Hydraulic calculations for stainless steel piping systems
Flow rate, medium velocity, pressure loss. Resistance coefficients and worked examples.
Basic hydraulic quantities
To design a TAVINOX PRESS piping system you need to know:
- Q — flow rate [l/s or m3/h]
- v — velocity of the medium [m/s]
- dp — pressure loss [Pa or bar]
- L — length of the pipework [m]
- d — inside diameter of the tube [mm]
They are related by: Q = v x A, where A = pi x d^2 / 4
Inside diameters of TAVINOX PRESS tubes:
- OD 15: di = 13 mm
- OD 18: di = 16 mm
- OD 22: di = 20 mm
- OD 28: di = 26 mm
- OD 35: di = 33 mm
- OD 42: di = 40 mm
- OD 54: di = 52 mm
Maximum velocities of the medium
Recommended maximum velocities for the various applications:
- Drinking water, cold: 2.0 m/s
- Drinking water, hot: 1.5 m/s
- Heating (closed circuit): 1.0 m/s
- Cooling: 1.5 m/s
- Compressed air: 10–15 m/s
- Fire protection pipework: 3.0 m/s
Exceeding these values causes excessive noise, erosion of the surface and increased pressure loss.
Calculating the friction pressure loss
Friction pressure loss from the Darcy-Weisbach equation:
dp = lambda x (L/d) x (rho x v^2 / 2)
Where:
- lambda = friction factor (approx. 0.017–0.020 for stainless steel)
- L = length of the run [m]
- d = inside diameter [m]
- rho = density of the medium [kg/m3] (water at 20 °C = 998 kg/m3)
- v = velocity of the medium [m/s]
Example: OD 28 (di=26mm), L=10m, v=1.5 m/s: dp = 0.018 x (10/0.026) x (998 x 1.5^2 / 2) = 7,765 Pa = 0.078 bar
Local resistances of fittings
The pressure loss across fittings is calculated with the zeta coefficient:
dp = zeta x (rho x v^2 / 2)
Indicative zeta values for TAVINOX PRESS fittings:
- Elbow 90°: OD 15–22: 1.2 | OD 28–42: 0.8 | OD 54–108: 0.5
- Elbow 45°: OD 15–22: 0.6 | OD 28–42: 0.4 | OD 54–108: 0.3
- Tee, straight run: OD 15–22: 0.5 | OD 28–42: 0.3 | OD 54–108: 0.2
- Tee, branch: OD 15–22: 1.8 | OD 28–42: 1.3 | OD 54–108: 1.0
- Threaded adaptor: OD 15–22: 0.4 | OD 28–42: 0.3 | OD 54–108: 0.2
Total pressure loss = friction loss + the sum of the local losses + the difference in height
Would you like the TAVINOX PRESS installer certificate?
Complete the online training and get a certificate valid for 2 years.