Std type diaghragm valves will not work as they introduce an air leak due to the nature of the design, as the Escort RS Turbo has a metering unit it cannot and will not run if it has an air leak of this size.
The twin piston valve has a secondary circuit to block the air leak if there is no positive pressure present.
Hai sa-ti spun o treaba cu BOV-urile.....eu am o Calibra Turbo.....si am schimbat vreo 4 BOV-uri pana acum printre care 2 twin piston de Subaru STI.............pana nu mi-am comandat exact pentru motorul meu nu mi-a mers nici una........asa ca ai grija ce cumperi.........Eu mi-am comandat de la FORGE MOTORSPORT un BOV twin piston si functioneaza impecabil(150E).