What is the difference between XV , HV and KV On Off Valve?

Dears In Petrochemical plant we have 3 types of codification of On-Off valves in P&ID which are XV, HV and KV valves.

I want to know what is the difference between the three codification?

XV valves are on/off valves that are typically used to quickly isolated a fluid and typically provide right shut off capabilities. They are not used to modulate or vary the flow.

HV Valves are Hand Valves. Manually operated.

KV Valves are Time, Schedule, Time Rate of Change Valves