Below 150 N. Hand-held operation is generally permitted under DGUV Rule 100-500, chapter 2.36.
From 10,000 bar·l/min, DGUV Rule 100-500, chapter 2.36, comes into scope.
The underlying calculation model
All four output quantities follow from the steady-state analysis of a single orifice. These are the same relationships used during the quotation stage, not a computational-fluid-dynamics simulation.
Q = 0.667 · cd · d² · √p · n- Q
- flow rate in l/min
- cd
- discharge coefficient
- d
- orifice diameter in mm
- p
- operating pressure in bar
- n
- number of orifices operated simultaneously
The squared influence of diameter is the dominant factor. Increasing the diameter from 0.30 mm to 0.40 mm raises demand by roughly 78%.
F = 2 · cd · A · p- F
- reaction force in N
- A
- orifice cross-section in mm²
- p
- operating pressure in bar
Force rises linearly with pressure and with the square of the diameter. For multi-orifice tools, the vector sum governs. For symmetrically arranged rotary heads, the axial component is well below the sum of the individual forces.
How to read the results
| Quantity | Used For | Typical Follow-on Decision |
|---|---|---|
| Flow rate | Pump selection, water balance, treatment plant sizing | Set the pump's rated flow with margin |
| Jet velocity | Plausibility check of the process window | Classify as pure-water or abrasive process |
| Hydraulic power | Comparing competing quotes on the same basis | Assess whether rated data are mutually consistent |
| Connected load | Electrical design, switchgear, cooling | Size the grid connection and recooling |
| Reaction force | Permissibility of hand-held operation | Decide between hand-held, fixture, or automation |
| Pressure-flow product | Scope of DGUV Rule 100-500, chapter 2.36 | Set operational briefing and inspection duties |
The 150 N and 250 N marks in the calculator reflect section 3.7.5 of DGUV Rule 100-500, chapter 2.36: the reaction force to be absorbed must not exceed 250 N in the long axis, and above 150 N additional measures on the jetting lance are required. The calculator does not replace a risk assessment or the manufacturer's specification for the permitted orifice configuration.
Limits of the model
- Steady-state analysisStart-up, shutdown, pressure transients, and pulsation are not represented
- No abrasive effectAbrasive mass flow, focusing-tube geometry, and mixing chamber are not accounted for
- Treated as incompressibleAt ultra-high pressure, water is measurably compressible; the real velocity is below the calculated value
- Line losses ignoredPressure losses in pipes, swivels, and hoses reduce the pressure actually available at the tool
- Efficiency as a flat figureThe real system efficiency depends on load and on the specific product line
Frequently asked questions about the calculator
Which discharge coefficient should I use?
For preliminary planning, 0.70. For a more reliable figure, measure it on the actual tool: record flow rate at a known pressure and diameter, then back-calculate cd. A value that deviates significantly is itself a diagnosis — an unusually high value often points to a worn, oversized bore.
Why is the estimated connected load so much higher than the hydraulic power?
Because several conversion steps sit between the motor shaft and the orifice: the drive, possibly an oil-hydraulic stage, pressure generation, and line losses. For intensifier systems, a factor of roughly 1.4 to 1.5 is realistic; for direct-drive systems, roughly 1.15 to 1.25.
Does the reaction-force figure also apply to rotary tools?
Only to a limited extent. The calculator sums the individual forces over the number of orifices. For symmetrically arranged orifices on a rotary head, the radial components largely cancel, so the axial force to be absorbed is lower. The manufacturer's specification for the specific tool governs in these cases.
- DGUV Rule 100-500, chapter 2.36 “Working with Liquid Jetting Equipment,” issue March 2017 – https://publikationen.dguv.de/media/pdf/27/3a/6a/R500_236.pdf
- DIN EN 1829-1:2021-04, High-pressure water jet machines – Safety requirements – Part 1: Machines – https://www.dinmedia.de/de/norm/din-en-1829-1/321847498