Suction pumps

A method of operating 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;
• the method comprising:
• operating the suction pump such that said drive flow oscillates in pressure/flow rate due to alternate switching of said valve arrangement, and such that an amplitude of the pressure variation in or at the compliant element is equal to or greater than a differential in pressure across the valve arrangement between the valve inlet and a closed-off valve outlet;
• locating said compliant element at or adjacent said valve arrangement;
• and
• switching said valve arrangement between alternate positions when a pressure at said valve inlet is at a minimum.

A liquid suction pump in combination with a pump driver, the pump comprising:

• a drive pipe to receive a liquid drive flow for the pump, the pump driver being coupled to said drive pipe;
• 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 at an operational frequency 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 a resonant frequency of the pump is matched to the operational frequency of the suction pump,
• wherein a characteristic inertance of the pump is less than or equal to
• nlZ
• BEP
• c
• ,
• where c is the speed of sound through the water in the liquid delivery arms, l is a length of one or both liquid delivery arms, n is a positive integer which is a number of outgoing and return expansion wave passages in one or both liquid delivery arms and ZBEP is an input impedance of the pump at a best efficiency point of the pump driver.