The control valve is operated by a vacuum servo with the vacuum control valve mounted close to the main control valve to reduce switching delays. The main control valve vents the crankcase of the IC engine or controls the recycling of exhaust gasses. The main control valve has a control membrane (78) arranged in parallel with an aux. membrane (110). The two valves are mounted in the same plastic moulded housing and the vacuum feed is connected directly to the solenoid control valve. The main valve is mounted in a section of duct (62) which clips into the inlet manifold duct. The return exhaust feed is via a side flange (10) and integral duct sleeve (40) with the valve element closed off the end.
