Checklist: Verifying Screw Compressor Noise and Vibration Data
Use this checklist to verify screw compressor noise vibration claims before commissioning. Check decibel measurements, vibration readings, documentation, and site conditions to confirm supplier data matches reality and meets your facility requirements.
- Record noise and vibration readings at the same time and under identical operating conditions.
- Verify that supplier decibel and vibration figures use the same measurement method you use on site.
- Check that the noise enclosure or silencer is included in the quoted data.
- Compare vibration readings against the machine manufacturer's published limits, not just your own expectations.
- Keep a signed inspection record for warranty claims and future maintenance planning.
Why verify noise and vibration data before commissioning
Supplier specifications for screw compressor noise vibration often look clean on a datasheet. In practice, the numbers change when the unit sits on a concrete pad, hears the intake air, and runs at full load. Before you hand over the commissioning keys, you need a repeatable way to check what the machine actually does in your plant.
A short inspection list does three jobs. It protects the installation from a mismatched expectation. It gives you a defensible record if a warranty claim is needed later. It shows the supplier you know what you are buying.
The core of the work is simple. Measure sound pressure level at a defined distance. Measure vibration at defined points. Compare both to the documented data. Repeat the test under the same load so the numbers are comparable.
How to prepare the site for a fair test
The first red flag is a noisy or uneven site. If the compressor is set on a vibrating foundation, near a running fan, or in a small room with hard walls, the readings will be inflated.
Before you start, confirm the base is level and the anchor bolts are torqued to the supplier’s specification. Check that the intake line is sealed and that the exhaust is not discharging into the immediate test area. If the unit has a sound enclosure, confirm it is closed and locked. If the data you are verifying assumes an open skid, do not test with the enclosure shut.
Pick a quiet time. Avoid running tests while a forklift is moving the same floor or a large door is open to a loading dock. A five minute pause in surrounding noise is usually enough to get a stable reading.
Write down the ambient conditions. Air temperature and humidity do not move the needle much, but a note about them helps if you revisit the test months later.
What to measure for screw compressor noise vibration
Sound pressure level is measured in decibels. The most common reference point is 1.5 meters or 3 meters from the loudest point of the compressor, depending on the standard the supplier follows. Do not rely on a phone app for this check. Use a calibrated sound level meter set to the same weighting and time constant the supplier used.
Vibration is usually measured in millimeters per second, or RMS, at the motor feet, the compressor housing, and the base frame. Use an accelerometer or a contact-type vibration meter. Take readings in three directions: horizontal X, horizontal Y, and vertical Z. A single number does not tell you where the problem is.
Keep the load stable. Run the unit at the same pressure setpoint for at least ten minutes before recording. If the compressor cycles, note the on and off times. A reading taken during the off cycle is not useful for comparing to a continuous load data sheet.
How to compare your readings to the supplier data
The comparison only works if the methods match. If the supplier quotes a free-field A-weighted reading at three meters, your test must use the same distance, the same weighting, and the same time constant. If they quote a vibration value in peak to peak but your meter reads RMS, convert before you compare.
A useful practice is to put the two numbers side by side on a single sheet.
| Measurement | Supplier Value | Your Value | Unit | Pass or Fail |
|---|---|---|---|---|
| Noise at 1.5 m | 84 dB(A) | 86 dB(A) | dB(A) | Pass |
| Noise at 3.0 m | 78 dB(A) | 78 dB(A) | dB(A) | Pass |
| Motor foot vibration | 2.5 mm/s | 3.1 mm/s | mm/s | Review |
| Base frame vibration | 1.2 mm/s | 1.4 mm/s | mm/s | Pass |
| Intake noise | 72 dB(A) | 75 dB(A) | dB(A) | Pass |
The “Review” row is where the real work happens. A vibration reading that is higher than the supplier’s number but still below the general industry limit for the machine type may be acceptable. A reading that is higher than the limit is not.
Common red flags during the inspection
Watch for a supplier that only provides one noise figure. A real data sheet will break the number down by load and by distance. If you only see a single decibel value, ask for the test standard and the operating condition that produced it.
Another red flag is a vibration reading that is very low on paper but the machine shakes visibly. If you can feel the skid move under your palm while the compressor is running, the accelerometer is likely not picking up the full picture. Re-check the contact point. A loose cable or a soft patch of foam between the sensor and the metal will give you a false low.
Do not accept a verbal assurance that the unit is quiet. A datasheet is a claim. A measured value is a fact. If the two do not match, stop and ask for an explanation before you sign the commissioning certificate.
How to document the results
A short written record is better than a long email thread. Use a simple form. Include the date, the time, the load pressure, the ambient temperature, the meter serial number, the calibration date, and the person who took the reading.
Attach the raw meter printouts. If you use a digital meter, export the CSV or the screen capture. Keep the file with the commissioning folder.
If a reading fails, write down the exact value and the exact point where it was taken. “The motor was loud” is not enough. “The right motor foot measured 4.8 mm/s in the horizontal X direction while the unit ran at 7 bar” is enough to start a repair.
How to handle a failed reading
If the noise or vibration data does not meet the agreed limit, do not just accept a promise of a future fix. Ask for a written corrective action. The supplier should identify the cause. A loose intake flange, a worn bearing, an unbalanced fan, or a missing rubber mount will each need a different fix.
If the cause is a site issue, such as a hard concrete pad that transmits vibration into the building structure, the fix may be on your side. If the cause is inside the compressor, the fix is on the supplier’s side. The inspection record is what separates the two.
Keep the unit running at the agreed load while the corrective action is performed. Re-run the full checklist after the fix. Do not move on until both the noise and the vibration pass.
How to integrate this into your commissioning plan
This checklist is not a one time event. It is a gate in the commissioning process. It comes after the unit is installed and anchored, but before you hand the unit over for normal production. It also feeds into your preventive maintenance plan.
Record the baseline noise and vibration values in your asset management system. When you do your annual inspection, compare the new readings to the baseline. A slow drift in vibration is an early warning for bearing wear. A sudden rise in noise can point to an intake restriction or a developing mechanical fault.
The same method that protects you at commissioning protects you for the next ten years of operation.
When to call in an independent inspector
If the supplier and your site team disagree about the readings, or if the noise is high enough to affect neighboring offices, bring in an independent acoustics firm. They can provide a formal report that both parties can use. The cost is usually small compared to the delay or the warranty dispute it prevents.
The same is true for vibration. If the machine is on a critical process line and the vibration is near a limit that could affect downstream equipment, an independent mechanical inspection is worth the time.
The goal is not to be difficult. The goal is to have a clear, shared record of what the machine does and what it was promised to do.
Frequently asked questions
What distance should I use to measure screw compressor noise?
Use the distance stated in the supplier's data sheet. If it is not stated, use the standard distance for the machine type, often 1.5 meters or 3 meters from the loudest point.
Can I use a smartphone app to verify vibration data?
No. A smartphone app is not a calibrated measurement instrument. Use a dedicated accelerometer or a contact-type vibration meter for a valid reading.
What is the difference between noise and vibration?
Noise is air pressure fluctuation measured in decibels. Vibration is mechanical movement measured in millimeters per second. They are related, but they are different physical quantities.
Should I test the compressor with the sound enclosure open or closed?
Test it in the state it will run in. If the data you are verifying is for the enclosed unit, close the enclosure. If it is for the open skid, leave it open. Do not mix the two.
What if the vibration reading is higher than the supplier's number but still within general industry limits?
Record it and review it with the supplier. A reading that is higher than the quoted value but still below the machine manufacturer's limit may be acceptable. A reading above the limit is a failure.
