Bypass valve on Volvo TAMD71

[chrisharris]

Hi all,

Just wondering if one of the volvo experts could explain how the bypass valve is supposed to work? I understand it is designed to reduce smoke on cold start, and possibly at low loads? I know it channels inlet air either through the charge cooler or heater element, but I don't understand how it operates? Is it by sensing vacuum from the inlet manifold? I noticed that on one of my engines the banjo fitting on the end of the actuator cylinder is not attached to anything - eg there is no pipe fitted to the banjo. I assume it was either never fitted, or a previous owner removed it? I have also heard that the mechanisms can seize up - is it worth trying to get them working, will it make a significant difference to cold start smoking?

Many thanks
Chris

 

[volvopaul]

The bypass valve is a round flap inline near the heater element, its sprung loaded when the turbo boosts up it forces the valve open allowing air to pass through the intercooler, it stop air passing into the bypass pipe that goes to the inlet manifold.

 

[chrisharris]

Many thanks VP, so the banjo fitting on the end of the actuating cylinder is not supposed to be fitted to a pipe? I guessed the flap was controlled by vacuum applied via the banjo connector, but could not work out where from....

 

[volvopaul]

There is no pipe to the actuator its controlled by boost pressure, the only pipe on the inlet manifold goes to the injection pump to control the fuel, when the manifold has a positive pressure it controls the governor so not to allow too much fuel being injected and cause black smoke, if the pipe on the inlet manifold is open then you will loose boost pressure.

 

[chrisharris]

Many thanks VP, I understand now..