The opening and closing part of knife gate valve is wedge. The movement direction of the wedge is perpendicular to the fluid direction. Knife gate valve can only be fully opened and closed, can’t be adjusted or throttled. Next, let's learn about the common malfunctions and solutions of knife gate valve in the application process with Dervos!

1. Leakage of Closing Parts of Knife Gate Valve

(1) Reasons of Leakage

① The sealing surface of knife gate valve is not well ground;

② The sealing ring is not tightly matched with the valve seat and disc;

③ Valve disc and valve rod are not firmly connected;

④ The valve rod is bent and twisted to make the upper and lower closing parts misaligned;

⑤ Closing too fast, resulting in poor contact or damage of sealing surface;

⑥ Improper material selection makes the valve unable to withstand medium corrosion;

⑦ Some media gradually cool down after the valve is closed, resulting in fine cracks on the sealing surface and erosion;

⑧ The valve can’t be closed tightly due to the embedding of welding slag, rust, dust and other impurities, or the valve core is blocked due to the falling off of mechanical parts in the production system.

(2) Solutions

① Conduct pressure test carefully before use. If leakage is found on the sealing surface or the root of the sealing ring, handle it before use；

② Check whether all parts of the valve are in good condition in advance. Do not use the valve with bent valve rod or the valve disc is not firmly connected with the valve rod;

③ The valve should be closed firmly without strong force. In case of poor contact or obstruction between sealing surfaces, it should be opened a little immediately to let sundries flow out, then closed tightly;

④ When selecting the valve, we should consider the corrosion resistance of the valve body and closing parts;

⑤ It should be used correctly according to the structural characteristics of the valve;

⑥ In case of medium cooling and large temperature difference after valve closing, close the valve after cooling;

⑦ A filter should be added to the valve that may enter impurities.

2. Filler Leakage of Knife Gate Valve

(1) Reasons of Leakage

① The filler does not adapt to the corrosion, temperature and pressure of the working medium;

② The filling method is wrong. In particular, the whole filler is placed in a spiral, which is most likely to cause leakage;

③ The machining accuracy or surface finish of the valve rod is not enough, there are ellipses or nicks;

④ The valve rod has pitted or rusted due to open air;

⑤ The valve stem is bent;

⑥ The filler has been used too long and aged;

⑦ Operation is too fierce.

(2) Solutions

① Proper filler selection;

② Correct method of filling;

③ If the processing of valve rod is unqualified, repair or replace it;

④ Protective measures should be taken to prevent corrosion;

⑤ The bent valve rod should be straightened or renewed;

⑥ The filler should be replaced after a certain period of use;

⑦ Pay attention to stable operation. Open and close slowly to prevent temperature change or medium impact.