CA1229024A

CA1229024A - Control valve with anticavitation trim

Info

Publication number: CA1229024A
Application number: CA000456253A
Authority: CA
Inventors: James A. Stares
Original assignee: McGraw Edison Co
Current assignee: McGraw Edison Co
Priority date: 1983-06-23
Filing date: 1984-06-08
Publication date: 1987-11-10
Also published as: IT8421574A0; DE3423338C2; ES8503811A1; IN163075B; GB2142160B; ES533536A0; JPS6040882A; GB8415739D0; GB2142160A; JPH052878B2; IT1175553B; DE3423338A1

Abstract

CONTROL VALVE WITH ANTICAVITATION TRIM
Abstract of the Disclosure A control valve includes a valve body with a fluid inlet and a fluid outlet. A valve seat is mounted within the valve body between the inlet and outlet. A valve plug is reciprocally mounted within the valve body to engage the valve seat. A plurality of valve cages are removably mounted on the valve seat and surround the valve plug. The valve cages are mounted to define axial flow galleries. One of the valve cages includes a plurality of apertures and fins that extend radially into a gallery between the first cage and a second cage. The second valve cage is adjacent to and surrounds the first valve cage. The second valve cage includes a plurality of apertures and fins that extend into the gallery area between the second cage and a third cage. The third cage surrounds and is adjacent the second cage. A
plurality of apertures are defined in an upper portion of the third cage member. The first, second and third cage members may be positioned such that the apertures in each cage member are out of alignment to define a tortuous path along which fluid must flow between the cage members.

Description

1~29~)24 02 sAcKGRouND OF THE INVENTION
03 A. Field of the Invention 04 The present invention relates to a new and 05 improved trim design for a control valve that provides 06 energy loss and high resistance to fluid flow by way of 07 collision and separation of the fluid stream thereby 08 preventing cavitation.
09 B. Description of the Background Art Cavitation occurring in control valves has a 11 damaging effect resulting in removal of material from 12 internal valve surfaces. Cavitation occurs when 13 pressure at the controlling orifice drops below vapor 14 pressure causing vapor bubbles to form. Beyond the controlling orifice where pressure increases above vapor 16 pressure, the vapor bubbles collapse. Internal portions 17 and components of the valve near the collapsing bubbles 18 suffer cavitation damage. To ~liminate cavitation, it 19 is necessary to prevent the pressure at the controlling orifice from dropping below vapor pressure level. This 21 can be accomplished by staging the single valve pressure 22 drop into multiple pressure drops thereby lowering the 23 amount of pressure recovery occurring at any one stage.
24 There have been three basic techniques employed by valve designers to control or eliminate 26 damage resulting from cavitation. A first technique 27 involves hardening the internal valve surfaces in areas 28 where cavitation may occur. A second technique employ3 29 flow-to-close trim designs that direct cavitating fluid jet streams to converge on one another at mid-stream 31 locations thereby causing the vapor bubbles to collapse 32 at locations away from critical internal surfaces and 33 components of the valves. Both of these techniques 34 attempt to minimize and contain the damaging effects of cavitation but do not eliminate ~22902~

-2-cavitation. Consequently, these techniques are normal-ly used for lower pressure drop applications where cavitation is not as severe as in other applications.
A third technique is one of cavitation eli-mination. Downstream restrictors are used to backupthe outlet pressure of a control valve. This technique necessitates the use of staging external to the con-trol valve resulting in expensive and bulky valves.
A trim assembly providing resistance to fluid flow by directing fluid through axially extend-ing fluid energy absorbing passages is disclosed in United States Patent No. 3,971,411. Radial flow pas-sages defined by slots in one or more cylinders is illustrated in United States Patent Nos. 3,813,079 and 3,987,809. A complex and cumbersome assembly for imparting resistance to flow is illustrated in United States Patent No. 3,780,767 that discloses a plurality - of plates with cut-out portions defining vortex chambers. Each of the designs disclosed in the above mentioned patents provides a single technique of resisting fluid flow. Each uses either radial or axial flow resistance and are primarily intended for noise abatment. These devices typically do not break the single large valve pressure drop lnto a number of smaller pressure drop ~tages to avoid creating vapor pres~ure bubbles in the fluid controlled by the valve.
SyMMARY OF THE INVENTION
An object of the present invention is to provide a new and improved anti-cavitation control valve.
Another object of the present invention is to provide a new and improved fluid flow valve includ-ing a trim design that breaks the valve pressure drop in~o a number of small pressure drops to prevent cavi-tation.

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-3-A further object of the present invention is to provide a new and improved control valve with a valve trim design defined by a number of close fitting~
concentric cylinders that provide both radial and axial tortuous fluid flow paths to prevent cavitation.
Briefly, the present invention is directed to a new and improved fluid flow control valve includ-ing a trim design that prevents cavitation within the control valve. The valve includes a valve body with a fluid inlet, a fluid outlet and a valve seat posi-tioned within the valve body between the fluid inlet and outlet. A valve plug is reciprocally mounted within the valve body to engage the valve seat in the valve closed mode.
The trim design includes a plurality of concentric, close fitting cages removably positioned on the valve seat encircling the valve plug. The concentric cages are slightly spaced from each other to define axial flow galleries between adjacent cages.
Properly located apertures and fins in and on the valve cages provide a high resistance flow path with specifically staged areas to prevent fluid pressure from dropping below fluid vapor pressure.
The apertures, fin~ and gallery areas are spaced and sized so that at variable plug lift positions, a con-tinuously changing flow path provides proper pressure drop distribution to prevent cavitation from occurring at intermediate stages as well as the last stage of fluid flow.
The valve trim provides a continuously in-creasing amount of combined feed area into a common gallery as the valve plug is lifted. ~his provides a constantly changing flow pa~h configuration and pres-sure drop distribution as contrasted with most other radially designed trim assemblies.

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03 The combination of radial apertures and fins 04 provides continuous collision and subsequent separation of 05 fluid streams in both radial and axial directions 06 providing for additional high energy loss further avoiding 07 the likelihood of cavitation. ~he location of the 08 apertures and fins on the cages provides for more staging 09 at the lower lift positions of the valve plug where the pressure drop is highest and higher capacity and less 11 staging at the higher lift positions where pressure drop 12 is less. Both radial and axial flow paths are provided at 13 the lower lift positions and radial paths only are 14 provided at the higher lift positions.
The staged areas defined by the apertures and 16 fins in the concentric cages provides a continuously 17 decreasing pressure drop from the inlet to the outlet of 18 the concentric cages due to a progressively increasing 19 flow area. This assures that the last stage at the outer cage causes the lowest pressure drop. This is 21 advantageous since it is at this last pressure ~tage drop 22 being closest to the vapor pressure level which i9 most 23 likely to cavitate.

The above and other objects and advantages and 26 novel features of the present invention will become 27 apparent from the ollowing detailed description of a 28 preferred embodiment of the invention illustrated in the 29 accompanying drawings wherein:
FIG. 1 is a vertical, cross sectional view of a 31 control valve constructed in accordance with the 32 principles of the present invention;
33 FIG. 2 is an enlarged, fragmentary, 34 cross-sectional view of cages of the valve illustrated in FIG. 1 with a valve plug in the partial open po~ition;
36 FIG. 3 is a view taken along line 3-3 of FIG. 2;

~, 3L2290;24 FIG. 4 is a view similar to FIG. 2 with the valve plug in a higher lift position;
FIG. 5 is a view taken along line 5-5 of FIG.

4;
FIG. 6 is a view similar to FIGS. 2 and 4 with the valve plug in the full open or lift position; and FIG. 7 is a view taken along line 7-7 of FIG.
6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference initially to FIG. 1, there is illustrated a control valve generally designated by the reference numeral 10. Valve 10 includes a body 12 with a fluid inlet port 14 and a fluid outlet port 16.
Flanges 15 and 17 are mounted on body 12 adjacent inlet 14 and outlet 16, respectively to allow connection of valve 10 to a conduit in a fluid system. A centrally located valve plug chamber 18 is defined within valve body 12 between inlet 14 and outlet 16. Chamber 18 is in fluid communication with inlet 14 by a inlet fluid flow passage 20 defined in body 12 and a port 22. Fluid outlet 16 is in communication with chamber 18 by an outlet fluid flow passage 24.
Valve 10 functions under a pressure drop between 500 p.s.i. and 3,000 p.s.i. in one commercial embodiment, which can cause cavitation that could damage the internal surfaces of valve body 12. Fluid flow through valve 10 is controlled by a reciprocally mounted valve plug 30 located within chamber 18. The upper end of chamber 18 includes an opening or aperture 32 to allow the insertion of the valve plug 30 into chamber 18. Valve plu~ 30 i8 reciprocated within the chamber 18 by an external valve controller ~now shown) mechanically connected to the valve 30 by a stem 34 that extends through aperture 32 and is secured to valve plug 30 by a pin ~ ~ . , .

~ 2Z9OZ4 36. Pin 36 provides a removable connection between stem 34 and valve plug 30 allowing easy removal of valve plug 30 for replacement or repair.
A removable valve bonnet 38 is secured to val~e body 12 by threaded studs or fasteners 40 and 42. A gasket 44 encircles aperture 32 and is main-tained in position by bonnet 38 to provide a seal between bonnet 3B and valve body 12. In the valve closed position (FIG. 1), valve plug 30 sealingly engages a valve seat ring 46 removably position~d in aperture 22~
¦ To prevent cavitatlon in valve 10, a high resistance fluid flow path is provided by a val~e cage assembly generally designated by the reference numeral 48. Valve cage assembly 48 includes a plural-ity of close fitting, concentric cages. In the pre-ferred embodiment illustrated, there are ~hree cylin-drical cages 50, 52 and 54 although any number may be used depending on the desired design. Cylinarical cages 50, 52 and 54 include apertures, fins and gallery areas that are spaced and sized such that at variable lift positions of plug 30 a continuously changing flow path provides the d0sired pressure drop distribu-tion to prevent cavitation.
Cages 50 and 52 include flanges 56 ana 58, respectively, that define spaces or gallery areas such as the axial flow gallery area 60 between cages 50 and 52 and the axial flow gallery area 62 defined between cages 52 and 54. Cage S0 further includes a plurality of ribs or fins 64 defined on a lower por-¦ tion. Cage 52 also includes a plurality of fins or ~ ribs 66 lw ated on a lower portion whereas cage 54 _ does not include fins.
Radial passages through first cage S0 are defined by a plurality of apertures or openings 68 in ~Z9024 03 the entire length of cage 50 corresponding to the ~ull 04 range of lift positions of valve plug 30. Second cage 05 52 includes radial openings or apertures 70 in a lower 06 portion and upper portion of the cage 52 with an 07 impervious portion 72 between the upper and lower 08 portions. Third cage 54 includes an impervious lower 09 portion 74 and an upper portion including a plurality of apertures 76.
11 Cages 50, 52 and 54 are removably positioned 12 within valve body 12 and radially held by a pin 78.
13 Removal of pin 78 allows the middle or second cage 52 to 14 be rotated relative to first cage 50 and third cage 54.
Rotation of cage 52 moves apertures 70 out of alignment 16 with apertures 68 in lower portion of cage 50 (FIG. 3)-17 This misalignment requires fluid to flow through a 18 tortuous flow with turns to flow through apertures 70.
19 Fluid flow in the lower lift positions (FIGS. 2 and 3) engages and is directed by fins 64 in the axial gallery 21 area 60. As flow passes through apertures 70 in the 22 lower portion of cage 52, it enters axial gallery area 23 62 flowing upward past fins 66 then turning through 24 apertures 76 into chamber 18. This configuration provides mo`re stages improving anti-cavitation. This is 26 desirable since it is at the lower lift positions that 27 the pressure drop is the highest with the greatest 28 potential for cavitation.
29 If valve plug 30 is lifted to approximately the half-open position (FIGS. 4 and 5), a larger number 31 of apertures 68 are exposed and flow through the 32 tortuous path already described. In the middle portion 33 of cages 50 and 52, apertures 70 and 68 are misaligned 34 with apertures 76 (FIG. 5) and flow is substantially radial.
36 In larger valves, the flow area defined by the 37 apertures 70 and 76 may be substantially greater 1229~24 0~ - 8 -03 than the flow area in the gallery 60 and there will be 04 little flow through and little pressure drop across the 05 lower portion of cage 52. To break up flow in gallery 06 60 in these larger valves, a fin 65 is included that 07 directs some of the flow in gallery 60 through apertures 08 70 in the lower portion of cage 52 thereby more evenly 09 distributing the total pressure drop over the full length of cage 52.
11 At the full open or top lift position of plug 12 30 (FIG. 6), apertures 68, 70 and 76 are fully exposed 13 but mis-aligned allowing a tortuous radial flow with 14 higher capacity and less ~taging since it is at this level that the pressure drop is less. Optionally, at 16 these higher lift positions, apertures 68, 90 and 96 can 17 be aligned (FIG. 7) and/or enlarged to provide for even 18 higher capacities. At the lower lift positions (FIGS. 2 19 and 3), there is a higher pressure drop and more severe conditions for potential cavitation. Accordingly, both 21 radial and axial flow paths at the lower lift positions 22 are provided whereas only radial flow paths are required 23 at the upper or higher lift position.
24 At the lower lift positions, the only axial flow path is in the gallery area 62. The axial flow in 26 gallery 60 is added as the valve plug 30 is lifted to 27 the middle lift positions (FIGS. 4 and 5) above the last 28 full fin 64. This configuration provides progressively 29 increasing flow area to assure that the last stage at the outer cage 54 takes the lowest pressure drop which 31 is advantageous as it at this last stage pressure drop, 32 being closest to the vapor pressure level, which is most 33 liekly to cavitate.
34 Since gallery areas 60 and 62 are always exposed to flowing fluid, there is always a pressure 36 drop distribution along the outer diameter of valve plug 37 30. In contrast, prior art radial designs separate flow 38 into individual radial paths at different lift levels 3~ and there is no pressure drop staging lZ~9~4 03 above the plug lift position. Thus, the full pressure 04 drop is across the leading edge of the valve plug 05 resulting in some cavitation damage occurring at the 06 leading edge of the plug.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A valve, comprising:
a valve body with a fluid inlet and a fluid outlet, a valve seat ring positioned in said valve body between said fluid inlet and said fluid outlet, a valve plug reciprocally mounted in said valve body engaging said valve seat ring in a valve closed mode, and a plurality of cage members positioned in said valve body, a first cage member includes a plurality of apertures and a plurality of radially extending fins, a second cage member includes a plurality of apertures and a plurality of radially extending fins, a third cage member includes a plurality of apertures, said plurality of cage members being positioned in said valve body to define axial flow passages between adjacent cage members.

2. The valve set forth in claim 1 wherein said plurality of cage members are cylindrical.

3. The valve set forth in claim 1 wherein said plurality of cage members are cylindrical and concentric.

4. The valve set forth in claim 1 wherein said first, second and third cage members are movably positioned in said internal chamber to allow rotation relative to each other.

5. The valve set forth in claim 1 wherein said plurality of cage members are concentric to and surround said valve plug.

6. The valve set forth in claim 1 wherein the inner peripheral surface of said first cage member surrounds said valve inlet, said fins on said first cage member radially extend from the outer peripheral surface of said first cage member.

7. The valve set forth in claim 1 wherein the lower end of each said cage member engages said valve seat ring, said apertures in said first cage member being in the entire length of said first cage member, said first cage member including a lower por-tion and an upper portion, said fins on said first cage member being on said lower portion of said first cage portion, said second cage member including a lower portion, a middle portion and an upper portion, said apertures in said second cage member being in said lower and upper portions of said second cage member, said middle portion being impervious, said third cage member including an upper portion and a lower portion, said apertures in said third cage member being in said upper portion of said third cage member, said lower portion of said third cage member being impervious.

8. A control valve with an anti-cavitation trim design, comprising:
a valve body, a fluid inlet in said valve body, a fluid outlet in said valve body, a valve chamber in said valve body in fluid communication with said inlet and said outlet, a valve seat in said valve chamber, a valve plug mounted for reciprocal movement in said valve chamber engageable with said valve seat in the valve closed mode, a plurality of concentric cages surrounding said valve plug, said plurality of cages being spaced from each other to define axial flow areas, a first cage including a plurality of apertures and a plurality of fins extending into one of said axial flow areas, a second cage adjacent to said first cage including a plurality of apertures and a plurality of fins extend-ing into one of said axial flow areas, and a third cage including a plurality of apertures.

9. The control valve claimed in claim 8 wherein said first, second and third cages are cylin-drical and encircle said valve plug.

10. The control valve claimed in claim 8 wherein said first, second and third cages are movably mounted in said valve chamber allowing movement rela-tive to each other.

11. The control valve claimed in claim 8 wherein said first cage includes said apertures through-out the length of said cage corresponding to the full range of lift positions of said valve plug, said fins being defined on less than the entire length of said first cage.

12. The control valve claimed in claim 8 wherein said second cage includes a first area with apertures and fins and a second area with apertures and an impervious area between said first and second areas.

13. The control valve claimed in claim 8 wherein said third cage includes said apertures in less than the entire length of said third cage.

14. A control valve, comprising:
a valve body including a fluid inlet and a fluid outlet, a valve seat positioned in said valve body between said inlet and said outlet, a valve plug reciprocally mounted in said valve body, a first cylindrical valve cage removably mounted on said valve seat surrounding said valve plug, said first valve cage including a plurality of apertures throughout at least a portion of the length of said first valve cage, said first valve cage includ-ing a plurality of radially extending ribs on at least a portion of said first valve cage, a second cylindrical valve cage concentric with said first valve cage removably mounted on said valve seat at a location to define a first axial flow gallery between said first and second valve cages, said ribs on said first valve cage extending into said first axial flow gallery, said second cage includ-ing a plurality of apertures in at least a portion of the length of said second cage, said second cage including a plurality of radially extending ribs, and a third cylindrical valve cage concentric with said first and second valve cages removably mounted on said valve seat at a location to define a second axial flow gallery between said second and third valve cages, said ribs on said second valve cage extending into said second axial flow gallery, said third valve cage including a plurality of aper-tures in at least a portion thereof.

15. The control valve set forth in claim 14 wherein said first valve cage includes an upper portion and a lower portion, said apertures being in said upper and lower portions, said ribs being on said lower portion.

16. The control valve set forth in claim 14 wherein said second valve cage includes an upper portion, a middle portion and a lower portion, said middle portion being impervious, said upper and lower portions including said apertures, said lower portion including said ribs.

17. The control valve set forth in claim 14 wherein said third valve cage includes a lower portion and an upper portion, said lower portion being impervious, said apertures being in said upper portion.

18. The control valve set forth in claim 14 wherein said apertures in said first valve cage being out of alignment with said apertures in said second valve cage.

19. The control valve set forth in claim 14 wherein said apertures in said second valve cage being in alignment with said apertures in said third valve cage.

20. The control valve set forth in claim 14 further comprising an additional fin on an upper portion of said first valve cage.