In message , Phil Addison
writes

The literature refers to a 'wedge' type actuator. Anyone know what that
means?

Where did you find that literature Roger? I couldn't find anything
further on that site. Mark says of his "its like a rubber wedge".

There is a style of valve with a triangular (like a cheese) section

This is to make the rubber perpendicular to each port as it swings from
one side to the other (badly explained, but YKWIM)

--
geoff