How to select the correct pressure switch for your application
The most important factor in selecting a pressure switch is to fully understand your requirements before beginning the selection process. Armed with that knowledge, you must consider a number of parameters in making a final selection. In this article, Barksdale discusses the main points to consider.
Pressure switches are one of the most commonly used fluid control components. We use them at home, in our refrigerators, dishwashers and washing machines. We use them in industrial settings, in hydraulic and pneumatic systems, injection moulding machines and lubrication monitoring. Whenever we handle a gas or liquid we almost always need to control the pressure.
Our home appliances do not demand high accuracy, nor do they experience high cycle rates. By contrast, the pressure switches used in industrial machinery and systems must be rugged, dependable, accurate and have a high lifecycle.
Most of the time we never think about pressure switches. They just show up with such machinery as paper machines, air compressors or pump sets. In this type of equipment, we depend upon pressure switches to act as safety devices, alarms, or as the control element within the system. But in most cases we give little consideration to this component when we make a purchase.
Take care of the details
As young engineers, we're commonly told to
take care of the details and the rest will take care of itself.
Why the focus on details? Because the tendency is to focus on the big, the expensive or the exotic. However, when we evaluate equipment performance, it is often the simple or inexpensive component failure that shuts a system down or affects performance. The cost of component failure can be measured in unscheduled outages, costly down-time and lost production.
One of the most common components in the plant is the one we may know least about. When a pressure switch fails, we tend to simply buy a replacement that is a duplicate of the one that just failed. If we are to improve the performance of our plants, however, we should break this paradigm. Rather than simply replacing the switch with "like for like," we need to consider what will best meet our needs.
Choosing a pressure switch
There are typically three situations when an engineer thinks about pressure switches:
- When a hydraulic or pneumatic system fails.
- When equipment or a system containing a pressure switch is purchased.
- When designing an in-house system.
When a pressure switch fails, the engineer is generally on his own in trying to figure out if he should simply replace the switch with the same product or try to upgrade to something better. To determine if a different pressure switch should be used, the following process can be useful.
First, Identify the type of switch currently being used and its operating specifications. This information should be printed on the switch label. If it isn't, contact the OEM or the switch manufacturer. Then, determine the failure mode. For example, if the switch does not actuate at the desired pressure, the problem could be cycle fatigue. Understanding system dynamics and the type of switch will help in diagnosis of the problem.
Finally, based on the failure mode, consider replacing the switch with one that better meets your system's dynamics and operating needs. The goal is to eliminate the failure mode. In this example, if the switch type currently used is a diaphragm switch and the system cycles rapidly, the solution could be to select a diaphragm-piston switch if accuracy is not an issue, or a solid-state switch for higher accuracy and rapid cycling.
Your four options to consider when choosing a pressure switch
When purchasing equipment or a system containing a pressure switch, the engineer has at least four options:
- You can specify the switch type, model number and manufacturer. This can be difficult for complex systems, especially if the system dynamics are not known.
- You can specify features such as, "Pressure switches shall be rated for a minimum life of 1.0 million cycles, an accuracy of 0.50 per cent, etc.", and leave it up to the vendor to select the correct switch.
- Combine the two approaches. For example, specify a quality switch manufacturer, such as Barksdale, the minimum cycle life and accuracy.
- Simply do nothing and hope for the best.
Know each pressure switch's strengths and weaknesses
Fortunately, when designing your own system it is relatively easy to identify operating parameters and critical switch characteristics. This allows you to optimize accuracy, life, ease of use, and other important features as they relate to your specific needs. All you need to know is the advantages and limitations each pressure switch design has to offer.
To be proactive and specify the correct switch for the application, or to successfully replace a problem switch, one must know the types of switches available and their strengths and weaknesses. Also, as with all specialties, pressure switches have their own unique language and terminology which needs to be understood simply to improve communications.
For more information about Barksdale’s full range of switch products please contact 01256 799721 or visit www.barksdale.co.uk.
Barksdale Control Products
Barksdale is an ISO 9001 registered manufacturer of controls for industrial applications, specialising in the control and measurement of fluids. Founded in 1949, Barksdale is headquartered in Los Angeles, with a UK office in Hampshire and a manufacturing facility in Germany.
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