Hoses and Branch Pressures

Loss of pressure due to friction loss

  • Friction loss varies directly with the length of the hose or pipe. (e.g. Double the length of the hose and you get double the friction loss.)
  • For the same velocity, friction loss decreases directly with the increase in diameter. (e.g. Double the diameter and you will halve the friction loss for the same velocity)
  • Friction loss increases in proportion to the square of the water velocity. (e.g. Doubling the water’s velocity increases the friction loss by four.)
  • Friction loss increases with the roughness of the hose’s interior. (e.g. All other things being equal, water moving through a rough unlined hose has a higher friction loss than in a smooth lined hose).
  • Friction loss, for practical purposes, is independent of pressure. In the RFS, the "rule of thumb" rate of friction loss is 100 kPa per 30 metre hose length.

Typical Branch Pressures

Branch Type Optimum Pressure Other Notes
Dial - A - Jet 500 kPa Each 30 m length of hose costs 100 kPa in pressure
AWG 500 kPa Every metre elevation costs 10 kPa of pressure
Elkhart 700 kPa  
Akron 700 kPa  

Questions

  • Using RFS "rules of thumb" for friction loss and height loss / gain, what pump pressure would be needed to supply a nozzle at 500 kPa at the end of a single line of hose consisting of 4 x 30 metre lengths, with the nozzle 15 metres above the level of the pump? (1050 kPa at the pump)