Basic knowledge of water supply fittings

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The article is from http://www.sdshuntong.net/industry/Index.html. In the past, the pipes used for water supply were mainly cast iron pipes. Outdoor areas mainly use sand-molded cast iron pipes, while indoor areas use galvanized cast iron pipes, which can be further divided into cold (electro) galvanizing and hot-dip galvanizing. Our country has mandated the phasing out of sand-cast pipe fittings and cold-galvanized cast iron pipes starting from June 1, 2000, gradually restricting the use of hot-dip galvanized cast iron pipes, and promoting the use of aluminum-plastic composite pipes, plastic pipes, etc. Therefore, there are mainly three categories of pipes in use today. The first category is metal pipes, such as hot-dip cast iron pipes with plastic lining, steel pipes, stainless steel pipes, etc. The second category is plastic-composite metal pipes, such as plastic-composite steel pipes and aluminum-plastic composite pipes. The third category is plastic pipes, such as PP-R (cross-linked polypropylene high-density network engineering plastic). **It also stipulates that various pipes and fittings related to drinking water pipelines must have approval from the health authorities before they can be sold. I. Common plastic codes used in water supply pipes and their meanings:
PP-R – Cross-linked polypropylene, a high-density networked engineering plastic.
PE – High-density polyethylene.
PP – Polypropylene.
PB – Polybutylene.
PEX – Cross-linked polyethylene.

II. Comprehensive performance requirements for water supply pipes: As water supply pipes, they are required to be hygienic, safe, energy-efficient, and convenient to use. Therefore, to inspect a pipeline, one should start by checking from four aspects. That is, hygiene: pipes and fittings must cause no harm to the human body. Safety: It possesses sufficient strength and excellent mechanical properties, as well as resistance to aging and heat. Energy saving: The inner wall is smooth, corrosion-resistant, presents low fluid resistance, and has good thermal insulation properties. Convenient: Easy to connect and install, reliable, and suitable for widespread use. If the above four requirements are not met, it will harm the health and property safety of the users. III. Introduction to Several Types of Water Supply Pipes 1. Aluminum-Plastic Composite Pipe The aluminum-plastic composite pipe was one of the first pipes to replace cast iron pipes in water supply systems. It consists of five layers in total, with plastic, hot melt adhesive, aluminum alloy, hot melt adhesive, and plastic arranged from the inside out. Aluminum-plastic composite pipes have good thermal insulation properties; their inner and outer walls are resistant to corrosion. Due to their smooth inner surface, they present very little resistance to fluid flow ； Furthermore, since it can be bent freely, installation is convenient. As a water supply pipe, aluminum-plastic composite pipes possess sufficient strength, but excessive lateral forces can affect their strength; therefore, they are suitable for use as exposed pipes or buried within walls, but not for burial underground. The connection of aluminum-plastic composite pipes is of the bayonet type; therefore, during installation, strict pressure testing is required to verify that the connections are secure. Second, it prevents frequent vibrations from causing the collar to loosen. Third, sufficient installation space should be left in the length direction to prevent pulling apart. 2. Plastic-coated copper pipe: This type of pipe uses pure copper (red copper) as the core material, with a PE plastic coating on the outside. In terms of overall performance, plastic-coated copper pipes are slightly superior to aluminum-plastic composite pipes. For example, it has better strength, a longer lifespan, and improved heat resistance as well. But its thermal insulation performance is slightly poor. Pure copper has extremely high corrosion resistance; after being used for a period of time, a layer of green oxide forms on its inner surface. But it has basically no effect on the pipe’s lifespan, flow rate, or resistance to the fluid. Patina is harmless to human health and has a certain ability to kill bacteria. There are two methods for installing plastic-reinforced copper pipes: the clamp-type and the welding type, with the welding method being more reliable. 3. Copper pipes and stainless steel pipes: Apart from their poor thermal insulation properties, these pipes have excellent other characteristics such as strength, service life, and resistance to fluid flow, making them suitable for use as cold water pipes. If used for hot water transmission, a thermal insulation sleeve should be added. The connection method is mainly bayonet-type, and copper pipes can also be welded. 4. Inner plastic-coated galvanized cast iron pipes involve coating the inner wall of a regular galvanized pipe with a layer of plastic, which gives them corrosion resistance, low resistance to flow, and good thermal insulation properties; at the same time, they retain the high strength associated with galvanized pipes. These pipes are mostly connected using ribbed joints. 5. Plastic pipes: As long as the material used for plastic pipes meets the standard requirements, they can possess sufficient strength, durability, safety, and hygiene. It has the best insulation performance of all pipes. Plastic pipes are welded using heat fusion, which ensures high reliability; as long as the welding is done properly and pressure testing shows no issues, there will be no leaks or failures at the welded areas