一, The selection of valves and setting parts
1. Pipe diameter is not greater than 50mm, it is appropriate to use globe valves, pipe diameter is greater than 50mm with gate valves, butterfly valves.
2. Need to adjust the flow, water pressure is appropriate to use control valves, globe valves.
3. The requirements of small resistance to water flow parts (such as pump suction pipe), it is appropriate to use the gate valve.
4. The water flow needs to flow in both directions on the pipe section should be used gate valve, butterfly valve, do not use globe valve. 5, the installation space is small parts of the appropriate use of gate valves.
5. Installation of small parts of the space should be used butterfly valves, ball valves.
6. In the often open and close the pipe section, it is appropriate to use the globe valve.
7. Larger diameter of the pump outlet pipe should be used on the multi-function valve.
(B) The following parts of the water pipeline should be set up valves
1. Residential water supply pipeline from the municipal water supply pipeline on the introduction of pipeline sections.
2. Residential outdoor circular pipe network at the node, should be set according to the separation requirements. Ring section is too long, it is appropriate to set up segmented valves.
3. The beginning of the branch pipe or the beginning of the household pipe connected to the water supply main pipe from the residential district.
4. Household pipes, water meters and branch risers (the bottom of risers, vertical ring network risers, the upper and lower ends).
5. the trunk pipe of the ring network and the connecting pipe through the branch network.
6. The beginning of the distribution pipe of the indoor water supply pipe to the households, public toilets, etc. If there are 3 or more distribution points on the distribution branch pipe, it is set.
7. Outlet pipe of water pump, suction pump of self-irrigation pump. 8. inlet and outlet pipe of water tank.
8. Inlet and outlet pipes and drain pipes of water tanks.
9. Inlet make-up pipes for equipment (e.g. heaters, cooling towers, etc.). 10. inlet and outlet pipes for sanitary fittings (e.g. large and small).
10. Water distribution pipes for sanitary appliances (e.g. urinals, washbasins, showers, etc.).
11. Certain accessories, such as automatic exhaust valves, pressure relief valves, water hammer eliminators, pressure gauges, sprinkler hydrants, etc., before and after the pressure reducing valves and backflow preventers.
12. It is desirable to provide a relief valve at the lowest point of the water supply network.
(C) Check valve should be generally according to its installation site, pre-valve water pressure, after the closure of the airtight performance requirements and the size of the water hammer caused by the closure of factors such as choice
1. When the water pressure in front of the valve, it is appropriate to use the rotary, ball and shuttle check valve.
2. After the closure of the tight performance requirements, it is appropriate to use the closing spring check valve.
3. When weakening the closing water hammer, it is suitable to use quick closing muffler check valve or slow closing check valve with damping device.
4. Check valve valve break or spool, should be able to gravity or spring force under the action of self-closing.
(D) Check valves shall be provided on the following sections of water supply pipelines
1. On the lead-in pipe;
2. On the inlet pipe of a closed water heater or water-using equipment;
3. On the outlet pipe of water pump;
4. On the outlet pipe of water tanks, water towers, and upland pools where the inlet and outlet pipes are combined in one pipe.
Note: Pipe sections equipped with pipe backflow preventers are not required to be fitted with check valves.
(E) The following parts of the water supply pipe shall be equipped with an exhaust device
1. The end and the highest point of intermittent use of water supply pipe network should be equipped with automatic exhaust valve.
2. Water supply pipe network has obvious ups and downs of the pipe section of the accumulation of air, has been in the section of the peak point of the automatic exhaust valve or manual valve exhaust.
3. Pneumatic water supply device, when the use of automatic replenishment of pneumatic tanks, the highest point of the distribution network should be set up automatic exhaust valve.
二, The advantages and disadvantages of various valves
1. Gate valve
Gate valve is the closing member (gate) along the channel axis of the vertical direction of the valve, in the pipeline mainly as a cut-off medium, that is, full open or full closed use. In general, the gate valve can not be used as a flow control. It can be applied to low temperature pressure can also be applied to high temperature and high pressure, and can be based on different materials of the valve. But the gate valve is generally not used in the pipeline to transport slurry and other media.
Advantages of gate valve:
① Small fluid resistance;
② Opening and closing requires less torque;
③ Can be used in the medium to the two directions of flow of the ring network pipeline, that is, the medium flow direction is not restricted;
④ Fully open, the sealing surface by the working medium of the erosion is smaller than the globe valve;
⑤ Shape structure is relatively simple, manufacturing process is better;
⑥ Structure length is relatively short.
Disadvantages of gate valve:
① External dimensions and opening height is larger, the space required for installation is also larger;
② In the opening and closing process, the sealing surface relative friction, wear and tear, and even at high temperatures can easily cause abrasion phenomenon;
③ General gate valve have two sealing surfaces, to the processing, grinding and maintenance has increased some difficulties;
④ Opening and closing time is long.
1. Butterfly valve
Butterfly valve is a kind of valve to open, close and regulate the fluid passage by reciprocating the disc-type opening and closing parts about 90°.
Advantages of butterfly valve:
① Simple structure, small size, light weight, consumables, don’t use in large calibre valves;
② Rapid opening and closing, small flow resistance;
③ Can be used for media with suspended solid particles, according to the strength of the sealing surface can also be used for powdery and granular media. Can be applied to ventilation and dust removal pipeline bidirectional opening and closing and adjustment, widely used in metallurgy, light industry, electric power, petrochemical systems, gas pipelines and waterways.
Disadvantages of butterfly valve:
① Flow adjustment range is not large, when open up to 30%, the flow will be into 95% or more.
② Due to the structure of the butterfly valve and sealing material limitations, should not be used for high temperature, high pressure piping system. General operating temperature below 300 ℃, PN40 below.
③ Sealing performance relative to the ball valve, globe valve is poor, so it is used for sealing requirements are not very high.
3. Ball valve
Ball valve is evolved from the plug valve, its opening and closing member is a sphere, the use of the sphere around the axis of the valve stem rotated 90 ° to achieve the purpose of opening and closing. Ball valve in the pipeline is mainly used to cut off, distribution and change the direction of media flow, designed as a V-shaped opening of the ball valve also has a good flow regulation function.
Advantages of ball valves:
① Has the lowest flow resistance (actually 0);
② Because it will not jam during operation (in the absence of lubricant), it can be reliably applied to corrosive media and low boiling point liquids;
③ It can achieve complete sealing in a wide range of pressure and temperature;
④ Can achieve rapid opening and closing, some structures of the opening and closing time is only 0.05 ~ 0.1s, to ensure that can be used in the test bench automation system. When opening and closing the valve quickly, the operation is shockless.
⑤ The spherical closing member can be automatically positioned at the boundary position;
⑥ The working medium is sealed reliably on both sides;
⑦ In full opening and closing, the sealing surfaces of the ball and seat are separated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surfaces;
⑧ Compact structure, light weight, it can be considered the most reasonable valve structure for low temperature media system;
⑨ Valve body symmetry, especially the welded valve body structure, can well withstand the stress from the pipeline;
(10) The closing parts can withstand the high pressure difference when closing.
(11) The ball valve with fully welded body can be buried directly in the ground, so that the inner parts of the valve are not subject to erosion, the maximum service life of up to 30 years, is the most ideal valve for oil and gas pipelines.
4. Globe valves
Globe valves are valves in which the closing member (valve flap) moves along the centre line of the valve seat. According to this form of movement of the valve flap, the change of the valve seat orifice is proportional to the valve flap travel. Because the stem opening or closing stroke of this type of valve is relatively short, and has a very reliable cut-off function, and because the change of the valve seat orifice is proportional to the travel of the valve flap, it is very suitable for regulating the flow rate. Therefore, this type of valve is very relocated for cutting off or regulating and throttling with.
Advantages of globe valves:
① In the process of opening and closing, due to the valve flap and the valve body sealing surface of the friction between the smaller than the gate valve, and thus wear-resistant.
② Opening height is generally only 1/4 of the valve seat channel, so much smaller than the gate valve;
③ Usually only one sealing surface on the valve body and valve flap, thus the manufacturing process is better, easy to maintain.
④ As its packing is generally a mixture of asbestos and graphite, it has a higher temperature resistance rating. Generally steam valves are used globe valves.
Disadvantages of globe valves:
① Due to changes in the direction of flow of media through the valve, so the minimum flow resistance of the globe valve is also higher than most other types of valves;
② due to the longer stroke, the opening speed is slower than the ball valve.
5. Safety valve
Safety valves are used as overpressure protection devices in pressurised vessels, equipment or pipelines. When the pressure inside the equipment, vessel or pipeline rises above the permissible value, the valve opens automatically and then discharges the full amount to prevent the equipment, vessel or pipeline and the pressure from continuing to rise; when the pressure is reduced to the specified value, the valve should be closed automatically and in time to protect the safe operation of the equipment, vessel or pipeline.
6. Steam trap
In conveying steam, compressed air and other media, there will be some condensate formation, in order to ensure the efficiency and safe operation of the device, it should be timely discharge of these useless and harmful media to ensure the consumption and use of the device.
It has the following functions:
① It can quickly remove the generated condensate;
② Prevent steam leakage;
③ Excluding air and other non-condensable gases.
7. Pressure Reducing Valve
Pressure-reducing valve is a valve that reduces the inlet pressure to a desired outlet pressure through adjustment and keeps the outlet pressure stable automatically by relying on the energy of the medium itself.
8. Check valve
Check valves are also known as backflow valves, check valves, back pressure valves and check valves. These valves are relying on the flow of the medium itself in the pipeline to generate the force automatically open and close, belonging to a kind of automatic valve.
Check valve used in piping systems, its main role is to prevent the media backflow, to prevent the pump and drive motor reversal, as well as container media discharge. Check valve can also be used to give which the pressure may rise to more than the system pressure of the auxiliary system to provide supply pipeline.
Mainly can be divided into rotary (according to the centre of gravity rotation) and lifting type (moving along the axis).
