The accumulation of particulate material on the valve guides (26) of slide valves is inhibited by providing the valve guides (26), and the shelves (34) which support them with slots (36, 38) which allow the particulate material to pass therethrough. The valve guides (26) may be mounted on their respective valve guides (26) by respective tangs (40) which permit differential expansion between the valve guide (26) and the shelf (34).