English to Italian Tech/Engineering Automotive / Cars & Trucks Cambi automatici

Sto traducendo un testo automotive in inglese americano e trovo questa frase:

3-5-Reverse Clutch Regulator Valve
The 3-5 reverse clutch regulator valve spring force moves the valve to allow 35 reverse clutch fluid from the 3-5 reverse clutch to pass through the valve and enter the exhaust backfill fluid circuit. The 35 reverse clutch fluid then enters the exhaust backfill fluid circuit and is routed through orifice #30 to the exhaust backfill pressure relief valve where excess pressure is exhausted.

(per altre frasi, vedere http://teamzr1.com/ubbthreads/ubbthreads.php?ubb=showflat&Nu...

Domanda: come tradurre "exhaust backfill"? Io non l'ho mai sentito ma mi son fatta un'idea. Qualcuno di voi utilizza più regolarmente l'inglese tecnico americano?

Grazie mille in anticipo!
silvia