A cylinder extending against a load has pressure applied at which end inside the cap end?

• A. On the piston rod
• B. On the outer surface
• C. Uniform around the housing
• D. Over all surfaces inside the cap end of the cylinder

Answer: (D)

When a cylinder extends against a load, the hydraulic fluid in the cap end is under pressure. In a confined fluid, pressure acts on every surface the fluid touches. So inside the cap end, the pressure is applied across all interior surfaces that contact the fluid—the cap-end cavity surfaces and, crucially, exerting force on the piston face on that side. This uniform pressure results in the axial thrust that pushes the piston to extend, with the driving force effectively equal to the pressure times the piston’s cap-end area. This is why the description that best fits is pressure acting over all surfaces inside the cap end.