The cylinder piston is a very close fit to the inside of the cylinder and/or pump body. This is what allows the pump to function at a high efficiency level. The close fit between the two surfaces means that any outside particles (e.g. sand) can cause excessive wear. As the piston moves inside the cylinder the particles rub against the piston causing grooves to be cut into the side. In addition, it is possible that the cup seals could be damaged from this action.
In addition, the system uses spring loaded check valves with rubber seats. Over time silt can accumulate on the rubber seal preventing it from closing properly. These check valves are in the piston and the end cap (foot valve). If the foot valve fails, then the pump will lose its prime. (See Lift Pump to better understand “prime”). Failure of the check valve in the piston will prevent the pump from drawing water into the cylinder/pump body. In either case the pump does not function.
To alleviate the influence of sand/silt Bison Pumps sells Stainless Steel Cylinder Silt Screens to attach to the end of the cylinder. This item has a 60 mesh stainless steel screen to filter out the sand/silt.
In the event that your pump has been exposed to sand/silt and you are having issues with your pump, you can purchase a Maintenance Kit that will have everything you need included to get your Bison Pump system back up and running.