The Orbit 57009 Sprinkler System 1 or 2 Horsepower Pump Start Relay is rated for pumps up to 2HP. It automatically triggers the water pump to start when your sprinkler timer activates. It is compatible with standard residential 24 volt sprinkler systems. The Pump Start Relay was built with a simple, trouble-free design. It also has a heavy duty, water-resistant plastic case for indoor or outdoor installation. It works with 1HP 110V or 2HP 220V pumps.