Abstract: A radial piston pump wherein the drive shaft for the pistons in radially extending cylinders of the housing has an eccentric which moves the pistons outwardly against the opposition of springs. The inlet port of the housing communicates with the cylinders by way of a first passage which contains a reciprocable valve member and can discharge fluid directly into one of the cylinders. The other cylinders receive fluid from the first passage by way of an annular space which surrounds or is adjacent to the inner end of the shaft and bores which are machined in the housing to connect the annular space with the other cylinders. The outlet port of the housing can receive pressurized fluid from the cylinders by way of check valves. The valve member is biased by a spring to normally assume a first position in which it allows fluid to flow from the inlet port to the cylinders as long as the pressure at the outlet port is within a first range of pressures.