BIZOMAT MAKEOS · Hydraulics
Jet Impact Force Check (Nozzle Flow and Velocity, Reaction, Force on a Plate)
For a water jet from a nozzle at this pressure, how much flow and speed does it have, what reaction does the operator or mounting feel, and what force does it put on a plate it hits?
Forces from a liquid jet: the flow and jet velocity through the nozzle from its size, discharge coefficient and pressure (as the orifice flow tool), the reaction force on the nozzle, and the force on a flat plate struck by the jet at an angle and possibly moving away from it, against the largest reaction force a hand-held nozzle or mounting should take.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Nozzle orifice diameter | mm | Diameter of the nozzle orifice. |
| Discharge coefficient | Discharge coefficient of the nozzle (about 0.95 for a smooth nozzle, 0.6 for a sharp orifice). | |
| Pressure at the nozzle | bar | Pressure just upstream of the nozzle. |
| Liquid density | kg/m³ | Density of the liquid. |
| Target | ||
| Angle between the jet and the plate | ° | Angle between the jet and the plate surface (90 = jet square to the plate). |
| Plate speed away from the jet | m/s | Speed at which the plate moves away along the jet (0 for a fixed target). |
| Largest reaction force accepted | N | Largest kick-back force for a hand-held nozzle (from your safety guidance) or rating of the mounting. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Nozzle orifice diameter
- What it is
- The diameter of the hole in the nozzle tip that forms the jet, which sets the jet area and therefore the flow.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Flow, nozzle reaction and plate force all rise with the square of the diameter.
- Get it right
- Measure the orifice itself, not the nozzle body or hose; worn nozzles grow larger and pass more flow.
What this means: Discharge coefficient
- What it is
- The ratio of the actual flow through the nozzle to the ideal flow for its area and pressure, which accounts for contraction and losses at the orifice.
- Units and format
- Enter a plain number with no unit. The form accepts 0.1 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.95 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Flow, reaction and plate force rise in proportion to it; the jet velocity does not change.
- Get it right
- Take it from the nozzle maker’s data or a flow test; it is a fraction, not a percentage.
What this means: Pressure at the nozzle
- What it is
- The liquid pressure just upstream of the nozzle tip, which is turned into jet velocity as the liquid leaves the orifice into open air.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0.000001 bar to 5000 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The nozzle reaction rises in proportion to this pressure; doubling it doubles the kick.
- Get it right
- Use gauge pressure measured at the nozzle; pump outlet pressure is higher because of the hose and lance losses.
What this means: Liquid density
- What it is
- The mass per cubic metre of the liquid in the jet, used for the jet velocity and the force it carries.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 25000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- For the same pressure a denser liquid gives a slower jet; the reaction itself does not depend on density.
- Get it right
- Take it from the fluid data at the working temperature, in kg/m³ rather than g/cm³.
Target
What this means: Angle between the jet and the plate
- What it is
- The angle at which the jet strikes the flat target plate, measured between the jet axis and the plate surface, so a square hit is a right angle.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 1° to 90°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The force on the plate rises with the sine of this angle; the nozzle reaction does not change.
- Get it right
- Measure from the plate surface, not from the normal to the plate.
What this means: Plate speed away from the jet
- What it is
- How fast the target plate moves away from the nozzle along the jet direction, for example a moving gate or vane; a fixed target does not move.
- Units and format
- Enter a number in m/s: metres per second. The form accepts 0 m/s to 1000 m/s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 m/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A faster plate takes less force, falling with the square of the speed difference; the nozzle reaction does not change.
- Get it right
- Enter 0 for a fixed target; it must be lower than the jet velocity or there is no force.
What this means: Largest reaction force accepted
- What it is
- The largest nozzle reaction you accept: the kick-back an operator can safely hold on a hand-held lance, or the rating of a fixed nozzle mounting.
- Units and format
- Enter a number in N: newtons. The form accepts 0.000001 N to 10000000 N. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only moves the pass or fail line; the calculated reaction does not change.
- Get it right
- Take it from your safety guidance or the mounting maker’s rating; this tool does not give a value.
Method and formulas
- Flow Q = C_d A √(2Δp ÷ ρ); jet velocity = √(2Δp ÷ ρ) (as the orifice flow tool).
- Nozzle reaction = ρ Q v.
- Force normal to a plate = ρ Q (v − u)² ÷ v × sin β.
- Example: 141.57 L/min at 31.623 m/s; 74.613 N reaction and 74.613 N on the plate.
Limitations
- Single plate; a series of vanes or a bucket that turns the jet back takes up to twice the force.
- Jet treated as coherent up to the plate; long throws break up and lose force.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check the kick-back of a hand-held cleaning lance
- Find the force of a jet on a target or gate
- Size the mounting of a fixed spray nozzle
Who it is for
- Process engineers
- Safety advisers
- Maintenance engineers
What you get
- Flow and jet velocity
- Nozzle reaction
- Force on the plate
Interpreting the result
- Reaction force grows in proportion to pressure for a fixed nozzle: doubling the pressure doubles the kick.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3024–3027, 352–368. Topic reference; no source tables or recommended settings are reproduced.
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Open the Jet Impact Force Check (Nozzle Flow and Velocity, Reaction, Force on a Plate) calculator