From water inlet to process effect
The technical chain begins with water supply and does not end at the orifice. After pressure generation, the medium must be carried to the tool through high-pressure components suited to the operating conditions. There, hydraulic energy is converted into jet velocity and momentum. What follows is decisive: how the jet strikes the workpiece, coating, or contamination, and how water and removed material are carried out of the process.
Inlet pressure, inlet flow, temperature, and pre-filtration per pump specification.
A plunger or intensifier pump generates operating pressure at the required flow rate.
Pipes, swivel joints, hose assemblies per EN 1829-2, pressure relief.
Converts pressure into velocity and momentum at the orifice or cutting head.
Collection, separation, filtration, recirculation, or disposal of water and solids.
The chain is specified back to front: first the required process effect at the part, then the jetting tool, then the hydraulic operating point, and only last the pump. The reverse sequence — pump first — is the most common cause of systems that end up sized past the actual need once in the field.
Operating pressure and flow rate together form the operating point
The highest possible maximum pressure is not a universal design criterion. Cutting processes often prioritise high power density at a small orifice; cleaning or removal processes may additionally require a substantial flow rate. Orifice, pressure, flow rate, and drive power must therefore be assessed as interrelated quantities.
High-pressure pumps and pump concepts →
Pressure classes and typical operating windows
| Class | Operating Pressure | Flow Rate | Typical Task |
|---|---|---|---|
| Industrial cleaning | up to 350 bar | 15–60 l/min | Standard cleaning; above 350 bar (current standard edition) the scope of EN 60335-2-79 ends |
| High pressure | 350–1,000 bar | 20–200 l/min | Duct and pipe cleaning, large-area coating removal, structural cleaning |
| Ultra-high pressure (UHP), cleaning | 1,000–2,800 bar | 15–90 l/min | Paint removal, concrete removal, tube-bundle and heat-exchanger cleaning |
| Ultra-high pressure (UHP), cutting | 3,000–4,200 bar | 1.5–8 l/min | Standard-range abrasive and pure-water cutting |
| Hyper pressure | 4,200–6,500 bar | 1–4 l/min | Cutting with increased traverse speed; higher wear and component cost |
Ranges from application practice. The 35 MPa (350 bar) boundary corresponds to the upper limit of the currently valid edition DIN EN 60335-2-79:2015-02, above which EN 1829-1 applies. Only the earlier IEC editions IEC 60335-2-79:1995 (1st edition) and IEC 60335-2-79:2002 (2nd edition) set this boundary at 25 MPa (250 bar).
The operating point is a value pair, not a pressure figure
Pressure and flow rate are rigidly coupled through the orifice. Specifying only the maximum pressure does not fix the operating point — it leaves that choice to the supplier. A request should therefore always state both quantities together with the intended orifice configuration.
Q ≈ 0.667 · cd · d² · √p- Q
- flow rate in l/min
- cd
- discharge coefficient, in practice 0.60–0.80
- d
- orifice diameter in mm
- p
- operating pressure in bar
Example: d = 0.30 mm, p = 4,000 bar, cd = 0.70 gives roughly 2.7 l/min. With multiple orifices, flow rates add; the pump must deliver the sum at the required pressure.
v = √( 2 · Δp / ρ )- v
- jet velocity in m/s
- Δp
- pressure differential in Pa
- ρ
- density of water, roughly 1,000 kg/m³
At 4,000 bar this calculates to roughly 894 m/s, about 2.6 times the speed of sound in air. Water's compressibility and friction reduce the real value; for specification purposes, the order of magnitude matters, not the third significant figure.
Phyd [kW] = p [bar] · Q [l/min] / 600- Phyd
- hydraulic power in kW
- p
- operating pressure in bar
- Q
- flow rate in l/min
Electrical connected load is higher. Intensifier pumps typically reach roughly 60–70% overall system efficiency; direct-drive plunger pumps roughly 80–90%, depending on manufacturer and load point.
| Operating Pressure | Flow Rate | Jet Velocity | Hydraulic Power | Reaction Force |
|---|---|---|---|---|
| 1,000 bar | 1.3 l/min | 447 m/s | 2.2 kW | 10 N |
| 2,000 bar | 1.9 l/min | 632 m/s | 6.3 kW | 20 N |
| 3,000 bar | 2.3 l/min | 775 m/s | 11.5 kW | 30 N |
| 4,000 bar | 2.7 l/min | 894 m/s | 17.7 kW | 40 N |
| 6,000 bar | 3.3 l/min | 1,095 m/s | 32.5 kW | 59 N |
Calculated with cd = 0.70, a 0.30 mm orifice, and 70% system efficiency. See the operating-point calculator for other configurations.
The jetting tool defines the local process effect
Cutting heads, round-jet orifices, fan-jet orifices, rotary nozzles, lances, and tank-cleaning heads perform different tasks. Orifice cross-section, jet geometry, stand-off distance, impingement angle, and motion determine how the available hydraulic power actually acts on the part.
In abrasive cutting, the focusing tube's internal diameter is usually two to three times the water-orifice diameter. A 0.30 mm water orifice is typically paired with a focusing tube of 0.76 mm to 0.91 mm. Too small a ratio causes focusing-tube wear to increase sharply; too large a ratio reduces cutting performance.
Tool guidance determines reproducibility and accessibility
Guidance can be manual, mechanically supported, CNC-controlled, remotely operated, or robotic. The choice depends on geometry, repeat rate, accuracy, reaction force, hazard, and the desired degree of automation. For special processes especially, kinematics is often just as important as pressure generation.
Reaction force limits hand-held application
F = 2 · cd · A · p ⟶ F [N] ≈ 0.11 · d² [mm] · p [bar]- F
- reaction force in N
- A
- orifice cross-section in mm²
- d
- orifice diameter in mm
- p
- operating pressure in bar
The notable feature of the exact form: reaction force is simply twice the product of pressure and orifice cross-section. It rises linearly with pressure, not with its square root. For multiple orifices, the vector sum governs; rotary heads with symmetrically arranged orifices partially cancel the axial component.
Under DGUV Rule 100-500, chapter 2.36, section 3.7.5, the employer must ensure that the reaction forces to be absorbed do not exceed 250 N in the long axis of the jetting lance. Where reaction force exceeds 150 N, only jetting lances with additional measures may be used — for example a foot switch with a safety-rated risk assessment, or a fixture that fully or partially absorbs the reaction force. Orifice selection for hand-held equipment must be made per the manufacturer's specification so that these values are respected.
Practical consequence: a single 0.8 mm orifice at 1,500 bar already generates roughly 106 N. Two such orifices on one hand tool exceed the 150 N threshold. Tool selection is therefore not only a performance question but a regulatory one. The operating-point calculator shows the thresholds for a specific configuration.
Water quality and residue management are part of process planning
Inlet water quality affects the service life of high-pressure components, depending on the pump and system concept. On the process side, water, abrasive, sludge, or removed material accumulate in turn. Collection, separation, filtration, recirculation, or disposal are therefore not secondary topics but part of the system layout.
| Parameter | Guidance Range | Rationale |
|---|---|---|
| Total dissolved solids (TDS) | 20–100 mg/l | Deposits and erosion at the orifice and seals |
| Total hardness | < 25 mg/l CaCO₃ | Scale formation at high-pressure valves and the orifice bore |
| Chloride | < 20 mg/l | Pitting corrosion on pressure-carrying components |
| Silica (SiO₂) | < 15 mg/l | Hard, difficult-to-remove deposits |
| Particle filtration | 1 µm, with a downstream 0.45 µm stage | Protects the orifice bore at tenths-of-a-millimetre scale |
| pH | 6.5–8.5 | Material compatibility of seal materials |
Guidance values for ultra-high-pressure applications. Only the pump and system manufacturer's water specification is binding.
Fully demineralised water is not automatically the best water. At very low conductivity, water can become aggressive toward certain materials and leach ions from component surfaces. Reverse osmosis should therefore be specified to a target band, not to a minimum, and the pump manufacturer's approval should be obtained.
The safety concept is engineered together with the system
High-pressure water carries substantial injury potential. Enclosure, interlocking, pressure relief, safe tool guidance, access control, and reaction-force management must fit the specific application. Automation can reduce operator exposure but does not replace an application-specific risk assessment.
Safety for high-pressure waterjet systems →
EN 1829-1:2021High-pressure water jet machines – Safety requirements – Part 1: MachinesSafety requirements for machines using pumps as the pressure source. Supersedes the 2010 edition. German implementation: DIN EN 1829-1:2021-04. Applies above the scope of EN 60335-2-79 (currently valid: DIN EN 60335-2-79:2015-02, 35 MPa / 350 bar; only the earlier IEC editions IEC 60335-2-79:1995 and IEC 60335-2-79:2002: 25 MPa / 250 bar).
Product standardEN 1829-2:2008+AC:2011High-pressure water jet machines – Safety requirements – Part 2: Hoses, hose lines and connectorsRequirements, test methods, and marking for high-pressure hose lines and for devices that secure connections against unintended release. German implementation: DIN EN 1829-2:2012-02.
ComponentsDGUV Rule 100-500, ch. 2.36Working with Liquid Jetting Equipment (issue March 2017)Operational rule (Germany). Scope from 25 bar permitted operating gauge pressure, or from a pressure-flow product of 10,000 bar·l/min. Contains the reaction-force thresholds.
OperationDIN EN ISO 12100:2011-03Safety of machinery – General principles for design – Risk assessment and risk reductionMethodological framework for hazard analysis, based on ISO 12100:2010. Basis for any machine-specific protection concept, including when integrated with robotics. A revision is in draft as of August 2026 but not yet published.
MethodologyA complete overview of the relevant standards and legal instruments, including the transition to the EU Machinery Regulation, is available under Standards and Directives.
Frequently asked questions about specification
Is stating “4,000 bar” enough for a request?
No. Without flow rate and orifice configuration, the operating point is not defined. Two systems with identical rated pressure can differ in connected load by a factor of five. What should be stated: pressure, flow rate at the operating point, number and diameter of orifices, and the load profile across the shift.
Does more pressure always mean more performance?
Only within the relevant process window. In abrasive cutting, cutting performance rises with pressure, but wear on seals, valves, and high-pressure conveyance rises disproportionately at the same time. In cleaning processes, flow rate is often the more effective control variable, because the layer to be removed must be mechanically released and carried away at the same time.
How does orifice diameter affect pump size?
With the square. Doubling the orifice diameter quadruples flow rate at the same pressure, and with it the required hydraulic power. Orifice diameter is therefore the single most cost-consequential decision in the entire specification.
Why is reaction force proportional to pressure while flow rate follows a square root?
Because reaction force equals the product of mass flow and velocity, and both quantities grow with the square root of pressure. The product of two square-root terms is a linear relationship: F = 2 · cd · A · p. That is why hand-held equipment reaches the 250 N threshold of DGUV Rule 100-500 at high pressures even with small orifices.
What role does water temperature play?
It affects density and viscosity only slightly, but it matters for seal service life. Compression work heats the water; most manufacturers limit inlet temperature and require recooling where water is recirculated.
- 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
- 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
- Flow International, Fundamentals of the Waterjet Pump – https://www.flowwaterjet.com/explore/basics-of-a-waterjet-pump
- Hammelmann, Waterjet Technology – https://www.hammelmann.com/de/produkte/wasserstrahltechnik/
- KAMAT, Water Jetting Applications – https://www.kamat.de/hochdruck-anwendungen/wasserstrahlen/