Hello, I have a 35mtr putzimeister concrete pump, recently I was doing one concrete pour, towards the end of the pour the concrete pumps pistons slowed down and eventually coming to a hault I had to clean up the pipe line and hopper, when after that I tried operating the pistons without any concrete it worked fine I thought there might have been some electrical glitch after which i ordered one mixer truck of 2 cubic and tried pumping it, than as the pistons were exposed to the cement it made three or fours stokes and slowed down than completely stops,the s tubes works fine and change over timing is also okay  I am Seeking help if anyone knows what has happened and what component could be at fault causing this failure please share.