<p>A priming valve for a liquid fuel supply system is arranged in parallel with a fuel metering device and includes a shuttle control element which opens the priming valve during movement, the priming valve being shut at opposite ends of movement of the shuttle. The shuttle is moved by an operating pressure derived from the priming valve inlet via a restrictor and applied to respective ends of the shuttle by a change-over control valve which is operated to deliver a priming charge of fuel.</p>
