Free Water Flow Rate & Orifice Calculator
Calculate fluid discharge flow in GPM and L/min, exit jet velocity, and required hole diameter from hydraulic pressure differential.
🌊 Orifice Geometry & Pressure
📊 Flow Rate & Jet Velocity
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Understanding Orifice & Nozzle Discharge
Fluid flowing through an opening converts static potential pressure energy into kinetic stream velocity. By Torricelli's Law and Bernoulli's theorem, the velocity of the liquid jet scales with the square root of the differential pressure ($sqrt{Delta P}$).
The Standard Orifice Discharge Equation
Why Vena Contracta Reduces Flow (Cd = 0.62)
As liquid approaches a sharp-edged hole, fluid inertia prevents it from making a sharp 90-degree turn around the lip. The streamlines continue converging just downstream of the hole, creating a narrowed jet waist known as the vena contracta with roughly 62% of the physical hole area. Well-rounded, tapered nozzles guide the fluid gradually, avoiding contraction and raising the discharge coefficient to $C_d approx 0.98$.
Frequently Asked Questions
How does pressure affect flow rate?
Because flow scales with the square root of pressure ($Q \propto \sqrt{P}$), doubling the flow rate through a nozzle requires quadrupling (4x) the pressure. If a nozzle flows 2 GPM at 1,000 PSI, achieving 4 GPM requires 4,000 PSI.
What is the nozzle orifice size on a pressure washer?
Pressure washer nozzles are coded by flow rate at 4,000 PSI. For example, a "040" nozzle delivers 4.0 GPM at 4,000 PSI (or approximately 2.8 GPM at 2,000 PSI).
Does fluid viscosity alter orifice flow?
For thin liquids like water, gasoline, and light oils, flow is purely inertia-dominated (high Reynolds number) and independent of viscosity. Only very thick, viscous fluids (honey, cold heavy gear oil) experience viscous laminar drag that reduces the discharge coefficient.