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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to pressure boosters for fluid
distribution circuits and to hydraulic distribution circuits incorporating
such boosters. More specifically, this invention relates to the
enhancement of the flow and pressure characteristics of fluid distribution
circuits. Accordingly, the general objects of the present invention are to
provide novel and improved apparatus and methods of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is
particularly well suited to use in or as a fluid supply circuit connected
to a general water distribution system wherein the flow demands can vary
between rather extreme limits. An example of such a system would be a
complex of living units where it is necessary to satisfy peak demands for
water while simultaneously preventing the pressure from dropping below a
predetermined value. Similar problems are presented in, and the present
invention is also applicable to, air distribution systems such as
ventilation circuits incorporating fans or blowers.
Problems of the type alluded to above have, in the case of hydraulic
distribution circuits, previously been solved through the use of
hydro-pneumatic pressure booster systems wherein one or more centrifugal
pumps were controlled in an on-off fashion. Such prior art systems
typically employ an elastic cushion, defined by a pressurized vessel
containing a quantity of air, and the volume variations between two
predetermined pressures are measured and used to determine the operating
cycle of the pump or pumps. Such prior art hydro-pneumatic pressure
booster systems have been characterized by relatively high maintenance
costs due, in part, to the necessity of periodically reinflating the air
cushion; such reinflation being necessitated by micro-leaks or by natural
dissolution of the air in water.
In the interest of reducing the size and complexity of pressure booster
systems in hydraulic distribution circuits, and also in reducing
maintenance requirements and power consumption, it has been proposed to
employ permanently operating pressure maintenance pumps. The use of such
continuously operating pumps enables elimination of the pressurized vessel
since the pump pressure head is added to the pressure of the system. At
first glance this would appear to insure adequate pressure in the fluid
distribution circuit. However, systems employing continuously operating
pressure maintenance pumps have encountered difficulties in insuring peak
flows. The provision of grossly oversized pumps to insure adequate peak
flows is not an economically feasible solution to these difficulties.
Comparative complex control systems employing both continuously and
intermittently operated booster pumps have also been proposed in hydraulic
distribution circuits of the type being discussed for purposes of
explanation. In such systems there has typically been a functional
disparity in size between the continuously operating units and the peak
load supplying units and such functional disparities have imposed
additional complications on the systems.
A further prior art attempts at solving peak flow problems in hydraulic
circuits has envisioned varying the speed of the booster pumps either
continuously or in stages. This approach has, however, resulted in
extremely complex and expensive systems. This complexity results from the
fact that the flow delivered by an electric motor drive centrifugal pump
varies with speed thereby making it difficult to multiply the flow
provided by a group of such pumps by three or four times as may be
encountered during peak load periods. Additionally, adding to system
complexity and thus lack of reliability, is the fact that pump compression
level varies with the square of pump speed. As a further complication, the
power required to drive such pumps also varies in a ratio of the cube of
the speed.
SUMMARY OF THE INVENTION
The present invention overcomes the above briefly described and other
deficiencies and disadvantages of the prior art by providing a novel
pressure booster system and a fluid flow distribution circuit
incorporating such booster system. The present invention is based on the
fact that it is possible to drive the rotor of any rotary pump in two
directions. This inherent possibility has never been exploited because the
potential usefulness thereof has not been appreciated and, perhaps more
particularly, because the desire for maximum efficiency has led to a
sacrifice of pump performance in one of the possible directions of
rotation in favor of the other. Nevertheless, pumps are commercially
available which will operate with a reasonable degree of efficiency in the
"off-design" direction. Consequently, it is possible to employ pumps which
may be selectively caused to rotate in either direction giving two
different flow rates for each pump and, in a distribution system, giving
2n flows per n pumps.
Thus, in accordance with the present invention, one or more pump units,
each comprising two pumps having the same characteristics, are employed to
provide 2n flows by utilizing each pump in both rotational directions.
This provides a plurality of pump combinations which, in turn, enables
provision of a system having a highly desirable pressure-flow curve.
A particularly advantageous feature of the present invention is that it
permits the use of a single reserve pump, if necessary or desired, because
all pumps used in the system are identical.
BRIEF DESCRIPTION OF THE DRAWING
The present invention may be better understood and its numerous objects and
advantages will become apparent to those skilled in the art by reference
to the accompanying drawing wherein like reference numerals refer to like
elements in the several figures and in which:
FIG. 1 is a graphical presentation depicting operation of the present
invention;
FIG. 2 is a schematic representation of an electrical control circuit for
the present invention; and
FIG. 3 is a schematic isometric view of a preferred embodiment of the
invention which may utilize the control circuitry of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 the abscissa of the graph represents increasing flow rates while
the ordinate indicates increases in pressure. FIG. 1 relates to a group of
two pumps, designated PA and PB, with the designations being followed by a
(+) or (-) according to whether the pump in question is rotating in the
"direct" or "opposite" direction. In the context of this disclosure the
direct direction is the direction of highest performance efficiency and is
indicated (+) and while the opposite direction is the direction of lowest
performance and is indicated by (-). Although better results can be
obtained, a typical ratio of the compression levels for a pump, depending
whether it turns in the (+) or (-) direction, is about 0.66. It is to be
noted that this ratio increases when the pumps have their intake ports
connected to a pressurized distribution system. As noted above,
bi-directional pumps suitable for use in the present invention are
commercially available. Such pumps may, for example, comprise centrifugal
pumps.
In FIG. 1 the point N represents the peak flow and pressure guaranteed by
the system. It may thus be considered that the solid line parallel to the
axis of the flows and passing through the point N represents the
theoretical Piezo-metric level of the system although the true curve is
shown as broken line N'. Thus, as will become obvious from the discussion
below, the ratio of the compression levels for low flows is further
improved, a fact which in practice is ignored, and the margin of
uncertainty improved with the use of the present invention.
In the selected operating mode, explained below, the following curves are
used:
Pa(-) -- represents operation of pump A only and in the (-) direction;
Pa(-) + pb(-) -- represents operation of pumps A and B in parallel and both
in the (-) direction;
Pa(+) -- represents operation of pump A only and in the (+) direction;
Pa(+) + pb(+) -- represents operation of pumps A and B in parallel and in
the (+) direction; and
T -- represents the increase in load losses in the circuit as the flow
increases with ideal or theoretical operation.
The actual preferred operating mode is represented by the saw-toothed curve
shown as an unbroken line based on the curve T. At the upper part of FIG.
1 portions of a typical cycle, represented in terms of percent of time in
a typical 24 hour period, during which the flow probably will be within
certain regions have been indicated.
In terms of FIG. 1, the operation of the invention is as follows:
Over the larger portion of the day, indicated as 90% on the diagram, pump
PA(-) rotates and supplies the required flow while maintaining circuit
pressure at levels up to that corresponding to point M on FIG. 1. As soon
as pressure M is reached by the development of the required flow by pump
PA the second pump PB(-) will be caused to support pump PA(-) by operating
in parallel therewith. If, after a predetermined time, the pressure M is
not detected by a pressure sensitive switch 26 (FIG. 2), pump PB(-) will
be stopped and only pump PA(-) will continue to rotate. However, if the
pressure remains above that of point M, pumps PA(-) + PB(-) will continue
to operate in parallel. If, with the pumps operating in parallel in the
(-) direction, the system pressure reaches a level corresponding to point
P, both the pumps PA(-) and PB(-) will be stopped and pump PA will be
restarted in the (+) direction. Pump PA(+) will remain in operation until
the pressure reaches that corresponding to point R. Should pressure level
R be reached pump PB is started in the (+) direction and thus pump PB(+)
supports pump PA(+) by parallel operation. If, after a predetermined time,
a pressure corresponding to that of point S is detected, the parallel
operation continues until pressure level K is reached. When pressure level
K is no longer detected, pump PB(+) will be stopped and the mode of
operation with PA(+) alone operating is resumed.
In FIG. 1, the broken lines passing respectively through points M, P and R
and parallel to the axis of flow respectively indicate the pressure levels
at which pump PB(-) starts operating, pump PA(+) starts operating, and
pump PB(+) starts operating. The relative position of these three parallel
lines is a consequence of and therefore a characteristic of the operating
mode selected as the preferred mode of operation of the invention.
The points Q and S on FIG. 1 correspond to a time delay, after a pump
initiation, after which the flow may be considered as momentarily
stabilized. The provision of such time delays is in the interest of
preventing "pumping" of the device in the vicinity of the peaks of the
curve; i.e., the time delays prevent too frequent changes in the system
operational mode. The length of the time delays are determined
experimentally and depend on the anticipated flow demand changes to be
imposed on the delivery circuit.
Taking into account the practical distribution of the high and low flows of
the operative period depicted in FIG. 1, which as noted is a 24 hour day,
it may be seen that pumps PA and PB operating in the (-) direction will
fulfill 70% of the requirements imposed on the system. During the
remainder of the time excess pressure on the order of 1 to 3 bars will
permit the supply of increasingly high flows. It is to be noted that this
pressure range corresponds to a maximum pressure commensurate with that
which would have been attained employing the conventional prior art
hydro-pneumatic type boosters for which the regulation range would
necessarily have to be entirely above the point K of FIG. 1.
It is also to be noted that, in the above discussed example which relates
to an installation with two pumps, it will usually be considered necessary
to have a third pump in reserve. The preferred operational mode is to keep
the reserve pump continuously operating. With the reserve pump
continuously operating the saw-toothed curve of FIG. 1 will have two
additional "teeth" which result in the overall curve approaching the ideal
response to a closer degree. Obviously, in the three pump system when one
pump breaks down the two remaining pumps will continue to provide the peak
flow.
FIG. 2 depicts an electric circuit for control of the distribution system
described above in the discussion of FIG. 1. In FIG. 2 the relays of the
control circuitry are represented schematically and the same reference
characters have been applied to the relay solenoids and the switch
contacts controlled thereby. Also, in the interest of facilitating
understanding of the invention, several of the switches or terminals have
been shown twice in FIG. 2.
The drive motors MA and MB respectively for pumps PA and PB may be presumed
to be three phase electric motors supplied by three phase alternating
current. The alternating current supply will be converted into a low
voltage direct current for use in the control circuitry by means of a
power supply including a transformer and rectifier. In the hydraulic
circuit represented in FIG. 3, the pumps PA and PB are connected in shunt
between the supply circuit 3 and the delivery circuit 4. The delivery
pressure is sensed by means of pressure sensitive devices MO, PR1 and PR2.
The pairs of ganged relay contacts, indicated at 50 and 51 (FIG. 2), are
employed to supply lower to pump motors MA and MB. Relay contacts 50 and
51 are mechanically interconnected as indicated schematically at 52.
The control device includes a four position selector switch 53. Switch 53
has two stop positions and two positions which control respectively the
excitation of the solenoids or relays of R1 and R2. Relays R1 and R2
supply power for initiating operation of the drive motor MA of priority
pump PA and are typical of similar such relays conventionally employed in
motor starting circuits. Conventional protective devices, indicated
schematically as MET are incorporated in the system to prevent the
operation of pump PA when there is no fluid at the pump inlet. As noted
above, PR1 and PR2 denote pressure sensitive switches and whereas MO
denotes a manometer type device which typically will have two contacts;
all of devices PR1, PR2 and MO having a time delay.
Presuming that pump PA has been selected as the priority pump, the
excitation of relay R1 by proper closing of switch 53 causes excitation of
relay R3 insuring, by the closing of contacts 21-22, the excitation of
relay PA(-). Excitation of relay PA(-) will cause the closing of contacts
51 and 52 and will result in the starting of pump PA in the (-) direction.
Referring jointly to FIGS. 1 and 2, pump PA(-) being supposed in service,
when the pressure level corresponding to point M is detected by device MO,
the contacts 7-10 and 7-27 of device MO will close causing the closing of
relay R1 and the excitation of relay RT 1. Excitation of relay RT 1 will,
by means of relay RP B(-) cause the closing of contacts 50-51; whereby
power will be supplied to motor MB of pump PB causing PB to start in the
(-) direction. After a predetermined time, if the pressure corresponding
to point M is no longer detected by device MO, the contacts of the device
will open and, via the action of relay R2, the pump PB will be stopped and
the PA(-) mode of operation resumed.
However, if the pressure corresponding to point M is detected, the PA(-) +
PB(-) operational mode continues until the pressure corresponding to point
P is reached.
When the pressure corresponding to point P of FIG. 1 is detected by switch
PR1, switch PR1 causes the excitation of relay RT 2. Excitation of RT 2
causes, via the excitation of relay RP A(+), the starting of pump PA in
the (+) direction. Excitation of RT 2 also causes, by means of relay R2,
contacts 21-22 and 24-25 to open thus shutting down pump PB(-). After a
predetermined time, if the pressure corresponding to P is not detected,
relay RT 2 is deenergized causing the PA(-) + PB(-) mode of operation to
resume. If, on the other hand, pressure P is detected the PA(+)
operational mode continues until the pressure corresponding to point R is
reached.
When pressure R is detected by switch PR2, the contacts of this switch
close causing the excitation of RT 3 whereby pump PB is started in the (+)
direction.
If, after a further predetermined time delay, the pressure S is detected by
PR2, the mode of operation PA(+) + PB(+) continues until a pressure level
corresponding to point K of FIG. 1 is reached. If, however, the pressure
falls below level R, the contacts of switch PR2 open causing relay RT 2 to
be deenergized and, by means of relay R3, the motor MB of pump PB to be
stopped.
It is to be noted that switches 54 and 55 are controlled by thermo-magnetic
relays, not shown, which act as safety devices to guard against
overloading or unbalance of the pump drive motors. Also, indicator lights
56 and 57 are provided. Control equipment for a stand-by pump may be
connected in parallel with the indicator lights. A number of push button
type switches MF, MF PR.sub.1, MF PR.sub.2 have been shown. These push
button type switches serve solely for control of the installation manually
when the automatic control is out of service or for operation of the
priority pump at a reduced level.
While a preferred embodiment has been shown and described, various
modifications and substitutions may be made thereto without departing from
the spirit and scope of the invention. Accordingly, it is to be understood
that the present invention has been described by way of illustration and
not limitation.
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