Fittings and Connectors

Fittings are used to connect the units of a fluid-powered system, including the individual sections of a circulatory system. Many different types of connectors are available for fluid-powered systems. The type that you will use will depend on the type of circulatory system (pipe, tubing, or flexible hose), the fluid medium, and the maximum operating pressure of a system. Some of the most common types of connectors are described below:

Threaded Connectors. Threaded connectors are used in some low-pressure liquidpowered systems. They are usually made of steel, copper, or brass, in a variety of designs (Figure 2-24). The connectors are made with standard female threading cut on the inside surface. The end of the pipe is threaded with outside (male) threads for connecting. Standard pipe threads are tapered slightly to ensure tight connections.

To prevent seizing (threads sticking), apply a pipe-thread compound to the threads. Keep the two end threads free of
the compound so that it will not contaminate the fluid. Pipe compound, when improperly applied, may get inside the lines and harm the pumps and the control equipment.

Flared Connectors. The common connectors used in circulatory systems consist of tube lines. These connectors provide safe, strong, dependable connections without having to thread, weld, or solder the tubing. A connector consists of a fitting, a sleeve, and a nut (see Figure 2-25).

Fittings are made of steel, aluminum alloy, or bronze. The fittings should be of a material that is similar to that of a sleeve, nut, and tubing. Fittings are made in unions, 45- and 90-degree elbows, Ts, and various other shapes. Figure 2-26, page 2-24, shows some of the most common fittings used with flared connectors.

Fittings are available in many different thread combinations. Unions have tube connections on each end; elbows have tube connections on one end and a male pipe thread, female pipe thread, or a tube connection on the opposite end; crosses and Ts have several different combinations.

Tubing used with flared connectors must be flared before being assembled. A nut fits over a sleeve and, when tightened, draws the sleeve and tubing flare tightly against a male fitting to form a seal. A male fitting has a cone-shaped surface with the same angle as the inside of a flare. A sleeve supports the tube so that vibration does not concentrate at the edge of a flare but that it does distribute the shearing action over a wider area for added strength. Tighten the tubing nuts with a torque wrench to the value specified in applicable regulations.

If an aluminum alloy flared connector leaks after tightening to the specified torque, do not tighten it further. Disassemble the leaking connector and correct the fault. If a steel connector leaks, you may tighten it 1/6 turn beyond the specified torque in an attempt to stop the leak. If you are unsuccessful, disassemble it and repair it.

Flared connectors will leak if—
• A flare is distorted into the nut threads.
• A sleeve is cracked.
• A flare is cracked or split.
• A flare is out-of-round.
• A flare is eccentric to the tube’s OD.
• A flare’s inside is rough or scratched.
• A fitting cone is rough or scratched.
• The threads of a fitting or nut are dirty, damaged, or broken.

Flexible-Hose Couplings. If a hose assembly is fabricated with field attachable couplings (Figure 2-27), use the same couplings when fabricating the replacement assembly, as long as the failure (leak or break) did not occur at a coupling. If failure occurred at a coupling, discard it.

When measuring a replacement hose assembly for screw-on couplings, measure from the edge of a retaining bolt (Figure 2-28). Place the hose in hose blocks and then in a bench vice (Figure 2-29). Use the front or rear portion of a hacksaw blade for cutting. (If you use the middle portion of a blade, it could twist and break.) For effective cutting, a blade should have 24 or 32 teeth per inch. To remove an old coupling on a hose assembly that is fabricated with permanently attached couplings, you just discard the entire assembly (see Figure 2-30).

Reusable Fittings. To use a skived fitting (Figure 2-31, page 2-26), you must strip (skive) the hose to a length equal to that from a notch on a fitting to the end of the fitting. (A notch on a female portion of a fitting in Figure 2-31 indicates it to be a skived fitting.) To assemble a conductor using skived fittings—

• Determine the length of the skive.
• Make a cut around the hose with a sharp knife. Make sure that you cut completely through the rubber cover of the hose.
• Cut lengthwise to the end of the hose (Figure 2-32). Lift the hose flap and remove it with pliers.
• Repeat the process on the opposite end of the hose.
• Place the female portion of the fitting in a bench vice (Figure 2-33) and secure it in place.
• Lubricate the skived portion of the hose with hose lubricant (hydraulic fluid or engine oil, if necessary).
• Insert the hose into the female socket and turn the hose counterclockwise until it bottoms on the shoulder of the female socket, then back off 1/4 turn.
• Place the female socket in an upright position (Figure 2-34, page 3-28) and insert the male nipple into the female socket.
• Turn the male nipple clockwise (Figure 2-35, page 3-28) until the hex is within 1/32 inch of the female socket.
• Repeat the above process on the opposite end of the hose.

When assembling conductors using nonskived-type fittings, follow the above procedures. However, do not skive a hose. Nonskived fittings do not have a notch on the female portion of a fitting (Figure 2-36, page 2-28).

Figure 2-37, page 2-28, diagram A, shows a female hose coupling. One end of the hose has a spiral ridge (course thread) that provides a gripping action on the hose. The other end (small end) has machine threads into which the male, fixed or swivel nipple, is inserted.

Figure 2-37, diagram B shows the male adapter, and diagram C shows the male and the female swivel body. These fittings contain a fixed or swivel hex-nut connector on one end. The opposite end is tapered and has machine threads that mate with the threads in a female fitting. With a long taper inserted into a hose and screwed into a female coupling, the taper tends to expand a hose, forcing it against the inside diameter of a female fitting.

Figure 2-38 shows the assembly of a clamp-type coupling. If you use this coupling, do not skive the hose. Lubricate the ID of a hose and the OD of a stem. Clamp a hose stem in a bench vice and install a hose. Turn the hose counterclockwise until it bottoms against the shoulder of the stem (Figure 2-38, diagram A). If you do not have a vice, force the stem into the hose by pushing or striking the stem with a wooden block. Place the clamp halves in position (Figure 2-38, diagram B) and draw them together with a vice or with extra long bolts until the standard bolts protrude far enough to grip the nuts. Remove the extra long bolts and place retaining bolts through the clamp. Tighten the nuts until you get the required torque (Figure 2-38, diagram C).

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