Importance of Flushing Velocity and Reference Guide

When it comes to flushing a big pipe network, multiple questions surround the project team. How fast should the water flow? Is there an ideal velocity for achieving the best results? There are many cases where the team doesn’t even know the flushing practices and their importance, where they struggle to get the right quality of water, and because they don't know the right practices, they end up losing time, resources, and extra water for flushing.

Hundreds of workers work on a project, which clearly indicates the high uncertainty of following healthy practices of maintaining pipes free from dirt, metal particles, etc. In my experience, I have come across many weird experiences, even post flushing I got to see, safety jackets, gloves, welding particles, and plastic in a strainer. Even there are many cases, where you won’t find the right quality of water.

In this post, we’ll uncover the right flushing velocity.

Bad Flushing Can Result In

1.????? Frequent chocking of strainers

2.???? Choking/damage of cooling coil

3.???? Puncture of copper tubes

4.???? Erosion of metal surfaces

5.???? Poor water conductivity

6.???? Corrosion of pipe

Let’s try to understand!

Why Velocity Matters in Flushing?

Every particle whether it is small or big has its inertia, hence some force is required to push it and this force is nothing but the water velocity (kinetic force). In the quest for the perfect flush, velocity plays a crucial role. The speed at which water flows through your pipes determines how effectively it can clear away waste and maintain a healthy piping system. Imagine a slow versus a rushing stream, the difference in speed can drastically impact the flushing performance.

Water that moves slowly may have difficulty pushing waste through pipes, which can result in partial clogs and settled particles. Achieving the right balance is essential for optimal waste removal while avoiding unnecessary water waste.

How to identify the right velocity?

well, it is simple, have a test rig with a transparent pipe with the expected foreign particles in the pipe. Run the pump and conduct the velocity measurement, increase the pump speed until the heaviest particle doesn’t move and mix in the main stream and that’s your right flushing velocity. Please take note, that flushing velocity is dependent on the particles and pipe size, it varies. But in practice it is not feasible to conduct a velocity identification test, where BSRIA (Building Services Research and Information Association) comes into the picture, BSRIA has published a pipe flushing guidance document “AG 1/2001.1” Pre-Commission Cleaning of Pipework System. This document provides the best industry practices for pipe cleaning and flushing, specifically for heating and cooling system pipes. Some more research papers give a theoretical approach to calculate the required velocity in the respective size of pipe.

The flushing velocities presented in Table 5 of “AG 1/2001.1”?Can be referred to as the pipe flushing activity. The recommended minimum flushing velocities increase with the pipe diameters and vary around 1.0 to 2 m/s to displace small particles present inside the pipework. This velocity can be referred to considering the average particle size of 10mm metal

Another important aspect of achieving the minimum flushing velocity is to

reach a minimum shear stress on the internal surface of the pipework to force the removal of any loose deposit or residue that would have formed or settled during installation.

Apart from flushing velocity, having a drain point at the right location and a flushing loop of sufficient size is very important. Draining water with a certain momentum is equally important; this will help to flush out the particle effectively. Many times, draining water creates a vacuum in the system, which disturbs the draining. Special care must be taken to avoid a vacuum trap by opening enough vents to replace water with air.

Referring to this table will help to develop the flushing program, and can define whether there’s a need for an extra pump to meet the targeted flushing speed or not.??

I hope this crucial information will help industry professionals to deliver good quality systems and ease life.