Abstract:
A pressure regulator configured to reduce fluid flow droop is provided. The pressure regulator comprises a regulator housing having an inlet port, an outlet port and a fluid flow passage therebetween. A valve seat is positioned in the fluid flow passage and a valve plug cooperates with the valve seat to control the flow of a fluid through the fluid flow passage. A bypass plate retains the valve seat in the fluid flow passage, and separates the fluid flow passage from a sensing chamber. The bypass plate includes a flow aperture positioned in the flow passage and at least one aspirator that provides communication between the flow aperture and the sensing chamber. The flow aperture is configured to provide a low pressure region relative to the pressure in the fluid flow passage, wherein the aspirators are configured to communicate between the low pressure region and the sensing chamber.

Description:
[0001]     This application claims priority of U.S. Provisional Patent Application Ser. No. 60/683,365 filed May 20, 2005. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to pressure regulators, and more particularly, to a pressure regulator with reduced outlet pressure loss.  
       BACKGROUND OF THE INVENTION  
       [0003]     A pressure regulator controls gas flow from a high pressure source to a low pressure user device, while attempting to maintain a constant system pressure. Pressure regulators are utilized for various applications including, but not limited to, facilitating the delivery of high pressure, high purity gas or liquid to a user device such as a gas analyzer, laser, fuel cell or welding system. A fluctuation in gas pressure can, in some instances, result in an adverse effect on the performance of the device. Thus, it would be advantageous for a pressure regulator to maintain a constant system pressure.  
         [0004]     To maintain constant system pressure, a pressure regulator should provide a constant outlet pressure. However, in practice, conventional pressure regulators commonly exhibit a phenomena called “fluid flow droop”, which yields an undesirable reduction in outlet pressure. More particularly, in regulators having a spring and diaphragm arrangement, droop is caused by at least two factors, namely, a change in the force exerted by the regulator spring over its travel and a change in the effective area of the diaphragm over its travel. These two factors, alone or in combination, lower the downstream control pressure.  
         [0005]     Thus, there is a need to provide pressure regulators systems that compensate for or limit droop.  
       SUMMARY OF THE INVENTION  
       [0006]     According to an aspect of the invention, a pressure regulator configured to reduce fluid flow droop is provided. The pressure regulator comprises a regulator housing having an inlet port, an outlet port and a fluid flow passage therebetween. A valve seat is positioned in the fluid flow passage and a valve plug cooperates with the valve seat to control the flow of a fluid through the fluid flow passage. A bypass plate retains the valve seat in the fluid flow passage, and separates the fluid flow passage from a sensing chamber. The bypass plate includes a flow aperture positioned in the flow passage and at least one aspirator that provides communication between the flow aperture and the sensing chamber. The flow aperture is configured to provide a low pressure region relative to the pressure in the fluid flow passage, wherein the aspirators are configured to communicate between the low pressure region and the sensing chamber.  
         [0007]     According to another aspect of the invention, the pressure regulator includes a bonnet mounted to the regulator housing, a non-linear spring positioned within the bonnet and a diaphragm positioned adjacent the spring and the valve plug. The spring urges the diaphragm to bias the valve plug toward an open position.  
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0008]     The invention is best understood from the following detailed description when read in connection with the accompanying drawing. Included in the drawing are the following figures:  
         [0009]      FIG. 1A  is a cross-sectional side view of an exemplary embodiment of a pressure regulator configured to limit flow droop according to an aspect of this invention;  
         [0010]      FIG. 1B  is an enlarged view of the top stage of the pressure regulator illustrated in  FIG. 1A ;  
         [0011]      FIG. 2A  is a top-side view of the exemplary flow bypass plate illustrated in  FIG. 1A ; and  
         [0012]      FIG. 2B  is a cross-sectional side view of the flow bypass plate illustrated in  FIG. 2A . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.  
         [0014]     Referring specifically to the exemplary embodiment illustrated in  FIGS. 1A and 1B , a parallel stage pressure regulator  100  comprising regulator stages  101  and  102  and configured to reduce droop is disclosed. It should be understood that the pressure regulator could be a single stage device having only one regulator stage  101  or  102 . A parallel stage pressure regulator of the type disclosed herein facilitates the controlled delivery of gas from either of two high pressure sources (e.g. compressed gas tanks, cylinder banks, etc.) to a device operating at a lower pressure (e.g. gas analyzer, laser, fuel cell, welding system, etc.). A single stage device, of course, controls the delivery of gas from a single high pressure source.  
         [0015]     The pressure regulator  100  comprises a valve body including central body member  105  and a pair of bonnets  111 ,  111  each of which is connected to the valve body by a threaded collar  119 . One bonnet  111  is located on one end of the body member  105  and the other bonnet is located on an opposite end of the body member. Thus, one bonnet  111  is part of one regulator stage  101  and the other bonnet is part of the other regulator stage  102 . Inasmuch as the regulator stages  101  and  102  are generally the same, only stage  101  will be described with the understanding that like reference numerals will be used for like structure in each stage and that any differences between the stages will be specifically pointed out hereinafter.  
         [0016]     The body member  105  is generally cylindrical and includes a pair of inlet ports  151  formed in its cylindrical wall and an outlet port  150  also formed in its cylindrical wall. Each inlet port  151  communicates with one of the inlet passages  145 ,  145  so gas can be fed from either of two high pressure sources to one of the inlet passage  145 . The outlet port  150  communicates with a pair of outlet passages  155 ,  155  each of which communicates with one of the inlet passages  145 ,  145  so that gas can flow from either high pressure source through one of the flow passages  145 ,  155  to the outlet port  150  and, thus, to a user device.  
         [0017]     Between each of the passages  145  and  155 , there is provided a valving assembly  130  each of which includes a valve plug  160  moveably carried in its associated inlet passage  145 , a plug spring  162 , and a valve seat  164  carried on the generally circular end face of the body member  105 . One end of the plug spring  162  is grounded against a base surface of inlet passage  145  and the other end of the plug spring contacts a shoulder formed on the valve plug  160 . A tapered surface  168  is formed intermediate the ends of valve plug  160  and the plug spring  162  biases the valve plug so that surface  168  is urged toward a conical surface  167  formed on the valve seat  164 . In a closed position of valving assembly  130 , surface  168  seats on surface  167 . In an open position of valving assembly  130  mating surfaces  167  and  168  are separated by a circumferential gap. For reasons to be made clear hereinafter, the valve plug  160  is formed with a stem that extends beyond the valve seat  164  where it terminates in a bearing surface  161 .  
         [0018]     The bonnet  111  is formed with a stepped bore  111 ′ having its smaller diameter adjacent its free end and its largest diameter adjacent the body member  105 . In the exemplary embodiment disclosed herein the bore  111 ′ is formed with four different diameters and these diameters increase in size from the free end to the end adjacent the body member  105 . The smallest diameter is threaded and accommodates an adjusting screw  118  which bears against a spring retainer  112  that is slideably carried in one of the bore sections. One end of a spring  114  bears on the spring retainer  112  and the other end bears on a piston  113 . The piston  113  is slidably carried in another section of the bore  111 ′. A diaphragm  120  is clamped between the outer edge of piston  113  and the radially outer edge of bypass plate  125  so that the plate is clamped on the generally circular end face of the body member  105  and which, in turn, clamps the valve seat  164  in place. The piston  113  bears on and urges the diaphragm  120  against the bearing surface  161  of the valve plug stem and, thus, biases the valving assembly  130  to an open position.  
         [0019]     As shown in  FIGS. 1A and 1B  and as more clearly seen in  FIGS. 2A and 2B , the bypass plate  125  is a generally circular disc member having a central opening through which the valve plug stem extends to its abutting relationship with the diaphragm  120 . Extending from one surface of the disc member is a generally cylindrical hub  126  which bears on the valve seat  164  to clamp the valve seat in place on the body member  105 . Extending radially through the hub  126  is a flow restricting passage  173  that communicates with the discharge side of the valve seat  164 .  
         [0020]     The circular disc portion of the bypass plate  125  divides the space between the diaphragm  120  and the end face of the body member  105  into a discharge chamber  142  and a sensing chamber  144 . As best seen in  FIG. 1B , the discharge chamber  142  is formed between the bypass plate  125  and the valving assembly  130  and it receives gas flow from the inlet passage  145 , through the valving assembly, and the flow restricting passage  173 . The discharge chamber  142  also communicates with the outlet passage  155 .  
         [0021]     The flow bypass plate  125  includes aspirators  172  and  172 ′ in the form of passages formed in its disc like portion. Aspirator  172  communicates between the flow passage  173  and the sensing chamber  144 . Aspirator  172 ′ communicates between the discharge chamber  142  and the sensing chamber  144 . When the valving assembly  130  is open, gas travels through the restrictive flow passage  173  where its pressure decreases. After the gas exits passage  173 , it expands into the discharge chamber  142  and its pressure increases. Thus, the pressure of the gas within flow passage  173  is lower than the pressure of the gas within the discharge chamber  142 .  
         [0022]     Initially, the gas pressure within the sensing chamber  144  and discharge chamber  142  are substantially equal and the gas pressure within flow aperture  173  is lower than the gas pressure within both chamber  142  and  144 . Since gas seeks to travel from a higher to a lower pressure region, the gas within sensing chamber  144  travels through the aspirators  172  and  172 ′ towards flow aperture  173  and into discharge chamber  144 . It should be understood that the aspirators  172  and  172 ′ may be positioned at any location at or near the low pressure region of flow aperture  173 .  
         [0023]     As the gas flows from the sensing chamber  142  to the discharge chamber  144 , the sensing chamber pressure drops. By virtue of the pressure drop, the regulator spring  114  expands and forces piston  113  to further separate valve plug  160  from valve seat  164 . The increased separation of valve plug  160  from valve seat  164  induces greater fluid flow through the valving assembly, thereby increasing the outlet pressure and reducing fluid flow droop.  
         [0024]     In addition to the aspirators  172 ,  172 ′, spring  114  of the exemplary embodiment also counteracts fluid flow droop caused by the spring effect. In this embodiment spring  114  comprises a vertical stack of non-linear disc springs, e.g., Belleville washers or any other type of non-linear disc spring. By virtue of the geometry and the material properties of the non-linear spring washers, the washers effect a higher outlet pressure at a given valve opening, thereby reducing droop. More particularly, the collective stack of washers of this embodiment has a lower spring rate than a standard helical range spring and applies less force to the topside of diaphragm  120  for a given amount of washer travel, as compared to a standard helical spring. Thus, less change in internal gas pressure is required to overcome the force exerted on the topside of diaphragm  120 , and the valving assembly  130  is permitted to open further with less of a drop in pressure.  
         [0025]     The diaphragm  120  of the exemplary embodiment is configured to reduce droop caused by the diaphragm effect. As seen in  FIG. 1B , the diaphragm is formed with corrugations  121 . As the diaphragm is extended toward the valving assembly  130 , by the piston  113 , the diaphragm flexes and the effective area of the diaphragm decreases, thus, maintaining a more constant outlet pressure. The diaphragm may have any number of corrugations  121 . The radii of the corrugations may be, for example, 0.1 inches or any dimension sufficient to produce a non-linear response of the diaphragm. The diaphragm is optionally composed of stainless steel.  
         [0026]     The valving assembly  130  is also configured to reduce droop. More particularly, the geometry of the mating surface  168  of valve plug  160  is tailored to facilitate a quick opening flow characteristic. The flow characteristic of a valving assembly is the relationship which exists between the flow through the valving assembly and the travel of the valve plug relative to the valve seat. A “quick opening” flow characteristic is defined by an increasing change in flow rate for a particular translation of the valve plug relative to the valve seat, as compared to a constant change exhibited by a “linear flow characteristic”. In this embodiment, the radius of the revolved mating surface  168  of valve plug  160  may be about 0.1 inches to generate a quick opening flow characteristic.  
         [0027]     The free end face of the seat hub  126  of flow bypass plate  125  clamps valve seat  164  on the body member  105  because of the clamping action between the bonnet  111  and collar  119 . In contrast, conventional valve seat retainers are typically threadedly coupled to the regulator housing to retain the valve seat in a substantially fixed position. It has been recognized that threads can be a source of virtual leaks or accumulated metallic particles thereby affecting the purity of the gas. Moreover, the use of elastomers in this type of regulator may not be preferred as the elastomers can contain and release harmful impurities into the regulator system. Thus, the valve seat  164  may be composed of a non-outgassing polymeric material such as PTFE, PCTFE, or Vespel® currently sold and distributed by DuPont.  
         [0028]     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.