1. Area of the Art
The invention relates generally to fluid-moving devices. More particularly, the invention is directed to fluid-moving devices, such as piston pumps, with fluid-tight dynamic clearance seals and internal passageways for connecting the fluid-moving device to secondary devices.
2. Description of the Prior Art
In many types of fluid-moving equipment, such as liquid pumps, slurry pumps, dry mixers, and numerous other devices, a sliding plunger, rod, piston, or another similar member, reciprocally moves inside a stationary bearing. Typically, fluid leakage around the moving member is prevented by utilizing sealing structures. The material of the sealing structure is required to have some resiliency to permit the moving member to slide back and forth through the axial opening of the sealing structure. On the other hand, the material of the sealing structure is required to possess some degree of stiffness to prevent, or at least minimize, leakage of the liquid around the moving member.
One type of a conventional sealing structure is a mechanical face seal. Typically, the mechanical face seal consists of one seal ring rotating with the driving shaft and one stationary seal ring attached to the surrounding housing. The two seal rings are pressed towards each other by a biasing force which, in this way, prevents liquid from passing between them. For example, U.S. Pat. Nos. 3,282,235; 4,754,981; and 5,772,217 describe a seal with a spring for providing the biasing force. Usually, additional elastomeric components are required to seal each ring from the shaft or housing, correspondingly. Typically, a thin lubricating film is required between the seal surfaces to prevent their damage by dry friction. Nevertheless, with time, wear and vibrations cause the mating faces of the sealing rings to become scored, resulting in leakage of the process fluid. Environments where the process fluid is abrasive or contains a coagulant are particularly damaging to the conventional seals and require their frequent replacement.
A packed stuffing box is another example of a conventional seal for a moving member. This type of seal has been disclosed, for example, in U.S. Pat. Nos. 3,659,862 and 5,333,883. Generally, the packing is sufficiently compressed to limit the passage of fluid through the packing, but not so compressed as to create excess friction between the packing and the moving member. Pressure is generally maintained on the packing by manually tightening a gland on the stuffing box until the point where leakage through the packing is minimized, yet before the point where friction between the packing and the shaft creates overheating of the packing.
Such seal configuration operates on the principle of controlled leakage to the atmosphere rather than zero leakage. This approach, however, requires frequent adjustments, which may result in over tightening of the seal. An over tightening leads to excess friction and heat buildup, excessive wear to the packing, and possibly even damage to the moving member. Even when the pressure on the packing is properly regulated, the pressure necessary to minimize the passage of fluid through the packing causes relatively high friction between the packing and the shaft. As a result, the packing wears out quickly and requires a frequent replacement.
Finally, referring to
Apparently, the sealing structures of prior art do not provide reliable and long-lasting seals between moving members and their housing. The conventional seals undergo a lot of wear during normal operation and have to be replaced frequently. The necessity to replace seals makes prophylactic maintenance of the equipment more laborious and increases its maintenance costs.
Another common problem of fluid-moving equipment is associated with the use of connecting tubing and fittings for connecting secondary devices, such as input/output valves, to the pump. As the fluid passes through each connection, pump to fitting, fitting to tubing, etc., the fluid flow is disturbed and the accuracy and precision of the fluid-moving equipment are adversely affected. Also, depending on the selected tubing type and operating pressure, the tubing may flex and bend, thus disrupting the fluid flow even more and further affecting the dispensing accuracy of the fluid-moving equipment.
Automated analytical instruments are broadly used in chemical, biological, and clinical laboratories, often for testing small sample volumes. When dealing with small volumes or diluted samples, even a minute change in sample dispensing accuracy may lead to substantial analytical errors. When conventional pumps are utilized for sample dispensing in an analytical instrument, the tubing and the fittings between the pump and the input/output valves require frequent maintenance checks for leaks and flow obstructions in order to provide a reliable operation of the instrument. Also, the worn-out tubing and fittings have to be replaced promptly.
Therefore, the conventional fluid-moving equipment does not provide consistent and accurate fluid dispensing, unless the connecting fittings and tubing are adjusted or replaced frequently. Consequently, the maintenance of the conventional fluid-moving equipment is laborious and costly, particularly when the equipment is used for processing large sample batches, diluted samples, or small sample volumes.
Accordingly, it is an objective of the present invention to provide a fluid-moving device which avoids the undesirable features of the prior devices. Particularly, it is an object of the present invention to provide fluid-moving devices utilizing seals which have a low wear, may be produced at relatively low costs, and provide superior performance in use. It is a further object of the present invention to provide fluid-moving devices without tubing and fittings for connecting to secondary devices such as valves.
These and other objects are achieved in a fluid-moving device of the present invention. The fluid-moving device comprises a housing defining a suction chamber; at least one internal passageway formed inside the housing; a moving member movably disposed within the chamber; and a sealing member circumferentially disposed between the housing and the moving member. The internal passageway has a first end that opens to the suction chamber and a second end that opens to an outside surface of the housing. The sealing member has a fluid-tight relationship with the housing. The sealing member and the moving member define a continuous and uniform gap, having a size that allows the fluid to fill the gap but prevents the fluid from flowing through the gap from the first side to the second side of the opening under an operating pressure differential between the first and the second side.
In one embodiment, both the sealing member and the moving member are made of a ceramic material. The fluid-moving device may also include a static seal disposed between the housing and the sealing member to allow a variable clearance therebetween while maintaining the fluid-tight relationship between the sealing member and the stationary member.
The fluid-moving device of the present invention may be connected to or integrated with a secondary device or structure by utilizing passageways formed in the housing instead of conventional tubing. In one embodiment, the secondary device is a valve with at least one fluid communication port. The fluid communication port of the valve is connected to the second end of the internal passageway. The valve may be mounted on the housing. Alternatively, a valve chamber may be provided in the housing and the valve may be positioned in the valve chamber, at least partially. The fluid-moving device of the present invention may also include valve passageways formed inside the housing. The valve passageways provide a fluid communication between fluid communication ports of the valve and the outside.
In another aspect, the invention provides a pump. The pump comprises a housing having an internal wall defining a suction chamber for containing a fluid; a piston movably disposed within the chamber; a valve, an internal passageway formed inside the housing; and a sealing member circumferentially disposed between the housing and the piston. The internal passageway has a first end opening to the suction chamber and a second end connecting to the valve. The sealing member has a fluid-tight relationship with the housing. The sealing member and the piston define a continuous and uniform gap having a size that allows the fluid to fill the gap but prevents the fluid from flowing through the gap from the suction chamber to an outside of the chamber under an operating fluid pressure.
In a further aspect, the invention provides a method of making a fluid-moving device. The method comprises: (a) providing a housing having a suction chamber; (b) movably disposing a moving member within the chamber; (c) forming an internal passageway, wherein a first end of the internal passageway opens to the suction chamber and a second end of the internal passageway connects to an outside surface of the housing; and (d) placing a sealing member between the housing and the moving member to result in a fluid-tight relationship between the sealing member and the housing, whereby the sealing member and the moving member define a continuous and uniform gap, wherein the gap has a size that allows the fluid to fill the gap but prevents the fluid from flowing through the gap from the suction chamber to an outside of the chamber under an operating fluid pressure.
By eliminating a direct contact between the sealing member and the moving member and by eliminating tubing and connectors between secondary devices, such as valves, and the pumping structure, the present fluid-moving device alleviates many of the problems associated with the conventional devices discussed above. In particular, the advantages of the present fluid-moving device include a minimal wear of the sealing member, a greater precision of fluid-delivery, simplified assembly and maintenance, significantly improved reliability, and a decreased maintenance cost. The device is well suited for use in any system that requires drawing, moving, and dispensing of fluids.
The invention may be particularly advantageous for use in high-precision pumps employed in analytical instrumentation. For example, a piston pump with a clearance seal and an integrated valve manufactured in accordance with the present invention may be beneficially utilized for sample aspiration and dispensing in Nexgen Access System (Beckman Instruments, Calif.), disclosed in a U.S. patent application titled “Method and System for Automated Immunochemistry Analysis,” Ser. No. 09/815,088, filed Mar. 16, 2001, which has been commonly assigned to the assignee of the present invention and relevant parts of which are incorporated by reference herein.
The invention is defined in its fullest scope in the appended claims and is described below in its preferred embodiments.
The above-mentioned and other features of this invention and the manner of obtaining them will become more apparent, and will be best understood by reference to the following description, taken in conjunction with the accompanying drawings, in which:
The present invention provides a fluid-moving device with a clearance seal and an internal passageway for connecting a suction chamber of the fluid-moving device to the secondary structures such as valves. The fluid-moving device of the present invention may be any device having a housing defining a suction chamber and a moving member reciprocating in the chamber. Examples of such devices include, but are not limited to, dispensing pumps, slurry pumps, and impeller pumps, used in a broad range of applications. The moving member may be, for example, a sliding plunger, rod, or piston. While a particular configuration of the invention may take on different or modified forms, a piston pump will be used to illustrate the invention in more detail. The fluid-moving device of the present invention may be used for pumping and dispensing any suitable fluid, including biological fluid samples, such as buffer solutions, reagents, patient samples.
The present invention solves the problems of prior art by providing a clearance seal, which does not require a direct contact between the piston and the sealing member. Referring to
For the purposes of the present invention, “a fluid-tight relationship” between two structural elements means that the fluid cannot pass therebetween. It would be appreciated by those skilled in the art that any sealing method between the sealing member 25 and the housing 21 may be used, as long as it provides a reliable seal. For example, in one embodiment shown in
Referring to
It is an unexpected discovery by the present inventors that a fluid seal can be formed between a moving and a stationary member without a direct contact therebetween. It has been observed that the size of the gap 26 may be selected to allow the fluid to fill the gap between the seal and piston, thus avoiding a dry friction, but to prevent the fluid from flowing through the gap. It may be hypothesized that when the clearance gap is sufficiently small, the adhesive forces of the fluid toward the piston and the seal are greater than the force exerted by the fluid due to an operating pressure, thus preventing the fluid from flowing through the gap.
The ranges of suitable sizes of the gap 26 depend on the physical properties of the fluid being pumped, such as viscosity, surface tension, adhesive force, and operating pressure. Low viscosity fluids will typically require a smaller gap 26 than higher viscosity fluids. Generally, the higher viscosity of a fluid, the broader the range of the gaps 26 that may be used. It should be recognized that the size of the gap greatly depends on a type of application. Those skilled in the art can easily select the size of the gap to accommodate fluids and operating pressures used in a particular application without undue experimentation in view of the instant disclosure.
Referring to
As shown in
Although the invention is described with a particular reference to a piston pump, it should be recognized that the general features of the clearance seal may be utilized in any device having a stationary member, such as the housing 21, with an opening, such as suction chamber 23, and a moving member, such as piston 24, moveably disposed through the opening. Generally speaking, the stationary member may have any shape so long as it defines two volumes, such as inside and outside of the pump, connected by the opening. The two volumes may contain different fluids and/or be under different pressures (e.g., operating fluid pressure inside the pump and atmospheric pressure outside the pump).
Referring to
For the purpose of this invention, the terms “connecting” and “providing a fluid communication” between two parts means connecting them in such a way that a fluid-tight seal is formed and substantially no fluid flow obstruction is created. The internal passageway may be directly connected to a secondary structure by extending the second end 34 through the housing. Alternatively, the internal passageway may be connected to the secondary structures indirectly, by utilizing additional passageways as will be described later.
The operation of the fluid-moving device of the present invention doesn't differ from the operation of conventional fluid-moving devices. As shown in
The housing 21 of the present invention may be made of any solid material. Preferably, the housing is made from a rigid material that does not visibly deform during operation, thus further improving accuracy and precision of the instant fluid-moving device. Examples of such rigid materials include metal and certain plastics. The suction chamber and the suction passageway may be machined, for example, drilled, in the housing. Alternatively, the housing may be made of two mating parts. Each part has a suction cavity and an internal groove formed between the suction cavity and the outside surface of the housing. The cavity and the groove on one mating part cooperate with the matching cavity and groove on the second mating part to form the suction chamber and the internal passageway. The grooves and cavities may be molded or machined. The methods and means of assembling two cooperating structures are well known in the art.
Referring to
Referring to
The fluid-moving device of the present invention may have an integrated valve with a plurality of fluid communication ports 36, each port connected to the internal passageway 30. Preferably, as shown in
Referring to
The fluid-moving device of the present invention may be connected to fluid supplies and sinks utilizing any appropriate interface. Preferably, the interface should create a minimal effect on the fluid flow. Referring to
Referring to
One or more housings may be attached to the manifold by any appropriate method, as long as it provides a secure and fluid-tight assembly. Examples of attachment methods include, but are not limited to, securing with fasteners, such as nuts and bolts or screws, clamps, and latches. These and other methods and means of assembling two structures are well known in the art and, therefore, are not illustrated in the accompanying figures.
The connection between the valve and the manifold passageways is preferably fluid-tight. It would be appreciated by those skilled in the art that any sealing method between the valve and the manifold passageways may be used as long as it provides a reliable seal. For example, in one embodiment, an elastomeric seal, such as an O-ring 65, is positioned between the valve and the manifold passageways of the inlet circuit 60, and an elastomeric seal, such as an O-ring 76, is positioned between the valve and the manifold passageways of the delivery circuit 70.
Another aspect of this invention is directed to a method of making a fluid-moving device. The method comprises: (a) providing a housing having a suction chamber; (b) movably disposing a moving member within the chamber; (c) forming an internal passageway, wherein a first end of the internal passageway opens to the suction chamber and a second end of the internal passageway opens to an outside surface of the housing; and (d) placing a sealing member between the housing and the moving member to result in a fluid-tight relationship between the sealing member and the housing, whereby the sealing member and the moving member define a continuous and uniform gap, wherein the gap has a size that allows the fluid to fill the gap but prevents the fluid from flowing through the gap from the suction chamber to an outside of the chamber under an operating fluid pressure.
Referring to
The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiment is to be considered in all respects only as illustrative and not as restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of the equivalence of the claims are to be embraced within their scope.
Number | Date | Country | |
---|---|---|---|
Parent | 09685474 | Oct 2000 | US |
Child | 10300283 | Nov 2002 | US |
Parent | 09685307 | Oct 2000 | US |
Child | 10300283 | Nov 2002 | US |