What is true about the reservoir piston located within the power package?

• A. Keeps the reservoir pressurized using compressed helium gas
• B. Protects the engine driven hydraulic pump by reducing the return side of the reservoir to 50 psi
• C. Keeps the reservoir pressurized using compressed nitrogen gas
• D. Releases excess pressure at 1790 psi

Answer: (B)

The reservoir piston in the power package serves as a gas‑charged cushion that maintains a small, steady back‑pressure on the return line to the reservoir. This keeps the engine‑driven hydraulic pump from losing its prime and protects it from pressure surges. As fluid returns, the piston shifts to keep the return pressure around about 50 psi, absorbing flow fluctuations and preventing cavitation in the pump. The other statements describe different gases or a high‑pressure relief, which aren’t the function of this piston.