How a Coffee Maker Uses a Floating Valve to Heat Water
A 1971 invention for a coffee maker that uses a floating valve to control water flow, ensuring water is heated efficiently without needing a massive, power-hungry heating element.
Original patent title: “Pour-in, instant brewing electric coffee maker”
A 1971 invention for a coffee maker that uses a floating valve to control water flow, ensuring water is heated efficiently without needing a massive, power-hungry heating element. Granted to Individual in 1972 with 23 claims and 26 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
This patent describes a coffee maker that manages water flow using a gravity-fed reservoir and a float-controlled valve. As water drains from the reservoir, the float drops, which mechanically shifts a valve to increase the size of the water outlet. This variable flow rate ensures that water enters the heating block at a speed that matches the heater's capacity, preventing the water from cooling down the heating element too quickly. Additionally, the reservoir sits directly on top of the heating block, using steam and heat rising from the brewing process to pre-warm the water in the reservoir.
The gap
What does this patent NOT cover?
- Does not cover coffee makers that use pumps to force water through the heating element.
- Does not cover systems that lack a floating valve mechanism to adjust flow based on water level.
- Does not cover brewing methods that do not rely on gravity-fed water flow.
- Does not cover heating systems that do not utilize the reservoir as a heat-transfer surface for steam condensation.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The invention uses a variable-orifice valve that increases flow area as the water level drops, effectively 'throttling' the water to match the thermal output of the heating block throughout the entire brewing cycle.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Drip coffee makers
Gravity-fed electric water heaters
Home brewing appliances
Why it matters
The bigger picture
This design was a clever solution to the problem of 'instant' brewing in the early 1970s. By optimizing heat transfer and flow, it allowed for smaller, more efficient home appliances that didn't require massive electrical components or heavy metal blocks to maintain stable temperatures.
Filed
July 26, 1971
Granted
September 26, 1972
Market context
Who's building on this
Companies in this space
The principles of gravity-fed, resistance-heated water systems are foundational to the design of most standard drip coffee makers produced by companies like Keurig, Hamilton Beach, and Cuisinart. While modern machines often incorporate electronic sensors, the mechanical logic of balancing flow rate with heating capacity remains a core engineering challenge.
Market impact
This patent helped define the architecture for the modern home drip coffee maker. By proving that a simple, lightweight, and efficient brewing cycle could be achieved through clever mechanical flow control, it enabled the transition from large, industrial-style coffee equipment to the compact, affordable appliances found in almost every kitchen today.
Claim 1 — Plain English
What this patent covers
This patent describes a coffee maker that manages water flow using a gravity-fed reservoir and a float-controlled valve. As water drains from the reservoir, the float drops, which mechanically shifts a valve to increase the size of the water outlet. This variable flow rate ensures that water enters the heating block at a speed that matches the heater's capacity, preventing the water from cooling down the heating element too quickly. Additionally, the reservoir sits directly on top of the heating block, using steam and heat rising from the brewing process to pre-warm the water in the reservoir.
The clever bit
The invention uses a variable-orifice valve that increases flow area as the water level drops, effectively 'throttling' the water to match the thermal output of the heating block throughout the entire brewing cycle.
What it does not cover
- Does not cover coffee makers that use pumps to force water through the heating element.
- Does not cover systems that lack a floating valve mechanism to adjust flow based on water level.
- Does not cover brewing methods that do not rely on gravity-fed water flow.
- Does not cover heating systems that do not utilize the reservoir as a heat-transfer surface for steam condensation.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Moderate
Citation count
29/40
Moderately cited
Claim breadth
15/20
Broad claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$32K – $103K
Midpoint $64K · expired or expiring · industry ×2.2
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
23 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Jr, E. A. A. (1972). How a Coffee Maker Uses a Floating Valve to Heat Water (U.S. Patent No. 3,693,535). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/3693535/mr-coffee-drip-coffee-maker
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How a Coffee Maker Uses a Floating Valve to Heat Water cover?
A 1971 invention for a coffee maker that uses a floating valve to control water flow, ensuring water is heated efficiently without needing a massive, power-hungry heating element.
Who owns patent US 3693535?
Individual owns this patent, granted in 1972.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 3693535 cited by?
This patent has been cited by 26 later patents that build on its ideas.
What problem does this patent solve?
This design was a clever solution to the problem of 'instant' brewing in the early 1970s. By optimizing heat transfer and flow, it allowed for smaller, more efficient home appliances that didn't require massive electrical components or heavy metal blocks to maintain stable temperatures.
What does this patent NOT cover?
Does not cover coffee makers that use pumps to force water through the heating element.
Same assignee
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