# 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. - **Patent:** US 3693535 - **Original title:** Pour-in, instant brewing electric coffee maker - **Owner:** Individual - **Granted:** 1972 - **Status:** Public domain (expired) - **Times cited:** 26 - **Field:** consumer_electronics, mechanical ## What it does 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. ## 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. ## 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. ## Real-world examples 1. Drip coffee makers 2. Gravity-fed electric water heaters 3. Home brewing appliances ## Why it matters 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. ## 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. **Full plain-English explainer:** https://patentbrief.org/patent/us/3693535/mr-coffee-drip-coffee-maker **Original patent:** https://patents.google.com/patent/US3693535 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Keurig's Original Single-Serve Coffee Pod System Works](https://patentbrief.org/patent/us/5325765/keurig-single-serve-coffee-pod) — This 1994 patent describes the original Keurig system for brewing single cups of coffee using a special filter pod that holds coffee grounds and separates them from the brewed liquid. - [How the Modern Waterbed Works](https://patentbrief.org/patent/us/3585356/waterbed-liquid-support) — A 1971 patent describing a liquid-filled, heated furniture support designed to cradle human bodies without letting them touch the bottom of the container. - [How Cup Noodles Are Designed to Cook Perfectly](https://patentbrief.org/patent/us/3997676/cup-noodles-instant-ramen-ando) — A 1976 patent describing the specific shape, density, and placement of dehydrated noodles inside a cup to ensure they cook evenly and quickly when hot water is added. - [How the First Automatic Pop-Up Toaster Works](https://patentbrief.org/patent/us/1394450/pop-up-toaster-strite) — Charles Strite's 1921 patent for the first toaster that automatically pops bread up after a set time, preventing it from burning. - [How the 1940 Nachumsohn Cooking Apparatus Works](https://patentbrief.org/patent/us/2187888/crock-pot-slow-cooker-naxon) — A 1940 patent for a cooking device designed to heat food efficiently using an enclosed chamber and specific heat distribution methods.