Strength test and sealing test method of valves detail the main technical specifications of valves

Strength test and sealing test method of valves detail the main technical specifications of valves

Valve can be regarded as a pressure vessel, so it needs to meet the requirements of bearing medium pressure without leakage, so the valve body, valve cover and other parts of the blank should not exist to affect the strength of cracks, loose pores, slag and other defects. In addition to the strict inspection of the appearance and internal quality of the blank, the valve manufacturer should also carry out strength test one by one to ensure the performance of the valve. The strength test is generally carried out after final assembly. The test is usually carried out at normal temperature with nominal pressure PN, siu valve is generally carried out at 1.1 times PN pressure.
Valve in the final assembly after the completion of the performance test, to check whether the product meets the design requirements and whether to meet the quality standards stipulated by the state. Defects in valve materials, blanks, heat treatment, machining and assembly can generally be exposed during testing.
Conventional tests have shell strength test, sealing test, low-pressure sealing test, action test, and according to the need, the next test after passing the test in sequence.
Valve test method
1.1 Strength test
Valve can be regarded as a pressure vessel, so it needs to meet the requirements of bearing medium pressure without leakage, so the valve body, valve cover and other parts of the blank should not exist to affect the strength of cracks, loose pores, slag and other defects. In addition to the strict inspection of the appearance and internal quality of the blank, the valve manufacturer should also carry out strength test one by one to ensure the performance of the valve.
The strength test is generally carried out after final assembly. In order to avoid and reduce all kinds of waste caused by unqualified test, intermediate strength test (often called wool pump) can be carried out after rough machining of parts. After the final assembly of the intermediate strength test parts, if the user does not require, the valve can no longer be strength test. In order to ensure the quality of su valve, after the intermediate strength test, the valve is all *** and then strength test.
The test is usually carried out at room temperature. In order to ensure safety, the test pressure P is 1.25~1.5 times of the nominal pressure PN. During the test, the valve is in the open state, one end is closed, and the medium is injected from the other end and pressure is applied. Check the shell (body, cover) exposed surface, requirements in the specified test duration (generally not less than 10 minutes) no leakage, can be considered that the valve strength test qualified. In order to ensure the reliability of the test, the strength test should be carried out before the valve is painted, and the air in the inner cavity should be drained when water is used as the medium.
The leakage valve, if the technical conditions permit repair welding can be repaired according to the technical specifications, but after repair welding must be renewed strength test, and appropriate extension of the test duration.
1.2 Sealing test
In addition to the throttle valve, whether cutting valve or regulating valve, should have a certain closed sealing, so the valve before leaving the factory to carry out a sealing test, with sealed valve sealing test.
The test is usually carried out at normal temperature with nominal pressure PN, siu valve is generally carried out at 1.1 times PN pressure.
With water as the test medium, easy to make the valve corrosion, usually according to the technical requirements to control the water quality, and after the test will be dried or dried residual water.
Gate valves and ball valves have two sealing pairs, so two-way sealing test is required. In the test, the valve is opened first, the channel is sealed at one end, the pressure is introduced from the other end, and when the pressure rises to the specified value, the valve is closed, and then the pressure at the sealing end is gradually removed, and checked. Repeat the experiment at the other end. Another test method for gate valves is to maintain the test pressure in the body cavity and check the valve for double sealing from both ends of the passage. When testing check valves, pressure should be introduced from the outlet end and checked at the inlet end.
Sealing test, valve closing torque should be determined by nominal pressure and nominal diameter. Manual valve is usually only allowed to be closed with normal strength, without the help of other auxiliary equipment, when the handwheel diameter ¡Ý320mm is allowed to be closed with two people. Valves with drive devices shall be tested with drive devices in use. If there is a requirement for closing torque specified in the technical requirements, the force measuring wrench is needed to measure the closing torque.
The sealing test should be carried out after the strength test of the valve assembly, because not only the sealing of the valve should be checked, but also the sealing of the packing and flange gasket.
The upper seal test is usually carried out together with the strength test. During the test, the stem is raised to the limit position, so that the stem is in close contact with the sealing surface of the valve cover, and the packing gland is loosened to check its sealing. Valves for gas medium or drawing technical specification requirements for low pressure gas seal test valve, must be in accordance with the test standard specification, test medium nitrogen or dry clean air. The test pressure was 0.6mpa.
Main specifications for strength performance of valves
The strength performance of the valve refers to the ability of the valve to bear medium pressure. The valve is a mechanical product that bears internal pressure, so it must have sufficient strength and stiffness to ensure long-term use without rupture or deformation.
The sealing performance
Valve sealing performance refers to the valve sealing parts to prevent media leakage ability, it is the most important technical performance indicators of the valve. There are three sealing parts of the valve: the contact between the opening and closing parts and the valve seat two sealing surface; Packing and valve stem and packing box matching; Joint of body to bonnet. One of the former leakage is called internal leakage, which is usually said to be lax, it will affect the ability of the valve to cut off the medium. For the block valve class, internal leakage is not allowed. The latter two leakage is called external leakage, that is, media leakage from the valve to the valve outside. Leakage will cause material loss, pollution of the environment, serious will also cause accidents. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance.
The flow of medium
Medium through the valve will produce pressure loss (pressure difference before and after the valve), that is, the valve has a certain resistance to the flow of medium, medium to overcome the resistance of the valve will consume a certain amount of energy. From the consideration of energy saving, design and manufacture of valves to reduce the valve resistance to the flow medium as much as possible.
Opening and closing force and opening and closing moment
Opening and closing force and torque are the forces or torques that must be applied to open or close the valve. Close the valve, the need to make the open-close part and send a form a seal between the two sealing surface pressure, but also overcome between stem and packing, the valve stem and between threads of the nut, valve rod end bearing friction and other parts of the friction force, and therefore must exert closing force and close moment, in the process of opening and closing, the valve is required for opening and closing force and the open-close torque changes, Its maximum value is at the end of the closed moment or at the beginning of the open moment. Valves should be designed and manufactured to reduce closing force and closing torque.
Opening and closing speed
Opening and closing speed is expressed as the time required to complete an opening or closing action of the valve. General valve opening and closing speed is not strict requirements, but some conditions have special requirements for opening and closing speed, such as some requirements for rapid opening or closing, in case of accidents, some requirements for slow closing, in case of water strike, which should be considered when choosing the valve type.
Movement sensitivity and reliability
This refers to the valve for medium parameter changes, make the corresponding response to the degree of sensitivity. For throttle valve, pressure reducing valve, regulating valve and other valves used to adjust the parameters of the medium as well as safety valve, trap valve and other valves with specific functions, its functional sensitivity and reliability are very important technical performance indicators.
The service life of the
It represents the durability of the valve, is an important performance index of the valve, and has great economic significance. Usually in order to ensure the sealing requirements of the number of times to express, can also be expressed by the use of time.