PULSELESS PISTON PUMP

Description

BACKGROUND OF THE INVENTION

[0001] A myriad of different types of pumps are known for use in pumping various materials. When it is desired to pump difficult materials, i.e., those that are highly viscous and/or abrasive, the number of choices of pumps suitable for such applications drops substantially, particularly when it is desired to pump such materials at relatively elevated pressures and/or at predetermined flow rates. While reciprocating piston pumps have been widely used in such applications, such pumps suffer from having pulses in the pressure output of the pumps during piston reversal. Such pumps also suffer to a certain extent from leakage and seepage of pumped material past the seals which is particularly critical when the material is air-sensitive such as isocyanates. This leakage is in both directions and can cause environmental contamination, pumped fluid contamination and regenerative abrasive wear damage to the pump. The reduction and/or elimination of pulses in the output is particularly important for circulating systems, fine spray applications and proportional metering to produce constant output.

[0002] Centrifugal pumps are capable of pumping abrasive materials without pressure pulses but suffer from the problems of not being positive displacement type (flow rate is not directly related to speed), inefficiency, shaft seal leakage and impose a high degree of shear on materials which may be shear-sensitive.

[0003] Gear pumps are commonly used for metering and proportioning apparatus due their ease in synchronising with other pumps. Such products, however, are ill-suited for pumping of abrasive materials which cause unacceptable wear.

[0004] US-A-4,453,898 discloses a dual-piston reciprocating pump having a rotating cam driving pistons spring-urged against it and reciprocable within a chamber having inlet and outlet check valves, and being sealed thereinto. The profile of the cam is chosen so as to synchronise the pistons for pumping and filling to minimise pressure pulsations and produce a substantially constant flow of fluid. The cam profile, which is engaged by rollers attached to the pistons on opposite faces, provides a parabolic rise, during rotation, from 0° to 30° to create an hydraulic pulse and a dwell from 345° to 360° to ensure complete cylinder refill. It has been found that this does not give pulseless output, which it is the object of the present invention to provide.

[0005] US-A-3,680,985 discloses a pump having a single piston which is reciprocated into and out of a cylinder to force fluid from the cylinder into a conduit. The piston is in a chamber to which inlet and outlet check valves have access and is sealingly connected to the reciprocating means by a diaphragm.

[0006] US-A-2,711,137 discloses a chemical feed pump with a piston reciprocated by a piston rod, the piston and rod carried by a diaphragm sealing the pumping chamber from the environment.

[0007] DE-A-3113737 discloses a multi-piston pump with a rotating cam whose profile is smoothly curved and engaged by each of the pistons through rollers.

[0008] DE-A-2608664 discloses a two piston pump driven by a cam whose profile is such as to give a dwell at the crossover points.

[0009] DE-A-437298 discloses a multi-piston pump driven by a cam whose profile is smoothly curved in Archimedean spirals and a dwell.

[0010] It has been found by the applicants that whilst a cam profile might be designed for theoretically pulseless output, this would not be achieved in practice.

[0011] It is therefore an object of this invention to provide a pump capable of handling such materials while providing substantially pulseless operation. It is further an object of this invention to provide such a pump which is easily manufactured and which is capable of being operated at varying speeds, flow rates and pressures in an efficient manner. It is yet a further object of this invention to provide such a pump which has leak-proof operation to avoid contamination of the environment in which the pump is located or contamination of the pumped fluid by the environment.

[0012] According to the invention, there is provided a fluid pump for providing substantially pulseless output, comprising a plurality of piston-cylinder combinations , cam means for driving each piston in its cylinder in a reciprocating motion alternating between intake strokes and pumping strokes, so that at least one piston is in a pumping stroke at all times and the sum of the velocities of the pistons in the pumping strokes is substantially constant at any given speed of the cam means, a pressure seal between each piston and its cylinder for sealing material to be pumped, and inlet check valves, and a sealing diaphragm attached to a housing and to each piston intermediate the high pressure seal and the cam means to form a chamber to contain any material that might leak past the high pressure seal and as a barrier between the material to be pumped and the environment, the cam means having a blip for increasing the velocity sum slightly near the point of check valve seating to compensate for the non-linearity of pump output during seating of the check valves.

[0013] In an embodiment of the invention described hereinafter, a multi-piston pump is driven by a cam. The use of pistons in conjunction with diaphragms allows a much higher pressure output capability that a simple diaphragm pump and a more positive displacement action than diaphragm pumps. The cam is powered by a DC motor or other type of conventional variable speed rotary driving mechanism (electric, hydraulic or the like). When used with these drives, the pump can be stalled against pressure just like a typical air-operated reciprocating piston pump. This mode allows adjustable constant flow. A constant speed motor driving the pump would use a pressure switch to turn the motor on and off. Because the motion input to the pump is rotary, it can be easily synchronized with another pump(s) to provide a plural component material proportioning system or with a conveyor to more fully automate production.

[0014] The cam profile is designed so that the reciprocating pistons (which alternate between pumping and intake strokes) have a net velocity sum of their pumping strokes which is generally constant. By doing so, one essentially can eliminate pressure losses that create pulses which result from the piston reversal of a conventional piston pump. In the preferred embodiment, two pistons are used although it can be appreciated that more pistons may be used if desired.

[0015] As shown in this application, intake flow is controlled by check valves which typically take a discreet amount of time to seat. Fluid can flow backwards during this time causing small pump output pressure variations during the valve seating but such can be compensated for by shaping the cam profile to provide a nearly totally pulseless operation.

[0016] Each piston is sealed in its respective cylinder by a relatively conventional type seal mechanism. Attached to the piston on the low pressure intake side of the seal is a diaphragm which serves to isolate the fluid from the environment and assure a leak proof device. As used in this application, the term "diaphragm" is understood to include membranes, bellows or other such structures performing a similar function. An intake passage provides flow directly over the piston between the main seal and the diaphragm to prevent the build-up and hardening of material in the intake section and on the piston. The intake flow then passes through the intake check and into the pumping chamber and then exits through an outlet passage which also has a check valve. This flow path minimises stagnant areas of non-flowing fluid where fluids may settle out and/or harden. The passage is oriented to minimise air entrapment and continually replenish the fluid in the intake area.

[0017] The cam can either be of a push-pull type, that is, where the roller rides in a track or can be a conventional outer profile cam wherein the piston assembly roller is spring loaded against the cam to maintain it in position.

[0018] The scope of the invention is defined by the appended claims; and how it can be carried into effect is hereinafter particularly described with reference to the accompanying drawings wherein:-

Figure 1 is an elevation of a pump according to the present invention, partly broken away and partly in section;

Figure 2 is a plan from below in the direction of the arrows 2-2 of Figure 1, showing part of the pump including the cam;

Figure 3 shows an alternative embodiment of cam; and

Figure 3A is a chart showing the velocities and outputs of a two piston pump.

[0019] A pump 10 (Figure 1) according to the present invention, comprises a main housing 12 in which runs a shaft 14 having a gear 16 mounted thereon. A motor (not shown) which may be a DC brushless type motor, drives gear 16 and shaft 14 to turn cam 18 mounted on the end thereof. A cam follower assembly 20 rides on cam 18 and comprises a follower housing 22 having a follower 24 mounted thereto via shaft 26. Follower housing 22 has guide rollers 28 mounted on the outside thereof which run in slots 30 in housing 12. Follower assembly 20 is spring loaded against cam 18 by means of a spring 32.

[0020] Follower assembly 20 is attached to a piston 34 and located in between follower 22 and piston 34 is a diaphragm 36. Those three parts are fastened together by a bolt 38 which passes consecutively therethrough. An initial inlet passage 40 leads into a flushing chamber 42 located about piston 34 between diaphragm 36 and main pressure seal 44 in cylinder 46. Flushing chamber 42 runs circumferentially around piston 34 thus inlet flow therethrough serves to flush material through which might potentially harden off the surface of piston 34. Inlet flow thence passes through passage 48 in to main inlet passage 50 which has located in series therein a check valve 52 of a conventional nature.

[0021] Pumping chamber 54 is located in the end of cylinder 46 over piston 34 and also has connected thereto outlet passage 56 having an outlet check 58 of conventional design therein. When the device is positioned as oriented in Figure 1, that is with the inlet and outlet ports 40 and 56 respectively facing upwardly, the product is designed so as to prevent the accumulation of air or other gas within pockets of the pump, that is, all such bubbles and gas may freely flow upwardly and out of the pump thereby reducing problems of priming and assuring full volumetric flow without air entrapment. It can be seen as piston 34 moves upwardly into pumping chamber 54, diaphragm 36 flexes upwardly to the point of nearly touching the upper surface 42a of flushing chamber 42 thereby continually assuring a fresh flow of material through the pump and the prevention of stagnant flow zones therein.

[0022] While the embodiment shown in the drawing figures utilizes a spring loaded follower and cam, it can also be appreciated that the cam drive may be of a different type wherein no such spring is necessary. Such a type of cam is often referred to as a desmodromic type cam, and an example of such a cam is shown in Figure 3 wherein the roller is guided in a track 60 and is driven in both its pumping and intake strokes. It can also be appreciated that seal 44 may be of any conventional type which is capable of performing a proper sealing function, however, it can be appreciated that because diaphragm 36 is subjected to relatively low pressures, its service life will be dramatically increased to maintain the pump in a substantially leak-free state. It can also be seen that if seal 44 should leak, its leakage is from the high pressure side back into the inlet rather than into the environment.

[0023] Up to this point, the description has been of a theoretically perfect pump. In reality, check valve physics (closing time, etc.), fluid compressibility and viscosity preclude perfect pulseless output. Satisfactory pulseless output may be obtained by modifying the cam profile to compensate for the above factors. By increasing the velocity of the opposite piston during check valve closing time by putting a "blip" in the cam to change the velocity profile, the pumping action can be slightly increased near the point of check valve seating to compensate for the decreased output during the seating time. The required net velocity profile for pulseless output may be different for any material which is pumped. Using a representative fluid such as oil for the purposes of optimizing the velocity profile of the pump results in a solution which is satisfactory for most other fluids.

[0024] Additionally, it can be appreciated that such a pump is easily adaptable to power operated valving, that is, valving which could be operated electrically and/or through a mechanical linkage not unlike an automotive engine such that the valve opening and closing time can be selected as desired.

[0025] It is contemplated that various changes and modifications may be made to the pump without departing from the scope of the invention as defined by the following claims.

Claims

1. A fluid pump for providing substantially pulseless output, comprising a plurality of piston-cylinder combinations (34,46), cam means (18,24) for driving each piston (34) in its cylinder (46) in a reciprocating motion alternating between intake strokes and pumping strokes, so that at least one piston (34) is in a pumping stroke at all times and the sum of the velocities of the pistons in the pumping strokes is substantially constant at any given speed of the cam means, a pressure seal (44) between each piston (34) and its cylinder (46) for sealing material to be pumped, and inlet check valves (52), and a sealing diaphragm (36) attached to a housing (12) and to each piston (34) intermediate the high pressure seal (44) and the cam means (18,24) to form a chamber to contain any material that might leak past the high pressure seal (44) and as a barrier between the material to be pumped and the environment, the cam means having a blip for increasing the velocity sum slightly near the point of check valve seating to compensate for the non-linearity of pump output during seating of the check valves (52).

2. A pump as claimed in claim 1, including a flushing inlet passage (40) leading from a source of material to be pumped around each piston (34) intermediate the diaphragm (36) and the high pressure seal (44) to minimise stagnation and prevent build-up or solidification of pumped material on said piston.

3. A pump as claimed in claim 2, wherein each cylinder (46), piston (34) and high pressure seal (36) form a pumping chamber (54) and the pump includes a main inlet passage (50) connecting the flushing inlet passage and the pumping chamber (54).

4. A pump as claimed in claim 3, wherein the main inlet passage (50) contains the inlet check valve (52).

5. A pump as claimed in any preceding claim, in which each piston (34) remains in contact with its seal (44) during reciprocation, characterised by a sealing diaphragm (36) attached to a housing (12) and to each piston (34) intermediate the high pressure seal (44) and the cam means (18,24) to form a chamber to contain any material that might leak past the high pressure seal (44) and as a barrier between the material to be pumped and the environment, a flushing passage (40) leading from a source of material to be pumped around each piston (34) intermediate the diaphragm (36) and the high pressure seal (44) to minimise stagnation and prevent build-up or solidification of pumped material on the piston (34) and a main inlet passage (50) connecting the flushing passage (40) and a pumping chamber (54) formed by each cylinder (46), piston (34) and high pressure seal (44).

6. A pump as claimed in claim 4 or 5, wherein the inlet passage (50) is located to run in a generally vertical direction and is configured to prevent the trapping of gases in the pumping chamber (54) and in the passage (50), whereby any gases will rise through the passage out of the pump.

7. A pump as claimed in claim 6, including an outlet passage (56) leading from the pumping chamber (54), the inlet and outlet passages (50,56) being located to run in a generally vertical direction and configured to prevent the trapping of gases in the pumping chamber (54) and the passages (50,56) whereby any gases will rise through the passages out of the pump.

8. A pump as claimed in any preceding claim, wherein the cam means (18) is driven by a variable speed motor.

9. A pump as claimed in any preceding claim, including power operated valving.

Ansprüche

1. Flüssigkeitspumpe zur weitgehend pulsationsfreien Förderung
mit einer Vielzahl von Kolben/Zylinder-Kombinationen (34, 46), mit Nockenvorrichtungen (18, 24) für die abwechselnde Hin- und Herbewegung eines jeden Kolbens (34) im zugehörigen Zylinder (46) während der Einlaß- und Pumphübe dergestalt, daß sich immer mindestens ein Kolben (34) in einem Pumphub befindet, wobei die Summe der Kolbengeschwindigkeiten während der Pumphübe bei jeder vorgegebenen Geschwindigkeit der Nockenvorrichtungen weitgehend konstant ist, mit einer Druckdichtung (44) zwischen jedem Kolben (34) und dem zugehörigen Zylinder (46), um einen Austritt des zu fördernden Mediums zu verhindern, mit einlaßseitigen Rückschlagventilen (52) und mit einer Dichtungsmembrane (36), die an einem Gehäuse (12) und an jedem Kolben (34) zwischen der Hochdruckdichtung (44) und den Nockenvorrichtungen (18, 24) angebracht ist, um eine Kammer zur Aufnahme eventuell entlang der Druckdichtung (44) austretender Leckagemengen und eine Sperre zwischen dem Fördermedium und der Umgebung zu bilden, wobei die Nockenvorrichtungen einen Zacken umfassen, um die Summe der Geschwindigkeiten in der Nähe des Rückschlagventilsitzes etwas zu erhöhen und auf diese Weise die Nichtlinearität der Pumpenleistung auszugleichen, wenn die Rückschlagventile (52) ihren Sitz einnehmen.

2. Pumpe nach Anspruch 1, gekennzeichnet durch einen einlaßseitigen Spülkanal (40), der von einem zu fördernden Medium ausgehend um jeden Kolben (34) zwischen der Membrane (36) und der Hochdruckdichtung (44) verläuft, um Stagnationszonen auf ein Minimum zu beschränken und die Ablagerung oder Verfestigung von Fördermedium auf dem Kolben zu verhindern.

3. Pumpe nach Anspruch 2, dadurch gekennzeichnet, daß jeder Zylinder (46), jeder Kolben (34) und jede Hochdruckdichtung (36) eine Pumpkammer (54) bilden und daß die Pumpe einen Haupteinlaßkanal (50) als Verbindung zwischen dem einlaßseitigen Spülkanal und der Pumpkammer (54) umfaßt.

4. Pumpe nach Anspruch 3, dadurch gekennzeichnet, daß sich im Haupteinlaßkanal (50) das einlaßseitige Rückschlagventil (52) befindet.

5. Pumpe nach irgendeinem der vorstehenden Patentansprüche, bei welcher jeder Kolben (34) während seiner Hin- und Herbewegung mit der zugehörigen Dichtung (44) in Kontakt bleibt, gekennzeichnet durch eine Dichtungsmembrane (36), die an einem Gehäuse (12) und an jedem Kolben (34) zwischen der Hochdruckdichtung (44) und den Nockenvorrichtungen (18, 24) angebracht ist, um eine Kammer zur Aufnahme einer eventuell entlang der Druckdichtung (44) austretender Leckagemengen und eine Sperre zwischen dem Fördermedium und der Umgebung zu bilden, durch einen einlaßseitigen Spülkanal (40), der von einem zu fördernden Medium ausgehend um jeden Kolben (34) zwischen der Membrane (36) und der Hochdruckdichtung (44) verläuft, um Stagnationszonen auf ein Minimum zu beschränken und die Ablagerung oder Verfestigung von Fördermedium auf dem Kolben (34) zu verhindern, und durch einen Haupteinlaßkanal (50) zur Verbindung des Spülkanals (40) und einer von jedem Zylinder (46), jeden Kolben (34) und jeder Hochdruckdichtung (44) gebildeten Pumpkammer (54).

6. Pumpe nach Anspruch 4 oder 5, dadurch gekennzeichnet, daß der Einlaßkanal (50) in einer allgemein vertikalen Richtung verläuft und so ausgebildet ist, daß der Einschluß von Gasen in der Pumpkammer (54) und im Kanal (50) dadurch verhindert wird, daß Gase durch den Kanal aufsteigen und aus der Pumpe abgeführt werden.

7. Pumpe nach Anspruch 6, gekennzeichnet durch einen von der Pumpkammer 54) abgehenden Auslaßkanal (56), wobei die Ein- und Auslaßkanäle (50, 56) in einer allgemein vertikalen Richtung verlaufen und so ausgebildet sind, daß der Einschluß von Gasen in der Pumpkammer (54) und den Kanälen (50, 56) dadurch verhindert wird, daß Gase durch den Kanal aufsteigen und aus der Pumpe abgeführt werden.

8. Pumpe nach irgendeinem der vorstehenden Patentansprüche, dadurch gekennzeichnet, daß die Nockenvorrichtung (18) durch einen drehzahlregelbaren Motor angetrieben wird.

9. Pumpe nach irgendeinem der vorstehenden Patent ansprüche, gekennzeichnet durch kraftbetätigte Ventile.

Revendications

1. Pompe à fluide pour fournir une sortie sensiblement sans impulsions, comprenant une pluralité de combinaisons de pistons-cylindres (34, 46), des moyens de came (18, 24) pour entraîner chaque piston (34) selon un mouvement alternatif à l'intérieur de son cylindre (46) en alternant les courses d'admission et les courses de pompage, de manière qu'un piston (34) au moins soit dans une course de pompage en permanence et que la somme des vitesses des pistons dans la course de pompage soit sensiblement constante pour une vitesse donnée quelconque des moyens de came, un joint de pression (44) entre chaque piston (34) et son cylindre (46) pour que le matériau soit pompé de manière étanche, et des clapets de retenue d'entrée (52) ainsi qu'un diaphragme d'étanchéité (36) fixé sur un boîtier (12) et à chaque piston (34) en une position intermédiaire entre le joint de pression (44) et les moyens de came (18, 24) de manière à former une chambre qui contienne un matériau quelconque susceptible de fuir le long du joint de pression (44), et pour servir de barrière entre le matériau à pomper et l'environnement, les moyens de came comprenant un accessoire pour augmenter légèrement la somme des vitesses près du point de fermeture des clapets de retenue afin de compenser la non-linéarité de la sortie de la pompe pendant la fermeture des clapets de sécurité (52).

2. Pompe selon la revendication 1, comprenant un passage d'entrée de rinçage (40) venant d'une source de matériau à pomper autour de chaque piston (34) en une position intermédiaire entre le diaphragme (36) et le joint de pression (44) afin de réduire au minimum la stagnation et d'empêcher l'accumulation ou la solidification du matériau pompé sur ledit piston.

3. Pompe selon la revendication 2, dans lequel chaque cylindre (46), piston (34) et joint de pression (36) forment une chambre de pompage (54) et la pompe comprend un passage principal d'admission (50) reliant le passage d'entrée de rinçage et la chambre de pompage (54).

4. Pompe selon la revendication 3, dans laquelle le passage principal d'admission (50) est équipé d'un clapet de retenue d'admission (52).

5. Pompe selon l'une quelconque des revendications précédentes, dans laquelle chaque piston (34) reste en contact avec son joint (44) pendant le mouvement alternatif, caractérisée en ce qu'un diaphragme d'étanchéité (36) est fixé à un boîtier (12) et à chaque piston (34) en une position intermédiaire entre le joint de pression (44) et les moyens de came (18, 24), de manière former une chambre destinée à contenir tout matériau susceptible de fuir au delà du joint de pression (44) et une barrière entre le matériau à pomper et l'environnement, un passage de rinçage (40) conduisant d'une source de matériau à pomper autour de chaque piston (34) en une position intermédiaire entre le diaphragme (36) et le joint de pression (44) pour réduire au minimum la stagnation et empêcher l'accumulation ou la solidification de matériau pompé sur le piston (34) et un passage principal d'admission (50) reliant le passage de rinçage (40) et la chambre de pompage (54) définie par chaque cylindre (46), piston (34) et joint de pression (44).

6. Pompe selon l'une des revendications 4 ou 5, dans laquelle le passage d'admission (50) est disposé pour être orienté dans une direction généralement verticale et est configuré pour empêcher l'emprisonnement de gaz dans la chambre de pompage (54) et dans le passage (50), de manière que les gaz éventuels s'élèvent à travers le passage pour sortir de la pompe.

7. Pompe selon la revendication 6, comprenant un passage de sortie (56) partant de la chambre de pompage (54), les passages d'admission et de sortie (50, 56) étant disposés de manière à être orientés dans une direction généralement verticale et étant configurés pour empêcher d'emprisonner des gaz dans la chambre de pompage (54) et dans les passages (50, 56), de manière que les gaz éventuels s'élèvent dans les passages pour sortir de la pompe.

8. Pompe selon l'une quelconque des revendications précédentes, dans laquelle les moyens de came (18) sont entraînés par un moteur à vitesse variable.

9. Pompe selon l'une quelconque des revendications précédentes, comprenant des vannes commandées par énergie.

Drawing