This article was originally published on February 28, 2022, and updated on December 4, 2024.
Pressure switches are important components in many industrial and OEM applications. By monitoring pressure levels in your system and automatically activating or deactivating equipment when pressure reaches a predetermined setpoint, they help ensure a safe and efficient process.
Choosing the wrong pressure switch could lead to actuation errors, damaged equipment, worker injury, or other dangerous issues. So, how do you know if you have the right pressure switch? And what factors should you consider if you need a new one? As the Ashcroft Product Manager for Switches, I’ve developed some best practices for things to consider while you’re researching. Read this article to learn about the primary factors to look for when choosing or replacing a pressure switch.
You will also find links to additional information that can deepen your knowledge of pressure switches used in different applications.
What makes a quality pressure switch?
Most pressure switches are used for applications that need the switch for safety: to start or stop a process, or to alert the user with an alarm. Therefore, the quality of the instrument is important.
There are many things to consider when selecting the best pressure switch for your application, including the style of the switch (diaphragm, piston, or electronic), wetted materials, housing construction, setpoint requirements, application pressures (working and maximum) and whether any approvals are required.
Another important attribute of a pressure switch is the accuracy of the setpoint. Accuracy is also known as the repeatability of the switch, or the ability of the switch to provide the same setpoint time after time.
The style of switch you use will depend on the application and is another factor that speaks to the instrument's quality. For instance:
- Electronic switches, for example, can have very high accuracies due to their digital output and precise electronic components, which allow for consistent and repeatable setpoints.
- Mechanical switches, including diaphragm or piston switches, may have lower accuracy specifications because their performance can be affected by many factors. Mechanical wear, temperature fluctuations and the limitations of their construction, for instance. can lead to variations in the setpoint over time.
Potable water applications demand a very specific type of quality. If you are purchasing pressure switches to measure water levels in aquifers, water towers, or any other potable water application, you need to ensure that every component you buy is certified to meet the strict NSF/ANSI/CAN 61 (NSF 61) standards.
This certification guarantees each component is safe for use in drinking water systems. The good news is Ashcroft offers several NSF 61-compliant switches to choose from.
9 Considerations When Selecting Your Pressure Switch
Once you have the answers to those questions, here are nine specific factors you will need to confirm using the product datasheet:
1. The standard operating pressure and maximum pressure of your application.
For safety reasons, you need to ensure that the pressure switch is suitable for your application. Select a switch that can manage both the regular operating pressure and any sudden pressure increases in your system.
2. The required setpoint can be achieved by the switch.
Whether you choose a mechanical or electronic pressure switch, each has setpoint limitations based on its range. For example, some mechanical switches can't set points in the 10% to 15% of their range. Electronic switches, however, can have set points almost anywhere within their range.
3. The compatibility of the process fittings and/or other materials.
Be sure to check the compatibility between the process media and the wetted materials of the switch (i.e., process fittings, pistons, O-rings and diaphragms). Incompatibility can cause corrosion issues, safety concerns, leaching into the process media, and more. For more guidance on compatibility, refer to the Ashcroft Material Selection & Corrosion Guide.
4. Temperature compatibility between the application and the switch specifications.
The datasheet typically lists the temperature ranges that your switch can withstand. Using a switch beyond its stated temperature specifications can lead to setpoint drift, component issues and possible safety concerns.
5. Microswitch electrical requirements.
The electrical ratings of the microswitch are guidelines of the voltages and currents that the switch can be used with to ensure the maximum cycle life of the switch. The listed ratings provided by microswitch suppliers are the voltages and currents tested by third-party independent test labs for the required cycle life.
However, keep in mind that microswitches are mechanical pass-through devices, that send the supplied voltage and current to your load. This means that the microswitch can be used with many different voltages and currents but may see a reduction in the cycle life.
6. Industry-specific or hazardous location approvals.
Knowing whether your application requires instruments with hazardous location approval and/or general-purpose safety approvals will dictate which switch can be used. Hazardous approvals include explosion-proof, intrinsically safe, and non-incendive. Some applications may also require industry approvals such as boiler and steam limit control approvals. These approvals are provided by independent and nationally recognized test labs known as NTRLs. Approvals include UL, FM, ATEX, CSA, IEC and CE.
7. Fixed or adjustable deadband.
Deadband in pressure switches refers to the difference between the pressure at which the switch activates (the setpoint) and the pressure at which the switch deactivates (the reset point). Switches can have two different kinds of deadbands:
- Fixed. Switches that have fixed deadbands have a deadband value that is determined by the mechanical properties of the switch. Items such as diaphragm material, the switching mechanism and the pressure range of the switch all influence this fixed value.
- Adjustable. These switches have deadbands that can be adjusted or selected within a specific range to meet a customer's application requirements.
8. Outdoor applications.
Using pressure switches outdoors presents challenges such as temperature fluctuations and weather conditions like snow, rain and sleet that can impact the functionality of your instrument. Be sure to consider what IP/NEMA ratings you need to satisfy the location of your pressure switch.
- IP ratings, such as IP65, IP66, or IP67, indicate the level of protection against dust and water ingress, with higher numbers offering greater protection.
- NEMA ratings, like NEMA 4 or NEMA 7, provide additional information about the enclosure's ability to withstand environmental hazards, including corrosion, icing, and explosion risks.
9. Factory calibration.
One of the most common requests is to have the setpoint of the switch calibrated at the factory. This is known as Factory Set (XFS). This ensures the accuracy of the switch when received by the customer while adding to the ease of installation because the switch is ready to install.
Other pressure switch options include material choices, special enclosures, mounting brackets, oxygen cleaning, NACE certification, metric labeling, pilot lights and much more.
Ready to learn more?
We covered a lot in this article, but the truth is there is so much more to know about switches. They are complex instruments that come in a variety of configurations to meet most installation requirements in nearly every industry. While you now know the primary factors to consider when selecting a pressure switch for your application, we think you will find these additional articles informative and relevant to your search:
- Cost of Mechanical Pressure and Temperature Switches
- When Should You Use an Electronic Pressure Switch?
- What is a Deadband on a Pressure Switch and How Does it Work?
- Choosing the right Microswitch for your Application
Feel free to talk to one of our industry experts if you have questions or need help.
