Hydraulic Flow Rate, Velocity & System Design

Flow rate measures the volume of hydraulic fluid moving through a system over time, typically expressed in gallons per minute (GPM).

Velocity measures the speed at which fluid travels through a pipe or hose, typically expressed in feet per second (ft/s).

Flow rate affects actuator speed and system capacity, while fluid velocity influences friction losses, pressure drop, and component sizing.

Titan Fittings recommends designing hydraulic systems to accommodate both requirements.

As fluid velocity increases, friction losses through hoses, pipes, valves, and fittings generally increase.

Excessive velocity can produce higher pressure drops, increased energy consumption, and unnecessary fluid heating.

Titan Fittings recommends selecting appropriately sized hoses and fittings to minimize restrictions while maintaining the required flow rate.

Fluid velocity can be calculated using flow rate and the internal cross-sectional area of the pipe or hose.

For U.S. customary units:

Where:

• V = fluid velocity in feet per second (ft/s)
• Q = flow rate in gallons per minute (GPM)
• D = actual internal diameter in inches

For example, 20 GPM flowing through a pipe with an actual 1-inch internal diameter produces an average velocity of approximately 8.17 ft/s.

Titan Fittings recommends using the actual internal diameter rather than nominal hose or pipe size when calculating velocity.

Hydraulic hose diameter determines the available flow area.

For a given flow rate, a smaller internal diameter increases fluid velocity and typically increases pressure losses. A larger diameter can reduce these losses, although it may increase cost, weight, and installation space.

Titan Fittings recommends matching hose diameter to flow requirements, allowable pressure drop, and manufacturer specifications.

Excessive fluid velocity can contribute to pressure losses, turbulence, and fluid heating.

In certain conditions, particularly near pump inlets or localized restrictions, pressure may fall low enough to create cavitation.

Titan Fittings recommends evaluating suction-line conditions, fluid velocity, pressure drop, and component restrictions to minimize these risks.

Hydraulic systems should be designed around both flow rate and fluid velocity.

Flow rate determines how much fluid is available to operate actuators and other components. Velocity helps determine the appropriate size of the hoses, pipes, and flow passages.

Titan Fittings recommends establishing the required flow first, then sizing components to maintain acceptable velocities, pressure losses, and operating efficiency.