Page 92 - Microsoft Word -Cow Book 10-06-09 final update.doc

Frost-free Hydrants:

These hydrants are designed for use where freezing is a problem to allow year-
round water service on private water supplies without the danger of damage to the
pipes or hydrants.

The hydrants are connected to the water distribution system and possess a drain-
back feature that allows the water standing in the column to drain below the frost line
and discharge through a weep hole to a gravel bed or tile drain. When the water is
turned on, the drain hole is automatically closed by a valve to allow water service
(Figure A). When the hydrant is turned off, however, the valve opens the drain hole
and permits the standing water in the hydrant column to escape through the
drainpipe (Figure B).

The use of frost-proof hydrants incorporating this drain-back feature allows
the possibility of back-siphonage of contaminated water into the water
distribution system. This possibility can become a reality should a valve leak
develop or a loss of pressure occur in the water distribution system.

Because the drain port is open when the hydrant is in the off position, it provides a
convenient route through which impure groundwater, insects and dirt can
enter the hydrant, thereby contaminating the water supply. Regardless of whether
the hydrant is in the on or off position, contamination of the hydrant and water
distribution system is possible under a variety of circumstances.

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