The Spectra S2 is a double electric breast pump that plugs into a wall outlet and uses two pumping modes to mimic a baby’s natural feeding pattern. Getting comfortable with it takes a few sessions, but once you understand how the parts fit together and what each button does, the process becomes straightforward. Here’s everything you need to know to set it up, dial in your settings, and keep it running well.
What’s in the Box
The S2 comes with two flange sizes (24mm and 28mm), two sets of tubing, bottles with caps and nipples, mounting rings, and the parts that control airflow: duckbill valves and backflow protectors. The backflow protectors have three pieces each: a white silicone membrane, a lower case, and an upper case. These snap together and sit between the flange and the tubing to prevent milk from reaching the motor. You’ll also get airtight caps for storing milk directly in the included bottles.
Assembling the Pump Parts
Start with the backflow protector. Place the white silicone membrane flat on the lower case, then press the upper case on top until it clicks. Attach the assembled backflow protector to the top of the breast flange. Press a duckbill valve onto the bottom of the flange, where it connects to the bottle. Finally, screw the bottle onto the flange using the mounting ring.
Connect one end of the tubing to the backflow protector and the other end to the port on the pump motor. If you’re double pumping, repeat the full assembly for the second side. Make sure every connection is snug. A loose duckbill valve or tubing that hasn’t been pushed on all the way is the most common reason for sudden suction loss.
Checking Your Flange Size
The flanges that come with the pump may or may not fit you. To find your size, measure your nipple diameter and add 2 to 3mm. So if your nipple measures 16mm across, you need a 19 or 20mm flange. A few things to keep in mind: measure both sides, because they’re often different. Don’t measure during pregnancy, as size changes after birth. And your size may shift again around 10 weeks postpartum once your supply stabilizes.
When the fit is right, your nipple moves freely inside the flange tunnel without rubbing the walls, and only a small amount of areola gets pulled in. If your nipple drags against the sides, the flange is too small. If you feel pain or swelling, it’s too large. Getting this right makes a bigger difference in comfort and output than any setting on the pump itself.
Understanding the Buttons
The S2 has a simple control panel. The power button turns the pump on and off. Directly above it is the letdown button, marked with a wave icon, which toggles between the pump’s two modes. There’s also a lightbulb button that turns on a small built-in light, useful for middle-of-the-night sessions when you don’t want to flip on the overhead lights. The remaining buttons adjust cycle speed (how fast the pump pulls) and vacuum level (how strong the pull is).
The LCD screen shows your current cycle speed in cycles per minute (CPM), your vacuum level, and a timer that tracks how long you’ve been pumping. A three-wave symbol in the upper left corner of the display means you’re in massage mode. When that symbol disappears, you’re in expression mode. The pump has a built-in safety shutoff that automatically stops it after 30 minutes.
Massage Mode vs. Expression Mode
Massage mode is designed to trigger your letdown reflex. It uses quick, light pulls at a fixed speed of 70 cycles per minute, with vacuum strength adjustable from level 1 to 5. Think of it as imitating the fast, fluttery sucking a baby does at the start of a feeding.
Expression mode switches to slower, deeper pulls. The cycle speed drops to a range of 38 to 54 CPM, and the vacuum strength opens up to a full range of 1 through 12 (the highest level reaches 250 mmHg). This mode does the actual work of drawing milk out once your letdown has started. You don’t need to crank the vacuum to the maximum. Most people find that a suction level of 4 to 6 in expression mode is effective and comfortable.
Running a Pumping Session
Place the flanges on your breasts, centering your nipples in the tunnels. Press the power button, then immediately press the letdown button (the wave icon) to start in massage mode. Set the vacuum to level 2 through 4. You’ll feel rapid, gentle tugging.
After about 1 to 3 minutes, you should see milk starting to flow. That’s your cue to press the letdown button again to switch into expression mode. Adjust the cycle speed to somewhere around 42 to 50 CPM and bring the vacuum up to a level that feels strong but not painful, typically level 4 to 6. Stay here for the bulk of your session.
If milk flow slows down or stalls partway through, switch back to massage mode for about a minute to trigger another letdown, then return to expression mode. You can cycle between modes as many times as you need. The pump will shut off automatically at 30 minutes, which is a reasonable upper limit for most sessions.
Finding Your Best Settings
There’s no single “correct” setting that works for everyone. The numbers above are starting points. Your ideal combination depends on your anatomy, your supply, and what feels comfortable. The general principle: the highest vacuum you can use without pain tends to produce the best output. Pain actually works against you because it can inhibit letdown.
If you’re not getting much milk, try adjusting cycle speed before increasing vacuum. Some people respond better to slower cycles (38 to 42 CPM), while others do better with faster ones (50 to 54 CPM). Experiment across a few sessions rather than changing everything at once.
Cleaning After Each Use
After every session, disassemble all parts that touch milk: flanges, duckbill valves, backflow protectors (separate all three pieces), bottles, and mounting rings. Rinse them in cool water first to remove milk residue, then wash with warm soapy water. You can also place them on the top rack of a dishwasher, using a closed-top basket for small parts like valves and membranes. Boiling disassembled parts for 5 minutes is another option for sanitizing.
Tubing does not touch milk when everything is assembled correctly, so it doesn’t need routine cleaning. If you ever see moisture, milk, or mold inside the tubing, throw it away and replace it. Wiping the outside with a damp cloth or disinfectant wipe is fine if it gets dirty. Never submerge the pump motor in water.
Replacing Worn Parts
The duckbill valves are the first things to wear out, and they’re also the most common cause of gradually declining suction. If you pump four or more times a day, replace them every 2 to 4 weeks. For less frequent pumping, every 2 months is usually fine. Look for visible stretching, fraying, or a valve that no longer snaps back into shape. If your suction feels weaker than it used to, swapping the valves is the first thing to try.
The white silicone membranes inside the backflow protectors follow a similar schedule: every 2 to 4 weeks for heavy use, every 2 months for lighter use. The backflow protector casings themselves are more durable and only need replacing every 3 months (if you pump more than 3 times daily) or every 6 months for occasional use.
Troubleshooting Low Suction
If suction drops suddenly mid-session, check that the duckbill valve is still attached to the flange and hasn’t popped off. Then check that the tubing hasn’t slipped from either the backflow protector or the pump port. These two issues account for most sudden suction failures.
If suction has been gradually declining over days or weeks, the valves are almost certainly the problem. A quick diagnostic: watch the backflow protectors while the pump runs. If they’re still moving back and forth with each cycle, the motor and tubing are fine, and the issue is downstream with the valves or membranes. If the backflow protectors aren’t moving at all, the tubing has likely disconnected. If they’re flopping loosely or hitting the casing harder than usual, that also points to worn valves.
Condensation building up in the tubing is another sign of a problem. It usually means the backflow protector isn’t sealed properly, a valve is worn, or a part was left out during assembly. Disassemble everything, check each piece, and reassemble carefully.
Power Requirements
The S2 requires a wall outlet. It uses a 12V adapter that accepts input voltages from 100 to 240V, so it works with international outlets if you have the right plug adapter. Unlike the S1, the S2 does not have a built-in battery, so you’ll always need access to an electrical outlet. Keep your adapter in your pump bag so you’re never caught without it.