A Compression Tank is a sealed hydronic system component that accommodates water volume expansion caused by temperature increases while maintaining system pressure. Unlike older open expansion tanks, compression tanks are closed, pressurized vessels with an internal bladder or diaphragm. They prevent system overpressure, water loss, and equipment damage.
Technical Specifications
Compression tank sizing follows the formula: Tank Size = System Volume × 0.04 × (Maximum Temperature – Minimum Temperature in °F) / (Atmospheric Pressure + System Pressure in PSIG). A typical 50-gallon system with 80-degree temperature differential requires a 3-5 gallon compression tank. Pre-charge pressure equals the static head of the system, typically 12-15 PSIG for residential applications.
Installation and Maintenance
Compression tanks connect to the system at the lowest point, upstream of the circulator. They prevent system pressure from exceeding relief valve settings of 25-30 PSIG. Annual pressure checks maintain proper pre-charge, as nitrogen charge loss reduces functionality and system life.