Piping, Pumps, and Distribution
Piping, Pumps, and Distribution
This domain tests how water is routed and moved: pipe sizing, pressure drop, pump head, circulator selection, near-boiler piping, air removal, expansion control, zoning, and balancing. Expect layout and selection items.
Core rules
- Size pipe for acceptable velocity and pressure drop; high velocity causes noise and erosion, while oversized pipe costs more and slows response.
- A circulator is selected where its pump curve intersects system head at design flow. Head includes pipe, fittings, boiler, valves, and specialities, not just vertical lift.
- Primary/secondary piping hydraulically separates the boiler loop from distribution, allowing different flows and protecting the boiler from low return temperature.
- Air control uses an air scoop or separator near the hottest point, an expansion tank connection, a feed valve, and vents. Air binds zones and causes noise.
- Zone valves, circulators, balancing valves, thermostatic valves, and manifolds distribute flow; balance before blaming the pump.
Worked example
A zone needs 60,000 Btu/h at 20°F ΔT: gpm=60,000/(500×20)=6 gpm. If the calculated system head at 6 gpm is 10 ft, choose a circulator whose curve gives at least 10 ft at 6 gpm. If the chosen pump gives 14 ft, excess head is throttled by a balancing valve or the zone may be noisy; verify actual flow and ΔT after adjustment.
Traps
Do not select a pump by horsepower or pipe size alone; do not ignore zone-valve and boiler pressure drop; do not place an expansion tank where it cannot absorb expansion; and do not leave a system air-bound after filling.