Water velocity
The faster water travels through a pipe the greater the friction losses will be. Conversely, the slower the water travels, the lower the friction losses will be. The rate of friction loss is not linear as water speeds increase. There is a soft maximum flow rate for each pipe size in excess of which the rate of friction increase rises dramatically:
- 38 mm (1.5 in.) = 144 litres per minute (lpm) (38 gallons per minute [gpm]) suction / 189 lpm (50 gpm) discharge;
- 51 mm (2 in.) = 235 lpm (62 gpm) suction / 322 lpm (85 gpm) discharge;
- 63.5 mm (2.5 in.) = 333 lpm (88 gpm) suction / 447 lpm (118 gpm) discharge; and
- 76 mm (3 in.) = 511 lpm (135 gpm) suction / 689 lpm (182 gpm) discharge.
These values are arrived at by following the guideline of not exceeding 1.8 m/s (6 fps) velocity on suction lines and 2.4 m/s (8 fps) on return lines. This basis for maximum water velocity exists not only as a safety standard, but also as a working standard for efficiency and longevity of plumbing systems and, therefore, has been widely adopted in the pool industry.
This introduces the concept of a working value for maximum water velocity. There is no true maximum flow rate for a given pipe size since increasing the pump power will increase the flow rate in any situation, at least to a certain degree. There is, however, a value to indicate the maximum flow rate beyond which there is a sharp decrease in efficiency as a result of an increase in the friction experienced from pushing the water through the pipes.
Turbulence becomes greater as the velocity of water increases, which has a direct negative impact on the circulation system’s efficiency.
Turbulence
Turbulent water does not move efficiently; therefore, pool systems should be designed to minimize turbulent water flow. Choosing the correct plumbing fittings and valves, and installing them in the proper orientation, will go a long way towards reducing turbulence in a plumbing system. For example, a pump should have a long, unobstructed run of pipe into the suction-side port.
Having a serious flow restriction like a valve, or a sharp-bend elbow, directly in front of the pump inlet, will increase the rate of turbulence in the water as it enters the pump chamber. The smoothness of the pipe wall also contributes to the amount of energy lost to friction in a plumbing system. This is one reason why flex PVC is inferior to rigid PVC, as the striations in the pipe wall are a flow restriction. Pool systems that use multiple sharp-bend elbow fittings or fittings too close to the pump inlet should be altered to reduce unnecessary energy loss due to poor flow dynamics from turbulence.
t’s surprising how often pipes that are too narrow or plumbing runs that include too many tight turns are designed into a pool’s core systems, causing the pump to work harder than it has to. Also a good tip is to Larger filters have a bigger surface area through which water can flow, which means your pump doesn’t have to work as hard to move the same volume of water. Not only does this lower the pump’s energy consumption, it can extend the life of the pump which saves you money as well. https://bluewaterspoolservices.com/variable-speed-pumps/