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Before diving into the construction and application of a diaphragm pressure gauge, let's first understand what it is. A diaphragm pressure gauge is a type of pressure measurement device that isolates the indicator mechanism from the measured medium using a diaphragm. This diaphragm is typically filled with a working fluid to transmit pressure effectively.
The diaphragm system in such gauges can be either a flat diaphragm or a bellows-type design, with the flat diaphragm being the most commonly used. In this explanation, we'll focus on the flat diaphragm type.
The structure and working principle of a diaphragm pressure gauge are illustrated below:
Diaphragm pressure gauges operate by drawing a spring tube into a vacuum and filling it with a liquid. This assembly is sealed by a diaphragm. When measuring pressure, the medium under test applies force directly to the diaphragm, causing it to flex upward. The pressure is then transmitted through the filling liquid to the spring tube, which deforms accordingly. This deformation moves the free end of the spring tube, driving a rod that moves the pointer across the dial to indicate the measured pressure.
Diaphragm pressure gauges are particularly useful when dealing with challenging media. For example, when measuring general gases, water, or oil, a standard pressure gauge may suffice. However, for corrosive substances like nitric acid, phosphoric acid, or strong alkalis, a stainless steel gauge might be used. But when the medium is highly corrosive (such as hydrochloric acid, wet chlorine, or ferric chloride), highly viscous (like latex), prone to crystallization (such as saltwater), or likely to solidify (like hot asphalt), or contains floating solids (such as sewage), traditional gauges are not suitable. Even stainless steel components can corrode, and solids can clog the pressure ports, rendering the gauge ineffective.
Diaphragm pressure gauges solve these issues by allowing users to select corrosion-resistant diaphragm materials tailored to the specific medium. Their design also prevents high-viscosity, crystallizing, or solidifying media from entering the pressure port, ensuring reliable operation. As a result, they are widely used in industries such as petroleum, chemical processing, metallurgy, power generation, food, and pharmaceuticals.
To wrap up, here are some common types of diaphragm pressure gauges: sanitary diaphragm gauges for medical and food applications, diaphragm gauges designed for highly corrosive, high-temperature, high-viscosity, or crystallizing media, and standard diaphragm pressure gauges.
Construction and use of diaphragm pressure gauge