Doc. #: A-718C, Rev. 1
Page 13 of 36
4.0 Maintenance Instructions
NOTE
: It is important that a periodic retest and preventative maintenance program be
established. The DOT and AAR have set forth a retesting interval that should be considered the
maximum length of time between tests. To assist in scheduling valves for retest, a tag showing
the installation date is attached to the valve.
However, there are two measurements that will
indicate if the valve should be repaired sooner, regardless of the scheduled retest date:
1. If there is more than 7/8" between the bottom of the hand wheel and the top of the bonnet in the
closed
position, the Teflon
®
seat has been deformed and needs immediate replacement;
Figure 4-1 Hand Wheel and Bonnet
2. If the top of the packing screw (item 7) is within 3/8" of being flush with the yoke surface, the valve
must be repacked since no adjustment is remaining.
Figure 4-2 Packing Screw
If either condition exists, the valve must be removed and repaired. When the valve is removed from
the cover plate, ensure the valve and stem is protected from damage.
NOTE:
It is an AAR requirement (refer to D4.04) that new O-rings be installed when a valve is
retested.
4.1
Prior to Maintenance Tasks Performed
4.1.1
Retesting of Valves in Storage
Midland valves are factory set and sealed. If they have been left in their original shipping containers, are
undamaged, and are no more than six (6) months old; they may be installed without being retested.
