pipe fitting, pipe coupling, pipe connector
A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded.

The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. By careful selection, installation and maintenance of couplings, substantial savings can be made in reduced maintenance costs and downtime.


2 Types
2.1 Rigid
2.1. 1 Sleeve coupling
2.1. 2 Flange coupling
2.1. 3 Clamp or split-muff coupling
2.1. 4 Tapered shaft lock
2.1. 5 Hirth
2.2 Flexible
2.2.1 Bush pin Type flange coupling
2.2. 2 Beam
2.2. 3 Constant velocity
2.2. 4 Diaphragm
2.2. 5 Disc
2.2. 6 Fluid
2.2. 7 Gear
2.2. 8 Oldham
2.2. 9 Rag joint
2.2.10 Universal joint
2.2.11 Others
3 Requirements of good shaft alignment / good coupling setup
4 Coupling maintenance and failure
5 Checking the coupling balance
6 See also
7 References
8 External links

Quick joints of aluminum pipe fitting
Body Material:	Aluminum, stainless steel, copper
Sealing material	Nitrile butadiene rubber(NBR), polyurethane, fluorine rubber, ptfe, ethylene propylene rubber
Size:	1/2 ", 3/4 ", 1 ", 1 1/4 ", 1 1/2 ", 2 ", 2 1/2 ", 3 ", 4 ", 5 "and 6"
Steel pipe sizes:	DN8 DN10, DN15, 3/4 ", DN25, DN32, DN40, (DN65, DN80, DN100, DN125, DN150)
eight models:	A, B, C, D, E, F, DC, DP DF.
Nominal pressure:	1.6-7Mpa
Applicable temperature:	- 30 ~ 120 ºC(aluminum), -20~+230ºC(stainless steel)
Applicable medium:	Petroleum and natural gas, transport machinery manufacturing, aerospace, metallurgy, chemical industry, transportation, electricity, central heating, vacuum, cooling, oil, gas, water, acid, etc
Thread standard:	the NPT, PT and PS DIN, ZG,G,BSPT, SBP, DIN259/2999
Connection:	Male/female Threaded, flange connection, welding, hose, Ferrule, camlock coupling, union.

Rigid
A rigid coupling is a unit of hardware used to join two shafts within a motor or mechanical system. It may be used to connect two separate systems, such as a motor and a generator, or to repair a connection within a single system. A rigid coupling may also be added between shafts to reduce shock and wear at the point where the shafts meet.

When joining shafts within a machine, mechanics can choose between flexible and rigid couplings. While flexible units offer some movement and give between the shafts, rigid couplings are the most effective choice for precise alignment and secure hold. By precisely aligning the two shafts and holding them firmly in place, rigid couplings help to maximize performance and increase the expected life of the machine. These rigid couplings are available in two basic designs to fit the needs of different applications. Sleeve-style couplings are the most affordable and easiest to use. They consist of a single tube of material with an inner diameter that's equal in size to the shafts. The sleeve slips over the shafts so they meet in the middle of the coupling. A series of set screws can be tightened so they touch the top of each shaft and hold them in place without passing all the way through the coupling.

Clamped or compression rigid couplings come in two parts and fit together around the shafts to form a sleeve. They offer more flexibility than sleeved models, and can be used on shafts that are fixed in place. They generally are large enough so that screws can pass all the way through the coupling and into the second half to ensure a secure hold. Flanged rigid couplings are designed for heavy loads or industrial equipment. They consist of short sleeves surrounded by a perpendicular flange. One coupling is placed on each shaft so the two flanges line up face to face. A series of screws or bolts can then be installed in the flanges to hold them together. Because of their size and durability, flanged units can be used to bring shafts into alignment before they are joined together. Rigid couplings are used when precise shaft alignment is required; Shaft misalignment will affect the coupling's performance as well as its life. Examples:

Sleeve coupling
A sleeve coupling consists of a pipe whose bore is finished to the required tolerance based on the shaft size. Based on the usage of the coupling a keyway is made in the bore in order to transmit the torque by means of the key. Two threaded holes are provided in order to lock the coupling in position.

Sleeve couplings are also known as Box Couplings. In this case shaft ends are coupled together and abutted against each other which are enveloped by muff or sleeve.