Water Distribution Operator Class III flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Pressure head conversion

One foot of water column equals 0.433 psi, and one psi equals 2.31 feet of head. Use these to convert between elevation and pressure in distribution systems.

Hazen-Williams equation

Predicts head loss in a pipe from flow, diameter, length, and a roughness coefficient C. Higher C means smoother pipe and lower friction loss.

Fire flow residual pressure

Fire flow testing measures available flow while maintaining a minimum residual pressure, commonly 20 psi, to protect the system from contamination and collapse.

Thrust block purpose

Rigid concrete blocks or restrained joints absorb the unbalanced force at bends, tees, reducers, and dead ends so pipe joints do not separate under pressure.

Pump affinity laws

For a given pump, flow varies with speed, head with speed squared, and power with speed cubed. Impeller diameter changes follow the same relationships.

Brake horsepower formula

Brake horsepower equals flow in gpm times head in feet divided by 3960, then divided by pump efficiency. It represents power delivered to the pump shaft.

NPSH available

The absolute pressure head at the pump suction minus vapor pressure head. It must exceed the pump's required NPSH to avoid cavitation.

Cavitation symptoms

Gravel-like noise, vibration, fluctuating discharge pressure, and impeller pitting indicate vapor bubbles collapsing. Reduce suction lift, friction, or water temperature to correct it.

Pumps in series vs parallel

Series pumps add head at the same flow; parallel pumps add flow at the same head. Choose based on whether the system needs more pressure or more volume.

Tank static pressure

Pressure at a service point equals the elevation difference between the tank water surface and the point, multiplied by 0.433 psi per foot.

Minimum and maximum pressure

Systems typically target 40 to 80 psi normal working pressure, maintain at least 20 psi under peak or fire demand, and use pressure-reducing valves above about 100 psi.

Tank turnover and water age

Storage should turn over often enough to keep water age low, generally under three to five days, to preserve disinfectant residual and limit nitrification.

Altitude valve function

An altitude valve throttles or closes tank fill based on water level, preventing overflow and controlling which tank or zone fills first.

CT disinfection concept

Disinfection credit equals residual concentration in mg/L multiplied by contact time in minutes. Required CT depends on pH, temperature, and target pathogen log inactivation.

Breakpoint chlorination

Adding chlorine past the point where ammonia demand is satisfied causes free chlorine to rise sharply. Before that point, combined chloramines dominate and cause taste and odor.

Air gap backflow protection

A physical unobstructed separation between a potable supply and a receiving vessel. It is the highest level of cross-connection protection and needs no testing.

RPZ assembly

A reduced-pressure-zone device uses two check valves and a relief valve to protect against backsiphonage and backpressure. It must be tested annually by a certified tester.

Turbidity limits

Conventional filtration systems must keep turbidity at or below 0.3 NTU in 95 percent of monthly samples, with an absolute maximum of 1 NTU.

New main disinfection

New mains are chlorinated to roughly 25 to 50 mg/L for 24 hours, flushed, then sampled for coliform bacteria before being placed in service.

Hydrostatic test

New pipe is pressure tested, often at 1.5 times working pressure for a set duration, and leakage must not exceed the allowable rate before acceptance.

Valve exercising program

Operating each distribution valve on a scheduled cycle and recording turns confirms it is operable. Stuck valves greatly slow emergency isolation of main breaks.

Utility separation distances

Water mains are typically kept at least 10 feet horizontally from sanitary sewers, with greater separation or casing where crossing, to reduce contamination risk.

Confined space atmosphere limits

Entry requires oxygen between 19.5 and 23.5 percent, flammable gas below 10 percent of the lower explosive limit, and toxic gases below exposure limits.

Total coliform repeat sampling

A positive routine total coliform sample requires repeat samples, typically at the same site and adjacent sites, to confirm or rule out contamination.

TTHM and HAA5 MCLs

Disinfection byproduct limits are 0.080 mg/L for total trihalomethanes and 0.060 mg/L for five haloacetic acids, evaluated as locational running annual averages.

Consumer Confidence Report

An annual report delivered to customers by July 1 that lists detected contaminants, their levels, applicable limits, and potential health effects.

Public notification tiers

Tier 1 covers acute violations and requires notice within 24 hours. Tier 2 allows 30 days, and Tier 3 is annual, based on violation severity.

Chlorine gas emergency

Chlorine gas is heavier than air and settles in low areas. Evacuate upwind, use SCBA, and never enter the area without respiratory protection.

Trench protective systems

Trenches five feet or deeper require shoring, sloping, or a trench box. Spoil and equipment must be kept back from the edge to prevent collapse.

Lockout tagout

Energy-isolating devices are locked and tagged before servicing pumps, motors, or valves. Zero energy must be verified before work begins.

Sodium hypochlorite storage

Store hypochlorite cool and out of sunlight to slow strength loss. Never mix it with acid, which releases dangerous chlorine gas.

Water loss accounting

Compare master-meter production to billed consumption. The gap includes apparent loss from meter error and real loss from leaks, guiding repair priorities.

Monthly operating report

A monthly summary of flows, chemical doses, residuals, and compliance samples submitted to the primacy agency to document ongoing regulatory compliance.