Most of the service questions I receive have to do with control and operation of Centrifugal blowers.  "It has always been operating fine, but now it is doing something different!"   When the equipment is new, and the piping connections are confirmed installed correctly, it is just a matter of setting the inlet & outlet valves, whether manually operated, or auto controlled, to achieve the desired air/gas flow and operation.  After they have been in operation for a few years, however, components can fail.

There is very little PM maintenance recommended for the piping components: butterfly valves, check valves, expansion joints, and isolation valves.  Recognizing when they are not working correctly is important to identifying the cause of a failure.   I've seen simple butterfly valves turn up with broken pins which result in the hand lever moving, but the shaft that turns the 'flapper' doesn't!  One time a busted up air filter media had gotten stuck in the valve preventing it from moving properly. The inlet butterfly valve needs to move freely from open to close, with the corresponding amp draw of the motor changing accordingly.  

Check valves can cause the most problem when the sealing element(silicone rubber) deteriorates, or the hinge pin breaks and half of the valve falls into the blower/piping.  This is usually due to the valve "clacking" too often, resulting in failure.  On the other side of the spectrum, if the check valve seldom cycles(a spare not in operation), the heat in the piping manifold can fuse the sealing element to the side of the pipe. In this case, one half of the valve could "stick" closed, resulting in low flow.  As the Lamson Service Manager years ago, I once had a customer in Taiwan who insisted the low flow conditions they were experiencing were due to incorrect impeller configuration.  They paid over $10K for me to go there and remove the check valve to confirm the valve was indeed stuck!

Expansion joints, and flex piping sleeves can last years before drying out and cracking.  The problem is, they can flake even more on the inside where you can't see the deterioration.  This can also result in decreased flow and/or low pressure.  A local WWTP reported severely deteriorated expansion joints and was looking for some sort of warranty replacement.  We later determined the "rubber" had been effected by the methane, and other noxious gases in the blower room.  They had to be replaced after only 4-5 years of operation, but not under warranty. 

Regular monitoring & inspection is the best defense in preventing unexpected failures.  When you can plan, and budget for, repairs, your world is a little better place to live in.    Invest in PM, it can save you money.