Dear Mr Zegait, I see that ...

Dear Mr Zegait,

I see that you already have a large number of useful replies, I will nevertheless add my take on the problem you describe.

I am assuming that you refer to a problem in a pipe network and not a problem in a house.

The problem you describe is influenced by a variety of factors such as flow velocity, vertical profile of the pipe, the speed with which the valve is shut and pipe material to name a few. The problem is best described by the Joukowsky equation that describes how the change in pressure (that causes the knocking) is influenced by the change in flow velocity and the celerity. The latter is a function of the pipe material properties and the properties of the liquid amongst others. Most modelling software packages are based on this equation.

Given the large number of factors it is not surprising that there are a large range of solutions and consequently there is not a "one solution fits all". I suggest that it may be worthwhile to engage an expert to assist you.

Kind regards,

Franciscus Maas

Senior Hydraulic Engineer

Opus International Consultants Ltd