Pool Info: Ball Valves for Pools
Ball valves are a common variety of pool valve found on pool plumbing. Relatively inexpensive to purchase, and simple to use, they are a good replacement valve for old brass gate valves.
The disadvantage to these valves is that they are not serviceable, that is, they cannot be opened up to make repairs or clear clogs from the valve. The handles on ball valves tend to break rather easily, and they can also be somewhat difficult to turn, especially if installed in an awkward position. If pliers are needed, use a large channel lock type, again grabbing near the center of the handle while turning, to avoid breaking the handle.
Their main advantage is their cost ($10 - $15), and ball valves may be easier to understand for novice pool operators than the three way type valve. Made by Hayward, Jandy and Lasco, ball valves are also more easily obtainable than 3-way valves, available at most home and hardware stores.
Here is a rather complicated look at a pool/spa system using both ball valves and 3 ways valves, with valve actuators. The advantage to a 3-way valve is that it has 3 ports instead of 2, and can control more than one line, with a single valve.