What are the selection and application of metal bellows for valves? - 3

Release time:

2024-03-19

Answer: introduce the application, design and selection of metal bellows in stop valve, gate valve, regulating valve, safety valve and ball valve. The solution to the problems in the use of metal bellows for valves is given.

3) selection mark of bellows for valves: according to the different classification of nominal size of valves for bellows application, according to the provisions of nominal size series in GB / t1047-2005, the nominal size of valves for bellows application can be divided into: 15mm, 20mm, 25mm, 32mm 40mm, 50mm, 65mm, 80mm, 100mm12mm, 150mm20mm, 250mm according to the different classification of nominal pressure of bellows, according to the nominal pressure series in GB / T 1048-2005 The nominal pressure of bellows can be divided into: 0.25MPa, 0.6MPa, impa, 1.6Mpa, 2.5MPa, 4.0Mpa, 6.3MPa and 10.0MPa

(5) for the inspection of bellows for valves, the inspection items of metal bellows for valves mainly include surface quality, geometric dimension, tightness, pressure and cycle life, etc.

1) surface quality: under standard lighting conditions, visually observe the surface and shape of bellows, and the quality shall meet the requirements of JB / T 6169-2006.

2) geometric dimension: use calipers with graduation value of 0.02mm or other measuring tools and instruments with accuracy equivalent to it to check the geometric dimension of bellows. The geometric dimension and tolerance of bellows shall meet the requirements of the drawing.

3) leakproofness: the bellows assembly assembled and welded by the manufacturer shall be subject to leakproofness inspection, and the bubble leak detection method can be used for inspection. The bellows and its components shall be filled with 0.6MPa compressed air or other non corrosive non combustible clean gas, and the pressure shall be maintained for 3min, and no leakage shall be detected in the water tank. The helium mass spectrometer leak detector can also be used to detect the leakage according to the user's requirements, and the leakage that can be detected shall not appear.

4) pressure: pressure test can be conducted on special equipment or valve. The chloride ion content of test water shall not exceed 25 × 10-7. According to the provisions of JB / T 9092-1999, the bellows assembly shall be subject to hydrostatic test at room temperature or 38 ℃ at 1.5 times of the nominal pressure.

Each bellows assembly shall be fixed to a length which is the length of the valve opening position during routine valve shell test. The bellows shall be prevented from being stretched and compressed during the test. The pressure shall be applied in the same way as that of bellows. During the pressure test, the weld shall not crack or leak, and the bellows shall not be twisted.

5) cycle life: the cycle life test can be carried out on special equipment or valves. When the main valve needs, the high temperature cycle life test shall be carried out according to relevant standards. The frequency of the cycle shall take into account the possible overheating caused by abnormal fast cycle. The cycle frequency should not exceed once per second.

The cyclic life test shall be carried out at room temperature or nominal pressure at 38 ℃. The pressurization method is the same as the pressure test. Each bellows assembly shall be tested for tightness after the cyclic life test and shall not show detectable leakage.

(6) conclusion: the metal bellows used for the valve is the core component of the bellows valve. The design and selection of bellows are related to the use safety of the valve, especially the application field of bellows valve is the key industrial field and military industry field. The form test shall be carried out in the trial production of new products, and the selection shall be applicable to the working conditions of the valve use system and the structural characteristics of the metal bellows.