Principles of pressure gauges and related knowledge

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1.1 Principle: The pressure gauge operates by means of the elastic deformation of sensitive elements inside it (Bourdon tubes, diaphragms, bellows); this deformation is then transmitted to the pointer through a conversion mechanism within the gauge, causing the pointer to move and thus indicating the pressure level. 1.2 Construction: Relief valve: In the event of an emergency such as a rupture of the Bourdon tube, internal pressure is released to the outside through the relief valve, preventing the glass panel from breaking. Note: To maintain the proper functioning of the overflow hole, leave at least 10 mm of space behind it; do not modify or block the overflow hole. Pointers: In addition to standard pointers, other pointers are also optional. (The zero-adjustment pointer, maximum-value pointer, or setting pointer) please list it in the selection table. Glass panels: In addition to standard glass, other special types of glass such as tempered glass and reflective-free glass are also available as options. Performance classification: Standard type, Standard type for steam use (M), Heat-resistant type (H), Vibration-resistant type (V), Vibration-resistant type for steam use (MV), and Heat- and vibration-resistant type (HV). For the classification of uses, refer to the JIS7505 Bourdon tube pressure gauge standard. Treatment method: Oil/protein exclusion treatment… Remove the water or oil remaining in the liquid-contacting parts during manufacturing. External finish specification: Shell color…Other than standard colors, please specify clearly. Throttle valve: (Optional) To reduce pulsating pressure, a throttle valve is installed at the pressure inlet. Pulsating pressure: Due to the pulsating characteristics of the pump in the pressure generator, the amplitude of the pressure gauge’s characteristic curve is high. This is very harmful to the pressure gauge. Connection methods: This product offers three connection methods for its joints: Soldering…used for connecting copper materials; Silver-copper soldering…used for connecting copper materials with stainless steel; TIG welding…used for connecting stainless steel materials together. 2. Gauge terms 2.1 Positive pressure and negative pressure 2.2 Relative pressure and absolute pressure 2.3 Vacuum level (as shown in the diagram) 2.4 Methods of expressing pressure Pressure can be expressed in two ways: one is based on absolute vacuum as a reference, and this is called absolute pressure ； Another type is the pressure expressed relative to atmospheric pressure, known as gauge pressure. Since the pressure measured by most pressure gauges is relative pressure, relative pressure is also known as gauge pressure. When the absolute pressure is less than atmospheric pressure, it can be expressed as a value that is less than one atmosphere of absolute pressure within the container. It is called “vacuum level”. Their relationships are as follows: Absolute pressure = Atmospheric pressure + Relative pressure. Vacuum degree = Atmospheric pressure – Absolute pressure. The legal unit of pressure in China is Pa (N/㎡), known as Pascal, abbreviated as Pa. Due to the extremely small size of this unit, its 106 times larger unit, MPa (megapascal), is commonly used. 2.5 Elastic sensitive elements: Bourdon tubes, bellows, diaphragms. A Bourdon tube pressure gauge uses an elastic C-shaped tube that is bent into a circular shape, with an elliptical cross-section. The pressure of the medium being measured acts on the inner side of the wave tube, causing the elliptical cross-section of the Bourdon tube to tend toward a circular cross-section. Due to the slight deformation of the Bourdon tube, a certain ring stress is generated. This hoop stress causes the Bourdon tube to expand outward. Since the head of the elastic wave Bourdon tube is not fixed, it undergoes slight deformation, and the extent of this deformation depends on the pressure of the medium being measured. The deformation of the Bourdon tube indirectly indicates the pressure of the measured medium through the hands of the movement. Diaphragm pressure gauge: The diaphragm sensing element consists of two membranes connected together and shaped like waves. 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 the pressure of gases; they can also detect low pressures, and to a certain extent, they can provide overpressure protection as well. When several diaphragm sensor elements are stacked together, a large transmitting force is generated to measure extremely small pressures. 2.6 Radial and axial types: Radial type: refers to a pressure gauge whose connection port is in an I-shaped configuration relative to the dial; Axial type: refers to a pressure gauge whose connection port is in a T-shaped configuration relative to the dial. 2.7 IP protection rating: The IP (INTERNATIONAL PROTECTION) protection rating system was developed by the IEC (INTERNATIONAL ELECTROTECHNICAL COMMISSION). Lamps are classified according to their dust and moisture resistance properties. The external objects referred to here include tools; human fingers and the like must not come into contact with the live parts inside the lamp to avoid electric shock. The IP protection rating consists of two digits: the first digit indicates the level of protection against dust and foreign objects entering the fixture, while the second digit shows the degree of protection against moisture and water intrusion. The higher the number, the greater the level of protection. The protection ratings indicated by these two digits are shown in Tables 1 and 2. Table 1: Degree of protection indicated by the first characteristic number (digit). First digit – Protection level – Definition: 0 – No protection; exposed to people from the outside or without any special protection. 1 Prevent solids larger than 50 mm from entering, and prevent human bodies (such as palms) from accidentally coming into contact with the internal components of the lamp. Prevent the intrusion of larger objects (with a diameter greater than 50 mm). 2 Prevent solids larger than 12 mm from entering; prevent human fingers from coming into contact with the internal components of the lamp; prevent objects of medium size (with a diameter greater than 12 mm) from entering. 3 Prevent the intrusion of solids larger than 2.5 mm – Stop tools, wires, or similar small foreign objects with a diameter or thickness greater than 2.5 mm from entering and coming into contact with the internal components of the light fixture. 4 Prevent the intrusion of solids larger than 1.0 mm – Stop tools, wires, or similar small foreign objects with a diameter or thickness greater than 1.0 mm from entering and coming into contact with the internal components of the lamp. 5 Dust protection: Completely prevents the entry of external objects; although it cannot fully stop dust from entering, the amount of dust that does get in does not affect the proper operation of the lamp. 6 Dust protection: Completely prevents the intrusion of external objects and also fully blocks dust from entering. Table 2: Degree of protection indicated by the second characteristic code (number). Second code number, Protection level, Definition: 0 – No protection; no safeguard provided. 1 Prevent water droplets from entering – Vertically falling droplets (such as condensation) do not pose any harmful effect on the lighting fixture. 2 It can still prevent water droplets from entering even when tilted at 15 degrees. When the lamp is tilted from a vertical position to 15 degrees, water droplets do not have any harmful effect on it. 3 Prevent water sprayed from entering – provide rain protection, or prevent water sprayed from directions with an angle of less than 60 degrees to the vertical from entering the lamp and causing damage. 4 Prevent water splashes from entering – Stop water splashing in from various directions from causing damage to the lamp. 5 Prevent water spray from entering: Stop water ejected from nozzles in various directions from entering the lamp and causing damage. 6 Preventing the intrusion of large waves: Lamps installed on the deck to prevent damage caused by large waves from entering. 7 Preventing water intrusion in case of flooding: The lamp can withstand being submerged in water for a certain period of time, or it can function properly even when the water pressure is below a certain threshold, thus avoiding damage caused by water ingress. 8 Prevention of water intrusion in case of submersion: The lamp can remain submerged under specified water pressure for an indefinite period, ensuring that it is not damaged by water ingress. 3. Types of pressure gauges 3.1 Indoor pressure gauges: A□□□ AA□□ A=Φ60 AC□□ C=Φ75 AE□□ E=Φ100 AG□□ G=Φ150 AJ□□ J=Φ200 3.2 Outdoor pressure gauges: B□□□ BA□□ A=Φ60 BAC□□ C=Φ75 BE□□ E=Φ100 BG□□ G=Φ150 BJ□□ J=Φ200 BL□□ L=Φ300 3.3 High-pressure gauges: GH□□ 700MPa 3.4 Differential pressure gauges: DG□□ 3.5 Double-needle pressure gauges: GD1□ 3.6 Vibration-resistant pressure gauges: GV□□ 3.7 Pressure gauges with contacts: JM□□ JC□□ CD□□ (pressure-resistant and explosion-proof) Model Type Pressure range Application industry A□□□ Indoor pressure gauge 0～40kPa, 0～100MPa, -0.1～0MPa, -0.1～3.5MPa General industrial use B□□□ Outdoor pressure gauge 0～40kPa, 0～100MPa, -0.1～0MPa, -0.1～3.5MPa General industrial use DG□□ Differential pressure gauge 0～0.05kPa, 0～30kPa, 0.01～-0.04kPa, -0.1～3.5kPa General industrial use GV□□ Vibration-resistant pressure gauge 0～0.1MPa, 0～200MPa, -0.1～0MPa, -0.1～2MPa For use in environments with severe vibrations JM□□ With microswitch 0～1.5MPa, 0～100MPa, -0.1～0MPa, -0.1～2MPa General industrial use JC□□ With contact switch 0～1.5kPa, 0～70MPa, -0.1～0MPa, -0.1～2MPa General industrial use SU□□ Hygienic pressure gauge 0～0.1MPa, 0～5MPa, -0.1～0MPa, -0.1～2MPa Food, cosmetics, pharmaceuticals CD□□ Explosion-proof pressure gauge with contacts 0～0.1MPa, 0～70MPa, -0.1～0MPa, -0.1～2MPa Flammable and explosive environments