In a fluid power loop, the pressure drop is equal to which pressure?

• A. The ambient pressure
• B. The supply pressure
• C. The return pressure
• D. The differential pressure

Answer: (B)

Pressure drop is the loss of pressure as fluid moves through a loop due to friction and restrictions. It’s determined by comparing the pressure on the supply side to the pressure on the return side: the drop equals the difference between those two pressures. If the return side is referenced to ambient (zero gauge pressure), the amount of pressure you start with on the supply side is what you observe as the drop in that context, so the drop can be described by the supply pressure. In general, the precise term for the difference between two points is differential pressure, but when the return is at ambient, the observed drop corresponds to the supply pressure.