US3545492A - Multiple plate throttling orifice - Google Patents

Description

' 0 United States Patent 11113,545,492

[72] Inventor Charles H. Scheid, Jr. [56] References Cited Middletown, Ohio UNITED STATES PATENTS [21] l 3*12 1,078,834 11/1913 Cook 48/180 [221 e 3,111,091 1 H1963 Hopkinson 13s/44x [45] Patented Dec. 8,1970 FORE N P TEN S [73] Assignee Armco Steel Corporation [G A T Middletown, Ohio 520,083 4/1940 Great Britain 138/40 3 corporafion of Ohio Primary Examiner-Laverne D. Geiger Assistant Examiner-R. J. Sher Attorney-Melville, Strasser, Foster and Hoffman ABSTRACT: A throttling device for hydraulic systems which prevents the cavitation of metal conduits by liquids under dif- [54] MULTIPLE PLATE THROTTLING ORIFICE ferential pressure comprising a series of orifice plates spaced 7 claimss Drawing Figs at intervals along the axis of the conduits, each plate having [52] U.S. Cl. 138/42, n or r rifi s her in t lower the pressure of the liquid 138/44 passing therethrough, the axes of the orifices being displaced [5]] 1115.] 1/02 radially and circumferentially about the plate centers so as to [50] 138/42, 44; be in l m n i h he xe f he rifi es in adjacent modate water must allowfor MULTIPLE PLATE rrmorrunc onmce BACKGROUND OF THE INVENTION ferentialpressure.

2. Description ofthe lemma.

Hydraulic systems such as thosefound on presses and the like have generally heretrifo're utilized oil' as the hydraulic .medium, and throttle valves, such as globe-type throttle valves, have proved generally satisfactory. Due to the fact that -oil as the hydraulic fluid is relatively dangerous, many newer,

hydraulic systems have. adopted water rather than oil as the hydraulic fluid. However, the cavitation problem is much greater with water sincethe vapor pressure of oil is lower than that of water. Also, since hydraulic oils are more compressible than water and thus exhibit more deflection under thesame pressure, the design of conduits and other vessels to accoma greater dissipation of energy through the walls. I r

By cavitation is meant the gradual erosion of a surface caused by the collapse of vapor bubbles in a fluid. These bubble's form whenthe staticpressure in a fluid is lowered to the vapor pressure of the fluid. When the bubbles collapse the fluid slaps the surface, causing a'small part of the surface to be stressed beyond its yield point. This eventually results in fatigue and pitting of the surface. 7 v i Cavitation, of course, causes frequent shutdowns of hydraulic systems so that new valves may be installed. The shutdowns become very expensive in terms of man hours of maintenance because of the general inaccessibility of the valves.

Prior art devices have offered no solution to this problem. Indeed, the prior art'does not seem to even recognize the cavitation problem. For example, U.S. Pat, No. l,078,834,'in the'name of Cook, discloses afgaseous fuel mixer which cornprises a numberofagitating plates within a tubular housing.

The plates arefmounted on'ashank and may be rotated to properly mix the gas flowing therethrough. Each of the plates has a number of apertures, the number of apertures increasing from the first to last plate, with respect to the flow, while the size of the apertures decreases as the number of holes increasesfiCookdoes not'indic'ate that the rotating orifice plates are to serve any other purpose than to properly mix the gaseous fuel. l b b j Another exemplary prior art patent U.S. Pat. No. 2,125,245

. in the name of McCray,.which discloses an apparatus for dispersingthermoplastichydrocarbon materials in water. The

are positioned between the dispersing plates and are formed 7 with restricted passages through which the materials being dispersed are passed. McCray makes no mention of the cavitation problem. I

The aforementioned references are simply exemplary of prior art teachings which disclose multiple orifice plates. The references are not concerned with the problem of cavitation and its prevention, and themultiple orifice plates are primarily used to mix various materials passing therethrough.

SUMMARY or Tris INVENTION The present invention. provides a throttling device for hydraulic systems which prevents the cavitation of metal conduits by liquids under differential pressure. Broadly speaking,

therethrough, and the axes of the orifices-are displaced radiallyand circumferentially about the plate centers so as to be in FIG. 1.

misalignment with the axes of the orifices in adjacent plates. This prevents the jet leaving one orifice plate from entering directly an orificein an adjacentplate. The orifice, plates are positioned such that the upstream plate provides the greatest pressure drop thereaCt'OSS and each succeeding plate provides a gradually decreasing pressure drop, whereby the static pressure in the liquid under differential pressure is at all points greater than the vapor pressure of the liquid.

The spaced intervals between orifice plates will preferably be such as to allow the most length for dissipation where the pressure drop is greatest, so that the flow entering thenext orifice plate will be as undisturbed as possible. I

In practice, the throttling device of the present invention will prevent the cavitation of metal conduits by any liquid under differential pressure. However, since in practice it has been found that cavitation is much more serious when water is utilized as the hydraulic fluid, the present invention will be most applicable in this connection. I

In a preferred embodiment, the number of orifice plates was found to be five."The first four orifice plates were provided with sharp edge orifices and thelastorifice plate was a short tube orifice type.

BRIEF DESCRIPTION OETHE DRAWING FIG. 1 is a cross section taken through the center of a multiple plate throttling orifice according to the presentinvention.

FIG. 2 is an end elevation of the multiple plate throttling orifice of FIG. g

FIG. 3 is a cross-sectional view. taken along the line 3-3v of FIG].

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 5 is a cross-sectional view taken along the line 5-5 of FIG. 1.

FIG. 6 is a cross-sectional view taken along the line 6-6 of FIG. 7 is a cross-sectional view taken along the line 7-7 of FIG].

FIG. 8 is a cross-sectional view taken along the line 8-8 of DESCRIPTION OF THE PREFERRED EMBODIMENTS As was previously explained, the cavitation problem is much greater when water is used as a fluid in an hydraulic system than when oil is used as the fluid. This is so because the orifice of this invention. This throttling device was designed to replace an existing globe-type throttle valve and to throttle.

water, which was used as the hydraulic fluid, to slightly above atmospheric pressure.

For purposes of explanation, the multiple plate throttling device 10 of this invention is heldwithina housing 12 having a from 4,200 p.s.i.

bore 12a therein. The housing 12 may join two conduits in a hydraulic system. It is, of course, obvious that the throttling device 10 of this invention maybe used in any hydraulic system where it is desired to throttle the flow across a large pressure drop and where cavitation is a problem.

The housing 12 hasbeen designed ,such that both the upstream and downstream ends thereof have flanged connections which permitthem to be joined to other sections of com duit by bolts and the like through the bolt holes 12c.

As can be seen from FIG l,the multiple plate throttling orifice of this invention comprises a series of orifice plates 13 through 17 which are separated by the spacers 18 through 21.

.therethrough. The axesof the orifices in each of the plates 14 through 17 are displaced radially and circumferentially about the respective plate centers so as to be in misalignment with the axes of theorifices inadjacentplates. This preventsthe jet leaving one orifice plate, the upstreamplate, from entering directly an orifice in an adjacent downstream plate.

It will be observed that the orifice plates 13 through 17 are positioned such .that. the upstream plate 13 provides the greatest pressure dropthereacross and ,each succeeding plate provides a gradually deereasingpressure drop. In this manner the static pressureinthe quid under differential pressure is at all points greater than the vapor pressure of the liquid.

It is, of course, well =know n that for a single orifice plate the flow rate Q is equal to CA*?"2g (Ah), where C is the coefficient of discharge, which is a combination of a velocity coefficient C,,) and a contraction coefficient (C A is the total cross-sectional area of the orifice, g is the coefficient for gravity, and Ah is the difference in head upstream of the orifice and downstream at the vena contracta. The velocity head which is recovered is equal to the standard orifice-differential pressure (Ah in the above formula) minus the net head loss due to me- ,tering; Thus, the static pressure at the vena contracta is less than the static pressurefurther downstream and will in fact decrease towards a staticpressure reading of zero. In actual practice, the sta'tic pressure atthe vena contracta may not be lowerthanthe-vapor pressure of the liquid, because once this V happens abubble forms and cavitation occurs.

Since theabove formula is for a single orifice ,plate, and the present inventionutilizes a number of orifice plates in series, a certain desired flow rate was assumed. This flow rate and the elevated position of {the fluid system utilizing this throttling device, a hydraulic press, resulted in a certain inherent back head. The area of the orifices in the furthest downstream orifice plate was determined so that the static pressure at the vena contracta, taking into a'ccountthe inherent back head and the velocity head recovered, was above the vapor pressure of the liquid. The area of the orifices in the next orifice plate upstream was then determined in the same manner using the inherent back head plus the'rret head loss due to metering of the 'farthest downstream orifice. The total pressure 'drop across'the multiplate throttling orifice plates could then be calculated as the sumof the net headloss due to metering for each orificeplate. It was then necessary to make several iterations of the whole calculation until the total calculated pressure drop for the throttling device was equal to the available pressure drop supplied by thehydraulic system, at which time the initially assumed flow rate was proved;

As may be seen from FIG. 1 and FIGS. 4 through 8, all but the last orifice platefhav'e' sharp edge orifices while the last plate is of the short tube orifice type. Appropriate orifice coefficients. were used for each in the aforementioned calculations/However, it should be'emphasized that the type of orifice which is ultimately selected'is merely a matter of design so long as'the appropriate orifice coeff cients are utilized in the aforementioned calculations.

It should be pointed out that. the number of orifices in each orifice plate is not important, only their total area. Thus plates with multiplate holes were considered as having a single hole,

the area of which was equal to the sum of the area of the multiple holes. The reason for using multiple holes and their specific location was to prevent the jet leaving one orifice plate from entering directly a hole in the next plate.

Obviously, if the static pressure ofthe liquid at any point in the housing is too close to the vapor pressurethereof, some cavitation will occur. It then becomes necessary to increase the number of orifice plates.

The distance between the orifice plates 13 through 17,

established by the spacers 18 through 21; has not been found .10 be critical..However, it has been found preferable to allow ,themost length for dissipation where the pressure drop is -the greatest in order that the flow entering the next orifice plate will beas'undisturbed as possible.

.vals along the axes of said conduits each plate having one or more orifices therein to lower the pressure of the liquid passing therethrough, the axesof said orifices being displaced radially and circumferentially about the plate centers so as to be in misalignment with the axes of the orifices in adjaceirt plates and to prevent the jet leaving one orifice plate from entering directlyan orifice in anadjacent plate, the total area 'of said orifices in each succeeding orirce plate on the downstream side being successively larger so that the u'pstream plate provides the greatest pressure drop thereacross and each succeeding plate provides a gradually decreasing pressure drop, whereby the static piessure in said liquid under differential pressure is at all points greater than the vapor pressure of said liquid.

' and to ensure that the flow entering the next adjacent orifice plate will be as undisturbed as possible.

3. The throttling device according to claim 1, wherein the total area of the orifices in each'on'fice plate is determined so that the minimum static pressure between said orifice plates is above the vapor pressure of the fluid according to the formula Q Ca**2g (8h), where Q is the fidw rate, C is the coefficient of discharge and is a combination of a velocity coefficient and a contraction coefficient, A is the total cross-sectional area of the orifice, g. is the coefficient for gravity, and 8h is the difference in head upstream of the orifice plate and downstream UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,5 6,492 Dated December 8, 1970 Inventorfl!) CHARLES H. SCHEID, JR.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, Line 22, please amend "CA 2g 11)" to read CA V 2g (Ah) Column 3, Line 2 4, please amend "C to read --(C Column 4, Line 50 in claim 3, please amend "Ca 2g (811)" to read --CA 2g (Ah Column 4, Line 53, in claim 3, please cancel "811" and insert Ah SEALED 161971 (SEMI Am Mum mun. swam. an.

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