Knowledge of a filter and a gate valve

2018-05-25

A gate valve is one of the most common types of valves in isolation valves. A gate valve can be found in every refinery, chemical plant, power station and industrial enterprise production facility, and its sizes range from DN6 to 4200. The main purpose of selecting the gate valve is to cut off the fluid. It is for this reason that gate valves are often referred to as “cutoff” valves or “block” valves. Gate valves are generally used in fully open or fully closed operation. When a gate valve is fully opened, the pressure drop through the gate valve is very small; when a gate valve is fully closed, it has good pressure sealing performance. When the gate valve is closed, almost no leakage occurs due to the cooperation of the valve disc and the seat ring. However, certain leaks may occur when the back pressure is very low (usually not less than 0.34 bar, lbar equals 105 Pa). Another advantage of the gate valve is that it is normally slow to be opened and closed. This feature prevents damage to the piping system due to the water hammer of the fluid.

Only flow characteristics of full bore ball valves can be equal to flow characteristics of gate valves among many common types of valves. Symmetrical design structures and peer-to-peer seals allow the gate valve to intercept the flow of media from either direction. Gate valves can also be made of a variety of materials. Small brass gate valves with a size of DN15 can be found on the shelves of hardware stores, and special alloy gate valves can also be found in nuclear islands of nuclear power plants. The main limitation of the gate valve is that it cannot be applied to throttling conditions. When the gate valve is used in throttling conditions, the fluid often has a very high flow velocity near the valve seat, which can cause erosion. Also, when the gate valve is partially opened, the valve disc will swing under the influence of the media, resulting in damage to the sealing pair. In general, the sealing surface of the valve seat and valve disc of the gate valve is more easily worn than that of the globe valve. And it is difficult to restore the wear by grinding and polishing methods.
Because the structural characteristics of the gate valves are very suitable for large-scale devices, the application of the gate valve is wider and developing toward the high temperature and high pressure environment. The maximum diameter of the gate valve has reached DN4200. The high-pressure gate valve with a pressure of PN320 has been widely used in the ammonia plant. The working pressure of the gate valve used for the drilling of oil and gas wells is as high as 138 MPa. Flexible valve seats and flexible floating valve seats have begun to be applied to enable gate valves to be used for inlet, outlet, double inlet and outlet seals. At present, a gate valve has shorter service life than that of the other valves. How to increase the service life is also an important issue for the development of the gate valve.

A filter is a small device for removing a small amount of solid particles in the liquid, which can make a compressor, a pump, an instrument and other equipment work normally. When the fluid enters the filter cartridge which has the strainer with a certain size, the impurities are blocked and the clean liquids are discharged through the filter outlet. If you want to clean the filter, you just need to take out the strainer which can be assembled. Install the strainer again after it is washed. Therefore, a filter is easy to be used and maintained. The debris such as scale deposits, rust, composite sealant, welding slags and other solid particles in the pipeline often causes damage to the equipment. We often use a filter in the pipeline in order to prevent the fluid containing dust and particles affecting the equipment. A filter should be installed at the upstream pumps so as to prevent the pump from being harmed by construction waste left in the pipeline. A filter can filter solid particles in liquids or gases and protect the device from being damaged and the pipeline from being blocked.

A filter is equipped with a strainer on the flow surface. When the liquid passes the filter, most impurities will be blocked by the strainer. The filter needs regular cleaning to avoid blocking the liquid.

Applications of filters

A filter is applied to liquid and gas materials used in chemical, petrochemical and light industrial production to filter solid impurities. A filter is usually installed at the inlet of a pump and a compressor or in front of a flow meter in order to protect this kind of equipment or instrument.

Standard filters include metric and British two series. Metric series include PN10, PN25 and PN40 three pressure ratings, while British series include Class150 (PN20) and Class300 (PN50) two pressure ratings. Pressure of the metric series filter such as filters with top ends and flat ends start from PN6 and the pressure include PN6, PN10 and PN25.

The main structural materials of the standard filter are cast iron, carbon steel, low alloy steel and austenitic stainless steel four kinds. The working temperature ranges of the filter are as the following. The working temperature range for cast iron is from -20 to 300C℃, carbon steel -20~400℃, low alloy steel 40~ 400℃ and stainless steel -196~400℃.

The stainless steel wire mesh is adopted for the filter, and it can intercept solid particles with a particle size of not less than 614μm.

Source: China Stainless Steel Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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Knowledge of a filter and a gate valve

Knowledge of a filter and a gate valve

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