WO2001025638A1 - Gear pump with double effort compensation - Google Patents

Abstract

Said pump consists of a drive axle (9) and a driven axle (9') on which three separate pump bodies are mounted, each of said bodies consisting of a drive gear (6a) (6b) (7) and a driven gear (6'a) (6'b) (7') that are mounted on the drive (9) and driven (9') axles respectively. Said three pump bodies embody two pumping elements, a central pumping element and a lateral pumping element that is formed by the two lateral pump bodies (6a) (6'a), (6b) (6'b) mounted in parallel. The device is used for the renewal of fluids or gases between a high-pressure container and a low-pressure container. The two pumping elements should be mounted in such a way that input and output pressures of the central pumping element and the lateral pumping element have the same value but are inverted in terms of the of the pumping body they act upon.

Description

 GEAR PUMP WITH DOUBLE EFFORT COMPENSATION

Description

The invention relates to a gear pump which, through a special arrangement of its constituent elements, achieves double stress compensation. The use of such a pump is especially useful in applications that require two simultaneous pumping at high pressures with a relatively low pressure difference. The pump object of the invention has been designed to solve the double pumping required by desalination plants by reverse osmosis, but it can also be useful in other applications such as, for example, in the renewal of seawater in large-scale swimming pools height.

The classic gear pump is well known to everyone. Two generally equal sprockets or sprockets are engaged and housed within two cylinders that are cut, which forms the periphery of the assembly, and which constitutes an envelope that is shaped like the outline of a guitar or number "8", made with two arcs of equal circumferences. One of the two sprockets is driving, driven by the engine or power plant, and the other, which is driven by the first, is a sprocket that has a shaft that rotates freely in its bearings or support bushings. These pumps have good characteristics such as the simplicity of their construction and performance, which can be even greater than that of pistons, but as a counterpart it has to be very precise machining, and that the friction between the teeth is large, The more the more the fluid pumping pressure. In other words, the teeth of the pinions are forced to resist a friction between them that is so much greater, the greater the working pressure there is, on the other hand, a radial thrust on the axes that is also proportional to this pressure. The aforementioned efforts cause an exaggerated wear of the teeth and of the bearings or support bushings, rubbing the tips of the teeth against the walls of the cylinders that wrap it and leaving at the same time a diametrically opposite clearance where significant leaks originate. . All this makes the gear pump a low life pump, even when trying to pump lubricating fluids such as oil. When it comes to pumping water at significant pressures, work is left for piston pumps or for multiple impeller centrifuges.

An important characteristic of this type of pump is that it is volumetric displacement, so the amount of liquid that it pumps is proportional to the turns that gives the axis, without considering the speed of rotation of this, or the pressure of the liquid.

The object of the invention is to have a triple body gear pump, specially designed for double pumping, and to demonstrate that work efforts are not important no matter how much the pressure. The application of this pump will be destined to when it is necessary to "renew" fluids from a vessel that is under pressure, by another that is at atmospheric pressure, or at a lower pressure. The energy consumption of the system is very low, that is, that the energy expenditure has nothing to do with the pressure at which the fluid must be pumped. The application is very clear, for example, changing the water of a pool that is high above sea level, changing hot water to cold of a cooling system that is under pressure etc., and especially changing brine for water to Desalinate as is the case of desalination of water by reverse osmosis. Of course, when we say renew, we mean taking out a quantity of liquid or gas, from a pressure vessel, and at the same time introducing into it, an equal amount, of this liquid or gas. As the operations of introducing liquid at higher pressure, and removing it from the container, are simultaneous operations, it is the same to reverse the terms.

The gear pump with double stress compensation object of the invention consists of three independent bodies and double pumping; one central and one lateral through the two lateral pump bodies. All the gears that constitute the pump are mounted either on a single drive shaft, or on a single driven shaft. Central pumping and lateral pumping must have equal inlet and outlet pressures, but reversed as to the side of the pump body on which they act.

In order to complement the description made and in order to help a better understanding of the features of the invention, a detailed description of three variants of a preferred embodiment will be made, based on a set of drawings that accompanies this specification , forming an integral part of it and where with a merely indicative and non-limiting nature, the following has been represented:

Figure 1 shows a section of a gear pump. Figure 2 shows a schematic side view of a double pumping solution using the prior art.

Figure 3 shows a perspective view of the solution represented in Figure 2, in which the pressures and stresses have been indicated.

Figure 4 shows the same solution of Figure 2, in an even more schematic representation. Figure 5 shows an intermediate solution between the prior art and the object of the invention.

Figure 6 shows a perspective view of the solution represented in Figure 5, in which the pressures and stresses have been indicated. Figure 7 shows the same solution of Figure 5, in an even more schematic representation.

Figure 8 shows the pump with double stress compensation object of the invention.

Figure 9 shows a perspective view of the solution represented in Figure 8, in which the pressures and stresses have been indicated.

Figure 10 shows the same solution of Figure 8, in an even more schematic representation.

Figure 11 shows the pump with double stress compensation object of the invention in a water renewal application in a pool located at high altitude. Figure 12 shows the pump with double stress compensation object of the invention in a double pumping application in a reverse osmosis desalination plant.

As what is intended to be demonstrated is that it is possible to avoid the water hammer and not consume the kinetic energy of the moving water, the system has been schematized to study only the physical phenomenon that originates when closing the entrance or exit of the water in The nurse camera.

In Fig. 1, we can see the conventional drawing of a gear pump, which consists of the casing (1) the motor pinion (2) and the driven pinion (3) that rotates freely, dragged by the pinion (2) . The fluid is suctioned through the inlet (5), and expelled through the outlet (4).

To better understand the operation of the system that we recommend, we have simplified the drawings, eliminating the external casing in the pumps and leaving only the internal part, being able to see in figure 8 the final design of the pump with double compensation of forces object of the invention where the three groups of gears 6a-6a ', 7-7' and 6b-6b 'have been represented, with their common axes 9 and 9' and their bushings 10-11-12 and 13 of axis 9 and 10'-11 '-12' and 13 'of the 9' axis. Each pair of gears corresponds to an independent pump and of course they are separated from each other by partitions that are in turn the supports of the bushings that, like the housing external, we do not represent in the drawing to improve its clarity.

Another simplification that we will make for the explanation of the operation of the system, is that when we talk about any pump represented as for example those of figure 9, we will refer to it citing its gears, for example the third pump, or the pump on the right is the pump (6b-6'b).

In Fig. 1, we can see the conventional drawing of a gear pump, which consists of the casing (1) the motor pinion (2) and the driven pinion (3) that rotates freely, dragged by the pinion (2) . The fluid is suctioned through the inlet (5), and expelled through the outlet (4).

The central pump (7-7 ') has the same pumping capacity as the sum of the other two side pumps, the (6a-6'a) on the left plus the pump (6b-6'b) on the right. In the drawings we represent the central pump (7-7 '), with the double length gears, which the side pumps (6a-6a') and (6b-6b ')

Figures 3 to 7 are not modalities of the pump in question, but only steps that we believe are convenient for the explanation of the final and final design represented in figures δ, 9 and 10.

The vectors that appear in the drawings with the letter "P" with black tip, such as the P1, P2, etc. are vectors that represent pressure or forces, and the vectors named with the letter "R" and with the tip of the White arrow, such as R10, R11 etc. are reaction forces that oppose the former.

The separation between the inlet and outlet pressure defines a plane that divides the pump into two volumes, of different working pressures, as we can see in the figure, which is divided by the axis of symmetry. It has a suction area to the right of the drawing that corresponds to the fluid inlet (5), and a compression one, scratched, to the left of the dividing plane, which corresponds to the fluid outlet (4). This dividing plane, which is a plane containing the centers of the pump shafts, is the site where the resulting forces P1 and P2 of the pump pressures indicated in figures 3, 4, 6, 7 are supposed to act. , 9 and 10.

One of the great advantages of volumetric displacement rotary pumps, compared to piston pumps, is that the former do not need valves, and the piston pumps do need them for operating with reciprocating motion.

The operation of a gear pump is very simple, as we can see in Fig. 1. The housing (1), precisely envelops the motor pinion (2) that in this case rotates counterclockwise, and the pinion (3) that rotates freely, dragged by the pinion (2), with a counterclockwise movement, that is, clockwise. The fluid is suctioned through the inlet (5), and is dragged along the periphery of the pinions, occupying the space between the teeth, being expelled by the outlet (4) at a higher pressure than the inlet. That is, the fluid circulates from right to left of the drawing. At the point "P" of contact between the two pinions (2) and (3), the force exerted by the pinion (2) to drag the pinion (3) is very large and proportional to the pumping pressure, and must not of passing fluid through it, hence the design of the tooth profile is much more important than in a gear intended only for the transmission of movements. Therefore, if in figure 3 which is a perspective of figure 2, we turn the motor shaft (9) counterclockwise, both the pump (6-6 ') and the pump (7-7 ') will move the fluid from right to left of the drawing.

In figure 2 we see the simplest way to connect two pumps to be driven by a single motor, this is the usual way to connect two pumps with series shafts.

It is not necessary to explain that the surface of action of the teeth of the pump, when pushing the fluid, is the same as the reaction surface when the teeth of the gear are requested by the pressure of the fluid. This physical effect is used so that a gear pump can be used as a hydraulic motor. Gear pumps have a design, very suitable for pumping liquids at high pressure, because the relationship of effort with the surface of attack to the fluid is a very large relationship, which does not make it suitable, when we intend to operate as a motor with low pressures, since it would be little sensitive due to the low relative surface area

In the case at hand, we do not intend to cause a movement with the fluid pressure, since that is what a motor is responsible for, what we want is a balance in the rotation of the axes (9) and (9 ') of the fig . 8 and a balance in the stresses caused by high pressures on the teeth of the gears, and in the radial stresses of the shafts against the bearings or bearing bushings.

The two pumps (6-6 ') (7-7'), manage the same amount of liquid since they are equal, volumetric pumps, and are mounted on a common axis, but "the condition for obtaining the desired effect with the The present invention is that the working pressures on both pumps are reversed. "

In Figures 1, 3 and 4 we can see that in the first pump body (6-6 ") the fluid is suctioned from the right of the drawing and expelled at a higher pressure to the left of the drawing. The separation surface (S1 ) is affected by a force (P1) that opposes the fluid outlet. But in the central pump (7-7 ') the fluid that enters from the right, does so at the pump outlet pressure (6-6') since it is supposed to come from the chamber, tank or enclosure, where the pump (6-6 ') is depositing its flow. The outlet pressure of the central pump fluid (7-7 ') is the same as the inlet pressure of the side pump (6-6'), since it is assumed that the fluid reaches the site from which it leaves. This makes the pump (7-7 ') be requested by a force (P2) contrary to (P1) and in favor of its direction of rotation that makes it work like a hydraulic motor. The shaft (9) has its pinions (6) and (7) with a tendency to rotate in opposite directions, forces that are absorbed by the torsional resistance of this, being in perfect balance in regard to the movement of rotation, although it is not balanced with respect to the efforts in its supports, since the radial reactions R10 and R12 appear. The pinions (6 ') and (7') pair of the first ones, also because of the efforts acting on them P1 and P2, intend to rotate in the opposite direction, but since they are not on a single axis, their turning force unloads it in contact with their respective partners (6) and (7) which in turn are absorbed by the torsional resistance of the motor shaft (9).

As we have seen, there are two major problems that are the cause of gear pumps having a short life. The first is caused by the great frictional forces that act on the teeth of the pinions and the second is due to the reactions that act on the supports of the shafts. The first solution to avoid the pressure between the teeth of the gears, is to join the separated axes (9'a) and (9'b) of figures 2, 3 and 4 to constitute a single driven shaft (9 ') as the represented in figures 5, 6 and 7. It is evident that if the torsional stresses do not exert deformation on the shafts there will be no more pressure on the teeth of the gears than there may be due to the lack of precision in machining, and They will slide with a soft friction, without loads.

If you would like to specify a lot in dynamic balancing by having the loss of load in the exchange of liquids, you can design the gears with a small difference on the surfaces S1 and S2, giving a little more length to the gear that receives the pressure with respect to the gear that pumps. The second solution refers to avoiding radial stresses R10-R10 'and

R12- R12 'that the axes (9) and (9') exert on their supports. The solution we propose is to put on the same axes (9) and (9 ') of Figures 8, 9 and 10 a third pump (6b-6'b) that added to the first (6a-6'a) present a capacity equal to the central pump (7-7 '). If the side pumps are added to pump with the pressure (P1) in one direction and the central pump receives the pressure (P2) by suction, see figures 9 and 10, and since P1 is equal to P2 the various reactions R10-R1C-R13 and R13 'are balanced.

The applications of this gear pump with double stress compensation object of the invention are shown in figures 11 and 12 where the solutions for renewing the contents of a tank that is at higher pressure than the liquid intended for renewal are presented and to carry out the necessary double pumping in a reverse osmosis desalination system.

It might seem that the solution of Figure 12 is the same as the one currently used for this same purpose where the brine's energy is recovered with a turbine, generally of the Pelton type, but in reality it is not.

In the traditional system with recovery turbine, excess power is used in the high pressure pump. In our system, just power is used and nothing needs to be recovered. Of course, this is independent of the performances that exist between a centrifugal pump with a turbine and a pump - hydraulic gear motor.

Traditional systems, with turbines, pump 100% power at the high pressure of the permeate, but as only a percentage that ranges between 30% and 40% of the total, the remaining 60% or 70% that is brine should be desalinated , is returned to the sea. The energy that accompanies this brine, which is the majority, must be recovered, cogenerated, must be harnessed. This type of machine, this traditional system, is something that goes against any principle of energy saving. For desalination of seawater, with reverse osmosis membranes there are two very clear consumptions, one is the loss of charge of the water to be desalted, which constitutes 30% or 40%, due to having to cross the osmosis membrane, this difference Pressure is large with current membranes, between 60 and 70 Kg / cm ² , causing perfectly justified energy consumption. Another small consumption is the one that suffers the brine in its route, which can be described as small, since its pressure loss ranges between 1 and 2 Kg / cm ² .

In the end, 60% or 70% of the flow rate to be desalinated is constituted by brine that leaves the membrane with an energy that in reality has not been useful for anything and is greater than the energy used, and which are also very important quantities in The world of desalination of seawater. The solution to recover this energy is no less painful; we put a turbine face that does not recover the total power and we apply it to the pump shaft. But another fact, which we usually forget, is that this 60% or 70% has been uselessly circulated through a pump with a performance that, in the Best case scenario is around 80%. The final performance of this machine does not actually exceed 50% or 70%.

The gear pump object of the invention only consumes the energy that is required, it is not provided with anything that it does not have to consume, of course having the own losses due to the performance of the pumps, but it is not necessary to take advantage of anything that It has been pumped uselessly.

In figure 12 we show the scheme of a desalination plant by reverse osmosis. The main high pressure pump supplies only the amount of water to be desalted.

60% or 70% of the desalination flow corresponding to the brine, is managed by the pump that we recommend, which exchanges the brine that is at high pressure leaving the membrane without great consumption, by sea water at atmospheric pressure.

Practical experiences give us consumption values ranging from 30% to 50% less than in the conventional system with recovery turbines.

Claims

Claims 1.- Gear pump with double stress compensation characterized in that on a single motor shaft and a single driven shaft there are three pump bodies separated laterally and each consisting of a motor gear and another driven gear mounted on the motor and driven axes respectively, in such a way that the three mentioned pump bodies configure two pumps, one central and the other side constituted by the two lateral pump bodies operating in parallel, such that the central pumping and the lateral pumping present inlet pressures and output equal in value but inverted as to the side of the pump body on which they act.