How Do You Choose the Right Pressure Switch? 9 Factors to Consider

Choosing the right pressure switch requires matching the instrument’s pressure range, setpoint capabilities, materials, electrical requirements, approvals, and environmental protection to the needs of your application.

Pressure switches monitor pressure levels and activate or deactivate equipment when pressure reaches a predetermined setpoint. They are used in many industrial and OEM systems to start or stop a process, control equipment, or trigger an alarm. Selecting the wrong switch can lead to actuation errors, damaged equipment, worker injury, or other safety concerns. 

With more than a century of experience in pressure measurement, Ashcroft helps engineers evaluate mechanical and electronic pressure switches for a wide range of industrial and OEM applications. Read this article to learn what makes a quality pressure switch and the nine factors to consider when choosing or replacing one.

What makes a quality pressure switch?

A quality pressure switch consistently activates at the required setpoint while withstanding the pressure, temperature, media, and environmental conditions of the application.

Because pressure switches are often used to start or stop a process or alert the user to an unsafe condition, reliable operation is important. Factors that affect pressure switch quality and performance include:

• Switch type, such as diaphragm, piston, or electronic
• Setpoint accuracy and repeatability
• Wetted materials
• Housing construction
• System pressure requirements
• Required industry or hazardous location approvals
• Environmental protection

How do electronic and mechanical pressure switches differ?

Electronic pressure switches generally provide greater setpoint flexibility and repeatability, while mechanical switches offer a straightforward design that can perform reliably without external power.

• They use sensors and electronic components to monitor pressure and control the output.

• They can offer highly repeatable setpoints, digital displays, programmable outputs, and diagnostic capabilities - depending on the model.

Mechanical pressure switches use a diaphragm or piston actuator and a microswitch.

• They can often switch higher electrical voltage and currents.
• Their setpoint performance can be affected by mechanical wear, temperature changes, and the limitations of the actuator and switching mechanism.

• The appropriate design depends on the pressure range, accuracy, electrical requirements, operating environment, and function of the switch.

What should you consider when selecting a pressure switch?

When selecting a pressure switch, confirm that its specifications match the application’s pressure, setpoint, media, temperature, electrical, approval, and environmental requirements.

The following nine factors can help you evaluate available options. Refer to the product datasheet for the specification verification you need for your application.

1. What are the operating and maximum pressures?

For safety reasons, the pressure switch must be rated for both the application’s normal operating pressure and its maximum expected pressure. To confirm this, you need to know what your system's standard operating pressure and then consider any startup conditions, pressure spikes, pulsation, or other events that could temporarily increase pressure.

Selecting a switch that cannot withstand the system’s maximum pressure can damage the sensing element, change the setpoint, or cause the switch to fail. When reviewing the datasheet, check the switch’s adjustable range, maximum allowable working pressure (MAWP), proof pressure, and burst pressure. Each rating describes a different pressure limit. 

2. Can the switch achieve the required setpoint?

The required setpoint must fall within the switch’s specified adjustable range.

Every mechanical and electronic pressure switch has limitations based on its pressure range and design. Some mechanical switches may not allow the setpoint to be adjusted across the switch’s entire range. Electronic switches may provide more flexibility, depending on the model.

3. Are the wetted materials compatible with the process media?

All wetted materials must be compatible with the process media to prevent corrosion, material degradation, contamination, and premature failure. Depending on the switch design, the wetted components may include:

• Process fittings
• Pistons
• Diaphragms
• O-rings
• Seals

Material incompatibility can create safety concerns or allow unwanted substances to leach into the process media. Consider both the chemical composition and concentration of the media when evaluating compatibility.

For additional guidance, you can refer to the Ashcroft® Material Selector and Corrosion Guide.

4. Can the pressure switch withstand the application temperature?

The pressure switch’s process and ambient temperature ratings must cover the conditions expected at the installation point. Temperature outside the switch’s specified limits can affect elastomers, electrical components, enclosures, and the performance of the sensing element. It can also contribute to setpoint drift or reduce service life.

When reviewing the datasheet, look for both process and ambient temperature limits. If temperatures at the switch could exceed those limits, the installation may require remote mounting, a cooling element, or another method of isolating the instrument from excessive heat.

5. What electrical ratings does the microswitch require?

The microswitch must be rated for the voltage, current, and type of electrical load it will control.

Microswitch electrical ratings identify the voltages and currents at which the switch has been tested to achieve a specified cycle life. These ratings can vary based on whether the load is resistive, inductive, or another type.

A mechanical microswitch passes the supplied voltage and current to the connected load. It may operate at electrical conditions beyond a particular published test rating, but doing so can reduce contact life or affect switching reliability.

When reviewing electrical requirements, confirm:

• Voltage to be switched
• Current to be switched
• AC or DC service
• Load type
• Required contact configuration
• Expected switching frequency
• Desired cycle life

6. Which industry or hazardous location approvals are required?

The pressure switch must carry the approvals required for the equipment, industry, and installation location.

Applications involving flammable gases, vapors, or combustible dust may require equipment approved for hazardous locations. Depending on the installation and governing requirements, protection methods may include explosion-proof, flameproof, intrinsically safe, or non-incendive designs.

Other applications may require approvals for functions such as boiler or steam limit control.

In the United States, OSHA-recognized Nationally Recognized Testing Laboratories, or NRTLs, test and certify certain products to applicable safety standards. Examples include UL, FM Approvals, and CSA Group. International requirements may involve ATEX, IECEx, or CE marking, depending on the product and where it will be installed.

A pressure switch may need NSF/ANSI/CAN 61 certification when its wetted components come into contact with drinking water.

NSF/ANSI/CAN 61 establishes minimum health-effects requirements for materials, components, and products used in drinking water systems. If a switch will be used in a potable water application, confirm whether the instrument and its wetted components carry the certification required for the installation.

Always confirm the required certification, area classification, gas or dust group, temperature class, and applicable regional requirements before selecting the switch.

7. Does the application need fixed or adjustable deadband?

Deadband, also called hysteresis, is the difference between the pressure at which a switch activates and the pressure at which it returns to its original state. Pressure switches generally offer one of two deadband configurations:

• Fixed deadband: The deadband is determined by the switch’s mechanical design. Factors such as diaphragm material, switching mechanism, and pressure range influence the value.
• Adjustable deadband: The actuation and reset relationship can be adjusted within a specified range to meet the application’s operating requirements.

Deadband that is too narrow may cause frequent cycling when system pressure fluctuates near the setpoint. Deadband that is too wide may delay the required reset action.

You'll want to choose a fixed or adjustable deadband based on the required difference between the switch’s actuation and reset pressures.

8. Will the pressure switch be installed outdoors?

An outdoor pressure switch needs an enclosure rating and temperature range suitable for the conditions at the installation site.

Rain, snow, sleet, dust, icing, temperature changes, and corrosive conditions can affect switch performance. Review the enclosure’s Ingress Protection (IP) or NEMA rating to determine the type of environmental protection it provides.

• IP ratings describe protection against solid particles and water ingress. Ratings such as IP65, IP66, and IP67 represent different degrees of protection, so the complete rating should be evaluated rather than assuming that a higher number is suitable for every condition.
• NEMA enclosure types address specific environmental conditions such as water, dust, corrosion, icing, or hazardous locations. Examples include NEMA Type 4 and Type 7 enclosures, although these ratings cover different hazards and are not interchangeable.

Also consider whether the enclosure material and external components can withstand corrosion, ultraviolet exposure, and the expected ambient temperature range.

9. Should the switch be factory set and calibrated?

Factory setting and calibration can provide a switch that arrives adjusted to the specified setpoint and ready for installation.

Ashcroft offers a Factory Set option, identified as XFS, for applicable pressure switch models. During this process, the setpoint is adjusted at the factory according to the customer’s requirements.

A factory-set switch can simplify installation and reduce the time needed for field adjustment. However, users should still follow applicable installation, commissioning, and testing procedures before placing the switch into service.

Additional options may include:

• Mounting brackets
• Oxygen cleaning
• NACE-compliant materials
• Metric labeling
• Pilot lights

Availability depends on the switch model and application requirements.

Ready to learn more?

You can choose the best pressure switch by defining the application requirements first and then comparing those requirements with the specifications of available mechanical or electronic switches. If you have questions, contact us, or review the related content offered below.