Pressure Switches

What are Pressure Switches?

Pressure switches are a form of switch used to open or close electrical circuits when a certain set fluid pressure has been reached on its input. They can be utilized to operate solenoid-operated valves or other devices used in the particular system.

Pressure switches are used to detect fluid pressure, which are designed to make contact on either pressure rise or fall. One or more of these switch contacts are activated by the sensor movement to indicate an alarm. Pressure switches are very commonly seen in industries wherein automatic supervision and control systems are required that involves pressurized fluids.

Construction Pressure Switches

A pressure switch for fluid pressure sensing typically consists of a capsule, bellows, bourdon tube, diaphragm that proportionally displaces to the pressure applied. Amplifying levers or a set of switch contacts are then used to create motions. In light of the volatile pressure changes and the fact that contacts should be operated quickly, an operation-quickening mechanism such as a miniature snap-action switch is often applied.

Some types of pressure switches are also equipped with mercury switches, which are mounted on bourdon tubes. These are the more sensitive types that are known for its useful over-center characteristics. Also, industrial pressure switches may be coupled with calibrated scale and pointer to indicate the set point of the pressure switch.

The pressure-sensing element is also an integral part of the switch that can be configured to respond to the difference of two pressures. This type of pressure switch is especially useful for detecting clogged filters in a water supply system in which a high pressure difference may be present. In this case, the pressure switch is designed to solely respond to the difference.

Different Types of Pressure Switches

There are generally way too many different types of pressure switches, but they can be classified into two categories: electrochemical or solid state pressure switches. Most traditional pressure switches are electrochemical devices, but solid-state devices are becoming increasingly popular.

The most common electrochemical pressure switches consist of an electrical snap-action switch and a sensing element. All of these sensing elements have one sole purpose – to move in response to pressure change in the system. The movement opens and closes the electrical circuit. Electrochemical pressure switches are further divided based on attributes like the operating pressure. Some of the common types of pressure switches include diaphragm switches, diaphragm piston switches, bourdon tube switches, etc., all of which are characterized by distinct pressure range, longevity and other attributes. For instance, a standard diaphragm switch has an operating pressure up to 150 psi with an accuracy to ± 0.5%, while a bourdon tube switch can have operating pressure up to 18,000 psi.

Solid-state pressure switches, on the other hand, can have one or more switch points. Aside from the basic opening and closing of the circuit, digital displays of analog or digital output are also provided. You can easily find solid-state models that are fully programmable and are compatible with a PLC or computers. Solid state pressure switches typically have a wide range of frequency response and operating pressures. They are exceptionally resistant to shock and generally have longer lifespan compared to an electrochemical model. 

Applications of Pressure Switches

Pressure switches are widely used across various industries. They are largely utilized in industrial equipment such as plastic molding injection, press machines, welding machines, etc. The air bellows in trucks and brake pressure are both controlled by hydraulic and pneumatic pressure switches. Automotive industry makes good use of the pressure switches as well, applying them for applications such as engine oil monitoring, power steering and transmissions. The oxygen delivery systems and equipment in the medical industry also utilize pressure switches to monitor the pressure of incoming gas.

To elaborate, the type of housing used for a pressure switch dictates whether the particular model is suitable for certain applications. But keep in mind that some pressure switches do not have housings, and are mostly used in situations where cost and space are the primary concerns. Pressure switch housings are likely to be exposed in corrosive chemicals, which is why pressure switches can be made from a variety of material relatively to the specific environment. Some explosion-proof pressure switches housings are also made with exceptionally robust material to prevent ignition. These are commonly seen in the oil and gas industries where flammables are always present.

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