Doc. #: A-718C, Rev. 1
Page 23 of 36
6.1.10
Seat Insert
(item 31). This is a critical part that must be examined carefully. The crown of the seat has a
full-radius (approximately 1/16"). Run your fingernail around the crown to be sure it is free of any nicks,
scratches or pits. This is a difficult part to re-machine because it has to be trued up with a dial indicator and
held with special jaws that grip just above the collar. Do not choke on the collar because any jaw marks
there may distort it out of tolerance. Also, any chatter or tool marks on the seat crown are potential leak
paths. The O-ring grooves and flat gasket seat surfaces must be free of imperfections that could potentially
cause a leak. If the tongue is to be redressed, use very light choking force to avoid distorting the tongue.
Use a dial indicator to get the part to run true. Do not face the thickness of the collar. The tongue’s
dimensions are 2.245 ± 0.003 inches OD by 1.505 ± 0.003 inches ID. If tolerances are exceeded or the
condition is questionable, do not to take a chance on it; replace it with a new part.
Figure 6-9 Seat Insert
6.2
Special Inspection Considerations
Previous procedures may not cover all conditions encountered in the field. Therefore, it is the responsibility
of the repair agency to obtain approval from Midland for inspection, evaluation, repair and maintenance
procedures not covered herein.
Facilities performing recommended dye-penetration and magnetic-particle testing must carry out such testing
according to a qualified procedure conducted by certified trained personnel.
Evaluation of critical component metal surfaces of the valves after cleaning, inspection and specialized
testing performed by agencies other than the repair facility are the responsibility of the repair facility.
Where numerical tolerances cannot be provided, the disposition of the internal integrity and surface quality
of parts is under the jurisdiction of the repair facility and dependent on its experience and judgment.
