Vibration isolators must be carefully selected to achieve the required deflection for the load that is to be supported. If the load is less than anticipated, the deflection will be reduced, as will the level of isolation achieved. If the load is more than anticipated, this may be beyond the vibration isolator’s capacity, in which case it is likely that it will become solid and not provide any isolation.
Common causes of differences between actual and anticipated loading include pipework or other equipment being supported from the isolated equipment, uncertainties/errors in the manufacturer’s data; equipment used being different to that anticipated or specified; equipment being operated incorrectly.
In this case, the supported cooling tower has been overfilled, resulting in the springs being over-compressed. There is just enough overload capacity in this spring to prevent it from ‘going solid’ so the spring is still providing good isolation—although the best solution is to ensure the cooling tower is correctly filled.