Water & Wastewater Pumping Systems

An MWEA Maintenance Committee Seminar

Fall 2017

Centrifugal & Positive Displacement

Pumps

Ken ColstonKDC Educational Consulting

40 Years in Water & Wastewater

Retired Director of Maintenance Operations, Ypsilanti Community Utilities Authority

PUMP AND SYSTEM BASICS

WHAT’S A PUMP?

What is a Pump?

A Pump is a Machine Which Adds

Energy to a Fluid for the Purpose of

Increasing the Pressure or Moving it

along a Pipeline.

A Pump, in fact, Doesn’t Create

Anything.

It Doesn’t Make Water

It Doesn’t Make Pressure

THERE ARE TWO BASIC TYPES OF PUMPS

• Positive displacement pump, AKA Force Pump, which adds energy directly to a movable boundary, which imparts the energy to the fluid.

• Examples include screw pumps, piston pumps, gear pumps.

ONE TYPE IS THE:

THERE ARE TWO BASIC TYPES OF PUMPS:

• Dynamic pump, AKA Kinetic Pump, which adds the energy indirectly through a rotating part in the form of velocity, and subsequently converts the velocity to pressure.

• These pumps are commonly referred to as Centrifugal pumps.

THE OTHER TYPE IS THE:

Imagine That You Fill A Bucket With Water.

• The water stays in the bucket (as long as there aren’t holes in it)

• If you take the bucket and turn it over, the water will pour out.

• However.....

If you spin the bucket, and ADD

ENERGY in the form of centrifugal

force...

The energy you add overcomes the force

of gravity, and the water is forced to the

outer part of the bucket.

The harder you spin the bucket, or the longer your arms, the more centrifugal force is generated. If there were a hole in the bucket, the water would fly out ---

A CENTRIFUGAL PUMP

WORKS THE SAME

WAY.

The Fluid Enters The

Pump Through The

Inlet Or Suction Eye,

Where The Impeller

Adds Energy (In The

Form Of Velocity)

Through Centrifugal

Force, And Forces The

Fluid Out The Edges

Of The Impeller To The

Discharge.

When the fluid leaves

the impeller, there is a

decrease in velocity.

Velocity and pressure

are inversely

proportional.

The decrease in

velocity results in an

increase in pressure

as the fluid leaves

the pump.

The Pump Can’t Do Its Job Until The Fluid Enters The

Impeller.

General Pump Classification

Kinetic

Pumps

Vertical Turbine

Lineshaft Submersible Axial Flow

Centrifugal

Split CaseOverhung Impeller

Kinetic Pumps

General Pump Classification

Axial Split Case vs. Overhung Impeller

Typical Overhung Impeller Pump Types

Frame Mounted

Close Coupled

Submersible

Basic Overhung Impeller Types

Enclosed Semi-Open

Open

Special Impeller/Pump Types

Centrifugal

Screw

Vortex

Special Impeller/Pump Types

Self Priming

“Trash”

Chopper

Basic Considerations

Flow and head conditions (avg, min, max)

Current vs. projected future flows

Liquid being pumped (rags, grit, grease,

chemical additives?)

Site constraints (space, power

availability, aesthetics)

Other challenges (retrofit, forcemain

network, terrain)

Important Details

Look closely at suction and discharge conditions

NPSHa > NPSHr

Potential for hydraulic transients

Pump speed (1200-1800 rpm)

Motor selection

Continuous vs. intermittent duty

Inverter duty (if VFDs are to be used)

Size motor for run-out condition

Packing vs. mechanical seals

Discuss/consider hardened materials?

An Overview of the Basic Centrifugal Pump Types

• General Purpose

• Overhung Impeller

• Thought of generally for flows less than 1000 GPM (Not Necessarily a good “end point”)

End Suction Pumps

An End Suction Pump Cross Section

• Basically same as End suction

• Big Difference between “circulators” and In-Line pumps

• An excellent choice when space is at a premium

In-Line Pumps

• DOUBLE SUCTION, SINGLE AND DOUBLE DISCHARGE

• Support Between Bearings

• Thought of as a “Cadillac”

• To 30,000 GPM

• The “devil’s in the details”

Split Case Pumps

A double suction impeller is really just

two end suction impellers, back to

back, with a common discharge.

Double Suction Split Case

TYPICAL SPLIT CASEPUMP

• Vertically suspended lineshaft driven non-clogs and Sump Pumps

• Good choice in mechanical rooms, where presence above cover is acceptable.

• Sump depths to 6-7’

• 1-1/2” TO 4” SOLIDS HANDLING in Non Clogs, ¼” in Sump Pumps. (Watch the Specs.)

Column Pumps

• CENTERLINE DISCHARGE, UL EXPLOSION PROOF Or Non-EXPLOSION PROOF.

• SLIDE RAIL SUBMERSIBLE NON-CLOGS

• Best for deeper sumps, or where above cover is unacceptable.

• (Except for elevator Pit, I’d go with Tandem Seals)

Submersible Pumps (Slide Rail Shown)

Submersible

Typically Central Plant in Municipal Wastewater Treatment.

A lot of details to pay attention to.

Dry Pit Non Clogs

CONFIGURATIONS

CHOPPER PUMPS

Externally adjustable

back pull-out design

All hardened

chopper

components

Oil lubricated

Ball bearings

Flushless

mechanical seal

BACK PULL-OUT DESIGN

No need to disconnect

from piping

Externally adjustable

back pull-out

Adjust ALL cutting

clearances externally

FLUSHLESS SEAL OPTION

Grinder/Chopper (Not a Pump)

Positive Displacement Pumps:

• Advantages

• Disadvantages

Positive Displacement Pumps:

•Models/styles•Rotary Lobe•Plunger/Piston•Peristaltic/Hose •Diaphragm•Disc Pumps•Progressive Cavity•Metering

Rotary Lobe

Plunger/Piston

Peristaltic/Hose

Diaphragm

Disc Pumps… A Type Of Diaphragm Pump

Progressive Cavity

Metering

Positive Displacement Pumps:

• Characteristics

• Maintenance

Questions?

•Kinetic – Dynamic – Centrifugal ???

•Force – Positive Displacement ???