Diaphragm seal

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An example of a diaphragm seal (in green) used to protect a pressure sensor. Seal (diaphragm).png
An example of a diaphragm seal (in green) used to protect a pressure sensor.

A diaphragm seal is a flexible membrane that seals and isolates an enclosure. The flexible nature of this seal allows pressure effects to cross the barrier but not the material being contained.

Seal (mechanical) device that helps join things together by preventing leakage

A mechanical seal is a device that helps join systems or mechanisms together by preventing leakage, containing pressure, or excluding contamination. The effectiveness of a seal is dependent on adhesion in the case of sealants and compression in the case of gaskets.

Pressure Force distributed continuously over an area

Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the pressure relative to the ambient pressure.

Contents

Common uses for diaphragm seals are to protect pressure sensors from the fluid whose pressure is being measured.

Pressure sensor

A pressure sensor is a device for pressure measurement of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the purposes of this article, such a signal is electrical.

In physics, a fluid is a substance that continually deforms (flows) under an applied shear stress, or external force. Fluids are a phase of matter and include liquids, gases and plasmas. They are substances with zero shear modulus, or, in simpler terms, substances which cannot resist any shear force applied to them.

Materials

Since diaphragm seals need to be highly flexible, elastomers are commonly used, and include a wide variety of both general purpose and speciality rubbers. Elastomers are limited to low pressure applications and those that are chemically compatible with the various plastics and rubbers used.

Metal diaphragms of stainless steel (several grades), Carpenter 20, Hastelloy, Monel, Inconel, tantalum, titanium and several other metals are in common use where high pressure ratings and specific chemical compatibility are required. Flanged assemblies or flush welded versions are available.

Depending on the PSI levels of the sealing application, the diaphragm may require fabric reinforcement. Typically, PSI under 5 does not require fabric reinforcement. A PSI between 5 and 10 is application dependent. Anything above 10 almost always needs fabric reinforcement. [1]

Applications

Diaphragm seals (also known as chemical seals or gauge guards) are also used to protect a process fluid from the pressure sensor. Examples of this use are:

Seal failure

Environmental scanning electron microscope image of ozone cracks in NBR diaphragm seal formed at sharp corners in seal Ozonecr2.jpg
Environmental scanning electron microscope image of ozone cracks in NBR diaphragm seal formed at sharp corners in seal

Diaphragm seals are susceptible to failure via several mechanisms, including cracking. Ozone cracking can occur in many elastomers for example used in pneumatic systems. If the gas contaminates the air supply, then many rubber diaphragms are at risk from the problem.

A fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops perpendicular to the surface of displacement, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially to the surface of displacement, it is called a shear crack, slip band, or dislocation.

Ozone cracking cracks in many different elastomers due to ozone attack

Cracks can be formed in many different elastomers by ozone attack, and the characteristic form of attack of vulnerable rubbers is known as ozone cracking. The problem was formerly very common, especially in tires, but is now rarely seen in those products owing to preventive measures.

See also

Related Research Articles

Pressure measurement technique to measure pressure

Pressure measurement is the analysis of an applied force by a fluid on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure in an integral unit are called pressure gauges or vacuum gauges. A manometer is a good example, as it uses a column of liquid to both measure and indicate pressure. Likewise the widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge.

A fire hose is a high-pressure hose that carries water or other fire retardant to a fire to extinguish it. Outdoors, it attaches either to a fire engine or a fire hydrant. Indoors, it can permanently attach to a building's standpipe or plumbing system.

Pneumatics use of pressurized gas to produce mechanical motion

Pneumatics is a branch of engineering that makes use of gas or pressurized air.

Gasket type of mechanical seal

A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression.

Check valve valve that allows to flow through it in only one direction

A check valve, clack valve, non-return valve, reflux valve, retention valve or one-way valve is a valve that normally allows fluid to flow through it in only one direction.

O-ring mechanical, toroid gasket that seals an interface

An O-ring, also known as a packing, or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface.

Hose flexible conduit for conducting liquid, gaseous, or particulate effluents

A hose is a flexible hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called pipes, or more generally tubing. The shape of a hose is usually cylindrical.

Solenoid valve

A solenoid valve is an electromechanical device in which the solenoid uses an electric current to generate a magnetic field and thereby operate a mechanism which regulates the opening of fluid flow in a valve.

Metal rubber is a broad, informal name for several conductive plastic polymers with metal ions produced by NanoSonic, Inc, in cooperation with Virginia Tech. This self-assembling nanocomposite is flexible and durable to high and low pressures, temperatures, tensions, most chemical reactions, and retains all of its physical and chemical properties upon being returned to a ground state. NanoSonic’s Metal Rubber™ is an electrically conductive and flexible elastomer. It can be mechanically strained to greater than 1000 percent of its original dimensions while remaining electrically conductive. As Metal Rubber can carry data and electrical power and is environmentally rugged, it has use as a flexible and stretchable electrical conductors in the aerospace/defense, electronics and bioengineering markets.

Nitrile rubber, also known as NBR, Buna-N, and acrylonitrile butadiene rubber, is a synthetic rubber copolymer of acrylonitrile (ACN) and butadiene. Trade names include Perbunan, Nipol, Krynac and Europrene.

Tire manufacturing

Pneumatic tires are manufactured according to relatively standardized processes and machinery, in around 455 tire factories in the world. With over 1 billion tires manufactured worldwide annually, the tire industry is the major consumer of natural rubber. Tire factories start with bulk raw materials such as synthetic rubber, carbon black, and chemicals and produce numerous specialized components that are assembled and cured. This article describes the components assembled to make a tire, the various materials used, the manufacturing processes and machinery, and the overall business model.

Introduction

Expansion joint construction detail designed to absorb temperature-induced volume changes of construction parts

An expansion joint or movement joint is an assembly designed to safely absorb the temperature-induced expansion and contraction of construction materials, to absorb vibration, to hold parts together, or to allow movement due to ground settlement or earthquakes. They are commonly found between sections of buildings, bridges, sidewalks, railway tracks, piping systems, ships, and other structures.

Diaphragm valve

Diaphragm valves consists of a valve body with two or more ports, a diaphragm, and a "weir or saddle" or seat upon which the diaphragm closes the valve. The valve body may be constructed from plastic, metal, wood or other materials depending on the intended use.

Injection molding of liquid silicone rubber (LSR) is a process to produce pliable, durable parts in high volume.

Metal bellows are elastic vessels that can be compressed when pressure is applied to the outside of the vessel, or extended under vacuum. When the pressure or vacuum is released, the bellows will return to its original shape, provided the material has not been stressed past its yield strength.

Forensic materials engineering

Forensic materials engineering, a branch of forensic engineering, focuses on the material evidence from crime or accident scenes, seeking defects in those materials which might explain why an accident occurred, or the source of a specific material to identify a criminal. Many analytical methods used for material identification may be used in investigations, the exact set being determined by the nature of the material in question, be it metal, glass, ceramic, polymer or composite. An important aspect is the analysis of trace evidence such as skid marks on exposed surfaces, where contact between dissimilar materials leaves material traces of one left on the other. Provided the traces can be analysed successfully, then an accident or crime can often be reconstructed. Another aim will be to determine the cause of a broken component using the technique of fractography.

A conductive elastomer is a form of elastomer, often natural rubber or other rubber substitute, that is manufactured to conduct electricity. This is commonly accomplished by distributing carbon or other conductive particles throughout the raw material prior to setting it.

References

  1. "Your Elastomeric Diaphragm Checklist". Gallagher Fluid Seals. Retrieved 21 July 2017.