Hi,I would like to know if choked flow can occur in a valve even if the velocity of air passing through the valve has not reached Mach 1.Also how will I determine is the flow is choked or not, given I know the upstream and downstream pressures.Chocked flow implies velocity is at sonic value, that is at Mach number of 1.Take a look to the Venturi's effect: it could be useful.If downstream pressure is less than P(crit)=P(upstream)*(2/(k+1))^(k/(k-1)Then the flow is critical and velocity is 1.0 M. For air this works out to 0.528 times upstream pressure (in absolute units). For typical natural gas (i.e., k=1.28) it is 0.549 times upstream pressure.

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