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. <EOS>