In piston machines such as axial piston compressors of both the swash plate and wobble plate type currently used in motor vehicle air conditioning systems, the suction ports for the respective pumping chambers (piston cylinders) are typically formed in a valve plate and are each normally closed by a reed valve that seals on the valve plate about the respective port and is formed integral with the other reed valves in a flat thin metal disc. When the pressure of the fluid (e.g. gaseous refrigerant) in the piston cylinder reduces below that in the compressor's suction chamber sufficiently to overcome the spring force in the reed valve, the reed valve lifts off its sealing surface allowing the then expanding pumping chamber to suck the refrigerant past the sides of the reed valve. The reed valve is a compact device that is easy to manufacture and assemble but does present more flow restriction than for example a poppet valve. And because of its cantilever mounting, the reed valve experiences stress levels that increase with increasing opening force and can therefore become a limiting factor.