The Donaldsonville chief. [volume] (Donaldsonville, La.) 1871-current, 1916-12-30
WATER SUPPLY DEFICIENT.
Methods of Improving System Recon-
mended in Engineers Report.

Following is the full text of the re
port submitted to the Municipal L1gh
and Water Commission by Engineer
E. NJ 1vens, who was engaged by the
commission to make an investigation
of the local water supply system ane
submit recommendation for its I'M
provement:
Municipal Light & Water Commits
sion, Donaldsonville, La.
Dear Sirs Having carefully IN
vestigated the conditions under which
your water pumping equipment is
operating, | beg to report as follows
Insofar as the actual mechanical
operation is concerned, there appears
to be no difficulty with any of the
pumps except the small general ser
vice pump. A visual shut-off pres
sure test of this pump indicates that
the impellars and rings are somewhat
worn and should be replaced with
new parts. Otherwise, the equipment
seems to be carefully and intelligent
ly operated.
Attention is therefore directed to
the conditions existing outside of the
plant itself and which influence to
a marked degree the results obtained
from the pumps now being operated.
I refer to the two 10-inch suction
pipes which connect the centrifugal
pumps with the river and through
which the water supply is obtained.
These suction lines, as you know, ex-
coed 500 feet in length and contain
several elbows and valves, and being
located as they are on a building
bank, the length must be increased
from time to time, making conditions
more severe, not to mention the ever
increasing difficulty and expense of
maintenance.
In order to impress upon you the
precarious conditions now existing
and the severity of the duty under
which your pumps are operating,
l will endeavor to explain the practi-
calreasons for avoiding long suction
lines on pumps of the type now in
stalled. l will refrain as far as pos
sible from the use of technical terms
and confusing theoretical data.
A centrifugal pump possesses no
positive displacement feature, and
consequently, before it can raise OF
pump water, all vapors such as air
must be expelled from the pump and
it's suction piping. Once in operation
pump of this type, advantageously
installed, can handle small quantities
of air, but the efficiency is impaired
and capacity reduced in so doing. If
the suction lift is severe, even small
quantities of air will either danger
ously reduce the efficiency and ca
pacity Of the pump Or suspend opera
ton entirely
A centrifugal pump installed under
sea level atmospheric conditions
(14.7-lbs. pressure, absolutely and
near the source Of supply of water,
has a practical suction limit of APP
proximately 25 feet. This includes
actual static head plus friction head,
and assumes an alright pump and
piping, Where long or tortuous sue
ton piping is necessary, the practical
suction limit is considered to be eigh-
teen feet, including the static and
friction heads. The difference in
limits is due to the difficulty of main
tanning long lines tight, the danger of
air pockets and "locking," and the
difficulty Of holding the relatively
high vacuum necessary.
Water, itself, carries a certain
amount of air in suspension. When
a vacuum is applied, as in printing,
the vapor tension rises and the volume
of the contained air increases. The
greater the lift, the higher the
vacuum necessary and consequently
the greater the volume occupied by
the air. An air pocket forms at the
point of least pressure in the system,
which is within the suction opening
in the pump impellar. This pocket
restricts the effective area for the
admission of water and acts as a
throttle. The accuracy of this state
ment is illustrated by the perform
ance of your small general service
pump. By connecting the suction ell
bow with a 2" barometric loop and
thence to the inlet of your drysva-
CUM pump, and by operating the
vacuum and centrifugal pumpss 81
multaneously, the discharge pressure
was increased about 5 pounds over
InaC formerly ODJalneQ.
The vacuum gauges on the suction
side of your pumps register between
22.5 and % inches. Allowing for a
possible discrepancy between the
gauges and the more accurate mer-
curry column, your pumps are operat-
ing with a suction lift of between "a
and 25.5 feet, or between and rs
Foot t0 tI,at rI-hic1
orally considered the practical com
nercial limit for installations of this
kind. The performance of the
pumps when heavy-demands for water
are made testifies to the soundness
IF the foregoing contentious.
Following are given several meth
DDS whereby the existing difficulty
nay be partially or completely over
come, together with the estimated
,ost of each. All estimates are based
lpon the present market prices of ma
erials and apparatus and the present |
Gale of labor wages. Revisions
will be necessary in the amounts nam
d for any material market fuctua-
ions.
First. The installation of a sur
ace reservoir having capacity of
bout 100000 gallons of water, to-
ether with a low-duty, motor-driven
Jump for cleansing. This reservoir
0 be used for storage purposes and
allied upon in case of fire only.
In addition to the reservoir and
ump, some extensions to the piping
ystem must be made. The two
resent suction pipes must be cross
onnected to the reservoir and suit
bic gate valves provided, SO that, by