Cassette

Abstract

A cassette for controlling fluid flow from a source to a sink, for example, a patient. The cassette comprises a housing, and a passive inlet valve for hydraulically controlling pressurized fluid flow from the inlet valve to a central chamber, and an actuatable outlet valve. The central chamber provides a fluid pathway between the inlet and outlet valves. The cassette further comprises a piston assembly for exerting pressure in the central chamber. The piston assembly comprises a movable member, a covering for the moveable member; and a flexible interface between the member and the housing for providing near frictionless movement between the member and the housing.

What is claimed  
     
         1 . A cassette for controlling fluid flow, the cassette comprising: 
 a housing comprising a central chamber; an inlet valve for hydraulically controlling pressurized fluid flow to the central chamber; and an outlet valve for controlling fluid flow from the central chamber; and    a piston assembly for exerting pressure in the central chamber; the piston assembly comprising a movable member, a covering for the moveable member; and a flexible interface between the member and the housing for providing near frictionless movement of the member.    
     
     
         2 . The cassette of  claim 1  further comprising: 
 at least one inlet flexible tubing, the inlet tubing providing a fluid pathway from a source into the inlet valve; and  
 at least one outlet flexible tubing, the outlet tubing providing a fluid pathway from the outlet valve to a sink.  
 
     
     
         3 . The cassette of  claim 2  wherein the inlet valve further comprises: 
 a stem;  
 a valve element attached to the stem; and  
 an elastomeric dome for biasing the valve element to the closed position.  
 
     
     
         4 . The cassette of  claim 1  wherein the inlet valve enters a closed position in response to the piston creating a positive pressure in the central chamber.  
     
     
         5 . The cassette of  claim 1  wherein the inlet valve moves from the closed position to the open position in response to the retraction of the piston from the central chamber, wherein said retraction creates a negative pressure in the central chamber.  
     
     
         6 . The cassette of  claim 1  wherein the outlet valve comprises: 
 a valve element;  
 a stem attached to the valve element; and  
 a diaphragm for biasing the valve element to a closed position.  
 
     
     
         7 . The cassette of  claim 6  wherein the outlet valve includes a diaphragm and an outlet valve element and the cross-sectional area of the diaphragm of the outlet valve is greater than the cross-sectional area of the outlet valve element.  
     
     
         8 . The cassette of  claim 1  wherein the outlet valve moves from the closed state to the open state in response to external activation.  
     
     
         9 . The cassette of  claim 8  wherein the external activation is achieved by an actuator.  
     
     
         10 . The outlet valve of  claim 1  wherein the outlet valve is constructed and arranged to be opened for a period of time shorter than the period of time for the fluid to reach a stable velocity.  
     
     
         11 . The outlet valve of  claim 1  wherein the outlet valve includes a tapered surface and a valve-housing seat, and wherein the fluid flow through the outlet valve is controlled by the distance between the tapered surface and the valve-housing seat.  
     
     
         12 . The outlet valve of  claim 1  wherein the outlet valve includes a valve stem and a valve-housing seat, and the fluid flow through the outlet valve is controlled by the distance between the valve stem and the valve-housing seat.  
     
     
         13 . The outlet valve of  claim 12  wherein the valve stem is bent.  
     
     
         14 . The cassette of  claim 1  wherein the outlet valve is acted on by a preload force and a hydraulic force, and wherein the outlet valve maintains a closed position when the preload force exceeds a negative hydraulic force.  
     
     
         15 . The cassette of  claim 1  further comprising a check valve for preventing fluid flow from the outlet valve to the central chamber.  
     
     
         16 . The cassette of  claim 15  wherein the check valve further comprises a valve element and an elastomeric wall, and wherein the valve element is connected to the elastomeric wall.  
     
     
         17 . The cassette of  claim 15  wherein the check valve enters an open position when pressure in the central chamber exceeds atmospheric pressure.  
     
     
         18 . The cassette of  claim 15  wherein the check valve enters a closed position when the negative pressure in the central chamber is less than atmospheric pressure.  
     
     
         19 . The cassette of  claim 15  wherein the check valve enters the closed position when the atmospheric pressure on the check valve exceeds the pressure on the proximal side of the check valve.  
     
     
         20 . The cassette of  claim 1  wherein the piston assembly has a means for receiving a shuttle mechanism.  
     
     
         21 . The cassette of  claim 1  wherein the piston assembly further comprises a means for releasing the shuttle mechanism.  
     
     
         22 . An inlet valve for use with a cassette of the type to be used with an infusion system, the inlet valve comprising: 
 a stem;    an elastomeric dome; and    a geometrically preloaded valve element which strains the elastomeric dome;    wherein the inlet valve has an unbalanced surface area perpendicular to the axis of the valve.    
     
     
         23 . The inlet valve of  claim 22  wherein the inlet valve enters an open position when negative pressure in the central chamber exceeds the sum of the preload force of the valve element and upstream fluid pressure.  
     
     
         24 . The inlet valve of  claim 22  wherein the inlet valve enters the closed position when upstream fluid pressure exceeds downstream negative fluid pressure.  
     
     
         25 . The inlet valve of  claim 22  having a valve orifice, wherein the inlet valve opens in response to a pressure differential across the valve orifice.  
     
     
         26 . An outlet valve for use with a cassette of the type to be used with an infusion system, the outlet valve comprising: 
 an outlet valve element;    a stem attached to the outlet valve element;    an elastomeric dome for biasing the outlet valve element to the closed position, wherein the cross-sectional area of the elastomeric dome is greater than the cross-sectional area of the outlet valve element; and    an actuator interface which opens the outlet valve.    
     
     
         27 . The outlet valve of  claim 26  wherein the outlet valve is constructed and arranged to be opened for a period of time shorter than the period of time for the fluid flow to reach a stable velocity.  
     
     
         28 . The outlet valve of  claim 26  wherein the outlet valve element includes a tapered surface and wherein the fluid flow through the outlet valve is controlled by the distance between the tapered surface and the valve-housing seat.  
     
     
         29 . The outlet valve of  claim 26  wherein the fluid flow through the outlet valve is controlled by the distance between the valve stem and the valve-housing seat.  
     
     
         30 . The outlet valve of  claim 26  wherein the outlet valve is acted on by a preload force and a hydraulic force, and wherein the outlet valve maintains a closed position when the preload force exceeds a negative hydraulic force.  
     
     
         31 . The outlet valve of  claim 26  wherein the stem is bent.  
     
     
         32 . A check valve for use with a cassette of the type to be used with an infusion system, the check valve comprising a valve element, and an elastomeric wall, wherein the valve element is connected to the elastomeric wall, and wherein the check valve prevents upstream fluid flow by moving between an open and closed position in response to a pressure differential between the atmospheric pressure and pressure on the check valve.  
     
     
         33 . The check valve of  claim 32  wherein the check valve has a preload force and wherein the check valve enters the open position when the pressure in the central chamber exceeds the atmospheric pressure and preload force on the check valve.  
     
     
         34 . The check valve of  claim 32  wherein the check valve enters the closed position when the atmospheric pressure is greater than the pressure in the central chamber.  
     
     
         35 . The check valve of  claim 32  wherein the check valve enters the closed position when the atmospheric pressure exceeds pressure in the outlet side of the check valve.