Compliant Dispenser Pump
A soap pump rebuilt around compliant mechanisms: one material, seven parts, no metal spring or glass ball.
- Year
- 2023
- Reading
- 04 min
- Figures
- 05
A redesign of the everyday soap-pump dispenser using compliant mechanisms — parts that move by flexing their own material, like a tweezer. Compliant plastic parts take over from the metal spring and glass ball, every component is made from one material, and the count drops from nine parts to seven, so the pump is easier to manufacture, assemble and recycle.
- Disciplines
- Mechanical Engineering
- Compliant Mechanisms
- Green Design
- Design for Disassembly
- CAD
- Tools
- CAD / Rendering / Engineering drawing / Hand sketching
I’m convinced that many of the solutions to our biggest problems can come from revolution on a small scale — renovating the mundane architecture of daily life, rather than focusing only on innovation that grabs headlines but has little practical value.
That belief drew me to what mechanical engineers call compliant mechanisms: mechanisms that achieve motion through the deflection of their own material, like a tweezer. Seeing how common they are in daily life, I wanted to design a line of them that followed the principles of Green Design — easy to manufacture, assemble and recycle.
Too many parts for a simple job
After some research, I became fixated on redesigning soap-pump dispensers. They had too many components for what seemed like an easy job: you pump down, and the liquid inside goes up.
In a conventional ball pump, a glass ball, a metal spring and a funnel at the bottom work together as a one-way valve. Press the head and the piston forces the liquid up and out, because the ball blocks its way back down the dip tube; release it and the spring pushes the piston back, drawing in a fresh charge past the ball.
I also learned that these pumps contribute heavily to plastic waste, made worse by the mix of materials inside them: polypropylene, polyethylene, a stainless-steel spring and a glass ball. No wonder they couldn’t be recycled properly. I interviewed a medical expert, who agreed with my diagnosis.
550 million
shampoo bottles thrown away every year in the US alone
7%
of the bottles collected were successfully recycled
9 → 7
components after the redesign
1
material for every component
The difficulty of recycling them has always been a concern. Our team tried different methods but were all unsuccessful.”
Three moving parts
Dispenser pumps are assembled so specifically that only industry workers can take them apart properly, and their spray mouths are permanently installed in the head. Both make recycling arduous.
Three parts stood out: the pump rod and lower piston rod, working together as an overly complex upper one-way valve; the stainless-steel spring, which makes the pump hard to recycle separately; and the moving glass ball, which brings wear, friction and hysteresis.
Using the ball pump as a structural reference, I focused the redesign on its moving parts — the lower piston, the spring and the ball — where compliant mechanisms could make a product that meets the criteria of Green Design.
A flap for the ball, a plastic spring for the steel one
The compliant flap started from the single-pivot flaps on toothpaste and small cosmetic bottles. The second iteration was less stiff, using long, flexible beams as pivots, which made it more flexible and durable. The final flap keeps that idea but with less complexity: a stationary base with narrow beams packed beside a centre cover, which lifts as liquid enters and spreads the stress along the beams. It is also easier to 3D print.
The first spring was built into the piston rod to save a part, but a monolithic spring proved hard to manufacture. The second was separate, with a central tube guiding a sliding cylinder. The final spring drops the tube and cylinder, which only added friction, because the pump body already keeps it moving vertically. As its own part, the spring can also be upcycled on its own.
Final redesign
- 01
Two compliant flaps
A bottom flap replaces the glass ball as the main one-way valve, and a top flap replaces the conventional pump plug, so pumped liquid can’t flow back down the body.
- 02
A compliant spring
Made from the same material as the pump body, it replaces the 304 stainless-steel spring and still allows long vertical travel.
- 03
One piston rod
The upper and lower piston rods are combined into one piece — one less component, less product waste.
- 04
One material
Every component is harmonised to polyethylene (PE), which drastically improves the pump’s recyclability.
- 05
Design for disassembly
All components come apart by twisting or pulling.
- 06
No loose small parts
The compliant flaps are attached to the body rather than isolated, so no component is a choking hazard.
