Abstract: Sub-surface water is pumped through a bore hole to an oil-bearing formation by a pump installation in the bore hole including a submergible pump and an adjustable control valve at the discharge side of the pump. The control valve closes automatically when the pump is not operating to prevent reverse flow and loss of flooding pressure and to insure a back pressure on the pump during starting, and is controlled hydraulically from the surface of the earth to vary the flow to the oil-bearing formation. A novel control valve structure provides accurate and reliable control without unduly restricting the flow volume.