Breast Pump Parts Explained — A Complete Guide to Every Component

You open the box, tip it upside down, and out tumbles a collection of flanges, valves, tubes, tiny silicone flaps, and connectors. No obvious labels. No clear sense of what goes where.

If that sounds familiar, you’re in good company. Understanding what are the parts of a breast pump — and what each one actually does — is something almost every new pumping mom has to figure out on her own. This guide changes that.

We’ll walk through every component in a standard breast pump kit, explain exactly what each part does, what happens when it wears out, and how often to replace it. If you’re completely new to pumping, you may want to start with our guide on what a breast pump is and how a breast pump works before diving into the individual parts.

Before going part by part, it helps to know what a standard kit contains. The exact contents vary by brand and model, but most breast pump kits include:

• Flanges (breast shields) — usually two, one for each breast
• Valves — one per flange, sometimes sold as a combined valve-and-membrane unit
• Membranes or duckbill valves — the small flexible inserts inside the valve
• Tubing — connects the motor to the flange assembly
• Backflow protector — found on closed-system pumps
• Collection bottles — typically two, with lids
• Bottle connectors / adapters — join the flange to the bottle
• Motor unit — the main pump body (electric) or handle assembly (manual)
• Power adapter or charging cable

Some kits also include a carry bag, spare parts, or storage caps. The core components above are universal across almost all pump types, even if the shapes and names differ slightly between brands.

The flange — also called a breast shield — is the funnel-shaped cup that fits directly over your nipple and areola. It is, without question, the single most important part of the entire pump.

Here is why: the flange creates the airtight seal that makes suction possible. Without a proper seal, no amount of motor power will express milk efficiently. The nipple sits inside the tunnel of the flange, and as the pump cycles, the nipple is gently drawn in and out of the tunnel with each suction pulse.

Sizing is everything. Flanges come in multiple sizes — typically ranging from 21mm to 36mm — measured by the internal diameter of the tunnel that surrounds your nipple. Most pumps include a 24mm or 28mm flange as standard, but many women need a size outside that range.

If the flange is too small, your nipple rubs against the tunnel walls, causing pain and reducing milk flow. If it’s too large, your areola gets pulled into the tunnel alongside the nipple, and suction is lost. Either scenario results in less milk expressed per session — and over time, reduced supply.

A correctly fitting flange should allow your nipple to move freely in the tunnel with only a small amount of areola being drawn in. Pumping should feel like strong pressure — uncomfortable for the first few seconds, then tolerable — but never painful.

If pumping is painful, check your flange size before anything else. It is the cause of the vast majority of pain and low-output complaints. Our dedicated guide on what a breast pump flange is and how to find your correct size walks through measurement and fitting in full detail.

The valve is a small component that sits between the flange and the collection bottle. Its job is straightforward but essential: it acts as a one-way gate that allows milk to flow downward into the bottle during each suction cycle, while preventing it from flowing back up.

Without a functioning valve, suction would be lost the moment the pump cycle reverses. Milk would splash back toward the flange rather than collecting cleanly in the bottle.

Valves are made from soft silicone or firm plastic depending on the pump brand. They snap or clip into position at the base of the flange or connector.

Signs your valve needs replacing:

• Noticeably reduced suction even though the motor sounds normal
• Milk moving back toward the flange during pumping
• A faint clicking or flapping sound that wasn’t there before
• Visible cracks, stiffness, or discolouration

Valves should be replaced every two to three months with regular use — sooner if you notice any of the above signs. They are inexpensive and widely available as spare parts for most major pump brands.

This is the most commonly overlooked part of a breast pump — and the most commonly worn out. If you have ever experienced sudden unexplained suction loss with a pump that otherwise seems fine, a worn or damaged membrane is almost always the cause.

What is a breast pump membrane? It is a thin, flexible silicone disc that sits inside the valve assembly. As the pump creates suction, the membrane flexes open to allow milk through, then snaps shut to prevent backflow. It opens and closes with every single suction cycle — hundreds of times per pumping session.

What is a duckbill valve? A duckbill valve is simply a different design of membrane. Instead of a flat disc, it is shaped like a small beak or duck’s bill. The two sides of the “bill” are pressed together at rest, opening under suction pressure and closing again immediately after. Both flat membranes and duckbill valves perform the same function — they are just different shapes, and different pump brands use different designs.

Why membranes fail so quickly: Because they flex constantly, the silicone fatigue sets in faster than on any other pump part. A membrane that looks intact can still have lost its elasticity, which means it no longer creates a proper seal — and suction drops.

How to check your membrane:

1. Remove it from the valve assembly
2. Hold it up to a light source
3. Look for any tears, holes, thinning, or stiffness
4. Gently flex it with your fingers — it should spring back immediately
5. If it feels stiff, stays deformed, or has any visible damage, replace it

With daily heavy use, membranes should be replaced every four to eight weeks. Many lactation consultants recommend keeping a pack of spares at all times — they cost very little and can save an entire pumping session.

Pro tip: When you buy your breast pump, order a pack of spare membranes at the same time. They are the cheapest part and the one most likely to fail at an inconvenient moment.

The tubing is the flexible tube that connects the motor unit to the flange assembly. It does not carry milk — it carries suction. Specifically, it transmits the negative pressure (the pulling force) generated by the motor down to the flange, where it is applied to the breast.

This distinction matters: milk should never enter the tubing. If you notice milk in your tubing, it is a sign that the backflow protector has failed or is missing (see next section). Milk in the tubing can reach the motor, cause mould to grow inside the tube, and potentially contaminate future expressed milk.

Keeping tubing in good condition:

• After each session, run the pump for a few extra minutes with the flanges removed to allow any moisture to dry out of the tubing
• Check regularly for kinks, cracks, or cloudy patches that indicate moisture inside
• If milk gets inside the tubing, replace it immediately — do not attempt to clean the inside of the tube
• Replace every three to six months as a general rule

Replacement tubing is available for most major pump brands and is usually sold in single or twin packs.

The backflow protector is a small filter component that sits between the flange assembly and the tubing connection point. Its job is to act as a physical barrier that prevents milk or moisture from travelling backward into the tubing or, further still, into the motor unit.

Its presence is what defines a closed-system pump — a pump where the milk collection pathway is completely separated from the motor and tubing. In an open-system pump, there is no such barrier, meaning moisture can potentially reach the motor or tubing over time.

For hygiene, the backflow protector is particularly important for anyone sharing a pump, pumping for a premature or immunocompromised baby, or using a rental pump. It ensures that no residue from previous sessions can contaminate new expressed milk.

Caring for the backflow protector:

• It should be kept completely dry
• Rinse after each session and allow to air dry fully
• Replace every three to six months, or immediately if milk gets inside it
• If you see milk in your tubing, check the backflow protector first — it has likely failed

For a full explanation of the difference between open and closed systems and why it matters, see our post on open vs closed system breast pumps.

The motor unit is the main body of an electric breast pump — the part that plugs into the wall or runs on battery. It generates the rhythmic negative pressure that drives the entire suction cycle.

Inside the motor, a small mechanical or electronic system creates alternating cycles of suction and release at a set rate, measured in cycles per minute. Suction strength is measured in mmHg (millimetres of mercury) — most personal-use electric pumps operate between 150 and 250 mmHg, while hospital-grade pumps can reach up to 300 mmHg or more.

Modern motor units also contain the programming that controls the two-phase cycle — stimulation mode and expression mode — and allow you to adjust both speed and suction level. For a detailed explanation of how the motor drives the pumping process, see our post on how a breast pump works.

Important: The motor unit is not a user-replaceable part. Unlike membranes or valves, if the motor fails, the pump needs to be replaced. Motor lifespan varies — most personal-use pumps are rated for one to two years of regular use. For guidance on when a pump has reached the end of its useful life, see our guide on how long breast pumps last.

If you are using a manual breast pump, the piston and cylinder take the place of the motor. This is the hand-operated mechanism that creates suction when you squeeze the handle.

When you squeeze the handle, it compresses the cylinder and pushes air out. When you release the handle, the cylinder expands and creates negative pressure — drawing milk from the breast down into the collection bottle. The piston is the component that moves inside the cylinder to create this compression and expansion.

The piston is fitted with a small rubber or silicone seal that must create an airtight fit inside the cylinder walls. If this seal wears out, suction is lost — even if you are squeezing the handle correctly.

Manual pump maintenance:

• Keep the piston clean and completely dry — moisture can degrade the seal
• Never lubricate with oils or lotions — this can damage the silicone seal
• Check that the piston moves smoothly without sticking
• Some manual pump models allow piston seal replacement; others require a full pump replacement if the seal fails

For more on how manual pumps compare to electric in terms of effectiveness, see our post on whether manual breast pumps really work.

The collection bottle is where your expressed milk gathers during and after the pumping session. It attaches directly below the flange assembly, connected via a bottle adapter or connector that joins the base of the flange to the bottle neck.

Most pump collection bottles are made from BPA-free polypropylene or borosilicate glass. Many are designed to attach directly to a standard bottle nipple so milk can be fed straight from the pump without transferring to a separate bottle — a useful feature for minimising handling.

Practical notes:

• Always check the bottle is securely attached before starting a session — a loose seal will reduce suction
• Most major pump brands use a standard 28mm or 32mm neck connector, but compatibility varies — always confirm before mixing brands
• Many pumps support pumping directly into breast milk storage bags with the right adapter, which saves a transfer step
• Bottles can go directly into the fridge after a session with the connector cap in place

Keeping small parts in good condition is the single easiest way to maintain consistent pumping output. Here is a straightforward reference guide:

The single most useful habit: When your pump starts underperforming, replace the membrane first. It takes thirty seconds, costs almost nothing, and fixes the problem more often than not.

For a deeper dive into pump lifespan — including when it is time to replace the whole unit rather than just the parts — see our post on how long breast pumps last and when to replace them.

Every part of a breast pump has a specific job — and when any one of them fails, your output suffers. The good news is that most pumping problems trace back to small, inexpensive, easy-to-replace parts rather than the motor itself.

The flange is the part that affects your experience most directly — get the size right and everything else becomes easier. The membrane is the part that needs the most attention over time — keep spares and replace it regularly.

From here, two posts are worth reading next. Our breast pump flange sizing guide will help you confirm you are using the right size for your body — the single biggest factor in pumping comfort and output. And our breast pump modes explained guide covers the stimulation and expression settings that control how all these parts work together during a session.

This guide reflects general breastfeeding and pumping knowledge and is not a substitute for advice from a certified lactation consultant (IBCLC) or your healthcare provider.

1. Meier, P.P. et al. (2016) — Breast pump suction patterns that mimic the human infant during breastfeeding. Journal of Perinatology, 36, 127–132. (Suction mechanics and flange function)
2. Kent, J.C. et al. (2008) — Response of breasts to different stimulation patterns of an electric breast pump. Journal of Human Lactation, 24(2), 116–124. (Pump cycle design and milk output)
3. Ramsay, D.T. et al. (2005) — The effect of ultrasound-guided Botox injections into the masseter muscle for breastfeeding-related pain. Pediatrics (Flange fit and nipple mechanics)
4. Becker, G.E. et al. (2016) — Methods of milk expression for lactating women. Cochrane Database of Systematic Reviews. (Broad review of pumping equipment effectiveness)
5. ABM Clinical Protocol #8 (2017) — Human Milk Storage for Home Use for Full-Term Infants. Academy of Breastfeeding Medicine. (Storage and hygiene guidelines relevant to collection components)
6. FDA — Breast Pumps (fda.gov) — Regulatory classification of breast pump components as medical devices; guidance on shared-use and hygiene. (Backflow protector and closed-system requirements)
7. La Leche League International — Pumping and Milk Expression. llli.org (General guidance on pump parts, maintenance, and replacement)
8. Cleveland Clinic — Breast Pumping: What It Is, Benefits & How To. my.clevelandclinic.org (Clinical overview including component care)