THREADED CONNECTORS.- Threaded connectors (fig. 3-38) are used in low-pressure pipe systems. The connectors are made with standard pipe threads cut on the inside surface of the connector. The end of the pipe is threaded on the outside for connecting with the connector. Standard pipe threads are tapered slightly to ensure a tight connection.

Figure 3-37.- Correct and incorrect installation of flexible hose.

Figure 3-38.- Threaded pipe connectors.

To prevent seizing, you can apply a suitable pipe thread compound to the threads. When a compound is applied to the threads, the two end threads are to be kept free of the compound so that it will not contaminate the fluid. Pipe compound, when improperly applied, may get inside lines and harm pumps and control equipment. Because of this reason many manufacturers forbid the use of such compounds when fabricating the piping for a system.

Another material used on pipe thread is sealant tape, made by TEFLON TM . This tape is made of polytetraflouroethylene (PTFE), which provides an effective means of sealing pipe connections and eliminates the need of having to torque connections to excessively high values to prevent leakage. It also provides for ease in maintenance whenever it is necessary to disconnect pipe joints.

FLARED-TUBE CONNECTORS.- Flared-tube connectors are commonly used in circulatory systems consisting of lines made of tubing. These connectors provide safe, strong, dependable connections without the necessity of threading, welding, or soldering the tubing. The connector consists of a fitting, a sleeve, and a nut (fig. 3-39).

The fittings are made of steel, aluminum alloy, or bronze. The fitting used in a connection should be made of the same material as that of the sleeve, the nut, and the tubing. For example, use steel connectors with steel tubing and aluminum alloy connectors with aluminum alloy tubing. Fittings are made in union, 45- degree and 90-degree elbows, tees and various other shapes (fig. 3-40).

Tubing used with flare connectors must be flared before assembly. The nut fits over the sleeve, and when tightened, draw the sleeve and tubing flare tightly against the male fitting to form a seal.

The male fitting has a cone-shaped surface with the same angle as the inside of the flare. The sleeve supports the tube so vibration does not concentrate at the edge of the flare and distributes the shearing action over a wider area for added strength. Correct and incorrect methods of installing flared-tube connectors are shown in figure 3-41. Tubing nuts should be tightened with a torque wrench to the value specified in applicable technical manuals.