US1996779A - Multistage packing - Google Patents

Description

April 9, 1935. H. 1'. WHEELER MULTISTAGE PACKING 2 Sheets-Sheet 1 Filed April 23, 1931 lll www RMN April 9, 1935. H. T. WHEELER Sheet INVENTOR.

Patented Apr. 9, 1935 UNITED STATES PATENT OFFICE MULTISTAGE PACKING Harley T. Wheeler, Dallas, Tex.

Application April 23, 1931, Serial No. 532,222

Claims.

This invention relates to certain improvements in rod packing, more especially to that class used to hold high pressure gases and vapours on reciprocating rods, and its chief Aadvantage lies in 5 its capability of performing any necessary adjustment of the friction of contact with the cessation of operation.

Another advantage is the use of an extra amount of packing to effect a-tight joint, yet working the packing at a very low stress and thrust pressure per unit of contact area.

Still another and important advantage is the compartments in the stufling-box adjusted by external means which obtain nearly a uniform pressure drop along the packing contact and thus create a uniform distribution of friction, so that foreign materials retained by the separator have least chance of scorng'the rod, should they pass thru the packing.

With these-advantages in view, further objects and advantages of construction will be displayed as the description proceeds, accompanied by the drawings, wherein:

Figure 1 is a. cross-section of the complete muling to this invention.

Figure 2 is a cross-section. of the externally operated expanding ring, on line 2-2 of Figure 1. Figure 3 is 'a cross-section of the separating baies, within the separator, on line 3-3 of Figure 1, the scale reduced.

Figure 4 is an internal-pressure chart showing the drop of pressure when the packing sets are operated as one set.

Figure 5 is an internal-pressure chart showing the drop of pressure when two sets are in operaion.

Figure 6 is an internal-pressure chart showing Ehe drop oi pressure when three sets are in operaion.

Modern pipe line systems transporting natural gas and kindred vapours at high pressures have complex conditions which the packing herein described is particularly designed to handle. The uncertainty of the amount and of the nature of foreign matter occurring in thg gases handled form an example and justification of the packing built according to this invention. Salt water Vcoming over from wells, is dried out as it is heated by the compression temperature, the crystallized salt glazing the packing surfaces. The pressure cuts small lanes thru the deposit and escapes. Water will wash the lubricant from the surface of the rod, and it occurs as a sweat on the pipes or comes over from the wells.

tistage packing and the separator built accord- Fine gas san comes from the wells to deposit in the packing and scores the rod surface and cuts the packing. Coarse sand lodges in the packing and cuts grooves in the rod. Iron scale from the pipe surfaces lodges in the packing and scores 5 both packing and the rod. Both tar and paramn coming over from the wells deposit lin the packing, gum the working parts and hinder the reactions to pressure and the movements to compensate for misalignment of the rod. Finally, the 10 operation of gasoline plants in connection with pipe line systems frequently permits the escape of gasoline and the lean oils used for absorption purposes; these when caught in the packing cu the lubricant and cause high friction and scorl5 The foregoing foreign substances may accumulate in the packing singly or in various combinations, and are the actual hazard to continuous operation of a. compressor. This packing is built 20 to automatically separate the foreign substances, with arrangements made to enable the operator to discharge them. To prevent any damage to the packing in case of excesses that run thru the separator, the packing is built to contact with 25 the shaft at a very low thrust pressure per unit of area, thus spreading the friction over a large area and reducing the possibility of scoring.

Referring now to Figure 1, the packing comprises two main parts, rst, the inner assembly 30 being 'the separating device inside the compressor body l, and second, the outer assembly in a cage 2, being a multistage packing. As designed, the packing cage 2 contains paclnng with an eflicient means of adjusting it at all times to 35 maintain the low operating stresses and to secure a tight joint, so that the inner assembly will continually slow down the velocities of the streams of gas as they are compressed, thereby causing the foreign matter to drop downward and into- 40 the series of baiiles, from where it may be discharged. The packing nut 3 is threaded to nt a corresponding thread on the cage 2. The compressor rod l passes thru the entire assembly with clearances between all stationary parts.

Inside and at the bottom of the compressor body l is placed a cup 1, forming a tight joint against the body l by means of a gasket 6. The cup 1 also contains a pair of sectional metallic packing rings 8 and 9, which are held in contact with the 50 rod 4 by the garter springs 8s. Against the cup 6 is placed a cup l0, the joint between the two being ground and pressure tight. A spool I I forms the internal surface of a battle chamber and has a clearance adjacent to the rod 4. The baffle compartment thus formed is closed by the cover I4. The edges ofthe bailles I2 t tightly against the inner surface of the cup I but have a clearance adjacent to the spool II. The edges of the bailles I3 t tightly around the outer surface of the spool II, but have a clearance adjacent to the inner surface of the cup I0. A passage 28 admits pressure from the compressor cylinder to the baiiie chamber in the cup I0.

A cup I is placed in the body I and forms by a ground joint a pressure tight t against the cup I0, and contains a pair of sectionalmetallic packing rings 8 and 9, the latter being held in close contact with the rod 4 by the garter springs Bs. A passage 29 passes vinto the baille chamber of the cup Il), and is by-passed to the clearance-around the rod by a passage 30.

The main cage 2 is held pressure tight against the cup I5 by bolts which pass thru the holes 2h. shown in Figure 2, and into the body I. 'I'he packing is divided into three sets, the two inside sets nearest the body I, being alike in every particular. The female rings I8, I8 adapt the coneshaped packing rings I9a, I9b and align them with the rod 4 and to the walls of the cage 2. The male rings 20, 20 also adapt the cone shape rings I9a and I9b, and receive and transfer the thrust due to pressure drop to the expanding rings 22a and 22b. The rings 22a. and 22h are expanded by the wedge blocks 2| a and 2lb, as will otherwise be shown by another gure. The bolts 23a, 23b are threaded into the walls of the cage 2 and locked in place by the nuts 2311., 23u, the before mentioned bolts being the means to expand the rings 22a and 22h against the walls of the cage 2. The female ring 24 adapts the packing rings 25 to the rod 4 and to the outer stuilng-box section of the cage 2, the male ring 26 receiving the thrust of the rings 25 and transferring this force to the packing nut 3.

A passage I6 is for admitting lubricating oil which is delivered thru the pipe I1. The petcocks 21, 21, 21, are operated by the handles 21h, 21h, 21h, and are threaded into the passages 29, 3| and 32, the latter leading to points where grit and dirty oil will collect. The passages 38 and 35 are alike and extend thru the wall'of the cage 2 and thru the expanding rings 22a and 22b respectively, and the pipes 31 and 33 are alike and threaded into the before mentioned passages 38 and 35, the manner of which is shown in Figure 2.

Referring now to Figure 2, a cross-section-thru an expanding ring on the line 2-2 of Figure l. The cage 2 has several bolt holes 2h, thru which the bolts 39 are passed to attach the cage 2 to the compressor body I, the latter being shown in Figure 1. The rod 4 passes thru the entire assembly and has a clearance adjacent to the ring 22h. A wedge block 2Ib fits into a correspondingly tapered slot in the yring 22h and is operated by theA threaded bolt 23h and locked in place by the nut 23u. A lock screw 36, threaded thru the cage 2, rests in a slot cut in the ring 22b and prevents the latter from turning. The suction pressure may be passed to the rod clearance by the pipe 35, the pressure being conveyed by the connected passages 33 and 34. I'he pipe 35 may be connected lto the pressure system at a required point. 'I'he threaded hole 21t may be used to connect a petcock, whereby grit and dirty oil may be exhausted thru the passage 32.

Referring now to Figure 3, a cross-section of the baile compartment on line 3-3 of Figure 1. The rod 4 passes thru the assembly and there is a clearance adjacent to the inner surface of the spool II. The edge of the baille I3 ts tightly around the outside of the spool II, but has a clearance adjacent to the inside surface of the cup IIJ. The edge of the baille I 2 is a tight fit to the inside of the surface of the cup I0, but has a clearance adjacent to the spool II. The body I houses the lforegoing assembly.

Before explaining the method of operation, it is necessary to consider the theory of the externally operated multistage compartment walls. In my application for Letters Patent, Serial Number'526,288, dated March 30th, 1931, the method of testing packing by internal pressure drop defines the friction between an elastic body, such as packing, and a solid rod. The thrust against the rod at any point is equal to the drop of pressure at that point, and the friction resulting from the thrust is created by and is proportional to that thrust. 'I'his conforms to the general law of friction between two solid bodies that friction increases proportionally to the pressure. There is also a general law of friction that the amount of friction is independent of the extent of the surface, within reasonable limits.

Itis chiefly on this last mentioned law that this type of packing is designed, so that it may be operated at a, very low unit of thrust per unit of area. Referring now to Figure 4, an internal pressure chart. 'I'he ordinate P is the pressure impressed on the packing in the cage 2, of Figure 1. The abscissa of Figure 4 is the length of the packing contact, to a scale. The line U represents a uniform d-rop of pressure thruout the length of the packing contact with the rod, and is considered to be'ideal only. The line a is the drop of pressure that actually occurs at -the rod surface, due to the pressure P acting on the packing in the cage 2, of Figure 1, when the bolts 23a and 23h are loose, and the packing rings I9a, I9b and 25 are acting as a continuous set, and the maximum rate of pressure drop is adjacent to the male ring 26.

Referring again to the law that friction is independent ofthe area in contact, it is obvious that a few rings of packing would do the sealing necessary, as well as the combined number of rings I9a, I9b and 25. Also that the total friction of a few rings which would properly seal the joint, would be the same as that made by the combined rings I9a, 19h and 25. But the friction per unit of area in contact would be far higher for the few rings, than when the total number of rings I9a, I9b and 25 were considered.

The packing herein described then is a method to decrease the friction per unit of contact area,

at the same time controlling the drop of pressure per increment of the packing length, by the externally operated compartment walls 22a and 22h, the friction perforce being created where the pressure drop occurs, according to my application, Serial Number 526,288, before mentioned.

Referring now to Figure 5, which represents the drop of pressure when the bolt 23h is tight, expandingthe ring 22h against the wall of the cage 2 in Figure 1, and the bolt 23a is loose permitting the packing rings I9a and I9b to operate as a continuous set. The ordinate is the pressure impressed on the packing, and the abscissa is the length of the packing contact to a scale, and the line U represents the ideal drop taking place uniformly. The pressure drop will be greatest in' the packing rings I9a and I9b, adjacent to the thrust-taking ring 22h, because of the combined length of the rings I9a and I9b, hence the friction will be proportional to the drop of the linea,

of Figure 5. The pressure which leaks by the packing rings Illa and ISb will pass on to the rings 25, the drop of pressure thru the latter being :represented by the line b. Thus by causing the pressure to drop at two definite points, namely at the expanding ring 22h and at the male ring 26, the friction is also distributed more equally between the combined set of rings Isa and IBb, and along the rings 25. The friction is very much lower per unit of area than as if the entire pressure drop had occurred at the ring 26, as shown in Figure 4.

Referring now to Figure 6, the ordinate being the pressure impressed on the packing in the cage 2, of Figure 1, the abscissa being the length of the packing contact to a scale, and the line U `representing the ideal uniform drop of pressure. 1

In this case both expanding rings 22a and 22b are tight against the wall of the cage 2, in Figure 1. There are now three denite points at which the thrust is taken and transferred to the walls of the cage 2, at the rings 22a, 22h and the male ring 26. The line a of Figure 6 represents the drop of pressure alongV the packing rings 19h and the line c represents the drop of pressure along the rings 25. As before proven, the thrust against the rod at any point is equal to the drop of pressure at that point, and it follows that the friction for any increment of length is created by and is proportional to the drop of pressure along that increment.. Therefore this arrangement makes possible the distribution of friction at various points along the length of the packing by an external means, and prevents any considerable drop of pressure in any given length of the packing contact, the friction per unit area being very much lower than that shown by Figure and begins to approach the line U as an ideal.

The addition of compartment walls could be continued indefinitely until the pressure drop thru the packing sections would very closelyI approach the uniform line U. This, however, would be cumbersome and of little practical value. The value of this design shown by Figure 1, is that the operator without hindering operation can' change the points of maximum pressure drop, thereby distributing or changing the vareas on which the friction is created by the thrust of the pressure. 'Ihus the varying conditions against which the packing may be subjected can be neutralized by the operator without any radical changes as to the amount-of packing. It should be seen that theoretically this device will operate as well on a rotating shaft as on the reciprocating model chosen for an example in this specification.

While preparing for operation, the gasket 6, the cups 1, I0 and I5 with their' parts are installed in the compressor body I and the cage 2 is bolted up tightly and concentric with the rod 4. The inside packing set composed of the adapter rings I8 and 2li and the packing rings I 9a are inserted and followed by the ring 22a and its wedge block -2Ia. In like manner the second set consisting of the adapters I8 and 20 and the packing rings I9b are inserted and folllowecl by the ring 22h and its wedge block the packing rings 2Ib. Then the outer set of packing is inserted, consistingV of adapters 24 and 26 and 25, and finally the packing nut 3 is screwed up snugly to set the packing rings.

If the range of compressor loading is varied greatly, that is, if there is much variation between the suction and discharge pressures so that the ratio of compression is variable, the pipes 31 and 35 are connected to points in the pressure system to assist in regulating the drop of pressure between the compartments. This, however, is necessary only in extreme cases and to provide for them valves may be put in the lines 31 and 35, to be operated as desired.

When the packing is newly installed, the bolts 23a and 23h are loosened and all of the packing sets operated as one continuous set until the rod warms up and the rings secure their expansion from the temperature, during the time the packing nut 3 is adjusted so that the packing neither binds nor is loose. Then the bolts 23a and 23b are tightened down and locked by the nuts 2311, 231, thereby forcing the wedge blocks 2Ia. and 2Ib into the slots of the corresponding rings 22a and 22h. By this operation the maximum rate of pressure drop which has been occurring adjacent to the male ring 26, is diminished in rate and is divided into'three points of pressure drop, occurring at the rings 2Ia, 2lb and 26. Each pressure drop maximum is now about'one-third of the drop when the bolts 23a. and 23h were loose. The maximum friction with the bolts 23a and 23h loose occurred adjacent to the male ring 26, but when the bolts before mentioned are tightened the friction is distributed between the groups of rings, Isa, I9b and 25.

The three sets of packing make a very tight joint, and operating as they do at a low unit of thrust for unit area, will hold very high pressures without leaking or overworking the packing at any one point. Therefore at each peak of compression in the cylinder, the streams of gas come to a stop, or have no velocity, within the confines of the cups 1, I0 and I5. When gases carrying moisture, grit, and the like come to a standstill, the foreign matter drops out from lack of suspension and adheres to the surrounding surfaces. The bailles I2 and I3 provide elongated paths thru which the gases must circulate back and forth with the fall and rise of pressure. The additional surfaces also induce the foreign material to settle out during circulation due to repeated contact. After sufficient material collects in the passages of the separator, it may be removed by opening the petcock 21 which connects to the passage 29.

Should salt water come in with the gas. the water will be evaporated and the salt/left as a glaze on the packing contacts and leakage will occur. To break the glazing loose andv eject it, the bolts 23a and 23h are loosened while the rod is operating and the packing nut 3 backed oi. 'I'his allows space for back-and-forth movement of the rings, the vibration and twisting thus secured quickly breaks the glazing loose and it is blown out along the rod. In like manner, sand and mill scale canl be ejected from the packing rings.

Water, gasoline, lean oils and other liquids will be slowed down in velocity and stripped from the fabrics must be much harder and more durable to withstand the high friction per unit of area.v

With this multistage and its low friction per unit of area, softer materials with a lower coeiilcient of friction may be used, effecting a considerable saving vin total friction and in power.

The method of externally regulating drop oi pressure to distribute friction over an'extended area of packing, or any elastic or inelastic body in contact with a solid body, may be applied to many conditions not described in this specification, but such applications as are based on the ideas herein developed, I do claim in the following manner:

1. In astulng-box having a rod therein, a rod packing adjusted to seal pressure around said` rod by a packing-gland, an annular-ring partition in said packing intermediate the ends of said box, a wedge block fitting a correspondingly tapered opening in said annular ring, a screw extending thru and to the outside of the stuffing-box walls and contacting with said wedge block, for forcing said wedge block into said opening in said annular ring, to expand said annular ring immovably against the walls of said stufng-box to become a thrust-taking point, dividing said packing into two separate umts, each independent of thrust from the other.

2. In a stuiiing-box-'having a rod therein, rod packing adjusted around said rod and compressible by a packing gland to seal the pressure thereof ranging between a maximum and a minimum value, a plurality of annular ring partitions in said packing intermediate the ends of said box, externally actuated means to position said annular rings immovably against the walls of the smiling-box, dividing said packing into a plurality of units each independent of thrust from the other; each clearance space around the rod at said externally controlled thrust-taking points, adapted to be connected by a passage to an outside point equal in pressure to the value derived by the relation of the uniform drop of pressure at said thrust-taking points and vents for foreign material outside said rings from said box.

3. In a stuiling box having a rod'therein, frusto-conical packing rings in said box about said rod, a packing gland on said box to force saidY packing rings into said box, annular partitions in said box intermediate the ends thereof, means operated when said packing has been adjusted by said gland to expand said rings into rigid engagement with the inner walls of said box at longitudinally adjustable positions of said rings to form thrust taking members in said packing, and vents adjacent each of said partitions whereb foreign material finding entrance to said packing may be flushed therefrom.

4. In a stuiiing box having a'rod therethrough, packing rings in said box about said rod, metallic rings at spaced points intermediate the ends of said box, said metallicv rings being split longitudinally at one point, a wedge to expand said metallic rings, means extending radially through the wall of said box to wedge said rings into rigid frictional engagement with the walls of said box, means to prevent rotative movement of said metallic rings, and a gland on said box.

5. In a stuiilng box having a rod therein, rod

packing therein to seal pressure around said rod,

a packing gland to compress said packing 1ongitudinally of said box, a plurality oi spaced annular thrust taking rings in said packing, externally actuated means to expand said rings and x said annular rings frictionally against the walls of the stuiiing box after said gland has been adjusted, dividing said packing into a plurality of units, each independent of thrust from the other.

HaRLEY T. WHEELER.

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