_The Turbine Pump_ is suited to very high lifts, _even exceeding 2,000
feet_. An admirable example of this class of pumps is described in the
following paragraphs:
The Worthington turbine pump has been developed by a long series of
experiments. _The diffusion vanes_ which form the distinguishing
feature, take the place of the usual whirlpool chamber and assist in
bringing the water to rest without internal commotion or shock. They
correspond in function to _the guide vanes of turbine water-wheels_.
One of the difficulties presented by high-lift centrifugal pumps has
been the great peripheral speed required when only a single impeller
is employed. _This has been overcome by mounting a number of discs or
impellers, each operating in a separate chamber, upon a single shaft
and passing the water through the impeller chambers in succession._ The
lift can thus be multiplied three, four or five times, while the number
of revolutions is kept within bounds. It has been demonstrated that on
the same work and within reasonable limits, multi-stage centrifugals
are more efficient than single-stage pumps, the increased efficiency
being due to _a decrease in the frictional losses_ coincident with the
reduced peripheral speed of the impeller.
It is well known that the turbine water wheel was perfected less by
mathematical processes than by intelligent cut and try methods. It has
been the same with the turbine pump, whereby the vanes and passages
have been shaped and tested by practical experiments, followed in each
case by comparison of results. The constant aim has been to avoid
eddies and secure a favorable discharge of the water.
NOTE.—At the St. Louis World’s Exposition three of the 36-inch
Worthington turbine pumps, each of a capacity of 35,000 gallons per
minute against 160 feet head, supplied the Grand Cascade.
[Illustration: FIG. 504.]
The ills. on the opposite page (Fig. 503), which represents in outline
a Worthington turbine pump, indicates the difficulty of exactly and
mathematically designing such a mechanism. In the system shown only
suction and discharge pipes are employed, the water entering axially
and issuing radially. _The impellers_ remain in perfect longitudinal
balance regardless of their number or the head against which the
pump is operated, this balancing of the impeller being secured by an
ingenious system of “triple vanes.”
_The diffusion vanes._ In the Worthington turbine pump the efficient
conversion of energy is assured by an original system of diffusion
vanes disposed in the throat opening between the periphery of the
impeller and the annular casing, in much the same manner that guide
vanes are placed in a reaction turbine water-wheel. These vanes form
tangential, expanding ducts from which the fluid emerges at about the
velocity existing in the chamber. They also eliminate all drag and
friction between the periphery of the rapidly revolving impeller and
the slowly moving water in the discharge chamber.
The turbine pump has created an entirely new field of application for
centrifugal pumps, embracing mine drainage, water-works, and numerous
other services where rotary pumps are desirable but have not been
employed, owing to their former limited efficiency at high heads.
As a sinking or station pump for mine service, the turbine pump is
ideal. There are no valves, guards or springs, no reciprocating parts,
and, most important of all, there is no contact surface in the machine
except the shaft and its bearings. The design is such that parts
subjected to the action of mine water may be made of acid-resisting
metal, and, when desired, lead-lined.
NOTE.—The space occupied by the turbine pump is less than one-third
of that required by a reciprocating pump of equal capacity, and
the first cost, including the motor for driving, is only about
one-half. Since there are no rubbing surfaces exposed to the water,
the pump will run for years without renewal or repairs. In case
of accident, the parts are so few and the construction so simple
that any part of the machine can be replaced in less than one hour.
The cost of attendance is reduced to the minimum, since the only
necessary attention is to see that the pumps and motors are properly
lubricated. The simplicity and reliability of the centrifugal pump
make it especially suitable for isolated stations.
[Illustration: FIG. 505.]
[Illustration: FIG. 506.]
[Illustration: FIG. 507.—See page 241.]
Turbine pumps of excellent design (Fig. 507) of high efficiency are
built by the Byron Jackson Machine Works of San Francisco, California.
The operating elements of these pumps are rotating impellers containing
spirally-curved water passages, and fixed guide passage between
successive impellers. The water enters the passages of each impeller
_at the center_ and by the rotation is forced out into a collecting
chamber surrounding the periphery of the impeller. The ducts which
lead the water from there back to the center of the next impeller are
suitably curved to act as guide passages, similar in action to the
guide buckets of a turbine. The water then enters the next impeller
parallel with the shaft, its rotary motion having been transformed by
the guide passages into rectilinear motion.
Fig. 509, a drawing of a vertical pump in section, shows the relative
arrangement of impellers (marked A) and guide passages (B). This
pump has the suction entrance at the top; the discharge leaves the
collecting chamber of the last (lowest) impeller tangent to the circle.
The shaft rests in a thrust bearing at the top, and is further held by
bearings formed in the successive sections of the case. At the bottom
it is provided with a special balancing arrangement, described here
after.
[Illustration: FIG. 508.]
Each impeller, where it joins the guide passages of the preceding
case section, is fitted into the case so as to form as tight a joint
as possible without introducing any great frictional resistance to
rotation. With the exception of the entrance opening, the external
surface of the impeller is exposed to the delivery pressure, so that
there is a resultant upward pressure on each impeller, equal to the
area of its entrance multiplied by the difference between the entrance
and discharge pressures of that stage. If all the impellers are alike,
the total upward thrust is equal to the product of entrance area
multiplied by the total head on the pump. The pumps are so proportioned
that this upward thrust slightly exceeds the weight of the rotating
portion, consisting of impellers and shaft. _The excess of upward
pressure, however, is relieved by the balancing device located at the
lower end of the shaft, with the result that the_ _rotating part is
precisely balanced, thus relieving the thrust bearing of all load while
the pump is running._
The balancing device referred to consists of two chambers, C and D,
formed centrally in the bottom of the lowest section of the pump case.
The large chamber, C, encloses a projecting hub, E, on the lower
surface of the impeller. This hub of course rotates with the impeller,
and the joint between the hub and the walls of the chamber is,
therefore, loose enough to allow water from the delivery side of the
last impeller to leak into chamber, C, and establish the full discharge
pressure in that chamber. The small lower chamber, D, contains a plug,
H, which may be adjusted endways by means of screws. The forward end of
this plug fits closely into a recess in the face of the hub, E, which
recess, communicates, by way of the hollow central part of the hub and
the passage, _g_, with the entrance side of the last impeller.
The action of the device is as follows: when chamber, C, becomes
filled with water, or rather when leakage through the joint around the
tube, E, has raised the pressure in the chamber, C, to the delivery
pressure, the total upward pressure on the impellers is greater than
the total weight of the rotating part of the pump. The rotating element
is therefore lifted until the recess in hub, E, is raised clear of
the plug, H. In this position the pressure in chamber, C, is relieved
through the passage, _g_, with the result that the rotating element
again settles down over the adjusting plug, H. As this action tends to
recur, a position of equilibrium is established near the point where
the plug just enters the recess in the hub, E. The precise position
of this point may be altered by the adjusting screws of the plug, H,
thereby adjusting the endwise position of the impellers in the casing.
When the pump is not in operation, of course the upward pressure of the
water does not act, and the weight of the rotating part must be carried
by the thrust bearing.
[Illustration: FIG. 509.]
When these pumps are built with horizontal shaft, the unbalanced
pressure which is thus turned to account in the vertical pump
becomes harmful and must be avoided. The arrangement by which this
is accomplished is shown in Fig. 510, where the letters, A and B,
designate respectively the impellers and the guide passages as before.
The rear of each impeller, that is, the side opposite the entrance
opening, bears a short annular projection, S, fitting within a similar
ring, _t_, projecting from the casing. The circular chamber formed
by these two rings communicates, through holes, V, in the web of the
impeller, with the entrance side of the impeller. The chamber being
slightly larger than the entrance opening of the impeller, it serves
to eliminate all thrust on the impeller in the direction of the
suction (since the remainder of the external surface is exposed to
the discharge pressure), and produces instead a small thrust directed
toward the discharge end.
This small resultant thrust is taken up by a balancing device at the
end of the shaft precisely similar to that used in the vertical type
of pump, as previously described. The balancing action thus secured
serves to fix the endwise position of the rotating part; moreover, it
affords sufficient margin to compensate for longitudinal thrusts which
may result from causes such as slightly non-central position of the
impellers in their casing.
Pumps of this design are built for heads of from 100 to 2,000 ft., the
number of separate impellers or “stages” being properly proportioned to
the head. _About 100 to 250 ft. head per stage_ appears to be allowed.
A high efficiency of working, from 70 to 80%, is said to be realized.
_The horizontal two-stage pump_ shown in Fig. 507 is one built for the
water-works of the city of Stockton, Cal., to deliver 1,500 gallons
per minute against a head of 140 ft., at 690 r. p. m. It is driven by
a 75-HP. induction motor of the Westinghouse Electric & Mfg. Co. type,
of Pittsburg, Pa. Pump and motor are mounted on a common base, and
their shafts are solidly coupled. This pump was guaranteed to have an
efficiency of at least 75%, but we are informed by the manufacturers
that the official test showed it to have an efficiency of 82%.
_The vertical pump of four stages_, shown in Fig. 508, has a discharge
capacity of 450 gallons per minute and delivers against a head of 500
ft. The same type of pump, however, will work against heads up to 800
ft. The mounting of the pump in the present instance is at the bottom
of a 200-ft. pit; the pump shaft leads vertically to the surface, where
it is driven by belt. A closely similar installation has been made,
where two vertical three-stage pumps operate under a head of 310 ft.
The pumps are located in a 30-ft. pit, and their shafts are extended
to the surface, where they carry each a 200-HP. induction motor mounted
directly on the shaft. The balancing action of the pump was in this
case designed to be sufficient to carry the entire weight of the
rotating part, that is, motor, shaft and pump impellers.
[Illustration: FIG. 510.]
INJECTORS
AND
EJECTORS
[Illustration: FIG. 511.—See page 251.]
[Illustration: FIG. 512.—See page 251.]