Fluid machine with secondary low pressure port opening before controlled primary valve

The machine comprises a controller, a cyclically varying volume working chamber 100, an electronically controllable primary low pressure valve 106 and a secondary low pressure port 120, each opening to a low pressure manifold 108, 122 in phased relation to the working cycle such that the machine releases working chamber fluid during a motoring stroke prior to opening of the primary low pressure valve to facilitate primary valve opening. In a radial piston machine, the secondary port may comprise an aperture 118 at the piston end of a cylinder which is brought periodically into alignment with a peripheral crankshaft slot 120. The primary valve is actively controlled to determine the net cycle displacement. The low pressure valve and the secondary port are openable concurrently during a portion of at least some working cycles to enable concurrent fluid flow into or out of the working chamber through both. The low pressure valve may close after the secondary port closes.