Control valve

A pressure unloading delivery valve for location between a pump outlet of a fuel injection pump and a pipeline connecting the outlet to a fuel injection nozzle of a compression ignition engine comprising an annular valve member biased into engagement with a valve seat formed about a flow channel through which fuel flows from the pump outlet to the pipeline, the valve member being lifted from the valve seat to allow fuel to flow to a delivery valve outset connected to the pipeline, a plunger slidable in said valve member, resilient means biasing the plunger in a direction away from the seat, said plunger following delivery of fuel by the pump and closure of the valve member onto the valve seat, moving under the action of the resilient means to control said pressure, and damping means operable to damp the movement of said plunger after a predetermined movement of the plunger against the action of said resilient means, in which said damping means comprises a piston mounted on the plunger, said piston cooperating with a cylindrical surface to form on one side a dash pot chamber, said chamber being in communication with said pump outlet until the plunger has moved through said predetermined movement.