Low noise valve

Abstract

A low-noise valve has a body with a fluid inlet to receive pressurized fluid, an oulet and a fluid passageway extending between the inlet and outlet. Located in the passageway are a number of spaced throats. The valve also includes a movable stem with a number of plugs each adapted to be closely received by a corresponding throat. Each plug includes a plurality of circumferential alternating grooves and lands, the lands being closely spaced within the throats to create a plurality of flow restrictions each incrementally restricting fluid flow when the stem is at a minimum flow position. Movement of the stem toward a full open position sequentially removes the lands from the throat to reduce restriction of said fluid flow in stages.

Description

a casting. Since the the initial spacing of the disks and their throats may vary, by machining face groove 98 subsequent to assembly, throat spacing can be precisely determined.

The third disk 88 is identical to the second disk 86 including another throat 96 with a face groove 98.

The fourth disk 90 is similar to the second and third disks 86 and 88 to radially span and partition the shell and includes an axial bore defining a fourth throat 96. Like the throats described above, the fourth disk throat 96 has a face groove 98.

To position the cage 82 in the chamber 24 so that the first disk 84 abuts the inlet connection 32 and to support the cage against the bonnet end 30, the cage 82 includes a cylindrical base 114. The base 114 projects from the fourth disk 90 to have an end defining a face 116 adapted to abut the cap face 72 to support the cage 82 when it is disposed in the chamber 24. An annular groove 118 is disposed about the face 116 to receive a gasket 120 which acts as a cushion to prevent the cage from rattling within the chamber under the influence of flow turbulence. Extending radially outward through the base 114 to register with the outlet 56 is a cage bore 122 which has substantially the same diameter as the outlet 56. By virtue of the pins 95, the cage bore 122 remains aligned with the outlet 56.

To guide the movement of the valve stem 14, the cage 82 includes ribs 126 disposed at 90° within the shell 83. The ribs 126 extend axially within the shell between the disks to define four tracks 127 extending from the first disk 84 to a point about half the thickness of the base 114 beyond the fourth disk 90. The ribs 26 function to support the stem 14 between the minimum flow and full open position.

As can be appreciated from the drawings, the shell 83, throats 96, base 114 and cage bore 122 define a fluid passageway 124 extending from the inlet 48 to the outlet 56.

To cooperate with the throats 96 to control fluid flow and give the valve 10 the desired rangeability of 340:1, the stem 14 has four equally spaced plugs 128 disposed at the end and along the shaft 16.

The plugs 128 are cylindrical, each adapted to be received in a closely spaced relationship in a throat 96 when the valve 10 is at a minimum flow conditions as shown in FIG. 4. Disposed circumferentially about each plug 128 are a plurality of grooves 134. Preferably, as shown in the drawings, each plug 128 has six such grooves 134. However, it should be noted that the number of grooves may be increased or decreased from the six shown and hereinafter described as desired. The grooves 134 are equally spaced from one another and from the downstream end, i.e., the right end as shown in the drawings, to define seven lands 135. The upstream side land 135 of each plug has a rounded leading edge 136. The leading edge 136 reduces wear on the plug and guides the plug to smoothly enter the designated throat. The lands 135 represent the outer perimeter of the plug 128 and accordingly are adapted to be closely spaced within the first throat 96 when the valve 10 is at the minimum flow condition.

In addition to the plugs 128 a cylindrical stop 132 is located about the shaft 16 to abut the cap 68 when the stem 14 is at full open.

For a 4-inch valve the cage 82 has an axial length of about 9.99 inches, the throats 96 being axially spaced apart by 2.125 inches. Each throat 96 has a diameter of 2.506 inches and an axial length of 0.500 inches, including the face cut 98 which has an axial length of about 0.090 inches. Each plug 128, to cooperate with the throats 96, has an outer diameter of 2.4995 inches with an overall axial length of 0.469 inches. The upstream end of each plug leading edge 136 is spaced from the upstream end of an adjacent plug leading edge 136 by 2.125 inches. The grooves 134 are 0.032 inches in axial length and 0.032 inches in radial depth and are spaced from the downstream end of each plug 128 to define the lands 135 having an axial length of 0.032 inches. The leading edge 136 and adjacent land 135 have a combined axial length of 0.070 inches.

When the valve 10 is at minimum flow, the plugs 128 are disposed within the throats 96 as shown at FIG. 4. The smaller diameter plugs 128 close the throats 96 to each define an annular flow area of about 0.0216 square inches representing the space between the plug lands 135 and the throat wall. Manufacturing tolerance variations in the throat 96 or plug 128 may alter the radial width of the restriction to a range of about 0.002 to 0.0035 inches influencing the flow area accordingly. As can be appreciated, the annular flow area defined restriction is about 0.44 percent of the area of the throat.

As can be appreciated the seven lands 135 of each plug, with the interposed grooves 134, create, in effect, seven discrete annular fow restrictions 138 in each throat 96. The fluid flowing from the inlet 48 toward the outlet 56 must flow through the seven annular flow restrictions 138 defined in each throat 96. In so doing, each flow restriction 138 incrementally restricts fluid flow. Contrasted with typical prior art choke valves which rely upon a single stage to control fluid flow, the annular flow restrictions of the valve 10 according to the present invention provides numerous stages, each incrementally restricting fluid flow. Accordingly, no individual stage is required to control fluid flow to such an extent that the pressure drop approaches the value K_c. K_c is the cavitation index of a valve configuration which, when compared with the value of ΔP/P₁ -P_v, indicates the presence of cavitation. ΔP is the pressure drop of each stage, P₁ is the inlet pressure absolute and P_v is vapor pressure of the liquid. When ΔP/P₁ -P_v is greater than K_c, cavitation is present; when ΔP/P₁ -P_v is less than K_c, cavitation is absent or minor.

The valve 10, as shown in the drawings, has four plugs, each having seven lands which cooperate to define 28 flow restrictions overall for the valve 10 when at the minimum flow position. In the illustrated embodiment, valve 10 is capable of controlling fluid from an initial flow rate and pressure of 1750 gpm and about 2300 psi to a flow rate and pressure of about 23 gpm and 300 psi. As discussed above, the pressure reduction is accomplished in 4×7 steps, thus avoiding cavitation by virtue of the incremental flow restrictions. Accordingly, the valve 10 is well suited to maintain a small flow rate through the associated piping to prevent freezing in arctic environs.

To increase the fluid flow through the valve 10, the shaft 16 is moved toward the full open position which is illustrated in FIG. 1. As the plugs 128 are displaced from the throats 96, the downstream land 135 of each plug is positioned such that the upstream adjacent groove 134 registers with the face groove 98. In this position the flow restriction 138 created by the land 135 disposed within the throat 96 is removed from being effective as a restriction. In view of the similarity of the position of the plugs 128 relative to the throats, restricting flow is initially reduced by four stages as the downstreammost land 135 of each plug 128 is displaced from its respective throat 96. Continued movement of the stem 14 displaces another land 135 of each plug 128 from its respective throat 96 to reduce the restriction by four more stages. At an intermediate position, as shown in FIG. 3, four lands 135 of each plug 128 have been displaced from the throat leaving, accordingly, three flow restrictions 138 per throat for a total of twelve flow restrictions 138 all together. Therefore, as shown in FIG. 3, flow is controlled by 12 stages as compared to 28 stages at minimum flow. It follows that in the position as shown in FIG. 3, the valve 10 will have a flow rate substantially greater than when the valve 10 is at minimum flow. As the shaft 16 is further displaced, the restricting effect is reduced by four-stage increments until the stem 14 is at full open. At full open the illustrative 4-inch valve 10 is adapted to pass 1750 gpm with a discharge pressure of about 2000 psi, the pressure drop across the valve 10 being a minimum.

It is to be noted that the area of annular space between the outside of the plugs and the inside of the sleeves 112 is preferably at least as large as the annular flow area between the throats and the shaft 14 to minimize pressure drop when the valve is fully open.

While I have shown and described certain embodiments of the choke valve 10, it is to be understood that it is subject to modification without departing from the scope and spirit of the following claims. For example, rather than fashioning the grooves in the plugs, the grooves could be disposed in the throat walls, the plug having a smooth circumference as shown in FIG. 5. Also, a seat 150 could be fashioned at the upstream edge of the throat nearest the inlet to the seat the leading edge 136 of the corresponding plug to provide for complete stoppage of fluid flow as shown in FIG. 6. Furthermore, the number of plugs and hence the number of throats may vary from case to case depending upon ΔP/P₁ -P_v at full open conditions. Additionally, it should be noted that the valve 10 may be reversed such that the fluid enters the outlet and is discharged through the inlet.

Claims

1. A low noise valve comprising:

a body having a fluid inlet and a passageway extending from the inlet to a fluid outlet, the body including a plurality of throats serially disposed in the passageway; and

a valve stem movable between a first position wherein a plug having a plurality of outer alternating grooves and lands is positioned within each throat to define a plurality of annular flow restrictions between the throat and the plug lands to restrict fluid flow from the inlet to the outlet and a selected second position wherein at least one land of each plug is disposed without the throat to reduce the number of annular flow restrictions restricting fluid flow.

2. The valve of claim 1 wherein the radial area of each flow restriction is about 0.44 percent of the area of the throat.

3. The valve of claim 1 wherein the plug has seven lands alternating with six grooves.

4. The valve of claim 1 further including a cage disposed in the housing, the cage including a shell having a plurality of spaced members each with a bore defining one of said throats and further including a rearwardly outwardly projecting face groove in each member adjacent the throat, said face groove cooperating to separate each throat from adjacent throats a desired amount.

5. A low noise valve comprising:

a body having an inlet to admit pressurized fluid, an outlet for the fluid to be discharged from the body, and a passageway communicating between the inlet and outlet, said body including a plurality of serially arranged cylindrical throats; and

a stem movably disposed in the body, the stem including a plurality of cylindrical plugs each having alternating circumferential grooves and lands, the stem movable between a minimum flow position wherein a plug is disposed in and the lands are closely spaced from each of the throats to restrict fluid flow to a full open position wherein the plugs are remote from said throats, movement of the stem from the first to the second position sequentially displacing said lands from said throats to reduce the restriction.

6. The valve of claim 5 wherein the body includes four throats spaced within the passageway and the stem includes four plugs each adapted to be disposed in a corresponding throat to restrict fluid flow in a number of incremental stages, the number of stages equal to the total number of lands on all plugs when the stem is at the minimum flow position.

7. The valve of claim 6 wherein each plug includes circumferential grooves alternating with six circumferential lands to effect a pressure drop from the inlet to the outlet in 28 stages.

8. A low noise valve comprising: a body having an inlet to admit pressurized fluid, an outlet for the fluid to exit the body and a passageway communicating between the inlet and outlet, said body including a plurality of throats; and

a stem movably disposed in the body, the stem including a plurality of plugs each adapted to be received by a throat, one of said plugs and throats including a plurality of alternating grooves and lands defining a plurality of flow restrictions to restrict the fluid flow when said stem is at a minimum flow position, said flow restrictions becoming sequentially ineffective to restrict fluid flow as said stem is moved toward a full open position wherein said plugs are remote from said throats.

9. The valve of claim 8 further including a cage disposed in the body, the cage having a shell with a plurality of members disposed generally transverse to fluid flow, each of such members having an axial bore defining one of said throats, and a face groove adjacent the downstream terminus of each throat, the face groove of each throat having an axial length to, in cooperation with the face grooves of other adjacent throats, space the throats a selected amount from one another. 10. The valve of claim 8 wherein the alternating lands and grooves are on the throats and the respective plugs each have a smooth cylindrical circumference. 11. The valve of claim 8 wherein the alternating lands and grooves are on the plugs, and the respective throats each have a smooth cylindrical circumference.