Difference between diaphragm pressure gauges and diaphragm-type pressure gauges

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This post was last edited by Stone_HOTO on 2019-1-18 at 10:07. Diaphragm pressure gauges are suitable for measuring the pressure of media that are highly corrosive, operate at high temperatures, have high viscosity, tend to crystallize or solidify, contain solid particles in suspension. In situations where it is necessary to prevent the measurement medium from coming into direct contact with conventional pressure instruments, to avoid the accumulation of deposits, and where easy cleaning is required, diaphragm gauges – which consist of a diaphragm separator combined with a conventional pressure instrument – must be used. Diaphragm pressure gauges are suitable for measuring the pressure or negative pressure of various fluid media that are corrosive, non-solidifying, or non-crystalline. The corrosion resistance of diaphragm pressure gauges depends on the diaphragm material. A diaphragm pressure gauge consists of a measurement system (including flange connectors and corrugated diaphragms), a transmission and indication mechanism (including connecting rods, gear mechanisms, a pointer, and a dial), and a housing (including the gauge case and cover ring). The casing of the diaphragm pressure gauge features a splash-proof design with good sealing properties, thus protecting its internal components from contamination. Since a diaphragm pressure gauge system uses a sealing fluid as the medium for transmitting pressure, the temperature expansion coefficient of this sealing fluid causes the gauge reading to increase as the temperature of the pressure-bearing part rises. The extent of this temperature effect is related to the expansion coefficient of the sealing fluid, the stiffness of the diaphragm, and the temperature of the pressure-bearing part; this effect is particularly noticeable in pressure gauges with low measurement ranges. Generally, the temperature error in the compressed area is specified to be no more than 0.1％/℃. Therefore, the overall temperature effect on diaphragm pressure instruments is generally the sum of the temperature effect of a general-purpose instrument and the temperature effect of the compressed part of the diaphragm device. In essence, diaphragm pressure gauges and membrane pressure gauges both transmit pressure through an isolation diaphragm; however, diaphragm pressure gauges use a fluid as the transmission medium, which is why they are unable to measure very low pressures ； A diaphragm pressure gauge can measure very low pressures through a mechanical amplification unit. Additionally, diaphragm pressure gauges can be disassembled, while diaphragm-type pressure gauges cannot. Diaphragm pressure gauges and diaphragm-type pressure meters are used in different applications: Diaphragm pressure gauges are primarily used with liquid media that are at high temperatures, corrosive, prone to crystallization, viscous, or contain solid particles or impurities ； Diaphragm pressure gauges are mainly used in liquid media that are somewhat corrosive but do not crystallize easily, and where the temperature is not very high. Introduction to capsule pressure gauges, advantages and disadvantages of diaphragm pressure gauges. I. Capsule pressure gauges use a capsule as the sensitive element for measuring low pressures. It is used to measure micro-pressure and negative pressure of gases that do not cause corrosion to copper alloys and pose no explosion risk, and is widely applied in boiler ventilation, gas pipelines, combustion devices, and other similar equipment. Stainless steel diaphragm pressure gauges are made of stainless steel for both the pressure transmission system and the housing. It is used for measuring micro-pressure and negative pressure of various gas media in process streams with high corrosion resistance requirements. The stainless steel diaphragm pressure gauge is a micro-pressure gauge with corrosion resistance, developed by drawing on the structural features of conventional diaphragm pressure gauges. It is used in equipment such as boiler ventilation systems and gas pipelines to measure the micro-pressure and negative pressure of various gas media in processes where high corrosion resistance is required. Accuracy class: 2.5 Measurement range: (kPa) 0～4 ； 0～6 ； 0～10 ； 0～16 ； 0～25 ； 0～40 ； 0～60 ； -4～0 ； -6～0 ； -10～0 ； -16～0 ； -25～0 ； -40～0 ； -2～2 ； -3～3 ； -5～5 ； -8～8 ； -12～12 ； -20～20 -30~30. Operating environmental conditions: -25 to 55°C, with relative humidity not exceeding 80%. Resistance to operational vibrations: V·H·3 level. Weight: 0.5 kg. Structural principle: The instrument consists of a measurement system (including connectors, diaphragm boxes, etc.), a transmission mechanism (including pull rod mechanisms and gear drives), an indicating element (including a pointer and dial), and a housing (including the case, gaskets, and glass face). The working principle of the instrument is based on the elastic deformation that occurs at the free end of the diaphragm box under the pressure of the medium being measured; this deformation is then transmitted and amplified by a gear drive mechanism, and the pointer fixed to the gear shaft indicates the measured value on the dial. There is also a zeroing device that allows for easy adjustment of the zero point. The measurement range of diaphragm gauge pressure meters is from -80 to 60,000 Pa. However, different types of diaphragm gauge pressure meters should be selected depending on the pressure range. For pressures between -1,000 Pa and 60,000 Pa, a disc-type diaphragm gauge pressure meter is recommended; whereas for pressures of -80 Pa, a rectangular diaphragm gauge pressure meter is suggested. Working position and environment: The instrument should be installed vertically; the working environment should have a temperature range of -25 to 55°C, with a relative humidity not exceeding 80%, and the surrounding area should not contain any harmful gases that could corrode the instrument. II. Diaphragm pressure gauges are suitable for measuring the pressure or negative pressure of various fluid media that are corrosive, non-solidifying, or non-crystalline in nature. Corrosion resistance depends on the diaphragm material. Structural principle: The instrument consists of a measurement system (including flange connectors and diaphragms), a transmission and indication mechanism (including links, gear mechanisms, a pointer, and a dial), and a housing (including the case and cover ring). The instrument enclosure features a splash-proof design with good sealing properties, thereby protecting its internal components from contamination. The working principle of the gauge is based on the deformation of an elastic element (the diaphragm in the measuring system). Under the pressure of the medium being measured, the diaphragm is forced to undergo corresponding elastic deformation – displacement. This displacement is amplified through a linkage system and transmission mechanism, and the pointer fixed to the gear then indicates the measured value on the dial. Key technical specifications: Accuracy class: 2.5. Operating temperature: -40~+70℃ ； Relative humidity should not exceed 90%. Temperature effect: When the operating temperature deviates by 20±5°C, the additional temperature error is no more than 0.04% per °C. Installation position: Vertical installation. Enclosure protection rating: IP64. The isolator (chemical seal) used in diaphragm gauges allows the measured medium to be separated from the instrument through the diaphragm, enabling the measurement of pressure in highly corrosive, high-temperature, or crystalline media. The elastic element of a pressure gauge: In mechanical pressure gauges, the elastic sensing element undergoes elastic deformation as pressure changes. Mechanical pressure gauges use sensitive elements such as Bourdon tubes, diaphragms, bellows, and corrugated tubes, and are classified accordingly. Sensitive elements are generally made of copper alloys, stainless steel, or special materials. Elastic sensitive elements: ?? ?? Bourdon tubes are classified into types such as C-type tubes, coiled spring tubes, and spiral tubes. Cold-work hardening type material billets are generally used; they possess high plasticity in their annealed state, and after pressure processing, cold working hardening, and heat treatment, they acquire high elasticity and strength. Under the action of pressure in the internal cavity, the Bourdon tube utilizes its elastic properties to conveniently convert pressure into an elastic displacement at its free end. The measurement range of a Bourdon tube is generally from 0.1 MPa to 250 MPa. ??: s- ?: The B’ O2 S diaphragm sensor element is a circular diaphragm with wavy patterns; it is located between two flanges, either welded to the flanges or with its edges held between two flanges. One side of the diaphragm is under the pressure of the medium being measured. The slight bending deformation generated by such a diaphragm can be used to indirectly measure the pressure of the medium. The level of pressure is indicated by the pointer. The diaphragm transmits greater force compared to a Bourdon tube. Since the perimeter edge of the diaphragm itself is fixed, it has good vibration resistance. Diaphragm pressure gauges can provide high levels of overpressure protection (for example, with the diaphragm attached to the upper flange). A protective coating can also be applied to the diaphragm to improve corrosion resistance. Diaphragm pressure gauges can be used to measure media with very high viscosity, that are dirty, or crystalline, by employing measures such as open flanges, flushing, and openings. The pressure measurement range of diaphragm gauges is from 1600 Pa to 2.5 MPa. The diaphragm sensor element consists of two diaphragms with a circular wave-shaped cross-section that are fitted together. The pressure of the medium is applied to the inside of the diaphragm chamber, and the deformation resulting therefrom can be used to indirectly measure the pressure of the medium. The magnitude of the pressure value is displayed by the pointer. Diaphragm pressure gauges are generally used to measure low pressures of gases, and they possess a certain degree of overpressure protection capability. When several diaphragm sensor elements are stacked together, they generate a large transmitting force to measure extremely small pressures. The pressure measurement range of the diaphragm gauge is 250 Pa to 60,000 Pa. ~