Basics of Pneumatic instruments

Introduction

A pneumatic system is a system that uses compressed air to transmit and control energy. Pneumatic systems are used in controlling train doors, automatic production lines, mechanical clamps, etc

 

What are pneumatic systems used for?

The pneumatic systems used in the industry are usually driven by compressed air or compressed inert gases. A centrally located, electrically powered compressor drives cylinders, air motors and other pneumatic devices.

Examples of pneumatic systems and components

  • Air brakes on buses and trucks
  • Air brakes on trains
  • Pneumatic actuator
  • Pneumatic cylinder
  • Pneumatic Launchers
  • Pneumatic mail systems
  • Pneumatic motor
  • Pressure regulator
  • Pressure sensor
  • Pressure switch
  • Air compressors

Disadvantages of pneumatic instruments

The disadvantages of pneumatic instruments are painfully obvious to anyone familiar with pneumatic and electronic instruments.

  • Sensitivity to vibration, temperature changes, mounting position and the like affect calibration accuracy to a much greater extent for pneumatic instruments than electronic instruments.
  • Compressed air is an expensive tool, much more expensive per watt-hour equivalent than electricity, which makes the operational cost of pneumatic instruments much higher than the electronic one.
  • One of the properties of pressurized air is like to always occupy the empty space and the air pressure is maintained in hard work. Therefore we need a seal so that air does not leak. Seal leakage can cause energy loss. Pneumatic equipment should be equipped with airtight equipment that compressed air leaks in the system can be minimized.
  • Pneumatic using open system, meaning that the air that has been used will be thrown out of the system, the air comes out pretty loud and noisy so will cause noise, especially on the exhaust tract. The fix is ​​to put a silencer on each dump line.
  • The installation cost of pneumatic instruments can also be quite high, given the need for special pipes (stainless steel, copper or resistant plastic) to transport supply air and pneumatic signals to distant locations. The volume of air tubes used to transmit pneumatic signals across distances acts as a low pass filter, naturally dampening the response of the instrument and, therefore, reducing its ability to respond quickly to changing process conditions .
  • Pneumatic instruments can not be made “smart” as electronic instruments either.

With all these disadvantages, one might wonder why pneumatic instruments are still used in modern industry.
Part of the answer is a legacy. For an industrial facility built decades ago, it makes little sense to replace instruments that still work well. The cost of labor to remove old pipes, install new conduits and cables and configure new (expensive) electronic instruments is often not worth the benefits.

Advantages of pneumatic instruments 

However, pneumatic instruments actually enjoy some definite technical advantages that ensure their continued use in certain applications even in the 21st century.

  • A decisive advantage is the intrinsic safety of pneumatic field instruments. Instruments that do not work with electricity can not generate electrical sparks. This is very important in “classified” industrial environments where there are gases, liquids, powders and explosive dusts.
  • The pneumatic instruments also purge themselves. Its continuous purging of compressed air from the ventilation holes in the relays and pneumatic nozzles acts as a natural clean purge for the interior of the instrument, preventing the entry of dust and vapor from the outside with a slight positive pressure inside the box of the instrument.
  • Ease of power and speed transmission
  • Ease of use
  • Ease of maintenance
  •  Infinite availability of the source ;Air is the most important thing in the pneumatic system, and as we all know, air is available in the world around us in unlimited quantities at all times and places
  • It is not uncommon to find a pneumatic instrument mounted in the field with incrustations of corrosion and dirt on the outside, but clean in the factory inside due to this continuous purge of clean air. Pneumatic instruments mounted inside larger enclosures with other devices tend to protect them all by providing a positive pressure air purge for the entire enclosure.
  • Some pneumatic instruments can also work in environments of high temperature and high radiation that would damage electronic instruments. Although it is often possible to “harden” electronic field instruments in such harsh conditions, pneumatic instruments are virtually immune in nature.
  • An interesting feature of pneumatic instruments is that they can work with compressed gases other than air. This is an advantage in remote natural gas installations, where natural gas is sometimes used as a source of pneumatic “power” for the instruments. As long as there is compressed natural gas in the pipeline to measure and control, the instruments will operate. No air compressor or power source is needed in these installations. What is needed, however, is good filtering equipment to prevent contaminants in natural gas (dirt, debris, liquids) from causing problems within the sensitive mechanisms of the instrument.

To know more about pneumatic instruments check the link below

https://automationforum.co/?s=Pneumatic+instruments

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