Differential pressure switch how does it work

What is a Differential Pressure Switch? How does a Differential Pressure Switch work? The diagram below shows this application in action. Back to Technical Blog Archive. Three key elements are used in various combinations to manufacture different kinds of differential and standard pressure switches to suit unique industrial needs. The purpose of the Differential Pressure Switch is to sense a difference in pressure between two pressure sources in a control process. When the pressure from two different sources is connected across a sensing diaphragm, the pressure difference creates a force which then acts upon the pre-tensioned spring.

This action moves a balancing arm or mechanism to effect the minimal movement required to activate the micro switch. High and low pressures are applied on either side of the specially contoured sensing diaphragm. This feature helps to eliminate errors due to a difference in area which is commonly a problem present in twin element Differential Pressure Switches.

Pressure ports for high-process pressure, as well as low-pressure are separated by an elastic diaphragm. The type of diaphragm material is selected based on the type of fluid and its temperature. Common diaphragm and sealing materials are:. These materials are highly resistant to oils or petroleum-based fluids but can degrade in the presence of ozone and ketones. Nitrile diaphragms and seals have a good balance of cost and physical properties making them suitable for most neutral fluids.

This is another elastomer that is widely used for high-temperature water and steam service. It is resistant to ozone, ketones, mild acids, alkalis, and other oxidizing chemicals. They are not used in petroleum service since EPDM can absorb oils and fuels which causes them to swell.

Viton is a proprietary material with properties similar to NBR. This material is resistant to petroleum-based fluids and solvents. They are not suitable for fluids containing ketones as well. PTFE is rarely used as a diaphragm membrane than the previous materials due to its polymeric chain structure. It is not as elastic as elastomers and is prone to creep. The switch housing protects the switch and other internal parts from the external environment.

An important specification of the switch housing is its protection rating. IP and NEMA ratings describe the protection level against the ingress of solid and liquid foreign objects. ATEX rating is for environments with risks of fire and explosion. The contacts are one of the conductive parts of the switch. Separating or linking the contacts will de-energize or energize the electrical circuit. Switch contacts are made of materials with high corrosion resistance and high electrical conductivity such as copper, silver, gold, or brass.

NO is for initially de-energized circuits which cut-in at the setpoint. NC performs the opposite by being initially energized. CO switches serve two connections or circuits, one open and one closed which is commonly used for control interlocking or more complicated circuits. For simple control activation, NO or NC is enough. This is where the control or instrumentation circuit is connected. Most pressure switches have markings on their nameplate about the configuration of the terminals with respect to the contacts.

The nameplate includes schematics or diagrams to determine the correct terminal connection in the circuit. Like the contacts, the terminals must be resistant to corrosion and highly conductive. There are two main types of pressure switches: mechanical pressure switches and electronic pressure switches.

Mechanical pressure switches are further divided according to the form and construction of the pressure sensing component. Electronic pressure switches are solid-state switches that do not require actuation from the pressure sensing element to operate the switch. They operate indirectly by using other properties such as resistance and capacitance. The previous chapters mostly describe mechanical pressure switches. They are more widely used than electronic switches due to their simplicity and lower cost.

All mechanical pressure switches have a mechanical pressure sensing part that deforms according to the fluid pressure. They are classified according to the type of pressure sensing component. This is the most popular and widely used pressure switch.

As the fluid pressure changes, it causes the piston to move axially which activates the switch. It can sense the fluid pressure directly or indirectly. Direct sensing involves seals such as O-rings to prevent the fluid from getting into the electrical components. Indirect sensing involves an elastic diaphragm that separates the piston from the fluid. This type consists of a metal membrane joined or welded directly into the wetted part of the pressure switch. Instead of having a piston, the diaphragm directly actuates the switch.

A bourdon tube is a flexible metallic or elastomeric tube fixed at one end while the other is free to move. When pressure is increased inside the tube, it tends to straighten. This movement is then used to actuate the switch. This is a special type of pressure switch used to compare the pressures between two points in a system.

These points are connected to two process ports. These can be upstream or downstream of equipment, or the top-side or bottom-side of a vessel. If the difference in pressures between the two-sides exceeds a certain threshold, the switch is activated. These are useful in interlocking controls for monitoring pressure drop across filters and screens and tank level. An electronic pressure switch has a pressure transducer, typically a strain gauge, with additional proprietary designed electronics that amplify and convert signals into a readable display.

Most electronic pressure switches have analog capabilities. This means they are not limited to an open or closed position but are capable of sending a continuous, variable signal that is used for more accurate monitoring.

Thus, electronic pressure switches are not switches but transmitters or measuring instruments. Additional features available for electronic pressure switches are on-site programmability of time delay, switching function, setpoint, hysteresis, etc. Like any other measuring or monitoring device, pressure switches have several selection criteria that need to be considered. Selecting the right pressure switch for a given application leads to lower costs and longer service life of the device.

Most user have accepted this problem as ineluctability, but, it' s a wrong opinion. If the user choose our GE series Differential Pressure type flow switches to replace the common target flow switch, the lifetime could achieve more than 10 years. Differential Pressure Type Flow Switches is detecting the pump water flow. Operating Principle: A differential pressure switch is designed to sense a difference in pressure between two pressure sources in the plant for control purposes.

When the pressures from two different sources in a process are connected across the sensing diaphragm, metallic or elastomeric as the case may be, the pressure difference creates a force which then overcomes that of a pre-tensioned spring and in the process moves a balancing arm or mechanism to effect the minimal movement required to actuate the micro-switch es of the switch.

High and low pressures are applied on either side of the specially contoured sensing diaphragm. This design feature helps to eliminate errors due to a difference in area which is often a common problem present in twin element pressure differential switches A particular design of the differential pressure switch is described below to illustrate the principle of operation.