Pump Basics



A pump is a machine that imparts energy to a liquid to increase its pressure and
move it from one point to another. We used the term
liquid (not fluid ) because the
word
pump is universally used to refer to a machine that pumps liquid whereas
one that  handles air, gas, or vapor, is specifically referred to as
air pump,  
vacuum pump, compressor, blower, or fan.

In this web site the word
pump is used to refer to a machinery that handles liquid.
It is important to make this distinction because air, gas, or vapor is an "
enemy" of
a pump that impairs its performance and operation. A pump, in its universal
meaning, should not be used for handling air, gas, or vapor.

Among non-electronic machineries pumps are the most widely used,next to
electric motors. Pumps play an important role in our daily lives more than we
probably realize it. At homes, pumps can be found in aquariums, swimming
pools, washing machines, etc. Our cars need water pumps and fuel pumps to
operate and run. In buildings where we work and shop, there are pumps to
ensure our comfort - in water fountains, in cooling towers for centralized air-
conditioning systems, in constant pressure water supply systems. And there are
fire pumps, jockeys pumps, and sewage pumps, etc., protecting buildings from
calamities and disasters. In agriculture there are irrigation, flood control, and
deepwell water pumps to support our food supply. And of course, there are
countless of other process, chemical, and specialty pumps in factories and other
industries.

A typical pump has hundreds of parts. No matter how simple or complex some
pumps are, their major parts are designed to perform specific functions
regardless of their sizes and shapes.  The major parts are:

  • casing
  • impeller
  • shaft
  • seal
  • bearing
  • coupling

Casing
The casing (or case) contains the liquid and acts as a pressure containment
vessel that directs the flow of liquid in and out of the pump. In most cases the
casing includes the suction and discharge nozzles of the pump that connect it to
the external piping. In some vertical pumps the casing may be referred to as
bowl,
and in some small pumps they may it call it
housing.

Impeller
The impeller is a vaned-disk (or disc) mounted on the shaft. Its function is to
increase the pressure of the liquid by means of its rotating action. The impeller
may be of open, semi-open, or enclosed type, and may have anywhere between
two to ten vanes. It may also be of single, or double, suction design.

Shaft
The shaft is usually the longest part of a pump and is made of one piece. Its
function is to transmit the input power from the driver into the impeller. In a close-
coupled pump, the motor has an extended length of shaft that acts as the pump
shaft. In some vertical pumps, the so-called
lineshaft pump, the shaft may be
supplied in more than one piece of ten Feet sections depending on the pump
bowl setting below the ground surface.

Seal
A pump may be provided with one of two types of sealing elements - packing rings
or mechanical seal. The sealing elements prevents the leakage of the pumped
liquid into the atmosphere.

Bearings
The functions of the bearings are to support the weight of the shaft (rotor)
assembly, to carry the hydraulic loads acting on the shaft, and to keep the pump
shaft aligned to the shaft of the driver.

Coupling
The function of a coupling is to connect the pump shaft and the driver shaft, and to
transmit the input power from the driver into the pump.

There are many other pump parts to consider but their function are collateral to
that of the main parts listed above.


A pump's performance is shown in its characteristics performance curve where its
capacity (in GPM) is plotted against its developed head (in FT), efficiency (in %),
required input power (in BHP), and NPSHR (in FT.) The pump curve also shows
its speed (in RPM) and other information such as pump size and type, impeller
size, etc. [For simplicity the discussions in this web site are based on the US
system of units and on 60 cycles power supply.]

The term head refers to the differential head developed by a pump expressed in
feet of liquid:

H = [Pd-Ps] x 2.31 / SG

where:

H  = pump head, FT of liquid
Pd = pump discharge pressure, PSIG
Ps = pump suction pressure, PSIG
SG = liquid specific gravity

If a pump were an ideal machine the required input power to drive the pump,
called hydraulic horsepower (HHP), is calculated from:

HHP = [Q x H x SG] / [3960]

where Q = capacity in GPM
[ANSI/HI 1.1-1.5-1994, section 1.2.6.3 refers to this term as water horsepower
which is a misnomer. If the specific gravity were omitted (SG=1) then the term is
correctly referred to as water horsepower, WHP]

But since a pump is not an ideal machine the required input power, called brake
horsepower (BHP), is calculated from:

BHP = [Q x H x SG] / [3960 x E]

where E = pump efficiency in decimal


R-1109-PUBA
File: pump basic

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Introduction
Pump types
Horizontal vs. vertical
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Parallel-series operation
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OH1, OH2
OH2, OH3, OH4, OH5
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