Abstract: A piston pump is provided comprising a cylinder with an inner cylinder wall. The piston pump comprises at least one working space including fluid intake and fluid outlet, a piston including a piston rod and a piston head. The piston head includes a lateral surface facing the cylinder wall, a front surface facing the working space, a rear surface and at least one piston head channel. Furthermore, the piston head's lateral surface is provided with a first projection and a second projection extending round the entire circumference of the lateral surface and in contact with the cylinder wall, thereby forming an annulus which is defined by the first projection, the second projection, the cylinder wall and possibly the cylinder head's lateral surface between the first and the second projections if the piston head is designed so that the projections are provided with an axial spacing between them.