Though differing by only one word in Chinese, these two are distinct types of pressure measuring instruments with significant disparities in structure, working principle, applicable media and operating conditions.
Diaphragm Capsule Pressure Gauge
Its appearance is basically the same as that of a Bourdon tube pressure gauge, but its pressure-sensing element is an elastic sensitive component called a diaphragm capsule. The capsule is formed by welding two circular corrugated diaphragms together. When the pressure of the measured medium acts on the capsule, elastic deformation occurs inside it, causing its free end to displace. This displacement is then amplified by a gear transmission mechanism, and the measured pressure value is indicated by a pointer on the dial.
Diaphragm Capsule Pressure Gauge: The corrugated small capsule expands directly to drive the pointer, and it can only measure gases.
Structurally, it consists of four parts:
Measuring system (connector, diaphragm capsule element, etc.)
Transmission mechanism (lever mechanism, gear transmission mechanism)
Indicating components (pointer, dial)
Enclosure (case, gasket, and sight glass)
It features a relatively simple structure, excellent seismic performance and good temperature adaptability.
Diaphragm Seal Pressure Gauge
It is a system composed of a diaphragm isolator, a general-purpose pressure gauge (e.g., Bourdon tube pressure gauge) and a sealed filling fluid. The diaphragm isolator serves to isolate the measured medium from the pressure-sensing element of the gauge. When the pressure of the measured medium acts on the diaphragm, the diaphragm deforms and compresses the sealed filling fluid in the closed system. The transmission effect of the fluid causes the elastic element (such as a Bourdon tube) inside the gauge to produce corresponding elastic deformation, thereby indicating the pressure of the measured medium.
The diaphragm (which acts like a drumhead) senses pressure and transmits it to the pointer via a liquid.
Its structure is relatively complex, but it boasts outstanding corrosion resistance. It can prevent the measured medium from directly entering the general-purpose pressure gauge, avoiding sediment accumulation and enabling easy cleaning.
Applicable Media and Operating Conditions
Diaphragm Capsule Pressure Gauge
It is suitable for measuring micro-pressure and negative-pressure gases that are non-corrosive to copper alloys and non-explosive. It is widely used in equipment such as boiler ventilation systems, gas pipelines and combustion devices.
It offers high measurement accuracy, with a typical measuring range of 0.001 MPa to 4 MPa. It is capable of measuring both micro-pressure and negative-pressure values, thanks to its simple structural design.
Diaphragm Seal Pressure Gauge
It is designed for media with strong corrosiveness, high temperature, high viscosity, crystallization tendency, solidification tendency or containing solid suspended particles. It is commonly used in industrial sectors including petrochemicals, caustic soda production, chemical fiber manufacturing, dye chemical engineering, pharmaceuticals, food processing and dairy making.
Its measuring range generally spans 0.1 MPa to 40 MPa. Isolation diaphragms made of different materials can be selected according to specific application scenarios and media properties.
Summary
Diaphragm capsule pressure gauges and diaphragm seal pressure gauges each have unique characteristics to meet different measurement requirements. The former is mainly used for high-precision measurement of micro-pressure and negative pressure, while the latter is suitable for measuring the pressure of complex media such as strongly corrosive, high-viscosity and crystallizable fluids. Users can select the appropria
