How to Make a Breast Pump Suction Gauge and Test Your Pump
If your breast pump suddenly feels weaker or you’re collecting less milk than usual, checking your equipment is a useful place to start. A vacuum gauge can help you see how much suction your pump is generating.
Below, I’ll show you the three parts you need, how to put them together, and how to read the result. You can also use the calculator to convert your pump’s published suction into the units on your gauge.
This suction gauge lets you check whether your pump is generating less suction than expected. Once you know the suction is low, the next step is figuring out why.
An incorrectly seated membrane, a loose connection, or a worn valve can all affect suction. If your reading seems off, check your attachments first: take the collection kit apart, inspect the parts, and put everything back together according to your pump’s instructions. Then test again before assuming the motor is the problem.
The gauge checks vacuum in this test setup. It doesn’t measure your milk supply or tell you whether your flange fits. For that, watching what happens while you pump still matters.
Here’s the assembled gauge inside a test flange. The stopper makes an airtight seal so you can read the vacuum generated in the collection kit. Use a spare flange that is compatible with your pump and keep this setup for testing.
What You Need: Three Parts for Your Suction Gauge
You’ll need a vacuum gauge, a matching threaded-to-barbed adapter, and a pre-drilled tapered stopper. You’ll also use a compatible hard plastic flange and the pump parts normally attached to it.
Use a hard plastic flange that works with your pump. If your pump came with a spare 24mm flange you don’t use for pumping, this is a great use for it. It’s also fine to use a different size. If you only have a smaller flange, the parts list includes different stopper sizes—just choose one that makes a snug seal in the flange you’ll use for testing.
Want to make this easier? I’ve put the parts together in an Amazon list so you don’t have to search for each one.
I don’t earn money from purchases through this list—I just wanted to save you the parts search. The list includes different stopper sizes, so choose one that fits the flange you’ll use for testing.
The photos below show the three parts. If you use another flange size, choose a stopper whose taper makes a snug seal without being forced deep into the tunnel.
A Vacuum Gauge: Choose a gauge that measures negative pressure, with a scale suited to breast pump vacuum. A 0 to −100 kPa or 0 to −1 bar range is one option. Check the unit printed on the dial—kPa, bar, and MPa are different scales.
A Matching Adapter: Use a threaded-to-barbed adapter that matches your gauge’s thread size and type. For a gauge with a 1/4-inch male NPT connection, you need a matching 1/4-inch female NPT adapter with a barb that fits your stopper’s hole.
A Vacuum Gauge: Choose a gauge that measures negative pressure, with a scale suited to breast pump vacuum. A 0 to −100 kPa or 0 to −1 bar range is one option. Check the unit printed on the dial—kPa, bar, and MPa are different scales.
A Matching Adapter: Use a threaded-to-barbed adapter that matches your gauge’s thread size and type. For a gauge with a 1/4-inch male NPT connection, you need a matching 1/4-inch female NPT adapter with a barb that fits your stopper’s hole.
A Pre-Drilled Stopper: The center hole needs to fit the barb securely, and the tapered outside needs to seal your test flange. Attach it to the adapter before placing it in the flange.
How to Assemble Your Pump Suction Gauge
Connect the adapter to the gauge. Screw the matching adapter onto the gauge connection. Follow the fitting instructions for a secure, airtight joint; don’t force mismatched threads.
Attach the stopper. Push the stopper’s center hole onto the barbed end until it fits snugly.
Fit it into your test flange. Place the assembled stopper in the flange tunnel and check that it seals without being pushed too far inside.
Before you start: Attach the stopper to the adapter first. A loose stopper pushed into the flange on its own can be difficult to remove.
Test the equipment by itself, with the flange off your body. The maximum setting used for a bench test is not a recommended setting for pumping milk.
Assemble the compatible collection kit. Attach the flange, valve, membrane, backflow protector, bottle, and tubing as your pump requires. The stopper replaces your breast for this test.
Set up for single pumping where supported. Close the unused port as instructed by your manufacturer. Dual-motor pumps and wearable cups may need a different test setup.
Insert the assembled gauge. Check the seal at the stopper and each connection. With the pump off and the gauge open to room air, the needle should return to zero.
Start low, then increase suction. Follow any manufacturer test instructions. When checking maximum vacuum, increase the test setting gradually with no breast attached.
Watch and record the reading. The needle may move with each suction cycle. Note the strongest repeatable reading, its units, the pump mode, and the setting used.
Compare with the manufacturer’s expected range and test conditions for your exact model. A published maximum is a reference point, not a pass/fail cutoff for every homemade setup. Gauge accuracy, leaks, pump mode, and the test arrangement can affect the result.
Pump Suction Lookup
Choose your exact model for a reference figure, then check its manual or ask the manufacturer about the expected test range. These numbers describe equipment capability; more suction is not automatically better for milk removal.
Pump Suction Calculator: mmHg to kPa, Bar, and MPa
Find the vacuum specification in your pump’s manual or ask its manufacturer. Enter its magnitude as a positive number—for example, enter 280 for −280 mmHg. The calculator shows the equivalent negative-pressure readings.
How to read your result: Look at your gauge to see whether it uses kPa, bar, or MPa. Then use the calculator result with that same label. You only need one of those numbers—the one that matches your gauge.
What to Check if the Reading Seems Low
Check the test kit’s seal. A leak around the stopper or adapter can make a working pump look weak.
Reseat the membranes and connections. Take the collection kit apart and put it back together according to your pump’s instructions. Check that membranes sit flat in their housings, backflow protectors are fully assembled, and tubing and connectors fit securely. Close the unused port if your single-pumping setup requires it, then test again.
Inspect the parts. Look for torn membranes, worn valves, damaged seals, loose connectors, or cracked tubing. Replace damaged or worn parts according to the manufacturer’s guidance.
Check the power source. Use the correct power adapter or a sufficiently charged battery.
Repeat under the same conditions. Keep the mode, suction, collection kit, and gauge consistent when comparing readings over time.
The gauge tells you whether suction is lower than expected; it doesn’t identify the cause on its own. If reseating the attachments or replacing a worn part brings the reading back up, you’ve found something useful. If it stays unexpectedly low, contact the manufacturer with your model, settings, setup, and reading so they can help you work out what to check next.
What if Suction Looks Normal but Output Is Still Low?
That result gives you one piece of information. It doesn’t rule out every equipment issue or explain how effectively this pump removes milk for your body.
One smaller session doesn’t tell you that your supply has dropped. Look at the pattern across similar sessions, and get support if pain continues or you consistently aren’t collecting the milk your baby needs. These ten things to know about pumping can help you look at the rest of your setup.
A Downloadable Guide for Feeding Professionals
If you want to put together a reusable testing kit for your practice, this guide gives you more detail about choosing parts and assembling the kit. Use this updated page’s unit conversions and your pump manufacturer’s current test instructions when interpreting results.
Reference figures checked October 29, 2026. Specifications vary by model, market, and test conditions. Manufacturer test ranges take priority over a general lookup figure.
🔒 Expanded Access includes step-by-step videos and resources that go beyond the blog to help you understand and work through common feeding challenges.
No. The gauge measures vacuum in your test setup. It does not measure milk production, flange fit, or how much milk your body can make. A low reading is a reason to check the setup and equipment. A normal reading does not rule out other reasons for lower pumping output.
You do not need one particular brand, but accuracy, range, and readability matter. Choose a gauge designed to measure vacuum, check its units, and make sure the fittings match. A broad or hard-to-read dial can make small differences difficult to see, whatever units it uses.
Use a pre-drilled tapered stopper that seals a compatible hard plastic test flange, with a center hole that fits the adapter barb. Attach the stopper to the adapter before putting it into the flange. A spare flange is useful, and it does not need to be your usual pumping size.
Follow the test instructions for your exact pump. For a pump designed to use one shared vacuum source, a single-flange test may require closing the unused tubing port. Dual-motor pumps and wearable cups can need a different setup. Do not assume one method works for every model.
Breast pumps apply and release suction in cycles, so the needle may move with each pull. Record the strongest repeatable reading along with your mode, setting, and test setup. A basic dial gauge cannot fully assess the pump waveform or cycle performance.
No. One bar equals 100 kPa. For example, 280 mmHg of vacuum is approximately minus 37.3 kPa or minus 0.373 bar. Check the unit printed on your gauge and use the calculator to compare equivalent readings.
No. Maximum suction is an equipment capability, not a goal for pumping on your body. Start low and adjust for comfort and milk flow. If pumping hurts, stop and reassess the fit, settings, and equipment rather than pushing through pain.
About the Expert Avery Young, IBCLC, is an International Board Certified Lactation Consultant who has spent more than a decade helping parents and professionals understand their baby’s reflexes, build confidence, and make latching and feeding feel better. Read more about Avery →
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