US1996780A - Variable pressure multistage packing - Google Patents

Description

April 3.5 l-i. T. WHEELER 1,996,780

VARIABLE PRESSURE MULTISTAGBPACKING led May 28, 19311 z Sheets-Sheet 1 mums/Ton April 1935- H. 1'. WHEELER r 1,996,780

VARIABLEPRESSURE MULTIsTAGE PACKING Filed may 28, 19:51 sheets-shade Patented Apr. 9, 1935 i TED STAT-ES PATENT OFFICE VARIABLE PRESSURE MULTISTAGE PACKING Harley '1. Wheeler, Dallas, Tex. Application May 28, 1931, Serial No. 540,565

' 6 Claims. (c1. 2se-.-27)

This invention relates to the holding of variable the shaft 2 extends and pressure exists in the high pressures by a multistage packing in a clearance between the shaft 2 and the body I. stufling-box, and its chief advantage lies in a A series of cups, forming compartments between capability of regulating the seepage flow due to their confines, the face of each being pressure pressure so that the saturation of the packing tight one with the other are held by the bolts 5 by the pressure, will be at the lowest possible 8 concentric with the shaft and pressure tight alu against the body I by means of the gasket 9.

Another advantage is that the greatest ranges Within the confines of each compartment as of variable pressure may be held at the greatest formed, are placed packing rings, as will now 10 possible packing efiiciency. be described in detail. 10

One other advantage is that the pressure com The spacing ring 3 is adjacent to the gasket 9 trolling device may be changed to govern difierand forms the inner seat of the cone-shaped packent ranges of pressures without disturbing the ing rings ID. The cup 4 has a cone-shaped endarrangement of the packing. wall against which the packing rings I0 may rest Still another advantage is that the internal while under pressure. The cup 5 has acone- 15 pressures within the packing structure are always shaped end-wall against which the packing rings in proportion to the ideal uniform pressure norll may rest while under pressure. The cup 6 mally applied. has a cone-shaped end- -wall against which the Still another and important advantage is that packing rings l2 may rest while under pressure.

' the multistage design is arranged to regulate the The packing gland lhas an inner cone-shaped seat 20 drop of pressure within the packing structure against which the packing rings I3 may rest while during the variation of impressed pressure,-at the under pressure. The spacing ring 3, the cups 4. same time regulating the flow of seepage due to 5, 6 and the packing gland '1 each have a clearthe pressure, so that the friction of contact will ance around the shaft to prevent contact. In the With these objects and advantages in view, I4 for seepage to flow from the pack rings in' other desirable features of construction will; be the compartment between the cup 4 and the spacv disclosed during the description, accompanied by ing ring 3 and into the adjacent compartment. the drawings, wherein: The seepage which would collect in the packing Figure 1 isv a cross-section of the multistage confined between the end-walls of the cups 4 and 30 packing built according to this invention, and of 5 is released thru the passages I5, and into the the pressure control system. packing rings 12, in'turn ls successively vented Figure 2 is an end view of the multistage packthru the passages l6, and finally fiows to the ating compartments on line 2-2 of Figure l. mosphere thru the passages made in the face of Figure 3 is an upper half view of a compartthe gland I. It should be apparent that the cone-' 35 ment along the line 3-3 of Figure 1. shaped end walls of the spacing ring 3 the cups Figure 4 is a lower half view of a compart- 4, 5, 6 and the packing gland 1, form compartment along the line 4-4 of Figure 1. ments of a definite space in which the packing Figure 5 is an internal pressure chart of the rings are confined, and that there is no adjust- 40 effect of the increase of pressure on a single set ment after-the assembly is placed against the 40 and on a true multistage packing, with friction body I of the machine. ,1 curves. I The internal pressure control system is oper- Figure 6.15 an internal pressure chart of the ated by the impressed pressure which rises and decrease of pressure on a single set and on a true falls in the clearance between the shaft 2 and multistage packing, with friction curves. the body I. A passage 22 leading away from this 45 Figure '7 is an internal pressure chart of the vaclearance and into a pipe 2| is extended into a riable pressure multistage packing built accord-- reservoir 23, the latter made pressure tight by ing to this invention, under increase of pressure, a cover 24. An orifice 25 is fixed pressure tight and with friction curves. into the reservoir 23 and discharges pressure into Figure 8 is an internal pressure chart of the a pipe 3|, attached to the orifice25 by a nut 28. 50 variable pressure multistage packing built ac- The pipe 3| is attached at its other end to a fitcording to this invention, under decrease of presting 32 by a nut 33, the fitting 32 being screwed sure, and with friction curves. into a socket made in the cup 4. The socket is Referring now especially to Figure 1, the body extended into a passage 34 which enters into the be created uniformly over the area, of contact. end-wall of the cup 4 isshown a series of outlets 25 v His an extension of the machine frame thru which seepage hole I4, and then enters a passage I8,

the latter carrying pressure into the clearance between the end-wall of the cup 4 and the shaft 2.

Another orifice 26 is fixed pressure tight into the reservoir 23 and discharges pressure into a pipe 30, the latter attached to the orifice 26 by a nut 28. The pipe 30 is attached at its other end to a fitting 32 by a nut 33, the fitting 32 being screwed into a socket made in the cup 5. The

socket is extended into a passage 35 which enters into the seepage hole l5 and then is extended into passage l9 to carry pressure into the clearance between the end-wall of the cup 5 and the shaft 2.

Still another orifice 21 is fixed pressure tight into the reservoir 23 and discharges pressure into a pipe 29 attached to the orifice 21 by a nut 28. The pipe 29 is attached at its other end to a fitting 32 by a nut 33, the fitting 32 being screwed into a socket made in the cup 6. The socket is extended into a passage 36 which enters into the seepage hole 16, and is extended into a passage 20 to carry pressure into the clearance between the end-wall of the cup 6 and the shaft 2.

Referring now to, Figure 2, an end view of the packing in the assembly of Figure l. The packing gland I is held to the machine frame by the bolts 8, 8 and the seepage passages l1, I! are vents from the outer packing compartment. An

end view of the outer cup 6 is shown in partial cross-section and along the line '22 of Figure 1. The seepage holes l6, l6 vent the pressure from the adjacent inner packing compartment. Around the shaft 2 is shown the fit of the packing rings I2.

In Figure 3 is indicated an upper half view of the cup 5 along the line 3-3 of Figure 1 with a partial cross-section thru the internal pressure control passages. The seepage passages l5 extend into the adjacent compartment. The sock-,

et 32a is extended by the passage 35 into a seepage passage l5 and is further extended by the passage l9 into the clearance between the endwall of the cup 5 and the shaft, 2. The fit of the packing rings II to the shaft 2 is shown.

In Figure 4 isshown a lower half view of the cup 4, having seepage passages l4 extending into the adjacent compartment. The fit of the packing rings III with the shaft 2 is shown.

Referringnow to my application for Letters Patent, Serial Number 537,658, dated May 15th, 1931, The elasticity of porous elastic structures, in which twenty-four laws of friction are described and related to the density and porosity of packing rings. A fibrous packing, such as is intended for use in this invention is a porous structure, becoming elastic when exposed to pressure. A structure which is porous is defined as an assembly of packing rings having pores, interstices and joints thru which pressure may pass. The chief advantage of a porous structure lies in its capability of gradually reducing an impressed pressure to a lower level, thereby distributing the drop of pressure along the area of contact between the packing and the shaft, thus in turn distributing the friction necessary to seal the pressure. It is proven by the first and second laws before mentioned, that the thrust of the packing structure against the shaft is equal to the drop of pressure at any point, and that the amount of friction on any increment of contact surface is that proportion of the total friction which is related to the proportion of pressure drop within that increment. Thus for a single set of packing The coefficient of friction is taken to be the ratio of the normal applied pressure to the force necessary to move the shaft. Considering a single set of packing with most of the measured friction occurring within a limited area, an excess of work is done which causes heat and rapid wear at that region. The purpose of this invention is to reduce not only the amount of friction created during the rise of pressure but to eliminate most of the friction which results after the pressure has once been impressed on the packing structure. The purpose is also to reduce the friction and at the same time insure the uniform distribution over the entire area, of that friction which does occur.

Referring now to Figure 5, an internal pressure chart, the ordinates being to a scale and the maximum value being the full impressed pressure P on the packing assembly of Figure 1. The abscissa to a scale are lengths of the actual surface of packing contact as of Figure l. The pressure readings are taken at the instant of maximum pressure. The divisional 'points on the chart 3, l8, I9, 20 and 1 represent the confines of the compartments formed by the corresponding cups and retainers 3, 4, 5, 6 andl of Figure l. The dotted line U is the ideal pressure drop thruout the length of the packing which will qualify any packing structure for the twentyfourth law of friction, that friction is independentof the area of contact, when the normal applied pressure is equal at all points of the contact.

First, the packing as shown in .Figure 1 is considered to be a single set, that is, the division walls are assumed to -be removed from Figure 1, the packing rings being adjacent to each other. The packing is therefore subjected to a seepage flow as the impressed pressure P rises to a maximum, and as shown at the highest pressure point by the line S of Figure 5, the line S being the actual pressure at any point along the packing surface of contact. It may be observed that the greatest rate of pressure drop is close to the packing gland 1, at which location most of the friction occurs. To demonstrate the distribution of the friction per increment of length according to the pressure line S, the amounts of friction are plotted on the abscissa'of the internal-pressure chart, the total friction being assumed to be F, a concrete quantity. The rate of pressure drop is taken for increments of length from the curve S and the proportional value of the total friction F solved for, resulting in the friction curve s, starting at the point I9, as the internal pressure is not reduced up to this point, and ending at fs. The area of contact between the points 20 and I is therefore subjected to most of the strain, resulting in high temperature locally and rapid wear, and giving a high coefficient of friction due to the low degree of porosity of the structure, being refined by the accumulated thrust. This is the condition of all single sets'of packing when exposed toan impression of pressure.

As has been proven in my method for determining the elasticity of porous elastic structures, the decrease of pressurecauses friction re in this specification is assumed to be greater than unity, that is,'the structure is in reflux and retains a part of the impressed pressure, coming under the fourth law of friction, that the friction created during the reduction of impressed tributed between three pressure varies proportionally to the reduction of the mean drop of pressure.

Referring now to Figure 6, an internal pressure chart of the packing discussed by Figure 5, the ordinates being in internal pressure as measured and the abscissa being the actual lengths of the packing surface, the points 3, l8, I9, 20 and I corresponding to the same points of Figure 5. The readings are taken after the impressed pressure P of Figure 5 has been reduced to zero. Still considering the packing of Figure 1 to be a single set, the internal pressure curve S indicates that sufficient pressure has been retained by the structure to thoroughly saturate the assembly. The maximum pressure obtaining is P, less than P and diminishes at both inside and outside extremities of the structure at points 3 and l to zero. That is, the quickness of the reduction of pressure has allowed time enough for the pressure P to be reduced to P as a maximum, leaving a high mean effective pressure within structure. When solved for the location of the friction from the total measured friction F, a concrete quantity, the friction curve s' is derived from the internal pressure line S adjacent to the packing gland, and the friction curve s' is derived from the internal pressure line S" from the packing exposed to the impressed pressure. Thus, with a single set of packing, on reduction of pressure, there are two regions in which friction occurs, the total being greater than that existing under the increase of pressure. This isthe condition of all single sets of packing exposed to variable pressure and the foregoing explanation is the reason engineers invariably place hard rings of packing at the inside and outside of a single assembly, placing softer rings in the center.

The condition inherent with the drop of pressure is that there must be seepage flowing thru the packing structure, however minute the necessary amount may be, for when the internal pressure becomes equalized in a packing structure, the effect is the same as replacing the packing gland I of Figure 1 with a tight gasket, eliminating the ability of the packing to react against the pressure. An examination of the first and second laws of friction indicates that when some mechanical means is provided to induce a drop of pressure at various intervals along the area of contact, that the friction will be distributed over a greater area than is possible with a sin-' gle set of packing. Referring again to Figure 1, the end-walls of the'cups 4, 5 and B and the seat in the gland 1 provide the partitions necessary to realize a pressure drop at four points, instead of the single point of a single set, which is the packing gland face. (As yet no consideration is being given to the seepagegpassages made thru the aforesaid end-walls.)

The use of partitioning walls between packing sections may be termed true multistaging, each compartment being separate and the only communicating passageway being the clearance between the end-walls of the compartment and the shaft. Reference'is again made to Figure 5, the theoretical effect according to the first and second laws of friction of true multistaging being shown by the internal pressure line M, only the,

friction arising from the drop of pressure being considered. The friction is now found to be discompartments, appearing in sections |8l9, l9-20 and 20-1, the value ,fm being about the same as is of the single set. The effect of a multistage on an increase of pressure is but little different from that of a single set as the interposition of the compartments, interferes with the seepage flow, reducing the number of paths, and after the pressure is retained in the compartments, it is practically no different than a single set. ,The friction curves -1n, m, and m are those due to the true multistaging.

Contrasting the foregoing theory, is the practical fact that a true multistage does not operate according to the first and second laws of friction.

It has been found that immediately after placing the true multistage in operation, a great amount of heat is created by the inside compartment of packing, accompanied with excessive wear. After a time the second compartment will begin to heat, and so on until the last compartment is reached, after which the assembly will hold little pressure. Referringagain to Figure 5, the line TM gives the actual internal pressure curve due to the first compartment sealing off too much of the impressed pressure, the corresponding friction curve tm being largely due to friction of contact from the increase of the volume of 00- cupancy. There is little seepage flow action when a true multistage is exposed to increase of pressure.

During the reduction of pressure a true multistage traps the impressed pressure, and at the best possible condition of uniform saturation, creates more friction than a single set of packing. Referring now to Figure 6, the curve M permits little drop of pressure in the area 19-20,

as does the curve M" in area iii-l9, the pressure retained in both areas being practically the same as P, the highest value. The friction curves m, m and m", m" show less distribution than that of the single set.

Referring again to Figure l, the interposition of the compartment end-walls interferes with the seepage flow that existed in the packing as a single set, the direction and location of the flow being constricted to the clearance between the end-walls and the shaft. The amount of the flow is also diminished by the lowering of the porosity due to the reaction of the packing against the pressure. It should be apparent thatdividing the packing into compartments, thus decreasing the number of paths of the seepage flow as well as the amount of flow, subjects the packing successively in each compartment to the maximum effect of saturation by pressure, bringing about an increase of volume, forcing the rings against the shaft to cause excessive wear until the volume of the packing is thereby reduced to correspond to the saturation condition obtaining. This series of conditions is expressed by the sixth, seventh, ninth and tenth laws of friction, which state that the volume of occupancy varies according to the rate and amount of the seepage flow, the friction created being in relation to the density of the structure as well as the degree of porosity as it is affected by the changes of volume. parent that to design a porous packing structure to conform to but part of the laws and relations obtaining, is to make an impracticable and troublesome device; sealing pressure by an excess of friction thru the medium of saturation is undesirable.

As the flow of seepage thru a porous elas ic packing reacts against and will seal off the impressed pressure, it should be apparent that whatever changes are made in design to distribute the It should be aD- structure is the fundamental reason why the I friction of contact, the seepage flow must also be considered as a part of the changes made and must not be restricted in a way to increase the friction. Referring again to'Figure 1, the series of seepage passages, l4, l5, I6 and I! provide ample means for the circulation of pressure within the packing structures, but the increase and decrease of pressure brings in further relations of saturation and the element of time, which in this invention must be accounted for to bring about the result approximating the uniform line of pressure drop U as is shown in Figure 5.

Referring now to Figures 7 and 8, internal pressure charts of the packing designed according to this invention, the ordinates being in pressure and the abscissa being actual lengths of the packing contact to a scale. The uniform drop of pressure line U is the ideal condition to be approximated. The desirable condition of a uniform distribution of friction over the area of contact is obtained by partitioning the packing into compartments and providing seepage passages to permit a flow on internal pressure. Since the uniform drop of pressure cannot be realized in a single set or by a true multistage by the seepage fiow alone, as has been proven, a mechanical device called the internal pressure control is added. Referring now to Figures 1 and 7 simultaneously, the internal pressures shown by the line U at points l8, l9 and 20 are Pa, Pb and Po. That is, if these pressures can be made to exist in the passages l8, l9 and 20 of Figure 1, the effect of saturation will be eliminated. It is considered that the pressure P is impressed in a very short period of time. The orifice 25 is made of such an area that when pressure P is at a maximum against the inner compartment packing, that pressure P will be reduced by constriction to value Pa and the latter pressure will obtain in the pipe 3| and the passages 34 and I8. Thus compartment 3-48 has to react against a net pressure of P minus Pa. The amount of packing in the compartment is not sufilcient to become highly saturated and the seepage may flow readily thru the structure and escape to the-lower level at point I 8.

In like manner the orifice 26 has an area that will constrict the pressure P to Pb at the point I 9, and the orifice 21 is still smaller in area and reduces the impressed pressure to Fe at point 20. Due to some'saturation in the packing compartments and a resulting seepage flow the actual pressures at the points I8, I 9 and 20 will be P1, P2 and P3, points on the internal pressure curve UF. The derived friction curves uf of each compartment are uniform and closely approximate the uniform line u derived from the line U.

It should be apparent that as the internal pressure control is operated by the impressed pressure. when the pressure P is reduced to zero gauge pressure, thatthe pressures in the control system will be reduced with a small time-lag. So in Figure 8. the cycle of reduction of pressure, readings taken when P is zero, the internal pressure line UF reflects at points 3, l8, I9, 20 and I only that small amount of pressure retained in the packing structure. The friction line uf is derived from the pressure line UF by the first and second laws, it being shown as having an average u.

It should be apparent that the mechanical internal-pressure control system is an exact means of controlling the saturation of a packing structure such as this multistage, and will operate the orifices to control the required construction of the pressure. It is also possible to seal a large range of pressure variation by the same packing by regulating the orifices accordingly. The friction values obtained by this design are the lowest possible for a complete cycle of all fibrous structures, due to the lack of saturation. The passages of the control system may be made very small so that the loss due to recompression of the liquids, gases or vapours is slight in comparison to the savings effected in friction.

Thruout this specification, a cone-shaped packing ring has been used as the example of a porous elastic structure. However, any fibrous packing ring or any combination ring which has pores, interstices and joints which reacts against pressure to seal that pressure will operate in this multistage, tho at a different efliciency than the cone-shape used.

This type of multistage is useful only for those conditions in which saturation of a packing structure is governed by the element of time of application and reduction of pressure. It should be apparent that the application is very useful for a variety of such purposes and that many variations can be made of the principles herein described, and such as are within the scope of the appended'claims, I do hereby claim:

1. A stufilng-box composed of a series of compartments having annular spaces therein and positioned around a rod subjected to variable pressure, said annular spaces separated by partitions integral with the walls of said compartments, said partitions having a clearance around said shaft, rod packing positioned in said annular spaces and in contact with said shaft, a series of passages connecting the clearances between said partitions and said shaft with the source of said variable pressure, an orifice in each said connecting passage of such an area as to constrict the impressed pressure to a lower value, to thereby establish a difference of pres: sure between said partitions to thereby regulate the friction created by the packing in each said compartment.

2. A stuffing-box composed of a series of compartments having annular spaces therein and positioned around a rod subjected to variable pressure, said annular spaces separated by partitions integral with the walls of said compartments, said partitions having a clearance around said shaft, rod packing positioned in said annular spaces and in contact with said shaft, aseries of passages connecting said clearances with the source of said variable pressure, an orifice in each said connecting passage of such an area as to constrict the impressed pressure to a lower value to thereby establish a difference of pressure between said partitions to thereby regulate the friction created by the packing of each compartment, passages made in said partitions to permit the flow of seepage thru the packing confined in any of said compartments to regulate the intemal-pressure within said packing to thereby control the distribution of the friction thruout the area of contact of the packing within each said compartment.

3. A stufiing-box composed of a series of compartments positioned around arod subjected to esa-r80 variable pressure, said compartments having a conically shaped depression at one-end and a conically shaped contour at the other end forming partitions between each of said compartments, packing rings of substantially the compartmental shape confined therein, ,means. to graduate the pressure level between any two of .said partitions in proportion to the pressure impressed, thereby controlling the amount of friction created by the packing in each of said compartments. 7

4. A stufling-box composed of a series of compartments positioned around a rod subjected to variable pressure, said compartments being formed by partitions between the compartments having a conically shaped depression at one end and a conically shaped contour at the other end, each of said partitions having a clearance aroimd said shaft, packing rings of "substantial- 1y frusto-conical shape confined therein, means to graduate the pressure levels between said partitions in proportion to the pressure im- 7 5 pressed, eachot flldpackmgrmubeingporous to regulate the distribution of friction created throughout'th'e area of contact oieach of said packing compartments.

5. In combination with a multistage packing having a plurality of spaced sets of porous packings thereima fluid passage into each set, means connecting said passages with the pressure being packed, and means positioned in each of said passages to cause a pressure drop equal to the pressure absorbed by the preceding packings.

6. In a multiple stage packing having a plurality of superposed independent packing assemblies, a means to balance the pressure ineach assembly with the pressure being packed including a passage to each assembly from the source of pressure, each of said passages being constricted to cause a pressure drop equal to the pressure absorbed by the packings preceding that passage.

' HARLEY '1. WHEELER.

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