In the daily use of large diameter butterfly valve users, we often reflect a problem, that is, large diameter butterfly valve used for differential pressure is relatively large media, such as steam, high-pressure water and other pressurized work, it is often very difficult to close, no matter how hard to close, always found that there will be a leakage phenomenon, it is difficult to close tightly, resulting in a problem caused by the structural design of the valve and the person's limit of the level of the output torque is insufficient.
Analysis of reasons for difficulty in switching large diameter valves
The general horizontal limit output force of an adult is 60-90kg, depending on different body sizes.
The general flow direction of the butterfly valve is designed to be low in and high out, when a person closes the valve, the human body horizontally pushes the handwheel to rotate, so that the valve flap moves downward to achieve closure, which is required to overcome a combination of three forces, namely:
1) Axial top thrust Fa;
2) packing and stem friction force Fb;
3) Stem and valve core contact friction Fc
The torque total is ∑M=(Fa+Fb+Fc)R
As can be seen, the larger the caliber, the greater the axial thrust force, when close to the closed state, the axial thrust force is almost close to the actual pressure of the pipe network (due to the closure of P1-P2 ≈ P1, P2 = 0)
If a DN200 caliber butterfly valve is used on a 10bar steam pipe, only the first closing axial thrust Fa = 10 × πr2 = 3140kg, and the horizontal circumferential force required for closing is close to the limit of the horizontal circumferential force that can be output from a normal human body, so it is very difficult for a person to completely close the valve under such working conditions.
Of course some factories recommend installing this type of valve in reverse, which solves the problem of difficulty in closing, but then the problem of difficulty in opening after closing arises.
Large diameter electric flange butterfly valve manufacturer Tianjin Zhongfa Valve-ZFA technology department finishing, large diameter electric flange butterfly valve leakage reasons have different conditions according to different systems, there are different reasons, the following to analyze the two cases:
First, the construction period caused by large diameter electric flange butterfly valve internal leakage reasons:
① transport and lifting improperly caused by the overall damage to the large diameter electric flange butterfly valve, thus causing large diameter electric flange butterfly valve leakage;
② factory, after the water pressure did not play the large diameter electric flange butterfly valve drying and anticorrosion treatment, resulting in the formation of internal leakage of the sealing surface corrosion;
③ construction site protection is not in place, large diameter electric flange butterfly valve is not installed at both ends of the blind, rain, sand and other impurities into the valve seat, resulting in leakage;
④ During installation, no grease is injected into the valve seat, resulting in impurities entering the back of the valve seat, or burns caused by internal leakage during welding;
⑤ The valve is not installed in the fully open position, causing damage to the ball. During welding, if the valve is not in the fully open position, welding spatter will cause damage to the ball, and when the ball with welding spatter is switched on and off, it will further cause damage to the valve seat, thus leading to internal leakage;
⑥ Welding slag and other construction remnants caused by the sealing surface scratches;
factory or installation time inaccurate position caused by leakage, if the valve stem drive sleeve or other accessories and its assembly angle misalignment, large diameter electric flange butterfly valve will leak.
Second, the operating period caused by large diameter electric flange butterfly valve leakage reasons:
① The more common reason is that the operations manager takes into account the more expensive maintenance costs of large diameter electric flange butterfly valve does not carry out maintenance, or the lack of scientific large diameter electric flange butterfly valve management and maintenance methods of large diameter electric flange butterfly valve does not carry out preventive maintenance, resulting in equipment failure in advance;
② improper operation or not in accordance with maintenance procedures for maintenance caused by internal leakage;
③ In normal operation, construction remnants scratch the sealing surface, resulting in internal leakage;
④ Improper pipe cleaning causes damage to the sealing surface resulting in internal leakage;
⑤ Long-term non-maintenance or inactivity of large-diameter electric flange butterfly valve, resulting in the valve seat and ball holding, causing sealing damage when switching large-diameter electric flange butterfly valve to form internal leakage;
⑥ large diameter electric flange butterfly valve switch is not in place to cause internal leakage, any large diameter electric flange butterfly valve regardless of the opening and closing position, generally tilt 2 ° ~ 3 ° may cause leakage;
⑦ Many large-diameter large-diameter electric flange butterfly valves mostly have a stem stop block, if used for a long time, due to rust and corrosion and other reasons between the stem and stem stop block will accumulate rust, dust, paint and other debris, these debris will cause large-diameter electric flange butterfly valve can not be rotated into place and cause leakage - if the large-diameter electric flange butterfly valve is Buried, lengthening the valve stem will produce and fall more rust and impurities impede the valve ball rotation in place, resulting in large diameter electric flange butterfly valve leakage.
⑧ general actuator is also limited, if the long-term cause of rust, grease hardening or limit bolts loose will make the limit inaccurate, resulting in internal leakage;
⑨ electric actuator valve position setting forward, not related to in place to cause internal leakage;
⑩ lack of periodic maintenance and maintenance, resulting in sealing grease dry, hardened, dried sealing grease accumulates in the elastic valve seat, hindering the movement of the valve seat, resulting in seal failure.
ZFA Valve Factory have professional QC teams to ensure that each factory valve inside and appearance is sound. At the same time, we have professional technology and after -sales teams to help customers solve various problems encountered during installation and use.
Post time: Nov-24-2023