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The small rubber valves that quietly keep a city running
14 Oct 2026
From dialysis units to flooded drains and office printers, small one-way valves keep a city's daily routine running, mostly without anyone noticing them.
Ask what makes a city work and the answers tend to come in large sizes, from skylines and metro lines to power stations and the plans that decide where the next district will go. These are the parts of urban life that can be photographed, debated and ranked.
A good share of a city's daily routine, though, depends on objects that nobody sees and few people could name. Inside dialysis machines, office printers and the drains under the pavement sit valves and seals, many of them made of rubber, whose main job is to let a liquid or a gas pass one way and stop it coming back. Following them from the hospital to the sewers and into the office shows how much rests on that modest task.
On the hospital ward
A dialysis unit treats the same patients several times a week, and each session sends their blood through tubing and a filter outside the body before it returns. Small one-way valves in this kind of equipment, and in breathing machines on the next ward, keep fluids and air moving in the right direction.
Getting such a part right is harder than its size suggests. It has to open under little pressure, close as soon as the flow reverses and be made of a material that is safe in contact with blood and medicines, yet the way rubber behaves depends on its recipe, its shape and how it is moulded.
Medical device makers often develop these components with specialist manufacturers of rubber valves rather than keeping all of that knowledge in-house. Among them is Vernay Fluid Control Solutions, a company founded in 1946 and based in Griffin, Georgia, which co-designs custom fluid control parts with the firms that make the finished products.
Below the streets
Many older districts send rain and sewage through the same pipes, and in a heavy downpour those pipes can fill faster than they empty. The water then looks for the lowest way out, which is often a basement toilet, a shower drain or a gully in a back yard.
The Environment Agency's guide to preparing a property for flooding suggests fitting flood resistant valves to drains and water pipes, which close under pressure and stop sewage and dirty water from flooding into a home or business. For the toilet it describes a simpler measure, an inflatable bung placed in the U-bend.
A valve of this kind has to stay open for years while waste flows normally, then shut on the one night the sewer backs up. Many close with a hinged flap or a flexible seal, and anything caught in the pipe can stop them sealing, so they need checking from time to time.
In the office
Back indoors, the printer down the corridor relies on tiny valves to control the flow of ink from the cartridge to the print head. Ink is a difficult liquid for rubber, since a compound that suits one formula may swell or harden in another. Each change of ink can therefore mean testing the valve again.
None of this appears in the rankings of smart cities. Still, a dialysis session in the morning and a dry basement after a night of heavy rain both depend on a part that opens one way and stays shut the other.
Frequently Asked Questions (FAQ)
Is a check valve the same thing as a non-return valve?
Yes. Both names describe a device that lets a liquid or a gas flow in one direction and closes when the flow tries to reverse. In Britain the term non-return valve is also widely used.
Why are many small valves made of rubber instead of metal?
A rubber valve can be a single moulded piece with no springs, balls or hinges, so there is little that can stick or wear out. The flexible material also closes by pressing against itself or against its seat, and different compounds can be chosen for drinking water, fuel, ink or medical use.
What is the difference between a duckbill valve and an umbrella valve?
A duckbill valve has two rubber lips that part in the direction of flow and are pressed together by back pressure, so the liquid follows a fairly straight path. An umbrella valve is a dome-shaped disc resting on a seat with holes in it, which stays closed until the pressure lifts its edge and works the same way whatever its position.
