Analysis of the four functions of pipeline valves Supply and drainage pipeline valve selection

Analysis of the four functions of pipeline valves Supply and drainage pipeline valve selection

First, cut off and release medium this is the basic function of the valve, usually choose the flow channel for the straight-through valve, the flow resistance is small. Downward closed valve (globe valve, plunger valve) because of its tortuous flow path, flow resistance is higher than other valves, so less selected. Closed valves may be used where high flow resistance is permitted. Second, the control
First, cut off and release medium
This is the basic function of the valve, usually choose a straight passage valve, its flow resistance is small.
Downward closed valve (globe valve, plunger valve) because of its tortuous flow path, flow resistance is higher than other valves, so less selected. Closed valves may be used where high flow resistance is permitted.
Two, control the flow
A valve that is easy to adjust is usually chosen to control flow. Downward CLOSING valves (such AS GLOBE valves) ARE SUITABLE FOR THIS PURPOSE BECAUSE THE SEAT size IS PROPORTIONAL TO THE STROKE OF THE SHUTOFF.
Rotary VALVES (PLUG, butterfly, BALL valves) and FLEXURE BODY VALVES (PINCH, DIAPHRAGM) ARE ALSO AVAILABLE FOR THROTTLING CONTROL, but USUALLY ONLY IN a limited range of valve DIAMETERS.
Gate VALVE IS A disc shaped gate to the circular seat port to do transverse motion, it only in close to the closed position, can better control the flow, so usually not used for flow control.
Three, commutation shunt
The valve may have three or more channels, depending on the need for reversing and diverting. Plug and ball valves are more suitable for this purpose, and therefore, most valves used for reversing and diverting are selected as one of these valves.
However, IN SOME CASES, other TYPES OF VALVES MAY ALSO BE USED AS commutATION diverTERS, PROVIDED THAT TWO or MORE VALVES ARE properly connected to EACH other.
4. Medium with suspended particles
When the medium with suspended particles, ** suitable for the use of the closing parts along the sealing surface of the sliding valve with wiping action.
If THE SHUTOFF IS VERTICAL TO THE BACK AND FORTH MOVEMENT OF THE SEAT, PARTICLES MAY BE TRAPPED, SO THIS VALVE IS ONLY SUITABLE FOR BASICALLY CLEAN MEDIA UNLESS THE SEALING MATERIAL ALLOWS FOR PARTICLES TO BE EMBEDDED. Ball valves and plug valves wipe the sealing surface during opening and closing, so they are suitable for use in media with suspended particles.
Analysis of water supply and drainage pipeline valve selection, valve selection and setting parts (a) water supply pipeline used on the valve, generally according to the following principles to choose 1. When the pipe diameter is not greater than 50mm, it is advisable to use globe valve, when the pipe diameter is greater than 50mm, it is advisable to use gate valve and butterfly valve. 2 need to adjust the flow, water pressure when the use of regulating valve, cut-off valve.
First, valve selection and setting parts
(a) the valve used on the water supply pipeline, generally according to the following principles
1. When the pipe diameter is not greater than 50mm, it is advisable to use globe valve, and when the pipe diameter is greater than 50mm, it is advisable to use gate valve and butterfly valve.
2 need to adjust the flow, water pressure when the use of regulating valve, cut-off valve.
3. Where the water flow resistance is small (such as the water pump suction pipe), the gate valve should be used.
4. Gate valve and butterfly valve shall be used on the pipe section where the water flow needs to be bidirectional, and stop valve shall not be used.
5. Butterfly valve and ball valve should be used in parts with small installation space.
6. Stop valve should be used in the pipe section that is often opened and closed.
7. Multi-function valve should be used on the water pump outlet pipe with larger diameter.
(2) The following parts of the water supply pipeline should be provided with valves
1. The water supply pipeline of the residential district shall be from the inlet pipe section of the municipal water supply pipeline.
2. The nodes of the ring pipe network outside the residential area shall be set according to the separation requirements. When the ring pipe section is too long, it is appropriate to set the segment valve.
3. The starting end of the branch pipe connected to the main water supply pipe in the residential area or the starting end of the household pipe.
4. Household pipe, water meter and branch risers (bottom of riser, upper and lower ends of vertical ring pipe riser).
5. The main pipe of ring pipe network and the connecting pipe through branch pipe network.
6. The indoor water supply pipe is connected to the starting point of the water distribution pipe connected to the household and public toilet, etc., and the water distribution point on the water distribution branch pipe should be set when there are 3 or more water distribution points.
7. Outlet pipe of water pump and suction pump of self-irrigation water pump.
8. Water inlet and outlet pipes and drain pipes of the water tank.
9. Water inlet and refill pipes of equipment (such as heater and cooling tower).
10. Plumbing for sanitary appliances (e.g. large, urinals, wash basins, showers, etc.).
11. Some accessories, such as automatic exhaust valve, pressure relief valve, water hammer eliminator, pressure gauge, sprinkler plug, pressure reducing valve and backflow prevention device before and after.
12. Drain valves should be set at the lower part of the water supply network.
(3) The check valve should be generally selected according to its installation position, the water pressure before the valve, the sealing performance requirements after closing and the size of the water hammer caused when closing
1. When the pressure before the valve is small, swing, ball and shuttle check valves should be selected.
2. When the sealing performance requirements are strict after closing, the check valve with the closing spring should be selected.
3. When the water hammer is required to be weakened, it is appropriate to choose the quick-closing noiseless check valve or the slow closing check valve with damping device.
4. The valve break or spool of the check valve should be able to close itself under the action of gravity or spring force.
Check VALVES SHALL be INSTALLED ON THE FOLLOWING SECTIONS OF the WATER SUPPLY PIPELINE
Lead into the tube; On the inlet pipe of the closed water heater or water use equipment; Water pump outlet pipe; The inlet and outlet water pipes are combined with the water tank, water tower, and the outlet pipe section of the highland pool of a pipe.
Note: It is not necessary to install check valves for pipe segments equipped with backflow preventers.
(5) The following parts of the water supply pipeline shall be equipped with exhaust devices
1. For intermittently used water supply network, automatic exhaust valves should be set at the end and high point of the network.
2. For the section of water supply network with obvious fluctuation and accumulation of air, automatic exhaust valve or manual valve exhaust has been set at the peak point of this section.
3. Pneumatic water supply device, when the automatic air filling type pneumatic water tank is used, the relatively high point of the water distribution network should be equipped with an automatic exhaust valve.
Two, the advantages and disadvantages of various valves
1, gate valves,
Gate valve refers to the closing parts (gate) along the vertical direction of the axis of the channel to move the valve, in the pipeline is mainly used as a cut off medium, that is, fully open or fully closed use. Generally, gate valves cannot be used to regulate flow. It can be applied to low temperature pressure can also be applied to high temperature and high pressure, and according to the different material of the valve. But the gate valve is generally not used for conveying mud and other media in the pipeline.
Advantages: (1) small fluid resistance; ② the torque required for opening and closing is small; ③ can be used in the medium flow to the two directions of the ring network management road, that is to say, the flow of the medium is not restricted; (4) When fully open, the sealing surface is eroded by the working medium than the stop valve; ⑤ The body structure is relatively simple, and the manufacturing technology is good; ⑥ The structure length is short.
Disadvantages: (1) the size and opening height is large, the space required to install is also large; ② In the process of opening and closing, the sealing surface is relatively friction, friction loss is larger, and even easy to cause abrasion phenomenon at high temperature; ③ The general gate valve has two sealing surface, to the processing, grinding and maintenance increased some difficulties; (4) Long opening and closing time.
2, butterfly
Butterfly valve is a disc type opening and closing parts reciprocating around 90 degrees to open, close and adjust the fluid channel of a valve.
Advantages: ① simple structure, small volume, light weight, consumables, not used in large diameter valve; ② rapid opening and closing, small flow resistance; (3) can be used for medium with suspended solid particles, according to the strength of the sealing surface can also be used for powder and granular media. It can be applied to the two-way opening, closing and adjustment of the ventilation and dust removal pipeline, and is used in the gas pipelines and waterways of metallurgy, light industry, electric power and petrochemical systems, etc.
Disadvantages: ① the range of flow regulation is not large, when opened up to 30%, the flow will enter more than 95%. ② Due to the structure and sealing material of butterfly valve, it is not suitable for high temperature and high pressure piping system. General operating temperature below 300℃, PN40 below. ③ The sealing performance is poor compared with the ball valve and globe valve, so it is used in places where the sealing requirement is not very high.
3, ball valve
Is evolved from the plug valve, its opening and closing part is a ball, the use of the ball around the axis of the valve stem rotation 90° to achieve the purpose of opening and closing. Ball valves are mainly used to cut off, distribute and change the direction of medium flow on the pipeline. The ball valves designed as V-shaped openings also have good flow regulation function.
Advantages: ① It has relatively low flow resistance (actually 0); ② Because it will not get stuck at work (without lubricant), it can be reliably used in corrosive media and low boiling point liquid; (3) In a large range of pressure and temperature, can achieve complete sealing; ④ Fast opening and closing can be realized. The opening and closing time of some structures is 0.05-0.1s, so as to ensure that it can be used in the automation system of the test bench. When opening and closing the valve quickly, the operation has no impact. ⑤ Spherical closing parts can be automatically positioned on the boundary position; ⑥ the working medium is sealed reliably on both sides; ⑦ in fully open and fully closed, the ball and the valve seat sealing surface and medium isolation, so high speed through the valve medium will not cause the erosion of the sealing surface; ⑧ Compact structure, light weight, it can be considered that it is the most reasonable valve structure for low temperature medium system; ⑨ Symmetrical valve body, especially welded valve body structure, can withstand the stress from the pipe well; ⑩ The closing parts can withstand the high pressure difference when closing. (11) fully welded valve body, can be directly buried in the ground, so that the valve inner corrosion, relatively high service life of up to 30 years, oil, natural gas pipeline is the ideal valve.
Disadvantages: ① because the main valve seat sealing ring material is PTFE, it is inert to almost all chemicals, and has a small coefficient of friction, stable performance, not easy to aging, a wide range of temperature application and excellent sealing performance comprehensive characteristics. However, THE PHYSICAL CHARACTERISTICS OF TEFLON, INCLUDING A HIGH COEFFICIENT OF EXPANSION, SENSITIVITY TO COLD FLOW, AND POOR THERMAL CONDUCTIVITY, REQUIRE THAT SEAT DESIGN BE MADE AROUND THESE CHARACTERISTICS. Therefore, when the sealing material becomes hard, the reliability of the seal is damaged. Moreover, Teflon has a low temperature resistance grade and can only be used under the condition of less than 180℃. Above this temperature, the sealing material will age. In the case of long-term use, it is generally not used at 120℃. (2) its regulating performance is worse than the globe valve, especially the pneumatic valve (or electric valve).
4, stop valve
A valve in which the closing member (disc) moves along the center line of the seat. According to this movement of the disc, the change of the valve seat through the valve is proportional to the disc stroke. Due to this kind of valve stem open or close stroke is relatively short, and has a very reliable cut off function, and due to the change of the valve seat through the stroke of the disc is proportional to the relationship, very suitable for flow regulation. Therefore, this type of valve is very suitable for cutting or adjusting and throttling.
Advantages: ① in the process of opening and closing, because the friction between the disc and the valve sealing surface is smaller than the gate valve, so wear-resistant. The opening height is generally * 1/4 of the seat channel, so much smaller than the gate valve; ③ There is usually only one sealing surface on the valve body and disc, so the manufacturing technology is better and it is easy to maintain. ④ Because the filler is generally a mixture of asbestos and graphite, it has a high temperature resistance. Steam valves are generally used with stop valves.
Disadvantages: ① due to the flow direction of the medium through the valve has changed, so the small flow resistance of the globe valve is higher than most other types of valves; ② Due to the longer travel, the opening speed is slower than the ball valve.
5. Plug valve
Refers to the closing part into a plunger shaped rotary valve, through 90 degrees of rotation so that the valve plug on the channel port and the valve body on the channel port is communicated or separated, open or close a valve. The plug can be cylindrical or conical in shape. Its principle is basically similar to ball valve, ball valve is developed on the basis of plug valve, which is mainly used in oil field exploitation, but also used in petrochemical industry.