Knowledge of pipe joints
Hydraulic terminology refers to the components in hydraulic systems that connect pipelines or mount pipelines on hydraulic components. This is a general term for detachable connectors in fluid pathways.
Pipe joints are one of the most important components of fluid handling systems, installed at critical connection points, and must provide sealing performance to improve operational safety and efficiency. There are many different accessories to choose from for pipe joints, each type suitable for different needs. How should we make the right choice? Let's take a look at the common available options.
Types of connectors
NPT is the abbreviation for National (American) Pipe Thread, which belongs to the American standard of 60 degree taper pipe thread and is used in North America. The national standard can be found in GB/T12716-1991PT is the abbreviation for Pipe Thread, which is a 55 degree sealed taper pipe thread and belongs to the Wyeth thread family. It is commonly used in the water and gas pipe industry, with a taper of 1:16.The national standard can be found in GB/T7306-2000. G is a 55 degree non threaded sealing pipe thread, belonging to the Wyeth thread family. The symbol G represents cylindrical thread. The national standard can be found in GB/T7307-200. In addition, the 1/4, 1/2, and 1/8 marks in the thread refer to the diameter of the thread size, measured in inches.Industry insiders usually refer to thread size in minutes, with one inch equal to 8 minutes, 1/4 inch equal to 2 minutes, and so on. G is the general term for pipe threads (Guan), and the 55 and 60 degree divisions are functional and commonly known as pipe circles. The thread is machined from a cylindrical surface.ZG, commonly known as pipe cone, refers to a thread that is processed from a conical surface. Generally, water pipe joints are like this. The old domestic thread standard is marked as Rc, and the external thread is marked as R. Metric threads are represented by pitch, while American and British threads are represented by the number of threads per inch. This is their biggest difference. Metric threads have a 60 degree equilateral profile, British threads have a 55 degree isosceles profile, and American threads have a 60 degree profile.Metric threads are measured in metric units, while American and British threads are measured in imperial units. Pipe threads are mainly used for connecting pipelines, with tight fit between internal and external threads, available in two types: straight pipes and tapered pipes. The nominal diameter refers to the diameter of the connected pipeline, and obviously the thread diameter is larger than the nominal diameter. 1/4, 1/2, and 1/8 are the nominal diameters of imperial threads, measured in inches.
● Classification.
Hydraulic hoses, high-pressure ball valves, quick couplings with unusual intentions, sleeve type fittings, welded fittings, high-pressure hoses. Transition type pipe joint, sleeve type pipe joint, three-way pipe joint, non-standard pipe joint, expansion type pipe joint, right angle pipe joint, rotary pipe joint, quick connector, stainless steel pipe joint, copper joint.
● application
A pipe joint is a connecting tool between pipelines, which is a detachable connection point between components and pipelines. It plays an indispensable role in fittings and is one of the two main components of hydraulic pipelines. Pipe joints are used for straight connections such as instruments, and the connection forms include socket welding or threaded connections. Mainly used for small-diameter low-pressure pipelines, for parts that require frequent assembly and disassembly, or as the final adjustment for pipelines using threaded fittings.The structural form should adopt a metal surface contact sealing structure, and the gasket sealing structure is usually used for conveying general pipelines such as water, oil, and air, and is made of malleable cast iron material. In addition, usage requirements and price are also factors considered when selecting.The connection methods of pipelines and pipe joints in hydraulic systems are also different, and the threaded end of the pipeline is used for connection. Cone threads, relying on their own vertebral body to tighten and sealed with materials such as polytetrafluoroethylene, are mainly used in medium and low-pressure hydraulic systems.The sealing effect of fine thread is very good and is often used in high-pressure systems. However, it requires the use of combination washers or O-rings to seal the end face. Sometimes, copper washers are also used, which are more suitable for connecting pipes with thick walls. Its main components are the joint body, connecting pipe, and nut.When in use, embed the joint body into the target and use the gasket mentioned earlier to seal the end face. Rubber sealing is used between the joint body and the connecting pipe, and sometimes spherical sealing is also used. Due to the fact that pipe joints are detachable connecting components, they must not only meet the requirements of stable connection, strong sealing, reasonable size, low pressure loss, good process performance, etc., but also meet the requirements of convenient disassembly and assembly.Therefore, do not underestimate those small pipe joints, because only their existence can support the existence of the entire hydraulic system.
Structure of pipe joints
A standard pipe joint consists of a nut, a retaining ring (some only have one retaining ring), a joint, and a pipe.
The shape of the standard pipe joint installed is shown in the figure:
The principle of sealing the pipe joint is to tighten the nut to compress the pipe and deform it, forming a seal.
●Types of pipe joints
Example of name annotation:
1/4 tube: a tube representing 1/4 inch OD
Tube 1/4: indicates the connector for connecting 1/4 inch OD tubes
8mm tube: a tube representing 8mm OD
Tube 8mm: indicates the joint for connecting 8mm OD tubes
The main sizes of the imperial system are 1/4, 3/8, and 1/2
The main sizes of the metric system are 6, 8, 10, and 12mm
Material selection for pipe joints
Pipe joints can be made of various materials, including stainless steel such as 316 SS, 6-Moly alloy, and 2507 Super Duplex, as well as other alloys, with 316 SS being the most common choice. However, components made of higher alloy materials with at least 12% nickel and 17% chromium have better corrosion resistance. Nickel can stabilize the austenitic structure of stainless steel and help provide more ductile or non brittle materials for a wider temperature range and system media. Chromium forms a passive oxide surface layer for manufacturing stainless steel, providing corrosion resistance, while higher levels of chromium can increase resistance to localized corrosion.
