BAT Water System Hydraulics & Pressure Principles Flashcards

What is 'differential pressure' in the context of backflow assembly testing?

Answer: The pressure difference measured between two specific points across a component

Differential pressure is the difference in pressure between two designated test points, used to evaluate whether check valves and relief valves meet performance standards.

What does the pressure differential relay (PDR) detect in an RPZ assembly?

Answer: A reduction in the pressure differential across the first check valve

The PDR monitors the pressure differential across the first check; when that differential drops to 2 psi or less, it opens the relief valve to protect the supply.

What is the minimum first check differential pressure required for an RPZ assembly to pass a field test?

Answer: 2.0 psi

The USC FCCCHR and most jurisdictions require the first check valve to hold a minimum differential of 2.0 psi to pass the RPZ field test.

How does a rise in water temperature affect pressure in a completely closed water system?

Answer: Pressure increases as temperature rises due to thermal expansion

In a closed system, water expands as it heats and, with no room to expand, pressure rises — a key consideration when backflow preventers create closed systems.

What is 'back pressure' as it applies to backflow in plumbing systems?

Answer: Downstream pressure that exceeds supply pressure, forcing water to reverse direction

Back pressure occurs when downstream pressure surpasses supply pressure — such as from a booster pump or elevated tank — causing reversal of flow through the assembly.

What is the approximate pressure loss per foot of elevation that a tester must account for when calculating test pressures?

Answer: 0.433 psi per foot

Water exerts approximately 0.433 psi of pressure per foot of elevation (or conversely, 2.31 feet of head per psi), a fundamental constant in US hydraulic calculations.