AU6160690A

AU6160690A - Throttling valve

Info

Publication number: AU6160690A
Application number: AU61606/90A
Authority: AU
Inventors: Max Kueffer
Original assignee: Keystone International Holdings Corp
Current assignee: Keystone International Holdings Corp
Priority date: 1989-06-14
Filing date: 1990-05-21
Publication date: 1991-01-08
Anticipated expiration: 2010-05-21
Also published as: WO1990015944A2; CN1048093A; JPH05502283A; ES2025391A6; KR920701729A; BR9007442A; AU640678B2; CA2016800A1; FI915872A0; EP0477299A4; HUT63236A; EP0477299A1; CN1023343C; WO1990015944A3; HU906770D0

Description

THROTTLING VALVE

Field of the Invention The present invention relates generally to an improved design for a throttling valve which prevents deterioration of valve surfaces. Specifically, the present invention is directed to the prevention of erosion and cavitation caused by the sudden vaporization of liquids and following implosion of these vapor bubbles.

Background of the Invention Throttling valves are used in the chemical, petroleum and utility industries for a variety of high pressure drop applications including continuous blow-down sampling, high pressure venting, turbine drain and boiler feed-pump bypass relief . There are a wide number of applications for heavy duty valves with critical service conditions. The damaging conditions are normally not permanent. They typically occur during transient operation and only a number of times per da or per week. Typically, such valves have been utilized as hig and low pressure drain and preheating valves, reheate application, reheater and superheater drain applications, stea turbine, stop and throttle valve drains, and vent application Throttling valves have always been subject to rapi deterioration due to erosion, cavitation damage and wire drawing in vital parts. Cavitation is the sudden creation an collapse of vapor pockets within a rapidly moving liquid. On type of throttling valve which minimizes such deterioratio employes a stellite disk and cylindrical seat coated with a erosion resistant material. Fluid flowing through the annulu between the disc and seat accelerates smoothly until it reache the blunt end of the disk. At this point, the flow are increases at the center of the flow path and the resultan pressure drop at the core of the flow path causes vaporizatio to occur in the cylindrical seat within a layer of continuously flowing unvaporized fluid along the wall of the seat.

A frequent problem encountered with such throttling valves is that the pressure drop caused within the valve causes vaporization and cavitation of the liquid medium as it passes through the outlet of the valve. Cavitation frequently occurs at locations along the surfaces of the throttling valve and deteriorates those surfaces. Because of the design of the disk and seat, a valve surface exposed to cavitation occurring at the blunt end of the disk must be coated with a wear resistant substance. The cost of coating the surfaces with a wear resistant material can be expensive.

It would be desirable to provide a throttling valve which can direct fluid away from the interior surfaces of the valve housing and members so as to minimize the damage caused by cavitation.

It would further be desirable to provide a throttling valve with a contoured plug defined by a special exponential equation which can direct the flow of material away from the interior walls of valve surfaces.

It is therefore an object of the present invention to provide a throttling valve specifically designed for severe service which restricts the location of vaporization and subsequent cavitation of a liquid medium away from valve surfaces. Another object of the present invention is to provide a throttling valve which accelerates the flow of a liquid medium through a passageway having a small cross-sectional area onto one having a larger cross-sectional area, so that any vaporization and cavitation occurs away from valve surfaces at a defined location removed from the valve surfaces.

A further object of the present invention is to provide a throttling valve which requires fewer valve surfaces to be treated with a wear resistant coatings, thereby reducing the cost of valve manufacture.

It is another object of the present invention to provide a multi-purpose valve which can handle gases, liquids, mixtures of water and steam or a slurry of liquid and abrasive material without eroding and damaging the seat and plug.

It is still another object of the present- invention ^" t provide a throttling valve which can accommodate cavitating an flashing liquids, liquids containing suspended solids, and tw phase flow.

Summary of the Invention In accordance with the present invention, a throttling valve which prevents the deterioration of valve surfaces is disclosed. The valve comprises a casing having an inlet conduit for introducing a gas or liquid medium into the valve, an outlet conduit for expelling a gas or liquid out of the casing, and a valve opening for supporting a valve member. An annular sealing member is situated within the housing between the inlet and outlet ports. The valve further includes a retractable valve member εlidingly housed within the valve for opening and closing the fluid flow between the inlet and outlet conduits, the valve member having a contoured nose defined by a complex exponential equation which slidingly mates with said sealing means, said nose contour directing the output flow toward the center of said outlet conduit. The valve of the present invention has two configurations, a straight line and an angular configuration. The straight line configuration incorporates a hard coated protection plate in the outlet section which can be removed. Brief Description of the Drawings The foregoing summary, as well as the following detaile description will be better understood when read in conjunctio with the drawings appended hereto. For the purpose o illustrating the invention, there is shown in the drawings a embodiment which is presently preferred, it being understood however, that this invention is not limited to the precis arrangement and instrumentalities shown.

Figure 1 is a time lapse section view of the throttlin valve of the preferred embodiment in both the open and close position.

Figured 2 and 2A are graphs of the profile of the nos section of the valve plug of the preferred embodiment.

Figure 3 illustrates the exponential formula for the plu of the preferred embodiment.

Figure 4 is a section view of a second embodiment of th inventio .

Description of the Preferred Embodiment The present invention is disclosed and described with reference to the enclosed Figures wherein the same numbers are used where applicable. Referring to Figure 1, a cross-section elevated view of a throttling valve 10 in accordance with the present invention is shown in both the open and closed positions. The throttling valve 10 of the present invention has a body 12 which is constructed from forged or cast heat resistant carbon steel. The valve configuration is of th angle shape design and can be manufactured according to th needs of a specific industry. Body 12 has an inlet conduit 13 and a prependicularly disposed outlet conduit 15 fo introducing a liquid medium into and out of the valve. Th valve body 12 further includes a bonnet 14 which is agains the pressure seal members by a locking nut 17. The locking nu is retained by a bolt 17a. The bonnet 14 is constructed fro heat resistant low alloyed carbon steel and has a hardene guiding ring 11 at the lower end which provides for vibratio free guidance of the plug. The axial portion of the bonnet 14 contains a bore 16 which retains a valve stem 18. The spac between the upper part of bore 16 and stem 18 is packed with a packing 20 which is compressed by a hardened gland 22 which iε moved by the threaded packing nut 21. A guide bushing 23 supports the valve stem. The bonnet is held in place by th segment ring 27 and the εupport ring 25.

Bonnet 14 includeε a cylindrical cavity 24 into which th body of plug 26 extends when raised. The inlet conduit 1 extends from a side wall of the body 12 and is connected to source of liquid medium or slurry which enters into the valve.

Various types of substances may be channeled through the valv including mixtures of water and steam or slurries of liquid an abrasive materials.

The outlet conduit 15 iε provided at a lower end of th valve housing through which vaporized liquids are discharged

Outlet conduit 15 is shaped as a conically expanding section

Conically expanding outlet conduit 15 is protected agains secondary cavitation effects and abrasion by a stellit hardfacing.

The valve housing includes an annular seal 32 which i situated between the inlet and outlet conduits. The sea compriεeε an inner annular seat 32 inserted within an oute annular seat 34. Annular seats 32, 34 function as a seal whe plug 26 is in a closed position and as a passageway throug which a liquid medium is constantly accelerated in a downstrea direction when the plug is retracted in an open position. Th outer annular seat 34 is welded within the body 12 at location adjacent to the outlet conduit. Inner annular seat 3 has an inner surface 36 which extends outwardly in an upstre direction from one end and a second inner surface 38 extending outwardly in a downstream direction.

Because the inner annular seat 32 is removably displaced within the outer annular seat 34, a gap 40 is formed between the two respective seats. Gap 40 allows for the thermal expansion of the inner annular seat 32 or distortion of body 12 when an extremely hot liquid medium or gas (500-1000°F) is passed through the valve 10 and over inner annular seat 32. Further, when outer annular seat 34 is welded within the valve body 12, it experiences thermal expansion caused by the extremely high temperatures. Only the inner surfaces 36, 38 are coated with a highly wear resistant substance such as tungsten carbide, chromium carbide or stellite. Durin fabrication, the two seat parts are welded together, machine and then inserted and welded into the body 12.

The valve plug 26 of the preferred embodiment is no described. Valve plug 26 directs the flow of a liquid mediu to a specific location downstream of the inner annular seat 32. In the present embodiment, valve plug 26 comprises a generall cylindrical body connected at an upper end to the valve stem 1 with a nose section 42 at its lower end. The valve plug slides up into the bonnet cavity by the valve stem. Nose section 42 comprises precisely contoured arcuate walls having a decreasin angle of curvature relative to the central axis of the body 12. The contour of the valve nose is defined by the graph shown i Figure 2 and the following equation which is illustrated in Figure 3.

Y = _A + (V - _A) x ,„ (WU/V-A) U( U/V-A) ^(u " ^x) where:

A = D/2, where D is the diameter of the plug at its tip

V = S x C ; U = S x Cj where Cl and C2 are constantε such that Cl iε a value betwee 0.1 and 5.0, and C2 iε a value between 0.5 and 5.0; and where S = the diεtance between the central plug axis and th inner εeat at its point of minimum diameter

W = C3, where C3 is a value between 0.1 and 2.0

X = stroke, where stroke is equal to the nominal size of th valve.

The arcuate walls of the plug 26 direct the flow of liqui medium away from the plug surface in a downstream direction thereby preventing its deterioration. Plug 26 may be made of ceramic material, and the contour should be coated with a ver thin and smooth layer of highly wear resistant Tungsten o

Chromium-Carbide 41. The seat flow path is hard-faced with material such as Stellite 6 or Haynes 25. The resulting liqui flow velocity vector is directed away from the plug contour

Plug 26 provides linear control characteristics with a ver small dead band 'in the beginning. The linear characteristi results in reduced seat sizes and therefore lower gap leakag rates. If the application requires an exponentia characteristic, it can be obtained with a cam in the positione or electronically.

The throttling valve 10 further includes an outlet condui

15 which expands conically outward and has a greater cross sectional area than the inner annular seat 32. This are provides a location where vaporization and subsequen cavitation can occur. The outlet conduit 15 has primary walls 43 which extend outwardly from the inner annular seat 32 in direction towards the outlet conduit 15 and connected to secondary walls 44 which extend parallel to the central axis of the valve housing. The walls of outlet conduit 15 are coated with a highly wear resistant subεtance similar to that of the first inner surface 32. Because of the difference in cross- sectional areas between the inner annular seat 32 (and surfaces 36, 38) and the outlet conduit 15, a liquid medium travelin over the inner annular seat 32 and into the cavity 1 experiences a large and sudden pressure drop coupled with subsequent decrease in velocity. This causes a liquid mediu at or near its saturation point to vaporize and cavitate. Thi phenomenon is further aided by the fact that the liquid mediu is accelerated over the inner annular εeat 32, aε deεcribe above. As a result, cavitation occurs at a specific locatio within the valve housing 12 downstream of the plug 26, not i the seat section which is specially treated to preven deterioration 43, 44.

Referring to Figure , an alternative Y-shaped inlin embodiment of the present invention iε disclosed. In thi embodiment, the inlet and outlet ports are substantiall parallel and the plug and seat asεembly extend tranεeversel to the inlet and outlet conduits. The body 12' is conεtructe of die forged or cast heat resistant low alloyed carbon εteel The bonnet aεεembly 14' iε identical to that of the firs embodiment. This embodiment includes a hard coated eroεio protection plate 58 in the outlet section- The plate i retained by rings and iε locked via a bolt 17a.

Operation The operation of the present invention iε now describe with reference to the attached Figures. The throttling valv of the present invention acts as a control valve for sever services utilizing gas, liquids, mixtures of water and stea and slurries of liquids and abrasive materials under hig pressure and temperature. The throttling valve is designed t protect valve surfaces from deterioration caused by erosion a cavitation.

A liquid medium emerging from a source enters t throttling valve 10 through the source input and conduit po 13. In a fully closed position, the nose portion of the pl 26 is engaged with the inner annular εeat 32 forming a se which prevents any liquid from passing through the valve 10.

A conventional activator device forces longitudinal upwa movement of the valve stem 18 towards an open position, there disengaging the plug 26 from the inner annular seat 32 a allowing liquid to flow through the valve 10. The plug reced into the cavity of bonnet 14.

Liquid flowing through the input port 13 iε direct downwardly over the inner annular seat 32 by the nose of t plug, the contour of the which iε defined by the followin exponential equation:

where:

A = D/2, where D iε the diameter of the plug at its tip

V = S x C_λ ; U = S x C₂ where Cl and C2 are conεtantε εuch that Cl iε a value betwee 0.1 and 5.0, and C2 is a value between 0.5 and 5.0; and where S = the distance between the central plug axis and th inner εeat at itε point of minimum diameter

V? = C3, where C3 is a value between 0.1 and 2.0

X = εtroke, where εtroke iε equal to the nominal εize of th valve.

Aε the liquid flowε over the first inner surface 36 o inner annular seat 32, it is continuously accelerated becaus the cross-sectional area at inner surface 36 continuousl decreaseε. The velocity of the liquid medium iε greatest whe it reaches the beginning of the second inner surface 38 of th inner annular seat 32. The cross-sectional area over th second inner surface 38 suddenly increases as it leads t outlet conduit 15. Because of the sudden change in cross sectional areas between the first and second inner surfaces 36, 38, an abrupt pressure drop occurs, causing vaporization an subsequent cavitation of the liquid medium at or near it saturation point. The contoured shape of the nose section 4 direct the liquid flow and resultant cavitation into the cavit 46 downward and away from the surface of the nose 42. The bubbles formed as a reεult of the cavitation implod within the cavity 46 whoεe wallε are coated and protects the from being deteriorated. The liquid and gas mixture iε the diεcharged through the output port.

In the present embodiment flanges 54 and 56 may b provided at the inlet conduit 13 and the outlet conduit 15 a seen in Fig. 1, and help connect the throttling valve However, depending on the syεte in which the valve will b utilized, it should be understood that any suitable mountin means can be employed.

The plug and εeat assembly operate in a similar manner i the alternative embodiment. However, the abraεion resistan attachment plate 58 protects the valve body from the cavitatin liquid.

It will be recognized by those skilled in the art tha changes may be made to the above-described embodiment of th invention without departing from the broad inventive concept thereof. It is understood, therefore, that this invention i not limited to the particular embodiment disclosed, but it i intended to cover all modifications which are within the sco and spirit of the invention as defined by the appended claims.

Claims

What is claimed iε:

1. A throttling valve which prevents the deterioration of valve surfaceε comprising: a casing having an inlet conduit for introducing a liquid medium into said valve, a conically expanding outlet conduit for expelling liquid out of said casing, and a valve port for supporting a retractable valve member; annular sealing means situated within said housing between said inlet and outlet ports; a retractable valve plug for opening and closing flow between the inlet and outlet conduitε, εaid valve having a contoured nose which slidingly mateε with εaid εealing means, εaid noεe being contoured to direct the flow of liquid toward the center of said outlet conduit, whereby vaporization and cavitation of εaid liquid occurs away from the walls of said outlet conduit.

2. A throttling valve according to claim 1 wherein said sealing means comprises an outer annular seat and an inner annular εeat inserted within εaid outer annular εeat.

3. A throttling valve according to claim 2 wherein said outer annular seat is welded to εaid housing.

4. A throttling valve according to claim 2 wherein the contour of εaid nose iε defined by the exponential equation;

where:

A = D/2, where D is the diameter of the plug at its tip V = S x C₁; U = S x C₂ where Cl and C2 are constantε εuch that Cl iε a value betwee 0.1 and 5.0, and C2 iε a value between 0.5 and 5.0; and where S = the distance between the central plug axis and th inner seat at its point of minimum diameter

W = C3, where C3 iε a value between 0.1 and 2.0

X = εtroke,- where εtroke is equal to the nominal εize of th valve.

5. A throttling valve according to claim 1 wherein εai valve plug iε coated with a highly wear reεiεtant substance.

6. The throttling valve of claim 5 wherein said high wear reεistant substance iε tungsten or chromium carbide.

7. A throttling valve which prevents the deterioration valve surfaces compriεing: a caεing having a generally cylindrical inlet condu for introducing a liquid medium into said valve; a conical expanding outlet conduit for expelling liquid out of εa casing and a valve port for receiving and retaining retractable valve member; annular sealing means attached to said casing betwe εaid inlet and outlet ports; a retractable valve member extending through sa valve port, said retractable valve member having a contour nose section which εlidingly mates with εaid annular εeali means, said nose being contoured to direct flow toward t center of εaid outlet port according to the equation;

Y = A + (V - A) x ,„ (WU/V-A) U(WU/V-A) (U - X) where :

A = D/2, where D iε the diameter of the plug at its tip

V = S x C_{1 l}' U = S x C₂ where Cl and C2 are constants such that Cl iε a value betwee 0.1 and 5.0, and C2 iε a value between 0.5 and 5.0; and where S = the diεtance between the central plug axiε and th inner εeat at itε point of minimum diameter

W = C3, where C3 iε a value between 0.1 and 2.0

X = εtroke, where εtroke iε equal to the nominal εize of th valve. whereby vaporization and cavitation of the liquid occurε awa from the contoured noεe εection and the conically expandin wallε of εaid outlet conduit.

8. A throttling valve which preventε the deterioration o valve εurfaces comprising: a casing having an inlet conduit for introducing liquid medium into said valve and an outlet conduit extendin substantially perpendicular to said inlet conduit for expellin said liquified medium, said outlet conduit having conicall expanding interior side wallε; annular εealing means affixed to said casing betwee said inlet conduit and εaid outlet conduit for forming a sea between εaid inlet and outlet conduits; a bonnet attached to said casing, said bonnet having channel for retaining a retractable valve plug; a retractable valve plug retained within said bonne and having a contoured noεe εection which εlidingly mates wit εaid εealing eanε to open and εhut off the flow of εaid liqui medium between εaid inlet and outlet conduitε, εaid contoure noεe εection directing the outflow of fluid toward the cente of εaid conically expanding outlet conduit whereby vaporizatio and cavitation of εaid liquid occurs away from the walls o said conically expanding outlet conduit.

9. The throttling valve of claim 8 wherein said contoure noεe εection iε defined by the equation:

Y = + (V - A) x ,_. (WU ^V-A)

U(WU/V-A) ^(u " ^x) where:

A = D/2, where D iε the diameter of the plug at itε tip

V = S x C_λ ; U = S x C₂ where Cl and C2 are conεtantε εuch that Cl iε a value betwe 0.1 and 5.0, and C2 iε a value between 0.5 and 5.0; and where S = the distance between the central plug axiε and t inner seat at itε point of minimum diameter

W = C3, where C3 iε a value between 0.1 and 2.0

X = εtroke, where εtroke is equal to the nominal size of t valve.

10. A throttling valve which prevents the deteriorati of valve surfaces comprising: a casing having an inlet conduit for introduci liquid medium into said valve and an outlet conduit extendi substantially parallel to said inlet conduit for expelling sa liquified medium, said outlet conduit having conical expanding interior side walls; annular εealing means affixed to εaid caεing betwe said inlet conduit and εaid outlet conduit for forming a se between εaid inlet and outlet conduits; a bonnet attached to εaid caεing, εaid bonnet extending εubεtantially tranεverεe to εaid inlet and outlet conduitε, εaid bonnet having a channel for retaining a retractable valve plug; a retractable valve plug retained within εaid bonnet and having a contoured noεe εection which εlidingly mates with said sealing means to open and shut off the flow of said liquid medium between said inlet and outlet conduits, εaid contoured nose section directing the flow of fluid toward the center of said conically expanding outlet conduit whereby vaporization and cavitation of said liquid occurs away from the walls of said conically expanding outlet conduit; and a removable eroεion protection plate located in εaid outlet εection oppoεite εaid plug and εaid annular εealing meanε.

11. The throttling valve of claim 10 wherein said contoured nose section is defined by the equation:

where:

A = D/2, where D is the diameter of the plug at its tip

V = S x C_]_; U = S x C₂ where Cl and C2 are conεtantε such that Cl is a value between 0.1 and 5.0, and C2 is a value between 0.5 and 5.0; and where S = the distance between the central plug axis and the inner seat at its point of minimum diameter

W = C3, where C3 is a value between 0.1 and 2.0

X = εtroke, where stroke iε equal to the nominal size of the valve.