If air release valves are wrongly selected or fitted in an incorrect position, air related problems will persist in the form of noisy pumps.
Remember, air and centrifugal pumps do not go together.
If air enters the suction side of the pump, be it positive displacement or centrifugal, pumping problems such as loss of performance and noise will occur.
Once air is entrapped in a system, it can take a long time to be eradicated. If air release valves are not fitted in the highest part of a system, it can take days to expel.
A recent experience we had was in a multi-density apartment block. We were called to perform a pump repair, and noticed that bleed cocks were fitted but not at the highest point. We released as much air as we could when we returned with the repaired pump. A few days later, tenants were complaining of excessive noise. An air pocket had formed in the remote part of the piping.
We returned to the site and fitted a small ¼” hose to the bleed cock and ran the hose to the floor drain. The bleed valve had to be monitored and left open throughout the weekend to ensure that all the air was released.
Had an automatic air release valve been fitted originally, these problems would have been avoided.
Another problem we’ve encountered is shown in this diagram. Again the air release valve position is incorrect as it will only properly service one pump.