English to Italian Tech/Engineering Food & Drink impianto per la produzione della birra

Impianto per la produzione della birra
"Valvola libera" e "valvola vincolata"? come si dice in italiano? Grazie in anticipo per qualsiasi suggerimento

The **free exhaust valve** and **restricted exhaust valve** are closed. The air feeding valves to the membranes are actuated for opening(...)
Air from membranes can be discharged in two ways :
· either freely in atmosphere by opening the **free exhaust valve** for a quick decompression
· or more progressively by opening the **restricted exhaust valve** for a low decompression through the hand-operated valve.