Orifice Size and Air Flow Control

Role of the Diffuser Holder Orifice Hole

Have you ever stood at the top of an aeration tank and observed what appears to be no air reaching the diffusers at the end of the pipes? One thing causing this may be an improperly sized diffuser orifice.

A diffuser holder orifice hole is required in all aeration systems because flowing gas takes the path of least resistance and flows to a point of lowest pressure. As air travels through the manifold and distribution system piping, friction headloss is created between the air and the wall of the pipe. With the distance between the diffuser closest to the dropleg and the diffuser furthest away from the dropleg possibly being over 100 feet, a method was required to overcome the difference in headloss caused by the piping system. The diffuser holder orifice does just that.

The roll of the orifice is twofold. First, the orifice creates a consistent amount of headloss throughout the aeration system which allows the air to evenly spread throughout the grid. This results in the diffusers operating at approximately the same air rate which increases oxygen transfer efficiency and minimizes premature fouling of the diffusers. If you have ever witnessed air leaving through the diffusers closest to the dropleg, an improper orifice size may be to blame.

Second, in the rare case of diffuser failure where the diffuser tears or substantially unseats from the diffuser holder, the orifice acts as a choke point to prevent all of the air from leaving through the point of failure (i.e. the newly created path of least resistance). This allows the aeration grid to continue functioning until the grid can be serviced.

Experienced teams will design every grid to ensure the air is properly balanced across the range of operating conditions while at the same time minimizing the back pressure on the blowers. Correctly sizing the orifice results in increased oxygen transfer efficiency of the system and minimizes the premature fouling of diffusers.