Fluid pumping process and system using a pump with a...

Pumps – Plural pumps with individual or relative control

Reexamination Certificate

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C417S005000

Reexamination Certificate

active

06244838

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reversible fluid pump that can work with a constant intake or delivery rate and to a hydraulic system using such a pump.
It more particularly relates to a reversible pump with two alternating pumping elements interconnected in series or in parallel, that can work with a constant intake or delivery rate in a fluid circulation system such as those that can be found in various industry types. The pump according to the invention finds applications notably in chromatography systems.
2. Description of the Prior Art
Various pump types can be used for circulating liquid mixtures such as, for example, alternating pumps comprising generally two alternating linear pumping units arranged in parallel.
According to the embodiment of
FIG. 1
, each of the two units arranged in parallel comprises a piston, sliding in a cylinder
2
communicating, by means of a one-way valve
4
opening during the intake phase, with an inlet line
3
coming from a first tee T
1
delivering a liquid L. The two units PU
1
, PU
2
also communicate, through an outlet line
5
and by means of valves
6
opening during the delivery phase, with a second delivery tee T
2
. Phase shift of units PU
1
, PU
2
is controlled by power sources M under the control of a control device PC so that the intake phase of one substantially corresponds to the delivery phase of the other.
Various types of power sources M can be used.
The stroke depth of each rod
1
in its cylinder
2
can for example be provided (
FIG. 3
) through the translation of a screw
7
resting on the head of piston
1
by means of a ball thrust
8
. The screw translation comprises for example a nut
9
threaded to screw
7
, that is for example housed in the hollow rotor of a stationary electric motor
10
and driven in rotation thereby. The direction of translation of the screw is changed by inverting the direction of rotation of the motor every pumping half cycle.
According to a second embodiment (FIG.
4
), the stroke depth of piston
1
in body
2
is provided by the rotation of a cam
11
resting against the head of piston
1
, whose pin
12
is driven in rotation by a motor
13
. The stroke depth of piston
1
in the inner cavity of body
2
is obtained by changing the offset &Dgr; of the cam on the axis thereof. In either case, motor
13
is driven by a control computer PC.
The speed of each piston
1
decreases at the end of its stroke, and consequently so does the flow delivered thereby. If the global rate of delivery of units PU
1
, PU
2
(
FIG. 1
) has to be substantially constant, the sum of the speeds of the two pistons must remain constant and the delivery phase of unit PU
2
for example must therefore start before first unit PU
1
has totally finished. During the relatively short fraction of each cycle where the two units deliver at the same time, the intake rate is zero, which results in a pulsed intake rate of the pump.
In a pump with two units PU
1
, PU
2
arranged in series (FIG.
2
), unit PU
1
draws fluid out of a fluid tank R through a line TE on which a first nonreturn valve V
1
is interposed. It drives it through a second nonreturn valve V
2
, towards unit PU
2
. The latter drives the pumped fluid through a line TS to the pump outlet. When piston
1
of unit PU
1
is in the delivery phase and drives a volume &Dgr;V towards unit PU
2
downstream, piston
1
of unit PU
2
is moved back so that it draws a volume &Dgr;V
s
=&Dgr;V/2 taken from the volume delivered by first unit PU
1
. The volume expelled through line TS is thus equal to &Dgr;V/2. When piston
1
of the same unit PU
1
goes into the intake phase and valve V
2
closes, piston
1
of second unit PU
2
goes into the delivery phase and expels the previously drawn volume &Dgr;V
s
=&Dgr;V/2 towards line TS. The flow expelled through line TS is constant provided that the motion laws applied to both pistons are so selected that the sum of their respective speeds is permanently constant. An example of a pump of this type is described in U.S. Pat. No. 5,755,561 filed by the assignee.
SUMMARY OF THE INVENTION
The present invention relates to a process for pumping a fluid in a circuit, comprising using in the circuit a pump with at least two alternating fluid pumping units comprising each a cylinder and a piston displaceable in the cylinder, with imposed displacement functions for the pistons, suitably phase-shifted in relation to one another so as to obtain a first operating mode corresponding either to a substantially constant intake rate or to a substantially constant delivery rate.
The pumping process is characterized in that the pump is operated in the same circuit according to a second operating mode complementary to the first mode, by inverting the direction of displacement of the pistons so as to apply thereto displacement functions symmetrical to those corresponding to the first mode.
The system for pumping fluids in lines according to the invention comprises at least one pump provided with at least two alternating fluid pumping units comprising each a cylinder and a piston displaceable in the cylinder. It comprises a drive for alternately displacing the two pistons, suited to apply respectively to the pistons of the pumping units displacement functions (f(t), g(t)) as a function of time t, suitably phase-shifted in relation to one another, in order to obtain a first operating mode of the pump with a substantially constant intake or delivery rate.
The pumping system comprises an inverting system acting on the drive for displacing the two pistons in order to apply displacement functions (−f(t), −g(t)) symmetrical to the previous ones and to obtain for the pump a second operating mode complementary to the first mode, with a substantially constant intake or delivery rate.
According to an embodiment, the system for displacing each piston comprises a screw alternately displaced parallel to its axis, by a driving motor, and a control device for changing alternately the direction of rotation of the driving motor in accordance with the operating mode selected.
According to another embodiment, the system for displacing each piston comprises shaped cams driven in rotation by a single motor, and a control device for controlling the motor according to the operating mode selected.
The pumping system can comprise several pumps installed for example on various lines of a set of lines and a control device suited to select, for each pump, the first or the second operating mode so as to comply with determined conditions of circulation in the set of lines.
According to an embodiment, the pumping system comprises several pumps in a circuit and on fluid injection and/or extraction branch lines, the control device being suited to control the motors of the various pumps so that the sum of the volumes of fluid injected at a constant rate according to the second operating mode is substantially equal to the sum of the volumes of fluid extracted at a constant rate according to the first operating mode.


REFERENCES:
patent: 4233156 (1980-11-01), Tsukada et al.
patent: 4278205 (1981-07-01), Binoche
patent: 4321014 (1982-03-01), Eburn et al.
patent: 4643649 (1987-02-01), Schmid
patent: 5406784 (1995-04-01), Vertens et al.
patent: 5641270 (1997-06-01), Sgourakes et al.
patent: 5719302 (1998-02-01), Perrut et al.
patent: 5755561 (1998-05-01), Couillard et al.
patent: 5993174 (1999-11-01), Konishi et al.

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