Unit pump refers to a cylinder of an oil pump, the oil pump here refers to the high-pressure pump, or as a fuel injection pump. The whole pump means that all cylinders share a high pressure oil pump. Unit pump body and the pump overall than done relatively large, such as high power diesel engine are generally single pump, in addition unit pump if damage to the oil pump only needs to replace a pump without the need to like the whole pump that all replacement and lower cost.
