms can help you make the most informed selection.
Electromechanical Switch
The most common mechanical pressure switch, they’re composed of a sensing element and an electrical snap-action switch. A variety of different types of sensing elements are available for use and they all have one thing in common: they move in response to changes in the system pressure. Through this movement, they directly act on the switch's contacts by opening or closing the contact.
Solid State Switch
These switches use a metal diaphragm about the size of a dime with a micro-miniature strain gauge etched onto its dry surface. Increasing pressure changes the impedance of the strain gauge. A digital comparator monitors the output from the strain gauge and compares it to the user-specified set-point. When the set-point is reached, the electronic circuit turns on a solid state relay, completing the circuit.
Pressure Range
Provides the pressures in which the valve will operate. The pressure the application is creating for its On/Off function must be within this set of numbers for the switch to function properly. Some switches are manufactured with a fixed setting that cannot be adjusted, and some are made adjustable to operate multiple applications. Be sure of which one you need when selecting a switch for your application. Example: Factory ON/OFF settings 20 to 40 psi.
Horsepower to Voltage
This shows the limit of horsepower the switch can transfer to the pump being controlled based on either a single- or three-phase power supply. Check the pump horsepower and power specifications before installing a switch to ensure it can handle the pump it is controlling. Example: 2HP @ 3 Phase—460V.
Differential Range
This is the range in which the switch contacts will not react to movement. Instead of a gradual drop to the contactors, the switch reacts when the pressure has dropped far enough from the set point to cause a quick snapping action to the contacts activating the controlled pump. Depending on the switch selected, some switches may have this range fixed while some are adjustable.
Burst Pressure
The maximum working pressure the switch can handle before the inner seals and mechanically controlled pieces begin to fail or break apart. Your application should use pressure settings well below this limit to prevent damage or product failure.
Special Features
Some special features of pressure switches include a manual switch for ON/OFF/AUTO, and an unloader connection for an air compressor unloader valve, designed to automatically relieve the pressure on the compressor pump to ease restart. Additional special features include low- or high-pressure cutoffs and multiple pole contacts. Be sure to check your application requirements for any of these features, including port connection sizes and types.
|
|
|
Zoro offers a wide selection of pressure switches for everything from portable electric air compressors to furnaces and heaters.
Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.