CF-15 Pre Lube Pump - 40924 Engineer’s Corner

This Prelube Pump delivers fifteen gpm of oil flow for pre-lubing diesel engines of 300 Horsepower and up. It includes a self-contained, low loss check valve to prevent backflow from the main engine lube pump.It also includes an internal 40 psi relief valve to protect its motor against overload in case the prelube pump remains running after the engine starts. The pump itself does not cause pressure, it produces flow. The engine connected to the pump has flow resistance that produces back pressure as the pump tries its best to maintain the flow through the engine. The pump can deliver its rated flow against 40 psi of back pressure from the system before its relief valve begins to open. Note that not all the back pressure at the pump comes from flow resistance within the engine. A good part of it comes from flow resistance within the piping, elbows and connections between the pump and the engine. This part of the back pressure doesn’t do the engine any good and should be minimized by using properly sized short pipes and, if possible, no elbows. Fifteen gpm of cold oil can easily eat up 40 psi when the plumbing is too small. Only the pressure measured at the engine is useful in separating the bearings by a film of oil before cranking the engine.As a general rule, the standard hydraulic valves and fittings customarily available are designed for use in systems that see several thousand psi and have significant horsepower to run them. Pressure drops of 20-30 psi each in various valves, pipes, or fittings are inconsequential compared to the operating pressure of such systems. But, a prelube pump delivering 15 gpm of cold engine oil can easily require all the output of a 1.0 horsepower motor just to move that much oil through the system. Since a prelube pump has a necessary pressure relief valve to avoid overloading the motor, then small pipes and restrictive fittings will reduce the flow of oil getting into the engine. So, when in doubt, use the largest and simplest piping available.