Compression faucet

A screw lifts a rubber washer off a hole. That's the whole valve. Mains pressure does the rest.

• Below the washer: mains pressure, about 3 bar, always.
• Past the washer: open to the air. Water just falls out.
• Three turns raise the stem 3 mm. The thread is a ramp wrapped around the stem.
• Past a lift of ¼ of the seat's width, the gap is bigger than the hole. Turning further adds almost no flow.
• Closed, pressure helps: it pushes up on the washer, but the screw holds it down. A worn washer leaks: the drip.