Diaphragm pumps are called positive displacement pumps because they pump a specific volume for each pump cycle. Diaphragm pumps move fluids more slowly than centrifugal pumps, but they can handle thicker mud and larger amounts of solids including abrasive materials. They also tolerate air being drawn into the pump, and can be run dry without damage, unlike centrifugal pumps.  Diaphragm pumps are widely used on construction sites to control slow seeping in evacuations, and for pumping out septic systems and operating well point systems.  Models DP2H and DP3H include Oil Alert to help protect the engine against damage from operation with an inadequate oil supply.  Riverside diaphragm pumps feature a straight-through, self-priming design. The rubber elastomer diaphragm and flapper valves are easily replaced on site, and the aluminum pump body makes the unit easier to move around the job site.