To understand the commonly used valves for water supply and drainage, we should first understand the water supply and drainage projects that are closely related to them. Only by understanding the purpose of water supply and drainage projects can we correctly select valves and serve us better.
Water supply and drainage engineering studies the problem of a social cycle of water. "Water supply": a modern water plant, after extracting natural water from rivers and lakes every day, uses a series of physical and chemical means to purify the water into tap water that meets the standards of production and living water, and then passes through the urban water network extending in all directions. Tap water is delivered to thousands of households. "Drainage": an advanced sewage treatment plant, which centrally treats the sewage and waste water used in our production and life, and then discharges it into the rivers and lakes cleanly. The process of taking water, treating, conveying, re-processing, and then discharging is the main content of water supply and drainage engineering to be studied.

Water supply project
Water supply project is a project that supplies living and production water for residents and factories, mines, and transportation enterprises, as well as water for firefighting, water for road greening, etc. It is composed of water supply water source, water intake structures, raw water pipelines, water supply treatment plants and water supply pipeline network, which has the function of collecting and transporting raw water and improving water quality.
1.The water supply sources include surface water, groundwater and reuse water.
2.Water intake structures include surface water intake structures and groundwater intake.
drainage works
Drainage project is a project that removes human domestic sewage, various waste water and excess surface water in production. It consists of a drainage pipe system (or channel), a wastewater treatment plant and a final treatment facility. Usually also includes pumping facilities (such as drainage pumping stations).

1.Drainage pipe system refers to the pipe network for collecting and transporting waste water (sewage), including confluence pipe system and branch pipe system.
2.Wastewater treatment plants include sedimentation tanks, sedimentation tanks, aeration tanks, biological filters, clarification tanks and other facilities, as well as pumping stations, laboratories, sludge dewatering machine rooms, repair factories and other buildings. The general goal of wastewater treatment is to remove suspended solids and improve oxygen consumption, and sometimes disinfection and further treatment.
3.Final treatment facility. Depending on the different drainage objects, there are pumps or other water lifting machines, and the wastewater that has been treated by the treatment plant and meets the specified discharge requirements is discharged into the water body or on the land.
Fire Engineering
Fire protection engineering includes urban and building fire protection system engineering: fire hydrant system, automatic sprinkler system, water spray system, water curtain fire extinguishing system, fire water cannon system, deluge system.

The selection of valves on water supply and drainage pipelines is based on the following principles:
1. When the pipe diameter is not greater than 50mm, a globe valve should be used, and when the pipe diameter is greater than 50mm, a gate valve and a butterfly valve should be used.
2. When the flow and water pressure need to be adjusted, a regulating valve and a stop valve should be used.
3. Where the water flow resistance is small (such as on the suction pipe of the water pump), a gate valve should be used.
4. Gate valves and butterfly valves should be used on the pipe sections where the water flow needs to flow in both directions, and stop valves should not be used.
5. Butterfly valve and ball valve should be used for parts with small installation space.
6. On the pipe section that is often opened and closed, the stop valve is directly used.
7. Multi-function valves should be used on the outlet pipes of pumps with larger diameters.