In addition to rotating and reciprocating sleeves and reciprocating valves, the rotating valve has been tried, in common with any number of other devices intended to supplant the ordinary poppet valve. This arrangement on a multicylinder motor consisted of a single valve for all the cylinders, which extends along the top or side of the cylinder head and is driven by shaft, chain, or otherwise, at one end. Naturally, this necessitated having the ports cut very accurately in the exterior of the valve, or rather the sleeve - for it usually assumed the form of a hollow shell - for not alone did it act as inlet and exhaust manifold but also as the timing device. This multiplicity of functions seems to have been its undoing, for the latest types using valves of this form have no longer one shell as at first, but a pair, one for the exhaust valves and one for the inlet valves. In the latter shape these have been more successful, but not sufficiently so to bring them into competition with the poppet and Knight sleeve valve forms.
A motor - a two-cycle motor by the way - which has been very successful in motorboat and aeroplane work although not much used for motorcars, is the Roberts, shown in Fig. 37, with the valve in Fig. 38. This valve is for the inlet ports only, and is located inside the crank case, while the cylinders exhaust freely into the open air, the exhaust issueing directly from the cylinders.