A clot removal system, comprising: a catheter having a distal end and defining a lumen filled with a liquid column having a proximal portion and a distal portion; a controllable vacuum valve; a vacuum source fluidically connected to the vacuum valve; a controllable vent valve having a vent liquid input; a vent fluid source containing a vent liquid and fluidically connected to the vent valve to retain the vent liquid at the vent fluid input; characterised in that the clot removal system further comprises a manifold connected to the catheter, to the vacuum valve, and to the vent valve, the manifold fluidically connecting the proximal portion of the liquid column in the lumen: to the vacuum source through the vacuum valve; and to the vent fluid source through the vent valve; a controller connected to the vacuum valve and the vent valve and configured to selectively open and close the vacuum valve and the vent valve such that: responsive to opening the vacuum valve, the vacuum source is fluidically connected to the liquid column in the lumen; and responsive to opening the vent valve, the vent fluid source is fluidically connected to the liquid column in the lumen, the controller configured to cyclically open and close the vacuum valve and the vent valve to: change a level of vacuum at the distal end; and prevent forward flow of the distal portion out from the distal end during each cycle. a catheter having a distal end and defining a lumen filled with a liquid column having a proximal portion and a distal portion; a controllable vacuum valve; a vacuum source fluidically connected to the vacuum valve; a controllable vent valve having a vent liquid input; a vent fluid source containing a vent liquid and fluidically connected to the vent valve to retain the vent liquid at the vent fluid input; characterised in that the clot removal system further comprises a manifold connected to the catheter, to the vacuum valve, and to the vent valve, the manifold fluidically connecting the proximal portion of the liquid column in the lumen: to the vacuum source through the vacuum valve; and to the vent fluid source through the vent valve; to the vacuum source through the vacuum valve; and to the vent fluid source through the vent valve; a controller connected to the vacuum valve and the vent valve and configured to selectively open and close the vacuum valve and the vent valve such that: responsive to opening the vacuum valve, the vacuum source is fluidically connected to the liquid column in the lumen; and responsive to opening the vent valve, the vent fluid source is fluidically connected to the liquid column in the lumen, responsive to opening the vacuum valve, the vacuum source is fluidically connected to the liquid column in the lumen; and responsive to opening the vent valve, the vent fluid source is fluidically connected to the liquid column in the lumen, the controller configured to cyclically open and close the vacuum valve and the vent valve to: change a level of vacuum at the distal end; and prevent forward flow of the distal portion out from the distal end during each cycle. change a level of vacuum at the distal end; and prevent forward flow of the distal portion out from the distal end during each cycle.