A retainer for movably securing a valve member within a fluid bore of a pump comprises a retainer head which includes at least one peripheral groove and a retainer hub which is connected to or formed integrally with the retainer head. The valve member is movably coupled to the retainer hub, and the retainer head is movable to position the groove over a radial protrusion in the fluid bore. In this position, the retainer is secured to the pump and the valve member is accordingly movably secured within the fluid bore.