There is one other type of pump-actually, an entirely different type of system. It's used by some aircraft, as well as some types of race vehicles that experience high G-forces where the oil may be forced away from the pickup. The oil pump is driven off an accessory belt, and actually is two or even more pumps. One pulls the oil out of a very small oil pan from several locations and pushes it into a specially designed storage tank that may hold as much as 20 quarts. Oil is then pulled from the tank and pressure-fed into the engine. This method always ensures that the engine is getting oil, as well as preventing the crankshaft from splashing in the oil. It is referred to as a "dry sump" system.
Clearances within an oil pump are quite close and are the only part of the engine that does not initially receive filtered oil. However, the oil does pass first through the filter before traveling to the rest of the engine.
There is one other type of oiling system that adds a crutch to the wet sump system called an "accumulator"-a special auxiliary oil tank that holds two to three quarts. Cylindrical in shape, it has one chamber for oil and another divided by a movable piston and seal that holds pressurized air. An electric valve triggered by an oil pressure switch connects the tank via a hose to a special adapter between the engine and oil filter. When the ignition key is turned to "On," the valve opens and pressurizes the oil passageways. When the engine is started and the engine's oil pump develops pressure above that on the pressurized side of the accumulator, the additional three quarts of oil are forced back into the storage side of the accumulator.
The first advantage to this system is the elimination of "no-oil-pressure" start-ups. However, the biggest advantage, especially to a vehicle that may be in a position where the oil is pulled away from the pickup tube, is that as soon as oil pressure drops below the setting of the oil pressure switch, pressurized oil from the accumulator is forced into the engine. Granted, three quarts flowing from the accumulator through the engine may not last more than a couple of minutes at slow speeds, and only a few seconds at high engine speeds, but it just may be long enough to prevent engine damage. For example: You're on a steep angular descent and suddenly a front tire drops into a hole and the back end comes up, almost pitching you over. All the oil in the pan's rear sump come rushing forward, thus uncovering the oil pickup tube. The oil pump would then be sucking air, not oil, and damage to the engine could occur. I consider it sort of an insurance policy against damage.
The oil pump, like the water pump we discussed last month, is a simple but very vital part of your engine.