Answer
The Booster 15 manual gives these causes of weak pumping: a worn wear plate or S valve disc, or an S valve that has drifted out of register (both fixed by adjusting the S valve); worn pistons, which need replacing; or a concrete mix that is too stiff and should be made more fluid. A low reading on the S valve pressure gauge or repeated S valve jams also points to an S valve out of register. Murky water in the piston cooling tank signals worn pistons, since concrete liquid is slipping past them. Low or overheated hydraulic fluid can also interrupt pumping.
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Reviewed by our parts specialists from IMER manuals and parts books. Check the part number on your machine or in its parts book before you order. Not sure? Ask a parts specialist.