There is no set schedule for lubricating wafer double door check valves, as the frequency depends on several factors:
Process fluid characteristics
Fluids that are dirty, corrosive or contain solids require more frequent lubrication.
Temperature
Higher temperatures cause lubricants to break down faster. Valves in hot processes need relubing more often.
Frequency of operation
Valves that open/close multiple times per day see more movement than infrequently used valves.
Environment
Harsh, wet or highly-vibrating environments accelerate wear and breakdown of lubrication.
As general guidelines:
Clean, non-corrosive services
Relube hinges/pivot points annually.
Moderately dirty or high heat services
Relube every 6 months.
Severe services (abrasive, chemical, heat)
Relube every 3 months or as needed.
Infrequent use valves
Relube if exposed to elements or after major shutdowns.
Always use a lubricant compatible with the process fluid. And inspect valves regularly for any signs of sticking, wear or damage that may require more timely lubrication or maintenance. Relubing prevents premature failure.