| Scenario | Inputs | Typical output |
|---|---|---|
| Low-pressure wash basin | ΔP 150 kPa, Kv 0.35, SG 1.0 | ~12 L/min (varies with aerator) |
| Standard public faucet | ΔP 300 kPa, Kv 0.56, SG 1.0 | ~23 L/min before flow restriction |
| Orifice-restricted outlet | ΔP 300 kPa, Cd 0.62, d 6 mm | ~11–14 L/min depending on losses |
Example outputs are illustrative; field losses can reduce flow.
1) Coefficient method
In US units, flow in gpm is estimated by Q = Cv · √(ΔP / SG), where ΔP is psi. In metric units, flow in m³/h is estimated by Q = Kv · √(ΔP / SG), where ΔP is bar.
2) Orifice method
The discharge equation is Q = Cd · A · √(2ΔP / ρ). Cd captures contraction and friction losses, A is area, ΔP is pressure drop, and ρ is density.
- Select the units used on site or in the specification.
- Enter upstream and downstream pressures to compute ΔP.
- Choose coefficient when Cv/Kv is known; choose orifice when diameter is known.
- Enter SG and density if you are not using clean water.
- Add faucet count and minutes per day for consumption planning.
- Click Calculate, then export results to CSV or PDF.
Why faucet flow matters on construction projects
Faucet flow affects commissioning time, water storage sizing, temporary works, and handwashing capacity. Underestimating flow can cause queues and hygiene risks, while overestimating flow can oversize piping, pumps, and treatment equipment. A repeatable calculation method supports consistent decisions across teams.
Key inputs that control performance
The dominant driver is pressure drop across the faucet or flow restriction. When pressure at the fixture is measured under flow, the estimate becomes more reliable. Specific gravity slightly adjusts performance for non-water fluids, and density is essential when using the orifice method.
Choosing between coefficient and orifice methods
If a manufacturer provides Cv or Kv, the coefficient method aligns with published performance curves. The orifice method is practical when the critical restriction is a known diameter, such as a flow insert or aerator. In both cases, real installations may lose pressure through hoses and upstream valves.
Example data for planning temporary facilities
Consider a site welfare block with 8 faucets used 12 minutes per day each. With ΔP = 300 kPa and Kv = 0.56, the calculator returns roughly 23 L/min per faucet. Total daily demand is about 2.21 m³/day, and a 30-day planning volume is about 66.3 m³.
Interpreting velocity and splash control
Outlet velocity is a practical indicator for splash risk and user comfort. High velocity can create excessive spray in shallow basins. If velocity appears high, specify a lower-flow aerator, increase restriction diameter control, or reduce pressure at the fixture using balancing valves or pressure regulators.
Quality checks and field verification
Validate results with a timed container test: capture flow for 10 seconds and scale to a minute. Compare measured flow to calculated flow to identify additional losses. When discrepancies are large, confirm gauge location, pipe fouling, supply pressure fluctuations, and any hidden restrictions.
Reporting and handover documentation
Exported CSV supports quick comparison across fixtures, while the PDF report fits into commissioning packs. Record the date, measured upstream pressure, faucet model, aerator type, and the calculation method used. This creates a defensible trail for audits and maintenance.
1) What pressure should I enter for upstream pressure?
Use pressure measured close to the faucet while water is flowing. Static pressure can be higher and may overpredict flow. If you only have static pressure, treat results as an upper estimate.
2) Should downstream pressure be zero?
For most open outlets discharging to atmosphere, downstream gauge pressure is near zero. If the outlet feeds a hose, spray gun, or equipment, use the backpressure you expect at the outlet.
3) I have both Cv and Kv. Which one is used?
The calculator prioritizes the coefficient that matches the chosen unit system. If only the other coefficient is provided, it converts it using a standard approximation and notes the conversion in calculation notes.
4) What Cd value is reasonable for an orifice?
Cd commonly ranges from about 0.60 to 0.98 depending on sharpness, thickness, and approach conditions. For quick estimates with small inserts, 0.62 is a practical starting value.
5) Why is my field flow lower than the calculated value?
Additional losses from flexible hoses, partially closed valves, clogged aerators, long runs, or undersized supply lines reduce pressure at the restriction. Measure pressure at the fixture under flow to reconcile the difference.
6) Can I use this for non-water fluids?
Yes, but enter the correct specific gravity and density. The coefficient method relies on SG, while the orifice method relies on density. Ensure compatibility with the fixture and verify with a controlled test.
7) How can I reduce excessive flow on site?
Install a rated low-flow aerator, add a flow insert, or use a pressure reducing valve upstream. Recheck pressure under flow and confirm that reduced flow still meets hygiene and cleaning requirements.