A frost-free yard hydrant is really just a variation on a standard compression faucet, in which a plunger at the end of a plunger stem opens and closes against a water inlet to control the flow of water. But in the case of a yard hydrant, the plunger is fitted onto the end of a long pump rod that runs down inside the vertical standpipe to the valve body. This pump rod can be quite long since it needs to reach down to where the water pipe is buried. When a yard hydrant begins to leak and dribble water, the standard repair involves extracting the pump rod and replacing the plunger, which restores the hydrant’s ability to seal off the water flow.
How a Frost-Free Hydrant Works
A frost-free hydrant can be thought of as a very long compression faucet. The horizontal water pipe running out to the hydrant location from the house must be buried deep enough to be below the frost line, which in some climates can be 4 feet or more below ground. The actual valve body is located at the junction where the horizontal pipe turns upward into a vertical standpipe. The standpipe is typically a 1-inch diameter galvanized pipe that is threaded at the top.
At the top of the standpipe, usually 3 to 4 feet above the ground, the hydrant head is screwed onto the pipe. The hydrant is a specialized type of faucet that uses a fulcrum-type lever to raise and lower a long pump rod (sometimes called an operating rod or riser rod) inside the standpipe. At the bottom end of the pump rod is a plunger with a rubber washer or seal fitted to the end. The valve is designed so that when the hydrant’s handle is lowered, the pump rod and plunger are squeezed down onto the water inlet, stopping the flow of water. Raising the hydrant handle lifts the plunger up away from the water inlet, allowing water to flow up the standpipe and out the spigot.
But what makes the hydrant frost-proof is a design variation that features a drain port built into the bottom of the valve. When the pump rod and plunger lift away from the valve seat, this drain port is blocked, forcing water to flow up the standpipe. However, when the pump rod and plunger are lowered down to close against the water inlet, the drain port is opened and any water in the standpipe drains away into the ground—the surrounding area is usually packed with gravel to facilitate drainage. Since no water remains in the pipe, it cannot freeze and cause the pipe to rupture. But if a leaky hydrant is not fixed, it can be susceptible to bursting, since water remains inside the standpipe.
There are many types of yard hydrants, and it’s important to get the exact replacement parts for your model. Many hydrant manufacturers offer repair kits for their products. Check with the manufacturer or shop for parts online or through a local plumbing supply house.
Source: The Spruce
