kahlenberg air and steam whistles are distinctive, powerful signals backed by decades of successful performance in marine and industrial applications throughout the world. Designed to operate on 50 to 200 p.s.i. Of air or steam pressure, these whistles produce an omni-directional warning which stands out from background noise. All kahlenberg whistles are made of cast bronze, with a one piece brass bell. Includes 3/4″ fnpt manual operating valve.