NO.1 First, the valve selection and location：
1.Valves used in water supply pipelines are generally chosen as follows：
- When the pipe diameter is not more than 50mm, the cut-off valve should be adopted. When the pipe diameter is greater than 50mm, the gate valve and butterfly valve shall be adopted.
- Need to adjust the flow rate, water pressure, the use of regulating valve, stop valve.
- Requirements of small water resistance (such as water pump suction pipe), gate valve should be used.
- Flow should be two-way flow of the pipe section should use gate valve, butterfly valve, shall not use stop valve.
- Small space should be installed using butterfly valve, ball valve.
- Cut-off valves are often used on the pipe sections which are frequently opened and closed.
- The larger size of the water pump outlet should use a multi-function valve.
2.Valves shall be provided at the following locations on the water supply pipe：
- The water supply pipe of the residential district is from the lead-in pipe section of the municipal water supply pipe.
- The outer ring pipe network of residential area should be set up according to the requirement of separation. When the annular pipe section is too long, a sectional valve shall be provided.
- The end of the branch pipe or the end of the receiving pipe from the water supply pipe of the residential district.
- The inlet pipe, the water meter and each branch vertical pipe (the bottom of the riser pipe, the vertical pipe of the ring pipe network, the upper and lower parts).
- Connecting pipe for dry pipe of annular pipe network and through branch type pipe network.
- The indoor water supply pipe starts at the end of the distribution pipe which is connected with the household and the public toilet, and the
- water distribution points on the water distribution pipe are set at or more than.
- Water pump outlet pipe, self-priming pump suction pump.
- Water inlet, outlet pipe and drain pipe of water tank.
- Water inlet pipe of equipment (such as heater and cooling tower).
- A water distribution pipe for sanitary appliances (such as urinals, basins, showers, etc).
- Some accessories, such as automatic exhaust valve, relief valve, water hammer eliminator, pressure gauge, sprinkler and so on, front and rear pressure reducing valve and backflow preventer.
- The drain valve shall be installed at the lowest place of the water supply network.
3.Check valve should be installed in accordance with its parts, the valve before the water pressure, the closure of the closed performance requirements and the water hammer caused by the closure of factors such as size to choose：
- Valve front water pressure hour, should choose swing type, ball type and shuttle type check valve.
- After closing the tight performance requirements, it is appropriate to use a closed spring check valve.
- In order to weaken the water hammer, it is better to choose a fast closing noise check valve or a slow closing check valve with a damping device.
- Valve check or spool shall be closed by gravity or spring force.
4.Check valves shall be provided on the following pipe sections of the water supply pipe：
- Inlet pipe; closed water heater or inlet pipe of water equipment; water pump outlet pipe; water inlet and outlet pipe; water tank with one pipe; water pipe tower; high water tank outlet pipe section.
Note： the pipe section with a backflow preventer does not need to be fitted with a check valve.
5.Exhaust devices shall be installed at the following parts of the water supply pipeline：
- Intermittent use of water supply network, the end of its pipe network and the highest point should be set up automatic exhaust valve.
- The water supply pipe network has obvious fluctuation and accumulated air, and the automatic exhaust valve or manual valve exhaust is arranged at the peak point of the section.
- When air pressure water tank is used in automatic air supply device, the exhaust water valve shall be provided at the highest point of the water distribution network.
NO.2 Advantages and disadvantages of various valves：
Gate Valve：Gate is closed parts (RAM) vertical movement of the valve in the pipeline along the channel axis, used primarily as a medium cut that open and close use. In general, the valve can not be used as a regulation flow. The utility model can be applied to low temperature pressure, and can also be applied to high temperature and high pressure, and can be made according to different materials of the valve. But the valve is generally not used to transport mud and other media pipeline.
- Advantage：
①the fluid resistance is small. ②the opening and closing of the required torque is small. ③you can use the ring pipe flow to the two direction in the medium, that is to say the unrestricted flow of medium. ④fully open, the sealing surface by the erosion of the working medium is smaller than the cut-off valve. ⑤body structure simple manufacturing process is better. ⑥the relatively short length of the structure. - shortcoming：
①the flow adjustment range is not large, when opened to 30%, the flow will be more than 95%. ②due to the butterfly valve structure and sealing material restrictions, should not be used for high temperature, high pressure piping system. The general operating temperature is below 300 degrees, less than PN40. ③sealing performance relative to the ball valve, cut-off valve is poor, so it is not used for sealing requirements are very high places.
Ball Valve：Is evolved from the plug valve, and its opening and closing parts are a sphere, using the ball around the axis of the stem rotation 90 degrees, to achieve the purpose of opening and closing. Ball valve in the pipeline is mainly used for cutting, distribution and change the direction of media flow, designed to V shaped opening of the ball valve, also has a good flow adjustment function.
- Advantage：
①with the lowest flow resistance (actually 0). ②because not stuck at work (without lubricant), it can be reliably used in corrosive medium and low boiling point liquid. ③in a larger range of pressure and temperature, can be completely sealed. ④it can realize fast some of the opening and closing, opening and closing time is only 0.05~0.1s, can be used to ensure the automation system of the test bench. When the door is opened quickly, the operation is free of impact. ⑤the spherical closure can be automatically positioned at the boundary position. ⑥the working medium in the two-sided reliable seal. ⑦in the fully open and fully closed, the ball and seat sealing surface and the dielectric isolation, the high-speed media through the valve sealing surface does not cause erosion. ⑧compact structure, light weight, can be considered it is the most reasonable structure of the valve for medium temperature system. ⑨body symmetry, especially the welded body structure, can well withstand the stress from the pipe. ⑩the closure of parts can withstand the pressure differential. ⑪all welded body ball valve, can be buried directly in the ground, so that the valve is not subject to corrosion, the maximum service life of up to 30 years, is the best oil and gas pipeline valve. - shortcoming：
①because the main valve seat seal material is PTFE, it has almost all the chemical substances are inert, and the friction coefficient is small, stable performance, easy to aging, temperature range and excellent sealing characteristics of a comprehensive. But the physical properties of PTFE include high expansion coefficient, sensitivity to cold flow, and poor thermal conductivity. The design of seat seals must be carried out around these characteristics. Therefore, when the seal material hardens, the reliability of the seal will be damaged. What’s more, polytetrafluoroethylene has a lower temperature range and can only be used at less than 180 degrees centigrade. Over this temperature, the sealing material will age. Consider long-term use, usually only at 120 degrees does not use. ②its performance is worse than the cut-off valve, especially pneumatic valve (or electric valve).
Globe Valve：A valve that closes the valve (valve) and moves along the centerline of the valve seat. According to this form of valve movement, the valve seat opening change is proportional to the valve stroke. Because of the valve stem to open or close the trip is relatively short, but very reliable cut off function, and because changes in the valve seat and the valve stroke is proportional, is very suitable for flow regulation. Therefore, this type of valve is very cooperative for cutting or regulating and throttling.
- Advantage：
①in the process of opening and closing, because the friction between the valve and the sealing surface of the valve body is smaller than that of the gate valve, the utility model is wearable. ②the opening height generally only seat channel 1/4, so much smaller than the gate valve. ③usually in the body and disc only one seal surface, so the manufacturing process is better, easy maintenance. ④as its filler is generally a mixture of asbestos and graphite, so the temperature rating is higher. Steam valves are normally used with stop valves. - shortcoming：
①because the medium through the valve flow direction has changed, so the minimum flow resistance valve is higher than most other types of valves. ②because of the long journey, the opening speed is slow.
Pressure relief Valve：By adjusting the inlet pressure to a required outlet pressure, and depending on the energy of the medium itself, the outlet pressure is automatically kept stable by the valve.
Check Valve：Also known as counter flow valve, check valve, back pressure valve and one-way valve. The valves are automatically driven and closed by the flow of the medium itself, belonging to an automatic valve. The check valve is used for piping system, the main function is to prevent the backflow of medium, prevent the reverse of pump and drive motor, and release the container medium. The check valve can also be used to provide a supply to the auxiliary system where the pressure may rise above the system pressure. It can be divided into swing type (rotating by gravity center) and lifting type (moving along the axis).
