Reduce pipework pressure by 90% with this trick

‘Friction losses’ is the name given to the friction caused by pumping fluid through a system. This includes the friction between the fluid being pumped and the walls of the pipe; or the pressure caused when the fluid goes through a restriction such as a valve.

Just considering the friction against the walls of the pipe, the amount of pressure created is dependant on four main variables:

The relative viscosity of the fluid being pumped
The volume of fluid being pumped
The material of the pipework
The size of the pipework

Many systems cannot change the first two variables, so this update focuses on the impact of the pipework.

The reason the friction losses are increased when the pipe size reduces is because the fluid has to move faster for the same volume to be transferred. For example, if 10 cubic metres per hour of water is being pumped in a 3" diameter pipe, it is moving at 0.55 metres per second. If the same quantity is being pumped in a 2" diameter pipe, it is moving at 1.42 metres per second. This increase in speed generates much more friction.

Calculating the actual friction losses involves some fairly complex mathematics, but here is a straightforward example. If 10 m3/h of water is pumped through 100m of straight 3" steel pipe, the extra pressure generated is equivalent to 0.79m head. If the same volume of water is pumped in the same conditions but with a 2” steel pipe instead of 3”, the friction losses are equivalent to 7.8m head. That’s 10 times as much pressure!

Considering the material of the pipework, if the 3” steel is changed for 3” uPVC pipework, the friction losses are equivalent to 0.62m head, a further reduction of approximately 22%. This is based on the pipework being new steel, but over time the steel will corrode which is another increase to the friction losses.

So why does this interest a pump technician? At deckpro pumps we’re always looking for the most effective pump solution, and this means considering how the cost of an installation can be reduced. If the pressure is kept to a minimum, then:

The pump size can be kept low, reducing the purchase cost
Energy consumption will be lower, reducing the running cost