To calculate extend speed of a cylinder, you need to know ______.

• A. Rod diameter and flow rate in
• B. Rod length and piston diameter
• C. Piston diameter and flow rate in
• D. Rod length, piston diameter, and rod diameter

Answer: (C)

Extend speed is determined by how much fluid can be pushed into the cylinder per unit time relative to the piston’s cross-sectional area. The piston moves a volume equal to its area times the distance it travels, so the speed of the piston is v = Q / A, where Q is the flow rate in and A is the piston area. The piston area depends on the piston diameter (A = πD^2/4). So knowing the flow rate and the piston diameter lets you calculate how fast the piston will extend.

The rod diameter and rod length don’t set the extension speed in this simple model. The rod reduces the effective area on the opposite side and can affect retraction speed or the force balance, but for extension you primarily use the piston’s diameter. Rod length affects how far you can travel, not how fast you extend.