Figure 16 - In a hydraulic system, the return pipe is normally at lower pressure during service conditions, and used only for draining water back to the reservoir or tank prior to the pumping engine. It is, consequently, of a lesser construction than the pressure pipe. However, it is required to withstand a test pressure, for safety, of 200 lbs per square inch which is considerably less than the 8" diameter bore pressure pipe which has the instruction to test to 2,500 lbs per square inch. [178]