By Chad Edmondson
Excessive vibration in cooling towers is a problem that must be avoided at all cost. At the very least, vibration can cause excessive noise, giving rise to complaints. At the other end of the spectrum, depending on the source of the vibration, it can result in serious damage to the cooling tower itself. Early detection and inspection of the cooling tower to find the source of the vibration (shaft misalignment, broken gear teeth, imbalances etc.) are key to avoiding downtime and more serious structural damage.
Vibration cut-out switches are installed on cooling towers as a safety measure to (1) detect excessive fan drive vibration and (2) shut off the fan before the vibration causes damage to the drive system or the tower itself.
There are two types of vibration cut-out switches, mechanical and electronic.
Mechanical switches, which are more common, are simple in set-up and operation. Factory built towers typically ship with mechanical switches installed on them. However, they must be calibrated and adjusted prior to start-up of the tower, which is a simple process that includes only a few steps. Directions for this set-up process are included in the tower set-up instructions.
A mechanical switch detects excessive fan drive vibration (caused by fan icing or any mechanical fault) and promptly shuts off the fan before serious damage results and signals an alarm so the operator knows to come look at the tower.
Electronic switches do the same, but they also have options that include remote reset and/or start-up delay (presumably to ensure the source of the problem is investigated). Electronic switches are designed to communicate with building management systems so the set-up naturally involves wiring and some amount of programing.
High Tech Isn’t Always Better
At first consideration it may seem that an electronic switch is the way to go. After all, they offer more features and sophistication. But there is a practical downside to their operational convenience. They make it a little too easy to remotely restart the fan before investigating the source of the problem and this can have dire consequences.
This is one of those instances where we at JMP advocate the simple over the sophisticated.
We tend to recommend mechanical vibration cut-out switches because they force inspection and repair of the vibration source before restart of the tower, which makes them great for overall protection of the tower. Mechanical cut-out switches do their job and that minor inconvenience of a local restart may actually save your tower.