SWITCHES

Quality Air Pressure Switches at Airtrol Components Inc.

Pressure switches are an important element of many fluid systems—both hydraulic and pneumatic. They are a type of switch that relies on fluid pressure to control the operation of connected devices and systems. After a specific pressure limit has been set, a mechanism connects or separates electrical contacts within the switch once it has been reached.

This action opens or closes an electric circuit to start or stop the flow of power into the load. Whether contact connection or separation occurs on pressure rise or pressure fall depends on the switch design.

These elements are found in a wide range of fluid systems for a variety of industries and applications, including automobiles, HVAC systems, and pumps. They come in different designs and sizes, ranging from mechanical to electronic, small to medium to large, and more.

Types of Pressure Switches

Pressure switches can be categorized into two main types: mechanical and electronic.

Mechanical

Mechanical pressure switches measure pressure changes through mechanical means, such as by using a diaphragm, piston, or Bourdon tube. The key advantages of these switches are their reliability and ability to operate without an auxiliary power source. They also offer higher voltage and amperage capacities than electronic switches.

Electronic

Electronic pressure switches measure pressure changes through electronic means—i.e., electronic pressure sensors. The key advantages of these switches are their flexibility, stability, and longevity. Various parameters can be individually adjusted to suit different applications, and the output parameters remain precise through the component’s service life. Some variations—solid-state switches—produce analog signals proportional to the pressure, which enables them to control connection/separation as well as transmit the pressure value.

What Is An Air Pressure Switch?

An air pressure switch is a pressure switch that actuates in response to air (pneumatic) pressure. They are used to control pneumatic devices and systems with strict operating pressure requirements, such as exhaust systems, fans, fire protection dampers, sound alarms, and ventilation ducts.

Components of Pressure Switches

While pressure switches can vary in design depending on the type, manufacturer, and intended application, they typically feature the following components:

• Terminals. The incoming and outgoing power wires are connected to the pressure switch at the terminals.
• Contacts. The contacts are conductive components that complete the electrical circuit when connected, allowing power to flow to the connected load.
• Diaphragm. The diaphragm—also referred to as the membrane—is a flexible component that moves in response to pressure changes. When the set pressure limit is reached, it connects or separates the electrical contacts.
• Adjustment spring(s). The adjustment spring is used to increase or decrease the on/off pressure range for the switch. Some pressure switches have a secondary adjustment spring that allows for the adjustment of the cut-off pressure setting without altering the cut-in pressure setting.

Selection Considerations for Pressure Switches

There are many factors to consider when selecting a pressure switch for a fluid system to ensure it works as intended, which can make it difficult or daunting when the time comes to choose a new or replacement component. Some of the main considerations to keep in mind include:

• Diaphragm size. The diameter of a diaphragm determines its sensitivity and, in turn, its scale. The larger the diaphragm, the more sensitive it is to changes in pressure. The smaller the diaphragm, the less sensitive it is to changes in pressure. Compared to small diaphragms, large diaphragms also provide wider scale increments and smaller deadbands.
• Setpoint. The setpoint is the pressure level at which a switch opens or closes the contacts. It can be preset at the factory by the supplier or set in the field. It can also be adjusted using the adjustment springs.
• Deadband. Deadband is the pressure difference between the setpoint and the reset point. Pressure switches with narrow deadbands are ideal for safety applications, while pressure switches with wider deadbands are suitable for control circuit applications. Typically, mechanical switches with diaphragms or Bourdon tubes have narrow deadbands, mechanical switches with pistons have wide deadbands, and solid-state switches have close to full-scale deadband.