US1999534A - Removable plug closure - Google Patents

Description

April 30, 19350 3 BRANDT 1,999,534

' REMOVABLE PLUG CLOSURE Filed March 2'7, 1933.

DA V/D G. BRANDT Patented Apr. 30, 1935 REMOVABLE PLUG CLOSURE David G. Brandt, Westfleld, N. 1., minor to Doherty Research Company, 'a corporation of Delaware New Y ork, N. Y.,

Application March 21, 1933, Serial No. 662,930 4 Claims. for 137-76) This invention relates to improvements in removable plug closures, and particularly to an improved design of removable plug closure adapted for hightemperature and high pressure '5 service as for example in the return bends of oil cracking tube stills.

In the operation of oil cracking tube stills the tubes have to Joe frequently opened and cleaned to remove accumulated carbon deposits. Return 10 bend closures or clean out plugs heretofore employed in such stills are in general so complicated in design that a great deal of time is required to remove and refit several hundred of such closures in the return bends connecting the tubes, during the cleaning operation. One of the principal objects of the present invention is to provide a clean out closure so constructed that the time for removing and replacing the closure is greatly reduced over present practice. A feature of the invention is a plug closure construction including a forcing element in the form of a bushing having external and internal threads of differential pitch respectively engaging the return bend and plug closure stem, whereby the positive seating and unseating of the closure can be efiected with a single tool. By providing coarse external threads in the bushing the re moval and insertion of the closure can be rapidly completed by a few turns of the bushing.

30 Another important advantage resulting from the employment of coarse external threads on the bushing, is that such threads are stronger and more accurately dimensioned than the relatively finer threads normally used on this type of equip- 35 ment, and accordingly there is less difficulty from cross threading and thread distortion.

Other objects of the invention are to provide a removable plug closure which is simple in design and readily seated and removed irrespective of the temperature and pressure existing in the apparatus which it removably engages; to provide a plug closure so constructed that it may be rapidly and tightly seated without injury to 45 its parts; to provide a plug closure having a construction affording a great mechanical advantage in effecting tight seating; and to provide a plug closure of the screw threaded plug stem and bushing type in which the threads are 50 protected against corrosion and in which the application of seating pressure is in direct alignment with the stress opposing seating.

With these and other objects and features in view, the invention consists in the removable plug closure which is hereinafter described and more particularly defined in the accompanying claims.

In the following description of the invention, reference will be made to the drawing, in which:

Fig. 1 is a view in side elevation,-with parts in section, showing a return bend fitted with a preferred embodiment of the removable plug closure; and v Fig. 2 is a view in sectional end elevation show ing valve chambers in a high pressure billet pump which are fitted with the removable plug closures.

In the drawing, numeral Ill (Fig. 1) designates a return bend having a pair of parallel openings in which the ends of a pair of parallel tubes I2 are rolled or expanded according to common practice. The bend I0 is provided with a return passageway l4 communicably connecting tubes l2. Likewise bend I0 is provided with a pair of hollow open-ended bosses or clean-out openings I6 leading off from passageway l4 and substantially aligned with tubes l2.

The bosses l6 are internally threaded at their outer ends preferably with square threads l8 adapted to mesh with corresponding external threads 20 on a packing 22. The inner ends of each of the bosses i6 is provided with a shoulder 24 faced with a corrugated ground seat 26 to fit a correspondingly contoured and dimensioned ground joint facing on closure plug 28. Lateral apertures 29 in the bosses l6 serve as escape outlets for any liquid which may leak past the closure. The plug 28 is mounted on the end of a stem 3ll'that extends upwardly axially through the passage "5. Stem 30 is externally screw threaded preferably with square threads 32 having a pitch less than the pitch of threads 20 on bushing 22. The central bore of the bushing 22 is screw threaded with threads adapted to mesh the external threads 32 of plug stem 30. The threads 32 of stem 30 and 20 of bushing 22 are pitched in the same direction; that is both are preferably right hand threads, threads 20 however being coarse as compared to threads 32.

At its outer end the bushing 22"-is formed exteriorly with an unthreaded head 34 which in the preferred design has projecting ears 36 adapting it for forcible rotation by a hammer or bar.

If desired, however, the head 34 may be shaped with square or hexagonal lateral faces for engagement by a socket wrench. Stem 30 of the closure plug is shown as having a polygonal socket 38 in its head, but it may be desirable in same cases to substitute a stud end for engagement by a socket wrench.

' Fig. 2 illustrates an adaptation of the closure plug to the hollow bossesll through which access ishad to the valves and charge and discharge ports' of a heavy pressure billet pump. Except for slight modifications in design, the closure elements illustrated on Fig. 2 are the same as those shown in Fig. 1 and accordingly bear the same numerical designations. The shoulder 24 on the interior of the boss is faced with a fri'isto-conical seat 21 to fit a matching face on the plug 28. Likewise the heads of the closure plugs 28 are shown as having depending coaxial extensions 40 which serve as stop members to limit the throw of wing guided valves 42 and 44. Removable valve seats 46 are illustrated. Fluid to be pumped enters cylinder 48 of the pumps from an inlet passage 50 through a port controlled by valve 42; and discharge from the pump takes place through valve 44 into outlet passage 52.

Access to the cracking tubes l2 of Fig. 1 or to the valves 42 and 44 of Fig. 2 for cleaning and inspection may be had by removing bushing 22 and plug 28. This may be the more readily done since the threaded portions of the bushing and of the plug stem 30 are on the low temperature and low pressure side of the closure and accordingly are not exposed to the corrosive action of fluids handled in the system. The sealing head of the closure plug 28 is of larger diameter than the inner bore of the bushing 22, and accordingly it is necessary, in inserting the plug into sealing position on the seats 26 or 21 (Figs. 1 and 2), that the threads 32 of plug stem 30 be first engaged with the internal threads of bushing 22. For rapid assembly it is preferred to screw stem 30 into almost full thread engagement with the bore of bushing 22, as marked by gauge 54 on the bushing. The bushing and plug as a unit is then screwed into light seating position by engaging the threads 20 of the bushing with the internal threads ll! of the bosses H5 or IT. The final seating of the plug is eifected by holding the plug stem against rotation with a wrench while forcibly turning the bushing 22 by means of a hammer or bar to drive the plug into tight sealing position.

Since the pitch of the external bushing thread 20 is greater than the pitch of plug stem threads 32, and since the threads 20 and 32 are pitched in the same direction, the result of screwing the bushing into the boss is to advance theplug toward its seat a distance, with each turn of the bushing, representing the difierence in'pitch between threads 20 and 32. For example, with threads 20 having a right hand pitch of four to the inch, and threads 32 having a right-hand pitch of 5 to the inch, each clockwise revolution of bushing22 will advance plug 28 one-twentieth inch toward its seat 26 or 21, and will simultaneously advance plug stem 30 one-fifth inch farther into the bore of bushing 21. Sufiicient clearance 53 is provided between the inner end of bushing 22 and the head of plug 28, with the head of stem 30 meshed to the gauge mark 54 in the bushing, to permit rotation of bushiiig 22 to advance the plug 28 to full tight seating position without rotation of the plug. To avoid friction stresses it is desirable that the final seating of the plug 28 be effected without rotation of the plug on its seat. Likewise it is desirable to have the threads 32 of the valve stem almost fully meshed with the internal threads of the bushing (i. e. in the position indicated by gauge mark 54 on the inner bore of the bushing in line with the top of stem 30) at the time the plug is fully seated, to better hold the plug to its seat. Any desired relative position of the plug stem and bushing may be secured by turning the one while holding the other stationary.

With the plug closure design illustrated and described, it will be apparent that there is a considerable mechanical advantage between the force applied to rotate the bushing 22 and the resulting force developed for advancing or retracting the closure plug 28 and its stem, owing to the differential inpitch between the threads on the bushing and plug stem whereby a considerable linear advance of the bushing results in a much smaller movement of the closure plug in the same direction. The screw thread connection between the plug stem and bushing allows for rapid correction of any tendency of the plug to leave its seat because of expansion or contraction of the parts under rapid temperature changes.

Obviously, changes in the details of construction and adaptation of the invention to other closure applications may be made, without departing from its spirit and apparent range of equivalency.

The invention having been thus described, What is claimed as new is:

1. A closure device comprising, a cylindrical open-ended casing provided with an inner annular closure seat and being interiorly screwthreaded, a plug closure having a head with a closure surface to fit the seat and having a stem exteriorly screw-threaded with threads of a pitch smaller but in the same direction as the interior threads of the casing, and a bushing exteriorly screw-threaded with relatively coarse threads to mesh with the interior threads of the casing, and interiorly screw-threaded with relatively fine threads to fit the threads of the plug stem.

2. In a closure device, a cylindrical open-ended casing provided with an inner annular closure seat, said casing being interiorly screw-threaded on the closure side of said seat, a plug closure having a head with a closure surface contoured and dimensioned to fit the seat, a stem for said closure having an exteriorly screw-threaded portion with threads of a pitch smaller but in the same direction as the interior threads of the casing, and a bushing exteriorly screw-threaded with relatively coarse threads adapted to mesh the interior threads of the casing and interiorly screw-threaded with relatively fine threads adapted to mesh the threads of the plug stem, the bushing and plug stem being dimensioned to allow clearance between the closure head and adjacent end of the bushing with the threads of the stem in full mesh engagement with the interior threads of the bushing,

3. In combination with a, return bend fitting having a pair of hollow open-ended bosses, each of said bosses having an inner annular closure seat and being interiorly screw-threaded on the closure side of said seat, leakage escape apertures in said bosses intermediate the closure seat and the screw-threaded portion thereof, a plug closure having a head with'a surface'contoured and dimensioned to fit the seat, and having a stem exteriorly screw-threaded with threads of a smaller pitch but lying in the same direction as the interior threads of the casing, and a bushing exteriorly screw-threaded with relatively coarse threads to mesh with the interior threads ofthe casing and interiorly screw-threaded with relatively fine threads to fit the threads of the plug stem, the outer ends of the bushing and stem being shaped for engagement by tools adapted to screw the parts into threadable engagement with each other and with the bosses.

4. In a closure device, a cylindrical open-ended casing provided with an inner annular closure seat, said casing being lnteriorly screw-threaded, a plug closure having a head with a closure surface adapted to fit the seat and having a stem 10 exteriorly screw-threaded with threads of a pitch smaller but in the same direction as the interior threads of the casing, a valve stop extension mounted on said closure head coaxlally with the stem, and a bushing exteriorly screw-threaded with relatively coarse threads adapted to mesh with the interior threads of the casing and interlorl'y screw-threaded with relatively fine threads adapted to fit the threads of the plug stem.

' DAVID G. BRANDT.

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