There are two main types of pipe fittings commonly used in heating, ventilation and air conditioning systems; flanged and screwed. Screwed pipe fittings use a male and female thread combination and when screwed together tighten to form the joint. A flanged pipe fitting has a lip or extension projecting at a right angle to its surface. This lip is bolted to the facing lip of the adjacent fitting for added strength. Because of the strength of this fitting, flanged fittings are recommended for 4-inch pipe or larger.
Both of these pipe fittings are used to meke temporary joints because you can ultimately take them apart when needed. If the joint is ever brazed, soldered or welded the join is considered permanent as the join will not come apart. The advantage of these two temporary joints is that it can be easily disassembled for repairs down the road.
The typical pipe fittings can be divided on the basis of the following six functions:
- Reducing or enlarging
- Extension or joining
- Shutoff or closing
- Union or makeup
Reducing or Enlarging Fittings: Both bushing and reducers are examples of reducing or enlarging fittings. Thier function in pipe installations is to connect pipes of different sizes. The difference between a bushing and a reducer is distinguished by their construction. A reducer is a coupling device with female threads at both ends. A bushing has both male and female threads on each end.