Seek help: What is the difference between a plug valve and a manual shut-off valve?

Plug valve, also known as a manual knife gate valve, is a type of valve in which the gate is in constant tight contact with the valve seat to ensure sealing. The principle behind it is that there is an opening of the same diameter as the passage in the gate, and by opening and closing this gate, the opening in the gate either comes completely out of alignment with the passage or aligns perfectly with it. The advantage of this valve is that the valve body has no grooves in its diameter, preventing the medium from getting stuck and causing blockages; it also features full-diameter flow characteristics, making it suitable for use in pipelines carrying powdered particles. Its sealing structure can be divided into soft-sealing and hard-sealing structures. The through-type knife gate valve features a precise design, good manufacturability, and a compact structure. Its sealing seat is designed to be movable, offering wear protection and automatic compensation functions, thus extending its service life. During the closing and opening process, the valve seat and the gate remain in close contact as they move, which ensures a stable force for opening and closing the valve and provides the ability to cut off the flow of the medium. By configuring a handwheel, it is possible to operate the handwheel directly to open and close the valve. 　　It entered our country in the 1980s. In less than two decades, its scope of use has expanded from ordinary fields to a wider range of industries. From coal sorting, gangue disposal, and slag disposal in mining power plants. It has evolved to include urban sewage treatment, progressing from ordinary industrial pipelines to specialized pipeline systems for food, hygiene, pharmaceuticals, and other fields. Ultra-thin gate valves, with their small size, low flow resistance, light weight, and ease of installation and disassembly, effectively solve the problems associated with conventional gate valves, flat gate valves, ball valves, globe valves, control valves, butterfly valves, and other similar types of valves – namely high flow resistance, heavy weight, difficulty in installation, and large space requirements. With the advent of knife gate valves, a large number of general-purpose shut-off and control valves have been replaced by them. To this day, the countries with the highest consumption of globe valve switches in the world are the United States and Japan. 　　Precautions for using knife gate valves and their characteristics: The moving part of a knife gate valve is the gate, whose movement direction is perpendicular to that of the fluid. Knife gate valves can only be operated in the fully open or fully closed position; they cannot be used for regulation or throttling. The gate has two sealing surfaces. In the most common type of gate valve, these two sealing surfaces are wedge-shaped; the wedge angle varies depending on the valve parameters, usually being 50 degrees. In wedge-type knife gate valves, the gate can be designed as a single unit, known as a rigid gate ； It is also possible to create gate plates that can undergo slight deformation, in order to improve their workability and compensate for any deviations in the angle of the sealing surfaces that may occur during processing. Such gate plates are known as elastic gate plates. When a knife-type gate valve is closed, the sealing surfaces can rely solely on the pressure of the medium to achieve sealing – that is, the pressure of the medium is used to press the sealing surfaces of the gate plate against the valve seat on the other side, thereby ensuring a tight seal. This is what is referred to as self-sealing. Most knife-type gate valves use forced sealing; that is, when the valve is closed, external force is required to push the gate plate against the valve seat in order to ensure the integrity of the seal. 　　Operating performance and installation of knife gate valves: Knife gate valves feature a simple and compact structure, rational design, light weight and material savings, reliable sealing, easy and flexible operation, small size, smooth flow passage, low flow resistance, light weight, as well as ease of installation and disassembly. They can operate properly under working pressures of 1.0 MPa to 2.5 MPa and at operating temperatures ranging from -29°C to 650°C. The knife gate valve features a gate plate with shearing capability, which can scrape off adherents from the sealing surface and automatically remove debris; the stainless steel gate plate prevents sealing leaks caused by corrosion. 　　Installation and use of knife gate valves: 1. Before installation, it is necessary to check the valve chamber and sealing surfaces for any contaminants or sand particles ； 2. The bolts at each connection point must be tightened evenly ； 3. Check that the packing area is properly compressed, as this ensures both the sealing performance of the packing and the smooth operation of the gate valve ； 4. Before installing the valve, the user must verify the valve model, connection dimensions, and pay attention to the flow direction of the medium to ensure consistency with the valve’s requirements ； 5. When installing the valve, the user must reserve the necessary space for valve actuation ； 6. The wiring of the drive device must be carried out in accordance with the circuit diagram ； 7. Knife gate valves must be maintained regularly; they should not be subjected to accidental impacts or compression to avoid affecting their sealing performance. 　　Product model: SCZ series Nominal diameter range: DN50-DN500 Nominal pressure range: 1.0MPa-1.6MPa Material: cast steel, stainless steel Gate plate material: 2Cr13, 201, 304, 316, 316L Connection type: flanged Valve seat seal: nitrile rubber, EPDM, fluororubber Cladding: 2Cr13, stainless steel, cemented carbide Packing seal: graphite packing, PTFE packing Applicable media: sewage, powder particles, pulp, slurry, coal cinders Throttle valve Cross-section diagram of the throttle valve and symbols for hydraulic systems A throttle valve is a valve that controls the flow rate of fluid by changing the throttle area or throttle length. Connecting a throttle valve and a check valve in parallel can form a one-way throttle valve. Throttle valves and check throttle valves are simple flow control valves. In hydraulic systems with fixed-displacement pumps, together with relief valves, they can form three types of throttle speed control systems: the inlet line throttle speed control system, the return line throttle speed control system, and the bypass throttle speed control system. Throttle valves do not have a flow negative feedback function, and thus cannot compensate for speed instability caused by changes in load; they are generally used only in situations where the load changes little or where high speed stability is not required. 　　The performance requirements for the throttle valve are: · A large range of flow regulation, with smooth changes in flow in response to pressure differences ； 　　·The internal leakage is low; if there is an external oil leakage port, the external leakage amount is also low ； 　　·It has a low adjusting torque and is responsive in operation. 　　The external structure of a throttle valve is identical to that of a globe valve; the only difference lies in the shape of their closing elements. The moving parts of throttle valves are mostly of conical streamline shape; by changing the cross-sectional area of the passage, flow rate and pressure can be regulated. Throttle valves are used to reduce the pressure of a fluid under conditions of extremely high pressure drops. 　　The flow velocity of the medium between the throttle valve disc and the valve seat is very high, causing rapid damage to the surfaces of these components – a phenomenon known as cavitation. To minimize the effects of cavitation, the valve disc is made of a cavitation-resistant material (alloy steel) and shaped into a streamlined cone with a tip angle of 140–180 degrees; this also allows the valve disc to achieve a larger opening height. Throttling at small gaps is generally not recommended. 　　Throttle valves have the following characteristics: 1. They have a simple structure, which makes them easy to manufacture and maintain, and their cost is low. 　　2. The adjustment accuracy is not high, so it cannot be used for adjustment purposes. 　　3. The sealing surface is prone to erosion, and it cannot be used for cutting media. 　　4. Poor sealing performance. 　　Throttle valves can be divided into straight-through type and angle type according to their channel configuration ； Based on the shape of the opening and closing element, there are three types: needle-shaped, groove-shaped, and window-shaped. The following points should be taken into account when installing and maintaining the throttle valve: Since this valve needs to be operated frequently, it should be installed in a location where it is easy to operate. 　　During installation, make sure that the direction of the medium is consistent with the arrow indicated on the valve body. 　　Reasons for clogging of the throttle orifice: 1. Mechanical impurities in the oil, along with gums, asphalts, carbon residues and other contaminants resulting from oxidation, accumulate in the throttle gap. 　　2. Due to the aging of the oil or the formation of charged polarized molecules as a result of compression, and because there is a potential difference on the metal surfaces of the throttle gap, these polarized molecules are attracted to the surface of the gap, forming a stable adsorption layer. The thickness of this adsorption layer is generally 5 to 8 micrometers, which in turn affects the size of the throttle gap. When the above deposits and adsorbed substances reach a certain thickness, they are washed away by the fluid flow, only to attach themselves to the valve opening again. Repeating this process over and over creates fluctuations in traffic volume. 　　3. When the pressure difference at the valve opening is high, the high temperature at the valve opening increases the degree of compression of the liquid, and the metal surface is more susceptible to frictional effects that result in a potential difference; therefore, blockages are likely to occur under high pressure differences. 　　Measures to reduce throttle port clogging: 1. Choose a thin-blade throttle port with a large hydraulic radius. 　　2. Perform precise filtration and replace the oil regularly. 　　3. Appropriately reduce the pressure difference before and after the throttle orifice. 　　4. Use metal materials with a small potential difference, select oils with good oxidation stability, and reduce the surface roughness of the throttle orifice. 　　Applications of throttle valves Since the flow rate through a throttle valve depends not only on the area of the throttle opening but also on the pressure difference before and after it, and because the valve has low stiffness, it is suitable only for applications where the load on the actuator changes little and high speed stability is not required. 　　In throttle speed control systems where the load on the actuator varies greatly and high speed stability is required, pressure compensation for the throttle valve is necessary to maintain a constant pressure difference before and after the throttle valve, thereby ensuring stable flow rate