A pump head suitable for use in a fuel pump for a common rail fuel injection system, comprises a pump head housing defining a plunger bore and a pumping chamber. Fuel is pressurized within the pumping chamber by a plunger reciprocating within the plunger bore. The pump head housing includes an inlet valve arrangement for controlling fuel flow into the pumping chamber. The inlet valve arrangement includes a valve member movable between open and closed positions in response to fuel pressure within a gallery. The gallery communicates with an external chamber defined by a closure member externally mounted to the pump head housing. In use, the gallery communicates with a source of low-pressure fuel via the external chamber. The pump head housing has a projection which locates the closure member on the pump head housing.