LO 10-5 Identify and describe the types, functions, construction features, and applications of diesel engine lubrication system components

1.6. Pressure-Regulating and Pressure-Relief Valve

Pressure-Regulating and Pressure-Relief Valve

Because the oil pump can pump more oil than the engine can use, an oil pressure-regulating valve is used to control oil pressure. Oil pressure that is too high can blow gaskets on the spin-on oil filter and burst or swell the oil filter into a pumpkin shape. Excessively high oil pressure can also erode engine bearings. Keeping the oil pressure regulated between 20–40 psi (138–276 kPa) when the engine oil is warm can reduce parasitic power loss caused by pumping more oil than is necessary TABLE 10-5.

The oil pressure-regulating valve is usually located in the main oil gallery or at the outlet of an oil pump Figure 34. Using a conventional spring-loaded bypass valve arrangement permits maximum oil pressure control by the valve. When oil pressure reaches a value equal to the spring tension of a pressure-regulating valve, spring pressure is overcome by oil pressure, which moves a spool valve to a bypass position. Oil returns to the sump in quantities proportional to the excess volume produced by the oil pump Figure 35. As long as clearances between engine bearings and other components using oil remain closed, adequate oil pressure is maintained by the oil pump and pressure-regulating valve. If an engine has excessive wear or internal oil leaks, oil pressure will drop as the pump tries to make up for the additional volume required by the leaks and larger operating clearances in the engine lubrication system.

FIGURE 10-34: The oil pressure relief valve of an HD diesel oil pump. Note that there are two points to attach the pump pickup tube. One can be used for either a front sump oil pan or a rear sump.

FIGURE 10-35: Operation of the oil pressure-regulating valve. When oil pressure exceeds a calibrated spring tension of the regulator, the check ball will uncover a passageway, permitting excess oil to return to the sump.

In the event that the pressure-regulating valve cannot relieve oil pressure fast enough, such as when the oil is cold and thick or when the regulator is not properly working, a pressure-relief valve is connected in series with the pressure regulator. This valve will typically open at 100 psi (689 kPa) and return oil to the sump Figure 36.

To electronically regulate oil pump pressure, an electronically controlled pressure-regulating valve can operate to spill or return excess oil back into the oil pump inlet. The pulse- width–modulated control valve will operate in a closed control loop with the oil pressure sensor and open to reduce oil pressure Figure 37.

FIGURE 10-36: A schematic view of typical oil circuits found in a diesel engine. This is a V8 engine.

FIGURE 10-37: An electronically controlled pressure regulator spills pressurized oil back into the oil pump inlet.