As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
OILY ODOR AND "SMOKE" IN COCKPIT AND CABIN UPON TAKEOFF. SMOKE BEGAN DISSIPATING AFTER CREW TURNED CABIN AIR SWITCH OFF. AIR RETURN BACK TO DEPARTURE WITH UNEVENTFUL LANDING AND TAXI. FOUND BLEED AIR PRESSURE REGULATOR INLINE TO RESERVOIR, BLOW OUT DUE TO FAILED CHECK VALVE. ALLOWED HYD FLUID TO BACKFLOW INTO PRESSURIZATION SYS. REPLACED BLEED AIR PRESSURE REGULATOR, FILTER AND CHECK VALVE. REMOVED AND CLEANED PRESSURIZATION SHUTOFF VALVE. OPS AND LEAK CHECK GOOD.