Abstract: The pump has a sleeve-like bearer. This contains a bush in which a piston is displaceable along an axis. The bearer inner surface and the bush outer surface are adjacent to one another in parts and are separated from one another in parts by an intermediate space. The inlet of the pump is connected through an intake chamber located at least partly inside the bush and through the piston, via a non-return valve, to a pump chamber, which is connected via another non-return valve to a primary outlet of the pump. The intermediate space connects the inlet and the intake chamber to a secondary outlet which is a distance away, along the axis, from the inlet and the intake chamber. During the operation of the pump, fluid flows from the inlet through the intermediate space to the secondary outlet and cools the bush.

Abstract: The pump possesses an inlet and an outlet for the fluid to be pumped, a housing bounded at one end by an end member and enclosing an inner space, in which a piston is displaceably guide. The inlet is connected, by way of the end members and by way of a first back-pressure valve, with the pump chamber provided between the end member and the piston, said pump chamber being connected, by way of the end member and a second back-pressure valve, with the outlet. The piston is equipped with a third back-pressure valve, which additionally connects the inlet with the pump chamber, and makes it possible to largely prevent--during the suction strokes and particularly during the beginning phases thereof--any pressure drops from occurring, that could cause in the pump chamber the reconversion of fluid from the liquid to the gaseous state.