Under NSTM 503, when should L/O seals be replaced?

• A. Leakage exceeds 5 drops per minute, expect leak to stop after 30 minute run time
• B. Routinely at every inspection
• C. When a minor leak is detected
• D. Only after complete pump failure

Answer: (A)

Under NSTM 503, lubrication-oil seals are not replaced on a fixed schedule but based on a measurable leak condition. The standard sets a clear criterion: if the seal leaks at a rate greater than five drops per minute, that indicates the seal has degraded and should be replaced. The 30-minute run time is the period used to observe the seal’s behavior as it operates and seats; some leakage can occur during start-up or warm-up, but after a proper run of about 30 minutes the leakage should settle. If it remains above the threshold after that observation, replacement is required. This approach avoids premature replacement while preventing ongoing oil loss and contamination from a failing seal, and it’s more appropriate than waiting for complete pump failure or replacing at every inspection.