Given flow rate and projecting area, how do you determine the velocity of the cylinder rod?

Given flow rate and projecting area, how do you determine the velocity of the cylinder rod?

• A. On the rod side, velocity is v = Q / (A_piston − A_rod); on the cap side, v = Q / A_piston.
• B. v = Q / A_piston for both sides.
• C. v = Q × A_piston.
• D. v = ΔP / ρ.

Answer: (A)

In hydraulics, the piston’s velocity is set by how much fluid volume enters per unit time and the area the fluid can push against. For the rod side, the rod takes up part of the bore, so the effective area is the piston area minus the rod area (the annular area). The velocity on that side is therefore v = Q / (A_piston − A_rod). On the cap side, the rod doesn’t intrude into the cross-section, so the full piston area is used: v = Q / A_piston. The other forms mix up these areas or use unrelated quantities, so they don’t give the correct piston speed.

In hydraulics, the piston’s velocity is set by how much fluid volume enters per unit time and the area the fluid can push against. For the rod side, the rod takes up part of the bore, so the effective area is the piston area minus the rod area (the annular area). The velocity on that side is therefore v = Q / (A_piston − A_rod). On the cap side, the rod doesn’t intrude into the cross-section, so the full piston area is used: v = Q / A_piston. The other forms mix up these areas or use unrelated quantities, so they don’t give the correct piston speed.