like safechav said, there isnt any shit or air getting into the actual inlet as they are TWIN piston dump valves, the second piston that you dont see is the one stopping any leaks and shit passing in/out unless when its dumping.

you may get a bit of shit in the dump valve - maybe - but its never put me off cause i like the noise too. i've had bailey's on all my turbocharged cars, never had any problems.