Peristaltic pumps may be conveniently subdivided into two major types, rotary or roller types, and linear or in-line types. Rotary types are frequently encountered in laboratory, instrumentation and light commercial settings. Rotary peristaltic pumps, in which compressive elements, generally rollers, fully occlude a flexible tube as them move in a circumferential, circular arc over tubing which is supported by a circular backstop, are known to offer very limited tubing life and generally are capable of pumping only low viscosity liquids at very low discharge pressures and at very modest flow rates. As the compressive elements move over the tubing, the tubing is subjected not only to occlusive crushing but also to a stretching action along the flow axis of the tubing. This fundamental design characteristic further contributes to short tubing life and to unstable and decreasing flow characteristics of the pump over useful tubing life. There are a few commercial examples of larger hose pumps capable of broad industrial use which employ a sheathed and reinforced hose, operating in a lubricating bath, capable of pumping at higher flow rates and pressures, such as the Bredel pumps manufactured by Waukesha Fluid Handling of Delevan, Wis. However, these pumps are relatively large, expensive, and are controllable only in terms of their flow rate which is a function of the rotations per minute at which the pump is driven, and they are not usually suitable for sanitary applications such as pharmaceutical manufacturing or food processing.
Linear peristaltic pumps, or in-line designs, are unlike the rotary types in that the flow tube is acted upon only at right angles to the direction of flow of liquid through the tube. This single compressive motion eliminates the stretching and torquing forces of the rotary approach. The simplest in-line design requires a minimum of three elements, typically active, acting in a defined sequence to produce positive displacement volumetric liquid pumping action. In general terms, pumping is induced by arranging an occlusive liquid infeed valve on one end of a length of flexible tubing, placing a compressive volume displacement structure after the infeed valve, and placing an occlusive outfeed valve at the end of the tube opposite the infeed valve, such that the pump displacement element is in-between the two valves. Flow is induced when the infeed valve and displacement elements are released from compression and allowed to fill with liquid either as a result of the suction action resulting from the creation of a lumen, or by an external feed means. During this priming phase, the outfeed valve remains occluded. The infeed valve is then closed, after which the outfeed valve is opened, after which the displacement element is compressed. The cycle is then repeated.
Linear peristaltic pumps, or in-line peristaltic pumps, are commercially largely confined to medical applications such as intravenous pumps and infusion pumps, but have a long and substantial history in the patent art. Phelps (U.S. Pat. No. 2,105,200; 1938) teaches a pump with three compressive blade-like elements, one serving as an infeed valve, one serving as a volume displacement element, and one serving as an outfeed valve. The flow tube is placed on a flat surface and all three actuators act upon the tubing only from one side. Tarbox (U.S. Pat. No. 2,393,838; 1946) teaches a three element linear design in which the infeed and outfeed valves act from opposite sides of the flow tube, the compressive section is an elongated structure, and the occlusive motion imposed upon the flow tube is entirely from one side or the other. Harper (U.S. Pat. No. 2,412,397; 1946) discloses a three element linear design in which the flow tube is on a flat surface and acted upon by all three actuators from the same side. Anderson (U.S. Pat. No. 3,518,033; 1970) teaches a three element linear peristaltic pump with two blade-like valves and a displacement compression plate, all operating upon a flexible tubing on a flat substrate and from the same side. Each of these cited designs utilizes a motor and cam arrangement to sequence and activate the three pump elements. Schill (U.S. Pat. No. 3,811,800; 1974) shows a three element pump wherein the infeed and outfeed valves are cone nosed rods actuated by pneumatic cylinders while the pump displacement actuator consists of another inflatable tube bearing upon the flexible liquid flow tube, all elements acting upon the same side of the flow tube. In U.K. Patent 1,426,963 (1976), Makarov discloses a linear pump, pneumatically operated, and sequenced, wherein pneumatically pressurizable chambers surrounding the liquid flow tube act to occlude the liquid flow tube. Bjorklund (U.S. Pat. No. 3,998,104; 1976) teaches a three element cam driven linear design where wedge shaped anvils serve as valves, a larger wedge serves as the displacement element, and all are acting upon the tube from the same side, the tube being supported upon a flat surface, and all occlusive motion is imparted to the tube entirely from one side. In U.K. Patent 2,020,735 A (1979), Schal discloses still another three element cam driven peristaltic design with two finger-like valves and an elongated center compression plate, all acting from one side of a tube supported against an abutment. In U.K. Patent 2,057,067 (1980) Moore teaches a design in which the flow tube is occluded in three successive pressure compartments by hydraulic pressure to create a linear peristaltic pump consisting of an inlet valve, an outlet valve and a displacement member. Kobayashi (U.S. Pat. No. 4,479,797; 1984) discloses a three element linear peristaltic pump consisting of cantilevered fingers, each cam driven from the same side of the tube against the straight flow tube. Blette (U.S. Pat. No. 4,967,940; 1990) presents a cam driven three element linear peristaltic pump with a fourth element added, termed a compensator, to provide a reverse flow such back in a dispensing arrangement. In U.S. Pat. No. 5,131,816 (1992), Brown teaches a cam driven three element pump with an infeed valve, an outfeed valve and a larger pump displacement element interposed between them. All elements bear upon the pump tube from one side, with the tube supported upon a flat surface. In PCT Publication WO 94/21918 Grapes discloses a three element linear peristaltic pump in which pneumatic cylinders and solenoid valves are utilized. The volumetric displacement section consists of a compression plate pressed upon by two pneumatic pistons which are, in turn, operated upon by a single solenoid valve. An infeed valve is occluded by a spring mechanism and opened by a pneumatic cylinder. An outfeed valve is formed by a V-shaped anvil pressed upon the flexible pump tube by a fourth pneumatic piston. The tubing rests upon a flat surface and tubing occlusion is from one side of the tube only, such that only one wall of the tube flexes across the entire internal diameter to effect occlusion.
Although the general form of the three element linear peristaltic pump has been widely applied in the prior art, many limitations and shortcomings of these designs are evident. Some of these will now be listed and briefly discussed:
1. Inability of prior designs to pump liquids at comparatively high pressures. Nearly all of the previous designs utilize a small scale and method of construction unsuited to provide the power needed for high pressure pumping. The liquid flow tubes are generally soft comparatively flexible material unable to contain high differential pressures and they are not typically contained to prevent pressure distortion or rupture. The compressive elements are most typically of a geometry unsuited to high force application to the tube wall in order to create the high pressure pinch valving required of a high pressure pump. Where high pressure linear peristaltic designs have been attempted, they have utilized hydraulic actuation, requiring expensive pump construction and limiting utility because of the requirement for a high capacity and pressure hydraulic supply.
2. Inability of prior designs to pump high viscosity liquids. Pumping high viscosity liquids will generate high pump discharge pressures. The inability of known types to pump at high pressures has previously been discussed. In addition, to pump high viscosity liquids a competent and useful pump must be capable, by its own action, of priming such liquids into the pump at start-up and during continuous running. The devices of the prior art are not generally suited to this in that the rebound capability of the liquid flow tube is extremely inadequate to such service. Further, there are usually no provisions or ability to allow independent control and adjustment of the priming function within the pump cycle, and the compression anvils which are in contact with the tubing are not geometrically suited to the high force operation required for such service.
3. Inability of prior designs to pump liquids at comparatively high flow rates. Three element designs of the prior art are typically designed for low flow medical or laboratory applications, or for dosing of very small volumetric quantities. The designs of the prior art are not suited to high flow applications due to the prevalent use of thin walled, relatively soft tubing which cannot rebound with sufficient speed to re-prime the pump with adequate speed to allow the fast cycle speeds necessary for high flow rates.
4. Inability of prior art linear three element peristaltic pump designs to provide long term pump tube service capability. Known designs are frequently intended for service where the pump tube is considered disposable and such disposal occurs frequently. In other cases, the liquid bearing tube is of single walled thin section construction and not able to withstand hundreds of thousands or millions of repeated flexure cycles in the same location on the tube wall without physical degradation or rupture. In most cases, other design elements of the prior art pumps, such as the tube compression elements or actuators or drive elements, are not sufficiently robust for long term service in general pumping applications.
5. Inability of prior art designs to be capable of increasing liquid flow rates by increasing the area of displacement compression on the flow tube without loss of pump pressure capability. Designs of known type do not disclose means for increasing the total compression force acting upon the flow tube in order to maintain the force per unit area as is required in order to allow for the increase in the square area of tube compression needed for increased pump flow rates without loss of pump discharge pressure capability.
6. Inability of designs of the prior art to provide a high degree of flexibility and versatility of service in the same embodiment, including the ability to provide sustained pumping, precision metering, and full dosing capability with electronic interface and control capability including independent adjustment of pump operating parameters such as pumping pressure, liquid flow rate, pumping frequency, and viscous priming capability, particularly while the pump is operating.
7. Inability of prior designs to provide long term stability and predictability of pumping performance. Designs of the prior art are known to exhibit a substantial decrease in volumetric flow rates over time as a function of the fatigue and compression set effects of the pump flow tubes and the mechanisms applied to these tubes. Designs of the prior art do not disclose mechanical or electronic means to monitor, extend and maintain pumping performance capability over the life of the device.
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