A piston pump is provided comprising a cylinder with an inner cylinder wall and a working space. The piston pump includes a piston inside the cylinder and has a piston head with a first and second projections extending from its lateral surface to the cylinder wall. These first and second projections enclose a cavity between the piston head and the cylinder wall. The piston head also includes a channel for routing a flushing fluid to the cavity. The first and second projections are configured to promote flow of the flushing fluid out of the cavity and into the working space of the cylinder.