The Double-Acting Hydraulic Ram pump (DAHR pump) is a deep-well water pump that converts a large-volume low-pressure oscillation at surface level into a high-pressure pumping effect. Based on the historic hydraulic ram pump, invented by the Mongolfier brothers in the 18th century, it uses the Joukowski (water hammer) effect in place of dynamic pistons/seals. The DAHR pump was invented by engineers at Thermofluidics Ltd. (www.thermofluidics.com/) in 2009 to enable solar heat engines such as the NIFTE and manually powered treadle pumps to access deep ground water and pressurise it for use at the surface. It has no moving parts other than non-return (one-way) valves.

This animation shows the operating principle of the DAHR pump. Water is forced to oscillate in a deep U-shaped tube made up of two vertical drive pipes and a 180 degree U-bend. The oscillation is forced by a heat engine, wind, hand or treadle pump (not shown). The U-shaped tube is situated in the well or borehole from which water is pumped. As the water oscillates, it displaces a neutrally buoyant shuttle or ball back and forth. The shuttle is a non-precision component and does not need to seal the bore in which it travels.

When the oscillation is large enough, the shuttle periodically hits end-stops, at each end of the "shuttle-run" through which it moves. In the centre of the shuttle run, a non-return valve only allows water out of the system, where it flows into a pressurised accumulator or "air-vessel", which is wrapped hermetically around the drive pipes. A dip-tube and delivery pipe (rising main) continuously carry water to the surface. The pressure in the accumulator is approximately equal to the pressure needed to lift water to the surface, plus any additional pressure required at the surface. At either end of the shuttle run, intake non-return valves only allow water to enter the system from the ground water in which the accumulator, shuttle run, U-bend and valves are submerged, when the pressure adjacent to them falls below atmospheric.

When the shuttle moves downwards and hits the bottom end-stop, a compression shock propagates up the right-hand drive pipe at the speed of sound. It may reflect a number of times (reverberate), and travel up and down the drive pipe. During this time, the pressure in the shuttle-run rises to the Joukowski pressure (density x speed of sound x velocity change) and water flows out of the system into the accumulator. At the same time, a rarefaction shock (expansion wave) propagates from the underside of the shuttle, around the U-bend and reverberates up and down the left-hand drive pipe. This lowers the pressure in the U-bend from the total hydrostatic pressure due to all the water above it, to below atmospheric, causing water to be drawn into the system. Similarly, when the shuttle hits the top end stop, a compression shock reverberates in the left hand drive pipe and a rarefaction shock reverberates in the right hand drive pipe. This causes the same discharge non-return valve to open, but the opposite intake valve at the top end of the shuttle run.

By using both the compression and rarefaction shock in this way (unlike the historic Mongolfier ram), and by recovering any kinetic energy in the drive flow as compression work at the surface, the DAHR pump can exhibit very high hydraulic efficiencies. An early prototype situated in Oxford University Department of Engineering Science can lift water over 30m with an efficiency of close to 80%. It is anticipated that efficiencies in excess of 90% are possible. The Oxford University DAHR prototype can be viewed at    • BetaRamMovie.wmv   .