You can freely build on How a Coffee Maker Uses a Floating Valve to Heat Water

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.

What is now free to use

All 1 claims of US 3693535 are in the public domain. Specifically:

The 1 dependent claim add narrowing limitations and are also free.

What is NOT covered

Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.

• 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.

Who is building on this today

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.

Products built on expired version of this technology

How to cite this patent in your documentation

Individual. US Patent 3693535. Pour-in, instant brewing electric coffee maker. Granted 1972, expired 1991. Now in the public domain.

Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.

PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.