Inexpensive yet rugged construction in a welded chamber control. The 291 series is specifically designed for single stage operation where pressure does not exceed 350 psig (24 bar) at 100°F (38°C) or 300 psig (21 bar) at 600°F (315°C) available with a variety of hermetically sealed snap switch or mercury switch circuits protected by a general purpose, weatherproof or explosion-proof enclosure and will accommodate specific gravities down to 0.60.