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Why do centri have blowoff valves while PD have bypass?
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- Jaxson
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- #2
Most people consider it a blow off valve if it vents to atmosphere. A centrifugal is a turbo a belt driven turbo so you can run a bypass valve by routing it back Into the air intake or blow off and vent to atmosphere. In a PD blower there’s not an effective way to blow off to atmosphere so they route it back into the rotors or before the rotors
engineermike
Well-Known Member
The centrif blowoff/bypass valve is to protect the compressor from “deadheading”. When you close the throttle the air has nowhere to go so it would go backwards through the compressor wheel. This is called “surge” and is destructive over time. Some go to atmosphere and some back to the sc inlet. It only matters if it’s a MAF system since the air is generally metered and fuel is added for it.
A PD blower is downstream of the throttle blade, so when you close the throttle it starves the compressor of air and doesn’t actually hurt anything, so it doesn’t need the same protection. A bypass valve just improves part throttle efficiency and reduces IAT’s since the blower is no longer building pressure with the bypass open at part throttle.
A PD blower is downstream of the throttle blade, so when you close the throttle it starves the compressor of air and doesn’t actually hurt anything, so it doesn’t need the same protection. A bypass valve just improves part throttle efficiency and reduces IAT’s since the blower is no longer building pressure with the bypass open at part throttle.
