38 can be approximately twenty two degrees on either side of the axis 39 as each cylinder moves through the lower half revolution of the cylinder barrel 16 its bore is open to a lower crescent shaped outlet aperture 42 formed in the valve plate assembly 12 each piston moves outwardly during the lower half revolution displacing fluid through the lower crescent shaped aperture 42 until it reaches its outmost stroke when a piston reaches its outmost stroke its cylinder opening 31 is blocked since the cylinder barrel 16 has rotated the associated opening 31 past the lower crescent shaped aperture 42 as each piston moves through the upper half revolution of the cylinder barrel 16 the associated cylinder bore 32 opens to the upper crescent shaped aperture 30 in the valve plate assembly 12 during the upper half of the revolution of the cylinder barrel 16 each piston strokes inwardly and draws fluid through the upper crescent shaped aperture 30 into the cylinder bore when the piston reaches its innermost position the associated opening 31 having passed the upper crescent shaped aperture 30 is blocked once more before beginning the lower half revolution again as illustrated in fig3 the degree of the swash block angle 38 determines the length of the piston stroke 40 and therefore determine the amount of delivery from the axial pump 10 as the delivery rate increases due to an increased piston stroke 40 there is also an.