The SAE 4-bolt split flange connection is a face seal. The shoulder containing the seal must fit squarely against the mating surface and be held there with even tension on all bolts.

The shoulder, in which the 0-ring is nested, protrudes past the flange halves by 0.010-0.030 in. This is to insure that the shoulder will make contact with the mating accessory surface before the flange does. The flange halves overhang the shoulder on the ends so that the bolts will clear the shoulder.

Potential for leaks. This connection is very sensitive to human error and bolt torquing. Because of the shoulder protrusion and the flange overhang, the flanges tend to tip up when the bolts are tightened on one end, in a seesaw fashion. This pulls the opposite end of the flange away from the shoulder and when hydraulic pressure is applied to the line, it pushes the shoulder back into a cocking position (Figure 6.26).

Corrective measure. All bolts must be installed and torqued evenly. Finger tightening with the use of feeler gauges will help to get the flanges and shoulder started squarely. When the full torque is applied to the bolts, the flanges may bend down until they bottom on the accessory. This also causes the bolts to bend outward (Figure 6.27). Bending of the flanges and bolts tends to lift the flange off the shoulder in the center area between the long spacing of the bolts (Figure 6.28).

When pipes and/or hose are joined together with this connection, the conditions become more severe because the spacing between mating flanges now is doubled and becomes a 0.020-0.060 in. gap. All conditions are now multiplied by 100%.

Bending of bolts and flanges soaks up much of torque value (Figure 6.29). High torque is required on all bolts which must be Grade 5 or better because much of the torque is lost in overcoming the bending of the flanges and bolts (Figure 6.30).

Proper installation. Lubricate the 0-ring before assembly. All mating surfaces Proper must be clean. All bolts must be evenly torqued. Do not tighten any one bolt fully before going to the next one. Torque to the values shown in Figure 6.31.

Because of the tolerance build up in all component parts plus the bolt bending, the flange halves can move sideways in direction A and B (Figure 6.32). This can lessen the shoulder contact with the flange to zero in the center area between the long bolt spacing. When flanges have a large radius on the edge "D," the leakage problem becomes even greater with the above conditions (Figure 6.33). Make certain flanges have a small break at edge "D" to insure full contact with the shoulder (Figure 6.34).

In spite of all of the care required for use of these flanges they have provided good service with minimal trouble when properly installed. Mobile and utility maintenance vehicles have many years of satisfactory service in the most hostile environment in which they must function with minimal maintenance.

The flange of Figure 6.35 employs a 15 degree port with matching nose on the flange. The flange is fitted with an elastomeric seal to backup the basic metal-to-metal seal (NWD International, Inc.; patented).

OTHER CAUSES OF LEAKS

Many other conditions can cause external leakage. Vibration (Chapter 5) that can loosen connections is obviously a major culprit. In addition, the troubleshooter should consider the possibility of improper piping assembly, where fittings were not tightened properly in the first place as previously outlined.

Damaged or worn seals (in linear as well as rotary components) are a common cause of leakage. While replacing defective seals, the troubleshooter should also consider steps that might be taken to eliminate or at least minimize seal leakage in the future. For instance, are seals made of the appropriate elastomer? Might a different seal design reduce leakage? Should cylinder rods be specified with different surface finish? Would boots help to extend seal life and thus reduce leakage?

Such thoughts should be communicated to the company's own top management who in turn should review these factors in the future when the company plans to buy additional machinery powered by hydraulics or pneumatics. Good planning before purchasing might help eliminate the necessity for a lot of troubleshooting.