Number of Throttling Valve

[Little Prince]

Dear All,
Is there any special requirement regarding number of throttling valve (J.T. Valve) which regulate refrigerant liquid level in the evaporators?
Is it mandatory to have one in operation and one reserve?
Please advise.
Best

[RANGER1]

Little Prince,
Normally 1 throttling valve for each evaporator.
IS the plant liquid over feed or surge drum mounted above evaporator?
JT , are you referring to Joule Thompson?

[Little Prince]

Little Prince,
Normally 1 throttling valve for each evaporator.
IS the plant liquid over feed or surge drum mounted above evaporator?
JT , are you referring to Joule Thompson?

Actually there is evaporator and there is super heater above it.
I also think of One throttling valve but I was not sure if there is any special regulation.