Despite careful design and implementation of sophisticated control electronics, fluid power system performance can be degraded by incorrect sizing or physical location of system components. A common design oversight is the use of undersized cylinders. In an attempt to increase actuator speed, designers may specify small bore cylinders, based on the assumption that for a given amount of oil flow, a smaller cylinder will produce higher velocities. However, this assumption only holds for very light loads.
For cylinders moving moderate to heavy masses, the acceleration, velocity, and deceleration are limited by the available force, rather than oil flow. Because cylinder bore determines the force an actuator can produce, if the cylinder diameter is too small, the actuator may not be capable of attaining the desired speeds or required cycle times needed for the application.
The Temptation of Simplified Formulas
Pressure of design, market, and time constraints, can make it tempting to use simplified, first-order approximations to govern system design. And this approach might achieve acceptable results for simple machines. As control systems become more sophisticated, and increased importance is placed on efficiency and economy, reliance on these design approximations tends to result in overly conservative designs. The cost of this approach can be measured in larger, more expensive cylinders, valves, and pumps. Consequently, a supplier or distributor may lose a bid to a competitor due to extra cost.
A formula such as V =Q / A is a starting point. However, this formula is true only when the mass is zero. Since most real-world systems need to move a mass of some kind, this formula should only be used in the alternate form, Q = V ´ A, when calculating system flow using velocity and area.