Bore-hole pump

In contrast to most conventional valves, in which the shut-off element moves in the flow direction while the valve opens, and moves counter to the flow direction while the valve closes, the further development of claim 4 is advantageous, according to which the valve is closed in the flow direction. The hydrostatic pressure in the bore-hole here reinforces the sealing action of the shut-off element, which is pressed into its seat. However, an essential advantage is that, with this design, the valve closes automatically when there is a sudden pressure drop in the solvent, e.g. because of break down of the pump at the surface. In the case of an accident, no undiluted, viscous petroleum can enter the pump part, which would make restart of the bore pumps difficult.