Vacuum Transmitting Valve (VTV)
Blow air through each side of valve. Air should pass freely from side "B" to side "A". (Black to Brown or Gray side) but be restricted from side "A" to "B" (Brown or Gray to Black side). See Figure.
Blow air through each side of valve. Air should pass freely from side "B" to side "A". (Black to Brown or Gray side) but be restricted from side "A" to "B" (Brown or Gray to Black side). See Figure.