Hey guys, if you’ve ever worked with double screw pumps (you know, the workhorses for moving everything from lubricants to food-grade syrups or even heavy crude oil), you’ve probably ran into that annoying noise issue. Like, one day it’s humming along fine, the next it’s sounding like a jet engine idling right next to your control room – and suddenly no one’s happy. As a double screw pump supplier, I get this question all the time: “How the hell do I actually measure the noise level of these pumps correctly?” It’s not as simple as just grabbing a random decibel meter and pointing it, right? Let’s break this down the way I actually do it for my clients, no fancy jargon that makes your eyes glaze over. Double Screw Pump
First, let’s cut through the confusion: noise level measurement for double screw pumps isn’t a DIY trick you can wing in 10 minutes. These pumps are precision built, but their noise comes from a handful of specific places – the rotating screws meshing, fluid turbulence in the chambers, even vibration from the base or pipes attached. Mess up the measurement setup, and you’ll get a number that’s way off, leading to you buying unnecessary noise dampeners or missing a real issue that’s gonna blow up later.
Let’s start with the basics of gear before you even pull out the meter. I’ve seen so many guys skip this part and mess the whole test. First, you need a decent sound level meter (SLM) – forget the $20 ones from the hardware store for this. We’re talking about a Class 1 SLM, the kind that’s calibrated for industrial use, not just your weekend concert checks. Class 1 means it’s accurate within like ±0.5 dB, which is critical because a 2 dB difference is the line between “normal operation” and “something’s broken.” Also, you need a calibrator – that little wand that blasts a known 94 dB or 114 dB tone. You calibrate your SLM before every single test, no exceptions. I once had a client skip calibration, got a reading 8 dB higher than actual, and spent $2k on acoustic panels that did nothing. Oops.
Next, the test setup. This is where most people go wrong. First, the pump has to be running under actual working conditions – not the half-load test run the warehouse does when it ships. If it’s a pump going into a refinery moving heavy oil, you run it with that exact oil, at the exact flow rate and pressure it’ll see in the field. No water testing here – fluid viscosity changes vibration and noise big time. Also, let the pump warm up for at least 30 minutes before testing. New pumps are tight when they’re cold, so they’ll hum louder until the oil heats up and lubricates the screws properly. I always tell my field techs to set a timer – no skipping warm-up, ever.
Now, the environment. You can’t test a pump in a big empty room with concrete walls, because those will reflect sound and make the reading higher. Ideally, you test it in a semi-reverberant space, or even better, outdoors on a flat, hard surface at least 10 feet away from any other walls or equipment. Also, you have to make sure there’s no background noise masking the pump’s sound. If the AC unit is blowing at 50 dB, that’ll throw off your pump reading if it’s only at 65 dB. So, you calculate the background noise: if background is more than 10 dB lower than the pump’s noise, it’s fine. If it’s less, you have to subtract it using this simple math: take the total measured noise, subtract a correction factor based on the difference. For example, if total is 70 dB and background is 63 dB (difference of 7 dB), you subtract 0.8 dB, so your pump noise is like 69.2 dB. Don’t stress the exact math – just remember: background noise matters, and if it’s too loud, pick another time or spot to test.
Now, the actual measurement points. This is specific to double screw pumps, because their noise isn’t evenly distributed around the unit. The two loudest spots are usually the inlet/outlet ports (turbulence from fluid moving through those) and the gear end (where the motor drives the screws – that’s the meshing noise you hear most). The standard we use (ISO 10816-7, but I’ll explain it like normal people) is to take measurements at 4 key points: 1 foot away from the pump’s centerline, at 0°, 90°, 180°, and 270° around the unit. Wait, why? Because the outlet might be facing east, and if you point the meter west, you’re picking up less noise from the high-pressure fluid exiting. Also, take readings at both the gear end and the pump head end, because sometimes wear on the screws will make the pump head quieter but the gears noisier. Oh, and don’t hold the meter right next to the pipes – pipe vibration amplifies noise, so keep it 12 inches away from the pump’s casing, not the connected hoses or pipes.
Another thing: time weighting. Most SLMs have a “fast” and “slow” setting. For double screw pumps, use fast (125 ms) because these pumps have periodic noise from the screws meshing, so slow will average it out and hide spikes that mean something’s wrong. Also, frequency weighting – use A-weighting, not C or Z. A-weighting matches how human ears hear noise, so it’s the standard for industrial pump noise. C-weighting is for super low-frequency noise that you can feel but barely hear, so that’s not what you want here.
Wait, let’s talk about what’s a “normal” noise level for a double screw pump, because that’s the whole point of measuring. From what I’ve tested with my pumps, a brand new double screw pump running at rated flow and pressure will be between 65 dB and 80 dB, depending on size. Small pumps (for food and beverage, 1-5 gpm) are around 65-70 dB, big ones for oil and gas (500+ gpm) are 75-80 dB. If it’s over 85 dB, that’s a red flag – something’s wrong. Common issues: misaligned motor or pump base, worn screw rotors, bad gear oil, or even a blockage in the inlet causing turbulence. I had a client last year who called saying his pump was at 90 dB – we ran the test and found a chunk of debris stuck in the inlet, causing cavitation. Fix that, and noise dropped 15 dB in 10 minutes. Game changer.
Also, keep a log. I tell every single one of my clients to write down every measurement: date, pump model, fluid type, flow rate, pressure, temperature, background noise, all the readings from the 4 points. That way, you can track changes over time. If the noise creeps up 5 dB over 6 months, that’s a warning sign before it turns into a catastrophic failure. I had another client who skipped logging, and his pump ran for 2 years with a small screw wear that turned into a full rotor replacement – cost him $15k, plus downtime. Don’t be that guy.
Wait, can you measure noise in the field without a Class 1 SLM? Yeah, if you don’t have one, but it’s less accurate. But if you’re troubleshooting, you can do a quick check: stand 3 feet away, if you have to raise your voice to talk over it, that’s over 75 dB. If it’s making a rattling or grinding sound instead of a hum, that’s definitely abnormal. But for official compliance (like OSHA limits, which are 85 dB for 8 hours of exposure), you need the proper gear. OSHA has specific rules for industrial noise, so make sure you’re checking that too – high noise levels aren’t just annoying, they’re a liability.
Let me also address a common myth: double screw pumps aren’t as loud as gear pumps, right? Yeah, that’s true when they’re working right. Gear pumps have that high-pitched whine that can hit 90 dB if worn, but a well-meshed double screw pump runs smoother, so lower noise. That’s one of the reasons my clients love them – less noise means a better working environment, no need for extra ear protection. But you still have to measure it to confirm it’s actually running like it should.
Another pro tip from my team: if your pump is installed with a flexible coupling between the motor and pump, make sure you’re not measuring the motor’s noise instead of the pump’s. If the SLM is picking up more noise from the motor, you’ll get a higher reading that has nothing to do with the pump itself. So, when you do the measurement, you can turn off the motor for 10 seconds (safely, after bringing the pump to a stop in a controlled way) to get a baseline of motor noise, then subtract that from your total to get pure pump noise.
Wait, let’s recap all the steps so it’s easy to follow, no skipping:
- Calibrate your Class 1 SLM with a certified calibrator right before testing. No exceptions.
- Prep the pump: run it at 100% rated flow/pressure with its actual working fluid, warm up for 30+ minutes.
- Control background noise: make sure it’s at least 10 dB lower than the pump’s noise. If not, adjust or subtract background.
- Test points: 4 points around the pump, 1 foot away from casing, 12 inches from pipes, measure both gear and pump head ends.
- Settings: A-weighting, fast time weighting, record for at least 10 seconds per point to catch any spikes.
- Log everything, compare to baseline for future checks.
Now, if you’re not sure how to do this, or you need help measuring noise for your double screw pump (whether it’s troubleshooting an old one or verifying a new pump you just got), hit me up. As a double screw pump supplier, I work with clients all over, helping them with noise testing, maintenance, and even custom pumps for specific noise requirements. We can walk through the process together, or if you send me your pump specs and operating conditions, I can even give you a baseline noise level to compare your measurements against. No pressure, just honest help for anyone working with these pumps.
And for anyone new here, trust me – measuring noise isn’t just a box to tick for compliance. It’s the easiest way to catch a problem early, before it turns into a huge, expensive mess. I’ve seen way too many pumps fail because of unaddressed noise issues, and half of those could’ve been fixed with a 10-minute noise test. So take the time to do it right, keep that log, and you’ll save yourself a ton of headaches down the line.
Progressive Cavity Pump References:
ISO 10816-7: Mechanical vibration – Evaluation of machine vibration by measurements on non-rotating parts – Part 7: Rotodynamic pumps for industrial applications, including measurements on rotating parts
OSHA 29 CFR 1910.95: Occupational noise exposure
ANSI S1.4: Specification for Sound Level Meters, Part 1: General Purposes
DEPAMU (Hangzhou) Pumps Technology Co., Ltd.
Address: No. 658, 20th Street, Hangzhou Economic & Technological Development Zone, Hangzhou City, Zhejiang Province, China
E-mail: international@depamu.com
WebSite: https://www.depamupumps.com/
