Calculator Inputs
Example Data Table
| Task | Flow | Pressure | Coefficient | Expected use |
|---|---|---|---|---|
| Light cleaning | 2.5 GPM | 2200 PSI | 0.62 | Patio, siding, and vehicles. |
| General washing | 4.0 GPM | 3000 PSI | 0.62 | Driveways and farm equipment. |
| High output rig | 8.0 GPM | 3500 PSI | 0.62 | Surface cleaners and commercial work. |
| Dual nozzle bar | 5.5 GPM | 2800 PSI | 0.62 | Split flow across two tips. |
| Soft wash rinse | 3.0 GPM | 900 PSI | 0.62 | Lower pressure rinsing. |
Formula Used
The calculator uses the incompressible orifice equation. It links flow, pressure drop, fluid density, area, and discharge coefficient.
Q = Cd × A × √(2 × ΔP / ρ)
For diameter, the equation becomes d = √(4A / π). For common pressure washer tip numbers, it also uses Nozzle size = GPM × √(4000 / PSI). GPM is divided by nozzle count first. Pressure loss reduces effective nozzle pressure. Flow margin increases the design flow used for sizing.
How to Use This Calculator
Choose the calculation mode first. Use diameter mode for selecting a new tip. Use pressure mode when you know the orifice and flow. Use flow mode when a tip size is fixed.
Enter pump flow and pressure in your preferred units. Set nozzle count for single tips, rotating bars, or surface cleaners. Keep the discharge coefficient near 0.62 for a sharp orifice. Adjust it when a tested value is available. Add line loss when hoses, fittings, or filters reduce pressure.
Press the calculate button. Review diameter, nozzle number, flow per tip, velocity, jet power, and Reynolds number. Select the closest real nozzle size below your pump rating. Test with a pressure gauge before final operation.
Pressure Washer Orifice Sizing Guide
A pressure washer tip is more than a simple hole. It controls how much water leaves the pump. It also controls the pressure the pump can build. A smaller opening restricts flow. That raises pressure, if the pump can supply enough water. A larger opening lowers pressure. It may give more rinsing flow, but less cutting force.
Why Orifice Size Matters
Correct sizing protects the pump. It also improves cleaning results. If the orifice is too small, pressure may climb above the rating. The unloader may cycle hard. Heat can rise quickly in bypass. Seals and hoses may see extra stress. If the orifice is too large, the washer may feel weak. The pump will move water, but pressure will fall.
Flow, Pressure, and Area
The main physics comes from the orifice equation. Flow depends on opening area and pressure drop. It also depends on water density and discharge coefficient. The coefficient corrects ideal flow for real losses. Sharp edges, wear, and internal shape all affect it. For many practical estimates, 0.62 is a useful starting value.
Using Multiple Nozzles
Surface cleaners and spray bars often use two or more tips. The total pump flow must be divided between the nozzles. Each tip only receives part of the flow. A two-nozzle bar on a four GPM pump gives about two GPM per tip. The calculator handles that split automatically through the nozzle count field.
Pressure Loss and Safety Margin
Long hoses and small fittings waste pressure before water reaches the tip. Filters, quick couplers, and bends can add more loss. The pressure loss field lets you reduce nozzle pressure for a realistic estimate. The flow margin field can oversize the calculation slightly. This helps when pump output is uncertain or when tips wear over time.
Interpreting the Nozzle Number
Pressure washer nozzles are often sold by angle and size. A 25040 tip means a 25 degree spray with a 4.0 orifice number. The number is based on GPM at 4000 PSI. It is not the physical diameter. The calculator gives both the physics diameter and the common size reference.
Practical Field Advice
Use the result as a design estimate. Then confirm with a pressure gauge. Real tips vary by brand and wear. Dirty water can change flow. Old nozzles usually pass more water than new ones. That lowers pressure and widens the stream. Replace worn tips when pressure drops or cleaning becomes slow.
Safety Considerations
High pressure water can cut skin and damage surfaces. Never point a nozzle at people, animals, wiring, or fragile materials. Match tips to the pump rating. Use proper hose ratings. Wear eye protection. Release pressure before changing nozzles. A correct orifice improves performance, but safe operation remains essential.
FAQs
What does pressure washer orifice size mean?
It is the effective opening that controls water flow through the nozzle. It is related to pressure, pump flow, and nozzle design. The common nozzle number is a sizing reference, not always the measured hole diameter.
What happens if the orifice is too small?
A very small orifice can raise pressure above the safe rating. The unloader may cycle often. Pump heat can increase. Hoses, seals, and fittings can be stressed. Always stay within equipment limits.
What happens if the orifice is too large?
A large orifice lets water escape more easily. Pressure drops, and cleaning force falls. The washer may still flow well, but hard dirt may take longer to remove.
Is nozzle number the same as diameter?
No. The nozzle number is based on GPM at 4000 PSI. Diameter is a physical or effective opening size. This calculator provides both values for comparison.
What discharge coefficient should I use?
Use 0.62 for a general sharp-edged orifice estimate. Use a manufacturer or test value when available. Real nozzle geometry can change the coefficient.
Why is water density included?
Density affects the conversion between pressure energy and jet velocity. Clean water near room temperature is close to 998 kg/m³. Hot water or chemical mixes can differ.
How do I size two surface cleaner nozzles?
Enter the total pump flow and set nozzle count to two. The calculator divides the flow evenly. Then choose two tips near the calculated size.
Can I use this for sewer jetter nozzles?
It can estimate simple orifices, but sewer jetter nozzles often have multiple ports and angles. Use manufacturer charts for final jetter nozzle selection.
Why add line pressure loss?
Hoses, filters, couplers, and fittings reduce pressure before the nozzle. Adding a loss percentage gives a more realistic effective nozzle pressure.
Does spray angle change orifice size?
The basic orifice equation does not require spray angle. The angle helps estimate fan width. Cleaning impact still depends on flow, pressure, distance, and surface type.
Should I round up or down?
Choose a real nozzle size that keeps pressure within the pump rating. Rounding down can raise pressure. Rounding up can lower pressure. Test with a gauge when accuracy matters.