A vibration isolator on a chiller, a pump set or an air handling unit does two jobs that are easy to confuse. It stops machine vibration reaching the building structure, where it becomes audible noise in occupied space. And it lets the pipework move — thermally, and in a seismic event — without loading the machine’s nozzle. They are different requirements and an assembly that is right for one can be wrong for the other.
What this service does to a hose
Noise transmission is a structural path. A chiller compressor at 50 Hz puts that frequency into everything bolted to it. Rigid pipe carries it into the building and it re-radiates as a hum in the floor below. A braided hose in the line breaks that path — but only if the assembly is long enough and slack enough to be compliant. A short taut hose between two rigid flanges is a mechanically stiff element and it conducts the vibration almost as well as pipe does. Length is the specification here, and it is the thing value engineering removes first.
Orientation decides whether it works. A hose is compliant in bending and offset and very stiff axially. Fit it in line with the movement and it takes the load rather than absorbing it. Fit it across the movement and it works as intended. On a chiller, that usually means the hose sits perpendicular to the direction the nozzle moves — see movement types.
The water chemistry is still the corrosion duty. Everything on the chilled water page applies. The isolator is a cooling-water assembly with a mechanical job on top.
Seismic movement is a different case again. A hose sized for 50 Hz low-amplitude vibration is not automatically sized for the large single displacement a seismic joint must survive. If the building has a seismic requirement, that is a stated displacement and it belongs on the enquiry.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Hose | 316L annular corrugated. 304L only where the water chemistry is known and controlled | It is a cooling water duty first and a mechanical one second |
| Braid | 316L wire, single braid at HVAC pressures; double where the assembly also restrains thrust | A braid carries pressure thrust; without it the assembly extends |
| Ends | Flanged or grooved to match the plant room standard, one end swivel where alignment is tight | So the pair can be lined up without twisting the hose |
| Length | Generous. Long enough to be genuinely compliant at the isolation frequency | A short taut hose transmits vibration nearly as well as pipe |
| Control | Control rods or a tied arrangement where the pipework is not otherwise anchored | Unrestrained pressure thrust will extend the assembly |
What we would not fit, and what happens
A short taut assembly. It looks neat, it satisfies the drawing, and it does not isolate anything.
A hose installed along the line of movement. It becomes a tie rather than an isolator.
An unrestrained assembly in a line with no anchors. Pressure thrust extends it and the machine nozzle takes the difference.
An isolator specified without the water chemistry. It will fail on corrosion long before it fails on vibration.
What we need to size it
| We need | Because |
|---|---|
| Machine type and its dominant frequency | It decides how compliant the assembly has to be |
| Direction and amplitude of the nozzle movement | It sets the orientation and the length |
| Whether a seismic displacement is specified, and how much | It is a different and much larger movement case |
| Whether the pipework is anchored either side | It decides whether control rods are needed |
| Chloride content of the circulating water and any glycol | The corrosion duty underneath the mechanical one |
| Flange or groove standard and the space available | Plant rooms are tight and the bend radius has to fit |