KEVOS® MAKEOS · Hydraulics
Pipe Bend Thrust Check (Pressure and Momentum Force, Resultant, Thrust Block Bearing)
What force does the water push on this pipe bend from its pressure and flow, and is the thrust block big enough for the ground to carry it?
Thrust on an unrestrained pipe bend: the flow velocity in the pipe (as the pipe friction tool), the pressure force and the momentum force of the flow, the resultant thrust bisecting the bend angle, and the bearing pressure of the thrust block on the ground with the block area needed, against the ground’s allowable bearing pressure.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Flow | L/min | Flow through the pipe. |
| Pipe inside diameter | mm | Inside diameter of the pipe. |
| Pressure (test pressure for the worst case) | bar | Internal pressure; use the test pressure, which is usually the worst case. |
| Bend angle (change of direction) | ° | Angle through which the pipe changes direction (90 for an elbow). |
| Liquid density | kg/m³ | Density of the liquid. |
| Thrust block | ||
| Block bearing area against the ground | m² | Area of the block face bearing on undisturbed ground. |
| Allowable ground bearing pressure | kPa | Allowable horizontal bearing pressure of the ground (from a site investigation; soft clays are low). |
Method and formulas
- Velocity v = Q ÷ A (as the pipe friction tool).
- Thrust = 2 (p A + ρ Q v) sin (θ ÷ 2), acting along the bisector of the bend, outwards.
- Bearing pressure = thrust ÷ block area; area needed = thrust ÷ allowable pressure.
- Example: 25.191 kN of thrust; the block bears at 25.191 kPa (needs 0.33588 m²).
Limitations
- Horizontal bend; vertical bends add or subtract the weight of the pipe, water and block.
- Static pressure dominates at normal velocities; water hammer surges raise the pressure.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a thrust block for a buried water main bend
- Check an anchor at a pump discharge bend
- Find the force on a bend during a pressure test
Who it is for
- Civil and water engineers
- Pipe fitters
- Plant engineers
What you get
- Velocity, pressure and momentum forces
- Resultant thrust
- Block bearing pressure and area needed
Interpreting the result
- At normal pipe velocities the momentum part is only about one per cent of the thrust: the test pressure is what matters.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3024–3027. Topic reference; no source tables or recommended settings are reproduced.
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