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newSchoolWorks.com › VoTechWorks › Agriculture, Environment & Public Service › Water / Wastewater Operator › Pumps & Distribution Systems › Lesson 2
AGR-WATE71-04 · Lesson 2 · 13 clock hours · theory

Pump Types, Components, and Selection

Objective. Students identify the major types of pumps used in water distribution—centrifugal, turbine, submersible, and booster—and explain the function of each major internal component.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Why Pumps Matter in Water Systems

Pumps are the workhorses of every water and wastewater system. They move raw water from sources, push treated water through miles of distribution pipe, lift wastewater to treatment plants, and maintain pressure for fire protection and public health. As a licensed operator, you must recognize each pump type, understand what every internal component does, and select the right pump for the job. Selecting the wrong pump wastes energy, accelerates wear, and can leave customers without water.

Centrifugal Pumps

Centrifugal pumps are the most common type in water distribution. A rotating impeller spins water outward by centrifugal force, converting rotational energy into velocity. The volute (or diffuser) surrounds the impeller and converts that velocity into pressure. Because they work by continuous rotation, centrifugal pumps deliver a smooth, non-pulsing flow and are well suited to high-flow, moderate-head applications such as clearwell transfer pumps and surface-water intake stations.

Major internal components of a centrifugal pump:

Vertical Turbine Pumps

Vertical turbine pumps (also called lineshaft turbine pumps) are designed to lift water from deep wells or sumps. Multiple impeller stages are stacked along a vertical shaft that can extend many meters below ground. Each stage adds head, allowing the pump to overcome great depths. The motor sits at the surface on a discharge head. Because the impellers are submerged, vertical turbines are highly efficient for deep groundwater sources. They require periodic inspection of the lineshaft bearings and correct alignment of the column pipe.

Submersible Pumps

A submersible pump places both the motor and the pump assembly below the water surface, typically inside a well casing. The motor is hermetically sealed and cooled by the water flowing past it. Submersibles eliminate the need for long lineshafts and are quieter. They are widely used in residential and municipal wells and in wet wells at lift stations. Because the motor is inaccessible without pulling the pump, thorough electrical checks (insulation resistance, amp draw) at the surface are essential for condition monitoring.

Booster Pumps

Booster pumps are installed within a distribution system to maintain or increase pressure in zones that are distant from the main pumping station or at higher elevations. They are usually centrifugal pumps and may be packaged in a booster station with pressure controls and backup power. Proper sizing prevents both insufficient pressure (below the minimum required for service) and excessive pressure that can damage service connections.

Positive-Displacement Pumps

Positive-displacement (PD) pumps trap a fixed volume of liquid and force it through the discharge. Common types include diaphragm pumps and gear pumps. In water and wastewater operations, PD pumps are most often used for chemical metering (chlorine solution, coagulant, fluoride) because they deliver a precise, repeatable dose regardless of system pressure. They are not used for bulk water transfer because they cannot tolerate a closed discharge valve—pressure will build until something fails.

Pump Selection Criteria

Selecting the right pump requires matching pump characteristics to system requirements:

1. Required flow rate (capacity) – gallons per minute (gpm) or million gallons per day (MGD) the system demands.

2. Total dynamic head (TDH) – the total pressure the pump must overcome, including static lift, friction losses, and velocity head.

3. Efficiency – the best efficiency point (BEP) on the pump curve should align with normal operating conditions.

4. Site conditions – depth to water (favors turbine or submersible), available power supply, footprint, and maintenance access.

5. Fluid characteristics – clean water, solids-laden wastewater, or chemical solution each favor different pump materials and designs.

Safety Notes

Key terms8

ImpellerThe rotating vaned disc inside a centrifugal pump that transfers energy to the water through centrifugal force, producing flow and pressure.
VoluteThe spiral-shaped pump casing that collects water discharged by the impeller and converts its velocity into pressure.
Wear ringsClose-tolerance rings fitted between the impeller and casing that limit internal recirculation; they are replaced when clearance exceeds the manufacturer's limit.
Mechanical sealA face-type seal between the rotating shaft and the stationary casing that prevents water from leaking along the shaft.
Total Dynamic Head (TDH)The total pressure a pump must overcome, expressed in feet or pounds per square inch, including static lift, friction losses in piping, and velocity head.
Best Efficiency Point (BEP)The point on a pump's performance curve where the pump operates at its highest efficiency; pumps should be selected so normal operation falls near the BEP.
Vertical turbine pumpA multi-stage pump with impellers mounted on a vertical shaft used to lift water from deep wells or sumps; the motor sits at the surface.
Positive-displacement pumpA pump that moves a fixed volume of fluid per stroke or revolution, used primarily for precise chemical metering; cannot tolerate a closed discharge valve.

Worked examples3

1. A centrifugal pump manufacturer specifies a maximum wear-ring clearance of 0.015 inches. During inspection you measure the clearance at four equally spaced points around the ring and record: 0.011 in, 0.013 in, 0.016 in, and 0.014 in. Should the wear ring be replaced?
  1. Step 1 – Compare each individual measurement to the specification limit of 0.015 in.
  2. Step 2 – Measurement 1: 0.011 in — within spec. Measurement 2: 0.013 in — within spec. Measurement 3: 0.016 in — EXCEEDS spec. Measurement 4: 0.014 in — within spec.
  3. Step 3 – Any single measurement that exceeds the manufacturer's maximum clearance indicates unacceptable wear.
Answer: Yes, the wear ring must be replaced. One measurement (0.016 in) exceeds the 0.015 in limit. Continued operation with excessive clearance allows high-pressure water to recirculate internally, reducing efficiency and increasing heat and wear.
2. A booster station must deliver 500 gpm against a total dynamic head of 120 feet. The pump curve for Pump A shows it produces 500 gpm at 125 ft TDH with an efficiency of 78%. Pump B produces 500 gpm at 120 ft TDH with an efficiency of 71%. Which pump is the better selection, and approximately how much more efficient is it?
  1. Step 1 – Confirm both pumps meet the minimum TDH requirement of 120 ft at 500 gpm. Pump A produces 125 ft (meets it with margin). Pump B produces exactly 120 ft (meets it at the design point).
  2. Step 2 – Compare efficiencies: Pump A = 78%, Pump B = 71%.
  3. Step 3 – Difference in efficiency: 78% − 71% = 7 percentage points.
  4. Step 4 – Consider operating point: Pump A's BEP appears to be near 500 gpm/125 ft, meaning this application falls close to BEP—favorable for reliability and energy use.
Answer: Pump A is the better selection. It meets the TDH requirement, operates near its best efficiency point, and is 7 percentage points more efficient than Pump B, which lowers long-term energy costs and reduces wear.
3. A well is 180 feet deep. The static water level is 60 feet below the surface, and drawdown during pumping lowers the water level an additional 20 feet. Friction losses in the column pipe and discharge piping total 15 feet. What is the approximate Total Dynamic Head the pump must produce?
  1. Step 1 – Determine static lift: water level at rest is 60 ft below surface, so static lift = 60 ft.
  2. Step 2 – Add drawdown: 60 ft + 20 ft = 80 ft of lift from pumping water level to surface.
  3. Step 3 – Add friction losses: 80 ft + 15 ft = 95 ft.
  4. Step 4 – (In a real design, velocity head and minor losses would also be included, but with only friction losses given, TDH ≈ 95 ft.)
Answer: The approximate Total Dynamic Head is 95 feet. The pump selected must produce at least 95 ft TDH at the required flow rate.

The math in this lesson1

Learners compare wear-ring clearance measurements to a 0.015 in maximum to judge wear.
N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Illustrated lecture comparing centrifugal, vertical turbine, submersible, and positive-displacement pumps; students label a cutaway diagram of a centrifugal pump identifying impeller, volute, wear rings, mechanical seal, and bearing assembly. · Case-study analysis: instructor presents three distribution scenarios (high-lift booster station, well pump, storage tank fill pump) and students justify in writing which pump type best fits each application and why. · Hands-on inspection of a disassembled centrifugal pump on a lab bench; students measure and record impeller clearances, inspect mechanical seal condition, and note observations on an equipment inspection form.
Materials: Cutaway centrifugal pump display model, disassembled pump for inspection, feeler gauges, pump manufacturer's O&M manual, AWWA M49 Butterfly Valves and AWWA M51 Air-Release/Air-Vacuum Valves references, student inspection forms
Check: Students correctly label all eight major pump components on a blank diagram and answer five short-answer questions on pump selection; pass mark is 75%.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Pumps and Hydraulics
1. In a centrifugal pump, which component is primarily responsible for converting water velocity into pressure?
Pumps and Hydraulics
2. A municipal well is 220 feet deep with a pumping water level 95 feet below grade. Which pump type is most appropriate for this application?
Safety and Emergency Response
3. Before removing the impeller from a centrifugal pump for inspection, the FIRST safety action an operator must take is:
Pumps and Hydraulics
4. Wear rings in a centrifugal pump are inspected and replaced because excessive clearance causes:
Water Treatment and Chemical Feed
5. A chemical feed system requires the precise, adjustable dosing of a fluoride solution into a distribution main. Which pump type is best suited for this application?
Pumps and Hydraulics
6. An operator measures wear-ring clearance at four points and finds values of 0.010, 0.012, 0.010, and 0.017 inches. The manufacturer's maximum allowable clearance is 0.015 inches. What is the correct action?
Distribution System Operation
7. A water district needs to boost pressure for customers in a hilltop pressure zone served by an elevated storage tank fill line. The best pump selection for the booster station would emphasize:
Pumps and Hydraulics
8. The best efficiency point (BEP) on a pump curve is important in pump selection because operating far from the BEP can result in:
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