Mechanical pressure switches are reliable and low-cost. And with the variety of options available, they meet the requirements of many different applications. This blog summarizes common features and factors to consider when selecting a mechanical pressure switch.
In a mechanical pressure switch, a diaphragm or a piston opens or closes a circuit when the pressure in the medium rises or drops to a certain value. Every time the pressure reaches the switch point, the diaphragm or piston transfers the pressure to a micro switch. The micro-switch contact snaps and generates an electrical output signal that is sent to a controller. Adjusting a pressure spring, either on-site or at the factory, presets the switch point. The hysteresis of the micro switch determines the switch-back or reset point of the pressure switch. Mechanical pressure switches do not require a power supply.
What to Take into Account When Selecting a Mechanical Pressure Switch
Mechanical pressure switches are a simple and affordable solution where single switch contacts are required. These switches perform reliably as long as they are carefully selected to meet the particular needs of the application. Here are some factors to consider include:
- Medium and temperature — The medium and its temperature are critical when determining the material for the case, the wetted parts, and the sensor element. Mechanical pressure switches, where the case and the process connections are made of galvanized or stainless steel, work well with most applications. Nitrile butadiene rubber (NBR) is a good diaphragm material for mechanical pressure switches that work with medium temperatures and air or hydraulic oil. When the medium is water, ethylene propylene diene monomer rubber (EPDM) is better. Flourosilicone rubber (FVMQ) withstands higher temperatures.
- Pressure — Diaphragms work well as sensor elements in vacuum and low-pressure applications. Pistons, usually made of stainless steel, are better suited for higher pressure ranges.
- Switching function — Mechanical pressure switches can operate as normally open (NO) that close when they reach the switch point, as normally closed (NC) that open when they reach the preset point, or as change-over to another circuit upon a decreasing or increasing pressure (single pole single throw, or SPST).
- Switch point adjustment — The switch point can be predetermined at the factory or can be adjusted on-site. An adjustable switch point is recommended for applications where system conditions, such as temperature and pressure, vary.
- Hysteresis — Hysteresis determines when the switch resets. If the reset value is too large, the functions stays active for too long. If the reset value is too short, the function will bounce between states.
- Other factors — Reproducibility, electrical current and voltage rating, weather protection, resistance to vibration and shock, mounting, and process connections also affect which model to use.
A carefully chosen mechanical pressure switch will have a long service life. Standard units should work for at least 1 million switching cycles. More expensive mechanical pressure switches should provide approximately 5 million switching cycles.
Starting with its standard PSM01, WIKA’s wide selection of mechanical pressure switches offer a variety of options that cover the requirements of most applications. WIKA’s experts can help you find the one that best fits your needs.
This article is a continuation of Mechanical Pressure Switches in Mobile Machine Applications.