increase pressure on the pig and thus help maintain pig speed at a constant level referring to fig2 an engine and pump configuration is shown that may be used to increase pressure on a pig temporarily as it passes obstructions in the pipe while fig2 depicts a double pass unit it will be understood that the teachings herein may be applied to a single pass unit a four pass unit etc in situations where there is more than one pass and the teachings are used primarily as an inspection tool it may be more economical to implement the teachings on only one path however the teachings may be used for more than just inspection purposes and may be applied to each path in a unit in fig2 engine 24 has an integral clutch 26 from which extends a drive shaft 28 the drive shaft 28 is connected to drive pump 30 a p 1 the engine 24 is shown with only one integral clutch but has a main shaft 32 that extends from the end of the engine 24 opposite to the clutch 26 main shaft 32 is connected through a stand alone clutch 34 to drive pump 30 b p 2 other clutch and drive shaft configurations may be used to configure a single engine to drive two pumps in this way for example engine 24 may be connected to drive two pumps each pump p 1 p 4 is connected into a valved pumping circuit.