BIZOMAT MAKEOS · Hydraulics
Water Supply Line Check (Velocity, Friction Loss, Outlet Pressure, Valve Surge)
Is this water line big enough: is the velocity reasonable, what pressure is left at the outlet after friction and lift, and will a quick-closing valve push the pressure past the pipe rating?
Check of a water (or other liquid) supply line: velocity in the bore against your limit and the smallest bore for it (as the pipe size for velocity tool), friction factor and pressure drop through the pipe and fittings (as the pipe friction tool), pressure left at the outlet after friction and static lift, and the surge when a valve at the outlet closes in your closing time added to the supply pressure and compared with the rating (as the valve closure surge tool).
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Flow | L/min | Flow the line must carry. |
| Pipe inside diameter | mm | Inside diameter of the pipe. |
| Pipe length | m | Length of the pipe from supply to outlet (also the distance to the reflection point for surge). |
| Sum of fitting loss coefficients | Sum of loss coefficients for bends, tees and valves. | |
| Outlet height above the supply | m | Height of the outlet above the supply point (negative if below). |
| Kinematic viscosity | cSt | Kinematic viscosity (about 1 cSt for water at 20 °C). |
| Density | kg/m³ | Density of the liquid. |
| Pipe roughness | mm | Absolute roughness of the pipe bore. |
| Pressures and limits | ||
| Supply pressure (gauge) | bar | Gauge pressure at the supply point. |
| Least pressure needed at the outlet | bar | Pressure the outlet equipment needs. |
| Largest velocity | m/s | Largest velocity you accept (noise, erosion, surge). |
| Pipe or component pressure rating | bar | Lowest pressure rating of the pipe, fittings and equipment. |
| Valve and pipe wall | ||
| Valve closing time | s | Time a valve at the outlet takes to close fully. |
| Pipe wall thickness | mm | Wall thickness of the pipe. |
| Pipe elastic modulus | GPa | Elastic modulus of the pipe material (steel about 200 GPa, copper about 117 GPa). |
| Liquid bulk modulus | GPa | Bulk modulus of the liquid (water about 2.2 GPa). |
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: Flow
- What it is
- The volume of liquid the line must deliver to the outlet when it is running, at the busiest demand you want it to cover.
- Units and format
- Enter a number in L/min: litres per minute. The form accepts 0.000001 L/min to 1000000 L/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 L/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Velocity and surge rise in proportion to flow; friction loss rises roughly with its square.
- Get it right
- Type litres per minute, not litres per second or cubic metres per hour.
What this means: Pipe inside diameter
- What it is
- The bore of the pipe the liquid flows through, from the pipe standard or a measurement, not its nominal size or outside diameter.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Velocity falls with the square of the bore, so a small increase cuts friction loss strongly.
- Get it right
- Nominal size is often not the bore; look up the actual inside diameter for the pipe class or schedule.
What this means: Pipe length
- What it is
- The length of pipe between the supply and the outlet, measured along the run. It is also the distance the pressure wave travels for the surge check.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 100000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 120 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pipe friction loss rises in proportion to length.
- Get it right
- Measure along the actual route including vertical runs, not the straight-line distance.
What this means: Sum of fitting loss coefficients
- What it is
- The total of the loss coefficients for every bend, tee, valve, strainer and entry or exit in the line, each taken from fittings data and added together.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 10000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Fitting loss rises in proportion to this sum.
- Get it right
- Count every fitting, including fully open valves; they all add loss.
What this means: Outlet height above the supply
- What it is
- How far the outlet sits above the supply point. The liquid must be lifted through this height, which costs pressure.
- Units and format
- Enter a number in m: metres. The form accepts -1000 m to 1000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Each metre of rise lowers the outlet pressure by the weight of a metre of the liquid.
- Get it right
- Type a negative value if the outlet is below the supply; it then adds pressure.
What this means: Kinematic viscosity
- What it is
- The kinematic viscosity of the liquid at its working temperature, used to find the Reynolds number and the friction factor.
- Units and format
- Enter a number in cSt: centistokes (kinematic viscosity, 1 cSt = 1 mm²/s). The form accepts 0.000001 cSt to 10000 cSt. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 cSt as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- One centistoke is one square millimetre per second; viscosity changes with temperature.
What this means: Density
- What it is
- The mass per unit volume of the liquid at its working temperature. It sets the friction loss, the static lift and the surge pressure.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 2000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 998 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Pipe roughness
- What it is
- The average height of the roughness on the inside wall of the pipe, from pipe or fluid-mechanics data for the material and its condition.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.045 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Old or corroded pipe is rougher than new; type millimetres.
Pressures and limits
What this means: Supply pressure (gauge)
- What it is
- The pressure available at the supply point above atmospheric, as read on a pressure gauge, when the line is flowing.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0 bar to 1000 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Outlet pressure and peak surge pressure move one for one with it.
- Get it right
- Use gauge pressure, not absolute; a static reading with no flow can be higher than the flowing value.
What this means: Least pressure needed at the outlet
- What it is
- The lowest pressure the equipment at the outlet needs to work properly, from its maker’s data. The outlet pressure is compared with it.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0 bar to 1000 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use gauge pressure, the same basis as the supply pressure.
What this means: Largest velocity
- What it is
- The highest liquid velocity you accept in the pipe, to keep noise, erosion and surge in check. The tool also finds the smallest bore that meets it.
- Units and format
- Enter a number in m/s: metres per second. The form accepts 0.000001 m/s to 50 m/s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 m/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from your design standard or the pipe maker’s guidance.
What this means: Pipe or component pressure rating
- What it is
- The lowest pressure rating among the pipe, fittings and equipment on the line. The peak pressure during valve closure is compared with it.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0.000001 bar to 2000 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 16 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the lowest rated item, at the working temperature; it must be above the supply pressure.
Valve and pipe wall
What this means: Valve closing time
- What it is
- The time a valve at the outlet takes to go from fully open to fully shut. A closure faster than the wave’s return trip gives the full surge.
- Units and format
- Enter a number in s: seconds. The form accepts 0.001 s to 3600 s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Slower closure beyond the critical time reduces the surge in proportion.
- Get it right
- Quarter-turn valves and solenoid valves can close much faster than you expect; time them.
What this means: Pipe wall thickness
- What it is
- The wall thickness of the pipe. With the bore and the elastic modulus it sets how much the pipe stretches and so the pressure wave speed.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3.7 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Pipe elastic modulus
- What it is
- The elastic modulus of the pipe wall material, from the material data. A stiffer pipe gives a faster wave and a higher surge.
- Units and format
- Enter a number in GPa: gigapascals (1 GPa = 1000 MPa). The form accepts 0.000001 GPa to 400 GPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 GPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Type gigapascals; 1 GPa = 1000 MPa.
What this means: Liquid bulk modulus
- What it is
- The bulk modulus of the liquid: how strongly it resists being compressed, from fluid data at the working temperature.
- Units and format
- Enter a number in GPa: gigapascals (1 GPa = 1000 MPa). The form accepts 0.000001 GPa to 5 GPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2.2 GPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Type gigapascals; entrained air reduces the effective value a lot.
Method and formulas
- Velocity = Q ÷ A; smallest bore = √(4Q ÷ π v_max) (as the pipe size for velocity tool).
- Δp = (f L ÷ d + ΣK) ρ v² ÷ 2 with the Colebrook friction factor (as the pipe friction tool); outlet pressure = supply − Δp − ρ g × rise.
- Wave speed a = √[(K ÷ ρ) ÷ (1 + K D ÷ E t)]; surge = ρ a v, reduced by 2L ÷ (a t_c) for slow closure (as the valve closure surge tool); peak = supply + surge.
- Example: 300 L/min in a 60 mm bore runs at 1.7684 m/s, loses 0.78521 bar and leaves 4.2361 bar at the outlet; closing in 2 s peaks at 8.1178 bar.
Limitations
- Steady, single-phase flow; branches and demand diversity are not modelled.
- Surge by the rigid-column estimate; long or branched systems need a transient analysis.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a water or coolant supply line in a plant
- Check pressure at the far end of a line
- Set a safe valve closing time
Who it is for
- Plant engineers
- Maintenance engineers
- Building services engineers
What you get
- Velocity and the smallest bore for the limit
- Friction loss and outlet pressure
- Valve closure surge and peak pressure
Interpreting the result
- If the surge is too high, close the valve more slowly or reduce the velocity with a larger bore.
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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Open the Water Supply Line Check (Velocity, Friction Loss, Outlet Pressure, Valve Surge) calculator