CAUTION: Check for Cracks. Cracks are stress concentrators and can cause
catastrophic failure of the stem and uncontrolled venting.
4.1.2.2 Also inspect for corrosion pitting. Any corrosion pitting is reason for rejection since it may
indicate more severe corrosion at the threads and the starting point for difficult-to-detect
cracking.
4.1.2.3 All nickel-bearing stainless steels have a likelihood of galling. Wrenching the adjusting nut
without relieving the spring’s load will frequently result in galled stem threads. Always check
for galled threads and chase the threads with a thread die or replace stems with significant
thread damage.
4.1.2.4 The sealing surface is the stem seat (Figure 4-4). Clean the stem seat with emery paper
(400 grit) then wipe it clean with a cloth and a suitable solvent. Run your fingernail over the
seat surface to detect any flaws.
Figure 4-4 Stem Seat Inspection
4.1.3 Valve-Stem Concentricity
4.1.3.1 The valve stem must be straight within 0.010” (maximum). Rotate and center the stem on V-
blocks set up with a dial indicator. If the dial indicator readings are not within the allowable
tolerance, replace the stem or return it to Midland for repair.
Figure 4-5 Valve-Stem Concentricity Check
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