In the old days, frost-free outdoor valves operated by keeping the water line below the frost level under ground. This is because outdoor faucets typically wouldn't have been connected directly to the house. The shut-off valve would be located under ground below the frost line and a riser would connect the valve to the above-ground faucet handle. These old-style frost-free faucets may still be seen on old farms but probably very few other places. Newer frost-free sillcocks are designed such that the shut-off valve is located about 8 to 12 inches inside the sillcock pipe. This puts the water line inside the house or building the faucet is attached to. The further the sillcock reaches inside the heated walls, the lower the chance of a bursting pipe.
Connecting Shut-Off Valve to the Outdoor Faucet
The pipe that runs from the indoor shut-off valve to the outdoor faucet in newer frost-free faucet configurations is known as a sillcock pipe. It simply carries the water from the valve to the faucet when the faucet is turned on and remains empty when off. In the older models, the function of the sillcock was carried out by a riser pipeline, which was simply a vertical pipe that ran the water from the location of the shut-off valve underground straight up the faucet above ground.
To keep the pipe between the shut-off valve and the faucet outside from freezing, a sillcock pipe is drained through a small hole known as a petcock to keep it free of water for winterization. In the older-style faucets, the riser simply drained back down into the water line, creating a back-flow. For this reason, many health departments do not allow these old frost-free faucets.