Vibration switches
A vibration switch shuts the fan down when something starts to come apart. It is the least expensive component in the mechanical train and it protects the most expensive ones.
Understanding the component
A vibration switch senses excessive vibration at the mechanical equipment and trips the fan motor before a developing fault becomes a catastrophic one. The faults it catches are the common ones: imbalance of a rotating member, misalignment, defective bearings and failing couplings account for the overwhelming majority of mechanical failures.
There are two families. Mechanical switches use an inertia-sensitive armature that trips a snap-action switch when acceleration exceeds an adjustable set point: simple, rugged, and requiring a manual or electrical reset. Electronic switches use a piezoelectric crystal, convert its output to a velocity-proportional signal and compare it to a calibrated limit. They have no moving parts, offer adjustable time delay and self-test, and their sensitivity is not affected by machine speed.
Either type is available in weatherproof enclosures, with explosion-proof models for hazardous locations, which on a refinery or petrochemical tower is normally the requirement rather than the option.
We supply components for cooling towers from every manufacturer, including towers whose original makers no longer exist. If it is on your tower, we can identify it.
What actually goes wrong
These are the failures we find in the field, roughly in order of how often we find them. If you recognize one, we can usually tell you what to check next over the phone.
| Failure | What it means |
|---|---|
| It was never tested | By far the most common problem. A vibration switch that has never been function-tested is not protection, it is an assumption. Test it semi-annually. |
| Bypassed after nuisance trips | The switch trips, nobody can find a fault, and eventually it gets jumpered out. The next real fault then runs to destruction. |
| Set too high | Sensitivity wound up to stop nuisance trips until the switch no longer trips on anything short of a thrown blade. |
| Corroded enclosure or wiring | Water in the enclosure or the conduit. The switch is fine and the circuit is dead. |
| Startup nuisance tripping | High-inertia fans can trip a switch during acceleration. The correct fix is a startup time delay, not desensitizing the switch. |
Manufacturers and product lines
We are independent, so the recommendation follows your tower, your water and your duty rather than a single manufacturer's catalog.
Frank W. Murphy
VS2 Series shock-sensitive switches: detect vibration in three planes of motion, fully adjustable, magnetic latching, manual or electric reset, weatherproof case with an explosion-proof model for hazardous locations.
PMC/BETA
440 Series electronic switches: adjustable time delay, calibrated dial for setting limits, self-test function, built-in or remote transducer, cast aluminum enclosures to NEMA 3, 4 and 12 with explosion-proof models in the 450 series. No moving parts.
Metrix
Model 5550 Vibralert: inertia-sensitive mechanism operating a snap-action switch, 0–3600 RPM, external set point adjustment, local reset with optional remote reset and a 20–30 second startup delay, NEMA 4 / IP65 standard and NEMA 4X optional. Baseplates are available to suit most earlier models, including other manufacturers', which makes it a straightforward retrofit.
Names you may find on the nameplate
Including lines that are no longer current. Many of the towers we work on are thirty to fifty years old, and identifying the modern equivalent of a discontinued component is part of the job rather than an obstacle to it.
- Murphy VS2
- PMC/BETA 440
- PMC/BETA 450
- Metrix 5550 Vibralert
- Robertshaw Vibraswitch 365
- Robertshaw Vibraswitch 366
- IMI
What we would tell you on the phone
Replacing a Robertshaw Vibraswitch.
The Robertshaw Vibraswitch (models 366 and the explosion-proof 365) was extremely common on cooling towers and is no longer a current product. It is the switch we are asked about most often. Retrofit baseplates make substituting a current mechanical switch straightforward; send us a photograph of the existing installation and we will confirm the arrangement.
Fit it, then prove it works.
Ask for the switch to be function-tested at commissioning and record the set point. An untested trip circuit has caught nothing in the entire history of the equipment.
It is not a substitute for inspection.
A vibration switch is a last line of defense that stops a failure becoming a disaster. It does not tell you a disc pack is cracking. That is what scheduled inspection is for.
Usually replaced or inspected at the same time
Gear reducers
Right-angle fan drives, including direct replacements for the Marley Geareducer line. Frequently rebuilt in place.
View componentMotors
Cooling tower duty fan motors: severe duty and premium efficiency, single and two-speed, any horsepower.
View componentDrive shafts & couplings
Composite and steel drive shafts with flexible disc couplings: Addax, Amarillo, Rexnord Thomas and TB Wood's.
View componentFans
Fiberglass and aluminum fan assemblies, blades and hubs: Hudson, Amarillo Chittom, Moore and Cofimco.
View componentSend us the nameplate and we will identify it
The fastest route to a correct quote is a photograph of the nameplate and of the component in place. Model numbers get superseded and drawings go missing; photographs do not lie.
- Phone
- (713) 643-0691
- Shop & office
-
3811 Cedar Blvd Ste A
Baytown, TX 77523