Storage Facilities, Tanks, and System Hydraulics
Core concepts
Storage provides equalization (meeting demand variation), fire flow, emergency reserve, and pressure maintenance. Know tank types: elevated, ground-level (standpipe), and hydropneumatic (pressure) tanks. Understand float level controls, altitude valves, overflow, ventilation, and inspection requirements. Recognize the importance of turnover - water must cycle to avoid stagnation and loss of residual.
Hydraulics
Master the pressure–head relationship: 1 psi ≈ 2.31 ft of water; 1 ft of water ≈ 0.433 psi. Understand static vs. residual pressure, head loss (friction) through pipe, and how elevation changes affect pressure. Know that a full elevated tank's water level sets the pressure at nearby customers by elevation difference. Recognize water hammer from sudden valve closure and the need for surge protection.
Traps to watch
- Forgetting that pressure depends on the elevation of the water surface, not tank volume.
- Confusing static pressure (no flow) with residual pressure (flowing).
- Overlooking tank turnover and stratification, which degrade quality.
- Missing the need for overflow and vent protection against contamination.
Rule of thumb / worked example
A tank water surface 150 ft above a customer's elevation gives about 150 × 0.433 ≈ 65 psi static pressure at that point (ignoring friction). If residual pressure drops far below static when a hydrant flows, friction or undersized mains are likely. Always convert elevation to pressure before comparing to minimum standards.