I have several 15mm and 22mm full-bore lever valves from different manufacturers. Some have a flow direction arrow marked on them, others do not. All appear to be symmetrical as far as the flow path is concerned, so it appears to me that orientation of the valve is immaterial. Why do some have the flow direction marked?
CRB
I don't know your particular valves but usually the meaning is that with the flow following the arrow, and the valve closed, the actuator shaft gets isolated from upstream and you can renew the packing without leaks.
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