EGR Backpressure Transducer: Description and Operation

Fig.49 - Integral EGR Valve Exhaust Back-pressure Transducer:

This valve, Fig. 49, performs the same function as the non-integral back pressure transducer used on some systems. The valve assembly has an internal exhaust gas chamber with a transducer diaphragm which senses exhaust back pressure through a hollow stem. When back pressure is low, vacuum is bled through the transducer valve and the EGR valve stem remains closed. When back pressure increases, the transducer diaphragm moves up and closes the transducer valve vacuum bleed hole.

With the vacuum bleed closed, the EGR valve opens, allowing exhaust gas to flow into the intake manifold. Because the EGR outlet is always exposed to manifold vacuum and EGR gas inlet flow is restricted by an orifice, back pressure at the transducer drops when the EGR valve opens. When the back pressure drops, the vacuum bleed hole opens, closing the EGR valve and allowing pressure to build up again. The cycle is continually repeated, modulating the flow of exhaust gas into the intake manifold.