Technical Handbook
Rev. 1.6
WWW.ROTREX.COM
Page 24 of 41
Designing and handling interfaces
4.5.2 Ducting
Proper attention to air ducting is core to a healthy forced induction system. The following
section should aid in understanding the main aspects involved in designing a ducting
system for a Rotrex supercharger installation.
A blow-off-valve (BOV) or recirculation valve is optional but recommended in most
applications to prevent surge under deceleration. It is critical to use an appropriate size
for the specific installation and install it correctly. Surge can occur when the supercharger
increases pressure ratio at low air flow (left border of the flow map, see technical
datasheets). Under surge, air flow through the compressor can no longer be maintained
and momentary backflow occurs resulting in a characteristic chirping sound. Surge can be
caused by a blocked inlet air stream, such as a throttle valve or a clogged air filter.
Continuous operation in surge will cause damage to the supercharger.
To prevent surge,
it is necessary to relieve the system from excessive pressure through re-circulation or
blow-off. A BOV will prevent surge by allowing air to circulate from outlet to inlet of the
supercharger under vacuum conditions. In case re-circulation is directed to the inlet of the
supercharger,
it is very important that the re-circulation valve is positioned after an
intercooler
, to avoid excessive heat soak of the supercharger. Under cruise and/or urban
driving with an incorrectly mounted re-circulation valve, the inlet temperature of the
supercharger can easily exceed 200°C.
Incorrectly placed re-circulation valve will cause
damage to the supercharger and voids warranty.
If an intercooler is not installed,
excessive pressure must be relieved through blow-off.
The crankcase ventilation system (Positive Crank Ventilation PCV) is to be connected to
the inlet of the supercharger to prevent pressurizing the crankcase. If the vehicle is
equipped with an air mass meter (AMM), the crankcase ventilation must be connected
downstream of the AMM to prevent oil vapours from corrupting the signal of the AMM.
Air filter
Air mass
meter
Supercharger
Intercooler
Recirc.
valve
Throttle
body
Manifold
Summary of Contents for C15-16
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