Piston pump with compact retention device for a restoring spring

A piston pump comprising a piston, a pressure chamber, a low-pressure region, and a retaining device for retaining a spring element which is designed for restoring a closing element of a valve, the retaining device including a receiving region for receiving and bracing the spring element and an integrally formed sealing region which is in sliding engagement with a surface of the pressure chamber, the retaining device thus sealing off the pressure chamber from the low-pressure region of the piston pump, wherein the sealing region is embodied essentially annularly and enables sealing between the pressure chamber of the pump and the low-pressure region of the pump in the radial direction and the axial direction, and wherein the sealing region includes an annular pressure chamber between the piston and the retaining device, and wherein fluid pressure in the annular pressure chamber increases the sealing in the radial direction, wherein the retaining device includes at least one through opening which connects the inside of the retaining device directly to the annular pressure chamber of the sealing region so that fluid from the pressure chamber of the pump is delivered directly to the annular pressure chamber of the sealing region.