Multi-Stage Pump Having Reverse Bypass Circuit

Abstract

A multi-stage pump includes a pump head having at least two compression stages disposed in series With espect to the direction of flow of fluid through the pump, and a reverse fluid bypass circuit including a fluid passageway through which fluid flowing between upstream and downstream ones of the compression stages can he circulated back upstream of the upstream compression stage. The reverse fluid bypass circuit may restrict or stop the flow of fluid through the fluid passageway as long as the pressure differential across the fluid passage is below a. predetermined value. To this end, the reverse fluid bypass circuit may be configured to restrict the flow of fluid while the fluid is in its transitional or molecular flow regime, and allow the flow of fluid while the fluid is in its viscous flow regime.

What is claimed is: 
     
         1 . A multi-stage pump comprising:
 an inlet portion having a pump inlet and constituting a low pressure side of the pump where fluid is drawn into the pump, and an exhaust portion having a pump outlet and constituting a compression side where fluid is discharged from the pump at pressure greater than that of the fluid at the low pressure side;   a pump head having an inlet opening to which the pump inlet extends, an exhaust opening leading to the pump outlet, at least two compression stages disposed in series with respect to the direction of flow of fluid through the pump, and a fluid bypass circuit, and   wherein each of the compression stages has an ingress through which the fluid enters the stage and an egress through which the fluid exits the stage,   a flow path along which fluid flows from the pump inlet to the pump outlet extends in the pump between the pump inlet and an upstream one of the compression stages, between the egress of the upstream one of the compression stages and the ingress of a downstream one of the compression stages, and between the egress of the downstream one of the compression stages and the pump outlet, and   the fluid bypass circuit defines a fluid passageway discrete from the flow path and connected to the flow path at a first location between the egress of one of the compression stages and the ingress of the next compression stage downstream therefrom and at a second location upstream of the ingress of said one of the compression stages.   
     
     
         2 . The pump as claimed in  claim 1 , wherein the fluid bypass circuit comprises a valve disposed in-line with the fluid passageway. 
     
     
         3 . The pump as claimed in  claim 2  wherein the valve is a spring-biased check valve that opens when the differential pressure across the fluid passageway, as between the second and first locations, is greater than a predetermined value. 
     
     
         4 . The pump as claimed in  claim 1 , wherein the fluid bypass circuit comprises a labyrinth seal providing a flow restriction between the first and second locations. 
     
     
         5 . The pump as claimed in  claim 1 , wherein the fluid bypass circuit comprises a capillary tube providing a flow restriction between the first and second locations. 
     
     
         6 . The pump as claimed in claim , wherein the fluid bypass circuit comprises an orifice disposed in the fluid passageway and providing a flow restriction between the first and second locations. 
     
     
         7 . The pump as claimed in  claim 1 , wherein the fluid bypass circuit comprises a flexible tube which collapses when the pressure differential between the inside and outside thereof is less than a predetermined value. 
     
     
         8 . The pump as claimed in  claim 1 , wherein the fluid bypass circuit comprises fluid flow control means for restricting or stopping the flow of fluid through the fluid passageway as long as the differential pressure across the fluid passageway, as between the second and first locations, is less than a predetermined value. 
     
     
         9 . The pump as claimed in  claim 1 , wherein the fluid bypass circuit comprises fluid flow control means for preventing the flow of the fluid from the first location to the second location while the fluid is in its transitional or molecular flow regime between the egress of said one of the compression stages and the ingress of said next compression stage downstream therefrom, while allowing the flow of the fluid from the first location to the second location when the fluid is in its viscous flow regime between the egress of said one of the compression. stages and the ingress of said next compression stage downstream therefrom. 
     
     
         10 . The pump as claimed in  claim 1 , wherein said one of the compression stages is that which is located closest to the inlet of the pump with respect to the direction of flow through the pump along the flow path. 
     
     
         11 . The pump as claimed in  claim 10 , wherein the pump is a multi-stage scroll type of pump including stationary and orbiting plate scrolls, and tip seals disposed in tips of scroll blades of the stationary and orbiting plate scrolls. 
     
     
         12 . A multi-stage pump comprising:
 an inlet portion having a pump inlet and constituting a low pressure side of the pump where fluid is drawn into the pump, and an exhaust portion having a pump outlet and constituting a compression side where fluid is discharged from the pump at pressure greater than that of the fluid at the low pressure side;   a pump head having an inlet opening to which the pump inlet extends, an exhaust opening leading to the pump outlet, at least two compression stages disposed in series with respect to the direction of flow of fluid through the pump, and a fluid bypass circuit, and   wherein each of the compression stages has an ingress through which the fluid enters the stage and an egress through which the fluid exits the stage,   a flow path along which fluid flows from the pump inlet to the pump outlet extends in the pump between the pump inlet and an upstream one of the compression stages, between the egress of the upstream one of the compression stages and the ingress of a downstream one of the compression stages, and between the egress of the downstream one of the compression stages and the pump outlet,   the fluid bypass circuit defines a fluid passageway discrete from the flow path and connected to the flow path at a first location between the egress of one of the compression stages and the ingress of the next compression stage downstream therefrom and at a second location upstream of the ingress of said one of the compression stages, and   the fluid bypass circuit comprises fluid flow control means for restricting or stopping the flow of fluid through the fluid passageway.   
     
     
         13 . The pump as claimed in  claim 12 , wherein the fluid flow control means comprises a valve disposed in-line with the fluid passageway. 
     
     
         14 . The pump as claimed in  claim 12 , wherein the valve is a spring-biased check valve that opens when the differential pressure across the fluid passageway, between said first and second locations, is greater than a predetermined value. 
     
     
         15 . The pump as claimed in  claim 12 , wherein the fluid bypass circuit comprises a capillary tube providing a flow restriction between the first and second locations. 
     
     
         16 . The pump as claimed in  claim 12 , wherein the fluid bypass circuit comprises an orifice disposed in with the fluid passageway and providing a flow restriction between the first and second locations. 
     
     
         17 . The pump as claimed in  claim 12 , wherein the fluid bypass circuit comprises a flexible tube which collapses when the pressure differential between the inside and outside thereof is less than a predetermined value. 
     
     
         18 . A multi-stage pump comprising:
 an inlet portion having a pump inlet and constituting a low pressure side of the pump where fluid is drawn into the pump, and an exhaust portion having a pump outlet and constituting a compression side where fluid is discharged from the pump at pressure greater than that of the fluid at the low pressure side;   a pump head having an inlet opening to which the pump inlet extends, an exhaust opening leading to the pump outlet, at least two compression stages disposed in series with respect to the direction of flow of fluid through the pump, and a fluid bypass circuit, and   wherein each of the compression stages has an ingress through Which the fluid enters the stage and an egress through which the fluid exits the stage,   a flow path along which fluid flows from the pump inlet to the pump outlet extends in the pump between the pump inlet and an upstream one of the compression stages, between the egress of the upstream one of the compression stages and the ingress of a downstream one of the compression stages, and between the egress of the downstream one of the compression stages and the pump outlet,   the fluid bypass circuit defines a fluid passageway discrete from the flow path and connected to the flow path at a first location between the egress of one of the compression stages and the ingress of the next compression stage downstream therefrom and at a second location upstream of the ingress of said one of the compression stages, and   the fluid bypass circuit comprises fluid flow control means for restricting the flow of fluid while the fluid is in its molecular flow regime, while allowing the flow of fluid while the fluid is in its viscous flow regime.   
     
     
         19 . The pump as claimed in  claim 18 , wherein the fluid flow control means comprises a labyrinth seal providing a flow restriction between the first and second locations.