Suction pumps

We describe a liquid suction pump, the pump comprising: a drive pipe to receive a liquid drive flow for the pump; a liquid conduit having first and second liquid delivery arms to provide pumped liquid, and a connecting valve arrangement between the arms; first and second pump inlets to said first and second arms, said first and second pump inlets having respective first and second one-way inlet valves; said valve arrangement having a valve inlet coupled to said drive pipe and valve outlets coupled to said first and second arms, to alternately close off a liquid connection between said valve inlet and respective ones of said first and second arms; and a compliant element coupled to said drive pipe; wherein the suction pump is configured such that, in operation, said drive flow oscillates in pressure/flow rate due to alternate switching of said valve arrangement; and wherein a compliance of said compliant element is such that a geometry of said suction pump in combination with said compliance defines a resonant condition for said pump and said oscillation is at a resonant frequency of the pump.