CH635659A5 - ALTERNATIVE PISTON PUMP. - Google Patents

Description

The present invention relates to a reciprocating piston pump.

Although piston pumps are appreciated for their volumetric characteristics, the use of most pumps of this type is not recommended at pressures clearly exceeding 138 MPa. In fact, even at s

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at lower pressures, the flexible sealing ring packings that are generally used in installations of this kind have at most a fairly limited service life and obviously deteriorate even more rapidly at higher pumping speeds and / or when used with chemically aggressive fluids. At operating temperatures well above 138 MPa, fatigue failure cracking occurring even for metallic parts of pumps creates an additional problem further limiting the service life of such installations.

Consequently, there are many high pressure and / or corrosive fluid applications, for which the use of a reciprocating piston pump would be of great economic interest when it is not because of the abnormally short service life and prohibitive maintenance costs associated with it.

The object of the present invention is to improve the durability and service life of reciprocating piston pumps at pressures far exceeding 138 MPa.

The pump which is the subject of the present invention is defined by independent claim 1.

To ensure maximum resistance to fatigue for this pump, which is of vital importance to extend the service life at the highest pressures envisaged, the monobloc housing should be subjected to autofrettage treatments including the application of pressures sufficient internal to initiate a partial deformation or work hardening of at least the internal layers of metal surrounding the core and the working chamber under pressure.

The service life of the elementary sealing means will generally be significantly improved by the use of forced liquid cooling circulating in an annular jacket surrounding the one-piece housing provided for these sealing means, the resulting improvement being particularly significant when 'We operate at very high pressures and / or very high pumping speeds as well. However, the most effective pressure sealing means to be used in the context of the present invention, in particular at the very high pressures envisaged, are, as has been found, the sealing means of the general type described in US Patent No. 3,834,715, involving a pressurized sealing fluid which is distributed by a cheek ring hollowed out in a series of elements forming sealing rings, some of which have a chevron or other transverse shape, creating a concave profile oriented towards the hollow cheek ring. Although a detailed explanation of the possibilities of application of various features and variants of this patent to the particular needs of the present invention are given in the following more detailed description, it may be pointed out here that one of the most interesting advantages lies in the exceptionally high degree of improvement in the service life of this preferred type, with pressurized fluid, of sealing means, which is achieved by application of this cooling by forced liquid circulating in the annular jacket surrounding the one-piece housing .

The invention can be better understood thanks to the following description given by way of example and with reference to the attached drawing.

The single figure is a sectional view, taken along its axis of symmetry, of a piston pump according to the invention.

The figure shows in its entirety and without section, a long cylindrical piston 1 shown in a position where it is located a short distance from the most forward point (represented by the dotted outline 2) reached by the front end of this piston during the reciprocating movement (the rearmost position reached during the race being correspondingly indicated by the dotted outline 2 '). This piston 1 is made of tungsten carbide or another hard material, resistant to abrasion. The rear part of the piston 1, which remains easily accessible for connection to an appropriate control mechanism, is provided with a collar or a stirrup 4 (shown in section).

The active part of the piston 1 acts inside a thick cylindrical monobloc housing 5, the main pressure working chambers of which are chamber 6 and chamber 7 which are axial and uniform. The chamber 6, which is provided in the front part of the housing 5, has a length exceeding the stroke of the piston 1 and an internal diameter which is only slightly greater than that of this piston. To ensure a uniform sliding assembly, the chamber 6 and the chamber 7 are effectively concentric and coaxially aligned, having a highly polished surface finish (for example not more than 0.4 micron). The surface finish of chamber 6 and chamber 7 is preferably about 0.2 microns. Likewise, the external surface of the active part of the piston 1 is exceptionally smooth, that is to say with a finish at least equal to that of the chamber and preferably even better (for example not greater than about 0 , 1 micron). The chamber 7 has a diameter greater than that of the chamber 6 so as to create a space for an annular seal 10 which serves as a seal for the pressure, between the piston 1 and the housing 5.

The seal 10 includes a hollow cheek ring 12 and a series of cooperating rings 11, 13 and 14, at one and the other end of the ring 12, thereby forming two separate series of rings. garnish. The front series, in this embodiment, comprises three individual rings 11 having a generally V-shaped or chevron-shaped section, while the rear series comprises four rings 11 of this kind, all these rings of the chevron type being arranged so that their concave end face is oriented towards the ring 12. In this preferred type of packing device, each of the above series of rings should comprise at least two chevron rings 11 mounted between a median annular cap 13 and an extreme annular cap 14, these caps having a planar radial surface at their end opposite to the chevron rings.

The packing rings 11, 13 and 14 are formed from an inert plastic material, for example from a fluorinated hydrocarbon polymer, such as "Teflon", reinforced by a finely subdivided solid filler material, of higher melting point, characterized by better thermal conductivity and better heat resistance, for example graphite, molybdenum disulfide, metal powders, glass fibers, carbon black, etc. According to a preferred but optional embodiment of the present invention, the annular caps 13 and 14 are formed of “Teflon” reinforced with copper powder, while the chevron rings 11 are made of “Teflon” loaded with graphite, so as to obtain a balanced combination of sliding ability, flexibility and thermal stability.

Block-shaped spacing rings 15 and 16 constitute the end elements of the seal 10 and, like the hollow cheek ring 12, they are made of metal or another hard, non-flexible material,

to support the flexible packing rings and help maintain their uniform mutual alignment as well as the concentricity of the complete assembly, including the reciprocating piston. In addition, the rear spacer ring 16, which is an essential characteristic even in the basic and minimal construction of the sealing means, also serves as a sliding contact element, free,

against the final flexible packing ring means

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sealing (that is to say the annular cover 14 in the illustrated construction). This ensures a uniform transmission of an axial thrust, oriented towards the front, envisaged to take up any play which could develop in the annular sealing means due to a compression deformation, an elastic deformation or other size changes in flexible packing rings.

Such axial thrust is obtained by advancing the annular sleeve 18 with an external screw pitch, as and when this sleeve is screwed into a corresponding tapped section 9 existing at the rear end of the housing 5, the relative dimensions being such that the radial end face 19 existing at the front of the sleeve 18 comes into contact with the spacer ring 16 well before fully cooperating with the threaded section 9.

We normally rely more on the adjustable connection device, constituted by this screwed mounting of the sleeve 18 in the rear end of the housing 5 in the case of the basic elementary construction of the sealing rings than in the case of the preferred type, with fluid under pressure, illustrated in this case. Thus, in the case of the basic construction, it may prove advantageous to apply a sufficient axial thrust by the above assembly to ensure sufficient shaping by compression of the flexible packing rings in order to obtain improved sealing of the contacting surfaces and thus reduce any leakage through the sealing means. On the other hand, in the pressurized fluid sealing device, the main counter-pressures which are applied to ensure improved sealing contacts come from the pressurized fluid. In this case, therefore, the main function of the adjustable connection device is to maintain a good tight fit between the adjacent packing rings in order to obtain an appropriate interaction between them.

The purpose of the annular cap 12 is to distribute the pressurized fluid appropriately through the interior of the pressure sealing means. To this end, a fairly wide, shallow groove 22 is provided in the middle part of the annular cap 12, with several passages 24 (two passages are shown) oriented inward, that is to say from the groove 22 to the outer periphery of the piston 1. As this pressurized fluid must be supplied from outside the pump, a radial passage 8 passing through the housing 5 is provided to supply this pressurized fluid.

All around the housing 5, a concentric annular jacket 30 is provided, the wall of which is substantially thinner than that of the housing 5 but is sufficiently thick for this jacket to have a stable structural rigidity under the mechanical forces to be applied. The internal diameter of the jacket 30 is essentially uniform in its main central part and only exceeds by a small fraction of cm the external diameter of the main body of the housing 5 (that is to say over the entire length of this except for a short larger head 28), thereby creating a narrow annular passage 32 all around the greater part of this housing 5. However, the internal diameter of the jacket 30 is reduced to points 31 and 33 to form short sections with an internal diameter which is just slightly greater than the external diameter of the main body of the housing 5 so as to ensure for this jacket 30 a narrow sliding mounting on this housing 5. Finally, at its front end, the jacket 30 also has an enlarged head 34, the front part of which is hollowed out sufficiently to fit on the head 28 of the housing 5.

The jacket 30 is of the kind designed to be able to be installed in the active position by a simple sliding on the housing 5 from the rear passing over two elastic O-rings 21 provided in housings 20 created in the external periphery of the housing 5 in the vicinity sections with minimum diameter of the jacket 30, so as to thus form the peripheral seals necessary for one and the other end of the annular passage 32. Tapped holes 35 and 36 are provided in the jacket 30 to end in the passage aforesaid 32 in the vicinity of the rear and front ends thereof, these holes allowing inlet and outlet connections for the circulation of a coolant in the passage 32. The jacket 30 is further modified by drilling a largest opening 38 in concentric alignment with the smallest opening 8 provided in the housing 5, in order to allow suitable access to this opening 8 for a pressurized fluid pro from external power.

After the jacket 30 has been slid into place all around the housing 5, the completion of the assembly described requires the installation of a few peripheral connection elements according to the following operating phases:

(1) the jacket 30 is slid into the cap member 40 so that the latter completely surrounds the enlarged head 34 of the shirt 30 thanks to its front axial passage 42 of appropriate dimensions and thanks to its smaller rear opening 44 , aligned concentrically;

(2) the nose portion of the connection rod 50 comprising the passage for fluid 52 coming from the valve chamber (not shown) is introduced into the front cavity 29, of suitable dimensions, provided in the housing 5, so that the conical-looking end face 54 of this nose can rest on the flat radial annular shoulder 3 provided at the bottom of this cavity 29;

(3) the joint between the connecting rod 50 and the cylindrical housing 5 is made watertight and the jacket 30 is simultaneously fixed in place by tightening, in tapped holes 45 provided in the cap 40, with a series of studs (not shown) passing through symmetrical holes 55 provided in a flange 56 which bears against the conical-shaped shoulder 58 provided on the rod 50;

(4) a supply of cooling fluid (not shown) can be connected to the inlet 35 and a suitable discharge system for this fluid (not shown) can be connected to the outlet 36;

(5) finally, to activate the preferred type of fluid under pressure of the sealing device, the flow system for this fluid must be completed by providing a pressure-tight connection to the passage 8 existing in the housing 5 by the intermediate of the access opening 38. In the present embodiment, this is achieved through the use of an auxiliary sleeve 60 which is adapted to slide all around the periphery of the jacket 30 so that its opening radial tapped 62 is in concentric alignment with the access opening 38 and the passage 8. A cylindrical tube 66 having an enlarged front part 68 with a diameter which is only slightly less than that of the opening 38 is introduced in the latter so that its obtuse angle end face 69 rests on the flat face 39 existing on the housing 5 at the outer end of the passage 8. A hollow nut 70 concentrically surrounding the tubing 66 thanks to its internal cavity closely follows the contour of the shoulder zone 67 provided at the rear of this tubing 66 is then introduced into the tapped opening 62 until a high pressure seal is obtained between the end face 69 and the flat face 39. The low pressure seal between the jacket 30 and the pipe 66 is obtained by means of an O-ring 65 mounted in a peripheral groove 63 located in the enlarged front part 68 of the pipe 66, which is surrounded by the wall of the shirt 30.

As mentioned in U.S. Patent No. 3,834,715, a good empirical method

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general for the operation of the pressurized fluid sealing device of the type preferred in the present case consists in supplying the pressurized fluid to the seal gasket at a back pressure essentially equal to the pressure at which the working or active fluid is pressurized. In fact, in most cases, optimal performance is achieved when the back pressure is within ± 10% of the operating pressure of the pumping elements. However, excellent results can sometimes be achieved with differences of more than 10% in terms of back pressure, particularly on the negative side. It all depends a lot on the particular combination of variables that exist in a particular case, for example pumping speed, number, type and design of packing rings, general operating pressure levels, etc.

Another characteristic of paramount importance in the case of the present invention is the obtaining of remarkable improvements in the resistance to fatigue at high pressure. Special consideration will therefore be given to the following discussion of the factors for achieving these improvements, most of which are related to the design and manufacture of the main cylindrical housing as this is the element which is exposed to all of the maximum fatigue stresses encountered in reciprocating piston pumping devices for high pressure.

The fundamental reason why an improved resistance to fatigue is ultimately obtained according to the present invention lies in the use of a one-piece and unitary cylindrical housing both for the piston and for the sealing means, in combination with a simple annular jacket for forced current liquid refrigerant for easy removal of heat generated internally through the walls of the housing.

Other characteristics closely related and of great importance in the implementation of the concept according to the invention are the construction materials and the methods of manufacturing the cylindrical housing. The best building materials for this purpose are iron-based alloys with high tensile strength, in particular alloys containing significant amounts of chromium and a certain amount of nickel. The chromium concentration should preferably be at least about 10% by weight and the nickel content should preferably be at least about 4% by weight. These materials provide the added benefit of excellent corrosion resistance, which further contributes to long-term integrity under severe conditions of use. Ideally, any alloy used should be in a highly refined form, containing no impurities and separate foreign matter, in order to avoid even slight discontinuities, which could serve as starting points for concentration of effort. Consequently, the alloy billet from which the cylindrical housing is made should be produced by a technique such as vacuum or slag arc reflow. Alloys of this kind based on iron, containing about 11-19% of chromium and about 3-9% of nickel as main additives, constitute interesting alloys.

Excellent results have also been obtained starting from similar alloys containing a small amount of molybdenum and which have been subjected to structural hardening by an appropriate heat treatment. An ideal alloy of this kind contains about 13% chromium, about 8% nickel and about 2% molybdenum, as well as 0.05% carbon and small amounts of other constituents.

In the manufacture of the cylindrical housing, it is of paramount importance to create a polished and smooth internal surface finish in the chambers or passages for high pressure, and this as already described. It is also desirable to avoid sharp edge corners in high pressure chambers.

To obtain maximum resistance to fatigue, these high-pressure chambers of the housing should be subjected to an autofrettement treatment sufficient to initiate cold creep or elastic deformation of the boundary metal layers adjacent to the openings and passages, then the surface internal of these should no longer be disturbed by machining, grinding, polishing, etc. It will therefore be obvious that, in assemblies such as that illustrated by the drawing, in which the external diameter of the seal 10 is much larger than the diameter of the piston, the autofrettage treatment should be carried out in two stages due to the large difference in internal pressure necessary to cause elastic deformation in the area surrounding chamber 6, compared to the area surrounding chamber 7.

In other words, in the manufacture of a cylindrical housing of this type at very high pressure, it is necessary to first pierce the chamber 6 through the entire body of the housing 5, then after grinding and polishing d 'At least the front part of it, the necessary autofrettage treatment, at very high pressure, should be carried out. Then, after machining the larger chamber 7 in the rear part, rectifying and polishing the latter in an appropriate manner, and carrying out any other internal machining, such as the radial passage 8, etc., the second autofrettage treatment at the lowest pressure necessary for the housing section 5 surrounding the chamber 7 should then be achieved.

One of the most promising applications for the pump according to the present invention resides in the supply of catalyst solutions to polymerization reactors operating at very high pressures, normally from 180 to 360 MPa. In such fields of use in connection with chemical reactions, it is very desirable to provide a constant flow rate at a speed which can be easily controlled and with minimum pressure pulsations. At lower pressures, it seems that the combination of the two pumps described above via an appropriate control mechanism would be very suitable. However, at pressures of 180 MPa and above, the compressibility of liquids becomes an important factor, so it is preferable to provide a combination of three or more pumps.

By way of example, a combination of three pumps of equal dimensions, each designed as illustrated by the drawing, comprising a piston with a diameter of 9.5 mm, was put into operation from a crankshaft common creating a stroke of 10.16 cm for each piston and ensuring a differential angle of 60 ° between the strokes of piston 1 and cylinder 5. The resulting assembly was tried in pumping a dilute solution of organic peroxides in a hexane solvent, this solution being supplied at a suction pressure of approximately 1.13 MPa and delivered at a reactor pressure of approximately 206.7 MPa, using a direct current motor, at variable speed, connected to this crankshaft by means of a reduction gear allowing crankshaft speeds from 10 to 200 revolutions per minute. The resulting performance is excellent with extremely precise flow velocities, and a pulsation in flow pressures rarely exceeding 3%, particularly in the mid range of crankshaft operating speeds from 40 to 120 revolutions per minute, which represents d 'elsewhere the most normal range from a practical point of view.

A particularly suitable type of variable speed motor for this service is a direct current shunt motor, the speed of which can be varied by changing the speed.

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armature while keeping the inductor voltage constant. The speed of these motors can be adjusted very precisely through the use of sensitive and feedback electrical circuits, which are available on the market. For example, such speed control equipment is sold by Reliance Electric Company under the trade name MAXPAK SOLID STATE DC V * S DRIVE.

Although the pumps made in full accordance with the teachings of the present invention have not yet been used in an extended manner over a period of time sufficient to estimate their ultimate fatigue strength, no signs of emerging failure have been identified during the preliminary inspections carried out to date. Furthermore, it is already evident that the average service life of the pressure seals has been greatly increased by the use of forced liquid cooling of the wall of the cylindrical housing.

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1 sheet of drawings

Claims (18)

635,659 1. Reciprocating piston pump, characterized by a cylindrical piston comprising an accessible part at the rear, equipped with means for connecting it to a reciprocating control mechanism, by a cylindrical monobloc housing, made of a metal alloy resistant to corrosion, the housing surrounding the active part of the piston and comprising a first smooth chamber with a diameter greater than that of the piston and extending rearwards from a point near its front end over a distance greater than that of the reciprocating stroke of the piston, a second similar coaxial chamber with a larger diameter than that of the first chamber being provided immediately behind the latter, by a pressure sealing device, filling the annular space included inside the second coaxial chamber surrounding the piston, comprising a series of solid packing rings and supported at the rear by a packing cap made of a material p ratically non-flexible, by adjustable connection means provided at the rear end of the housing for the application of a thrust against the packing cap which, in turn, transmits a compressive force on the series of packing rings, and by an annular jacket concentrically surrounding the housing but of a thinner wall construction, the jacket having an internal diameter which is not more than a fraction of cm greater than the external diameter of the housing, thus creating an annular passage all around the greater part of this housing, peripheral sealing rings being provided between the jacket and the housing at one and the other end, two openings being provided through the jacket for the 'use as inlet and outlet connections for the circulation of a coolant through the passage. 2. Pump according to claim 1, characterized in that the cylindrical piston is constructed of tungsten carbide. 2 3. Pump according to one of claims 1 and 2, characterized in that the external surface of the piston is rectified to a smooth surface finish not greater than 0.4 micron, preferably not greater than 0.05 micron. 4. Pump according to one of claims 1 to 3, characterized in that the means provided for connecting the piston to the control mechanism consist of a collar mounted by force around the accessible rear part of the piston. 5. Pump according to one of claims 1 to 4, characterized in that the metal alloy from which the one-piece housing is formed is an alloy based on iron, with high resistance to fatigue and containing at least about 10% of chromium and at least 4% nickel by weight. 6. Pump according to claim 5, characterized in that the alloy also contains molybdenum and is subjected to structural hardening by heat treatment. 7. Pump according to one of claims 1 to 4, characterized in that the metal alloy from which the one-piece housing is made has been subjected to a vacuum arc reflow to remove the separated foreign matter and the resulting discontinuities. 8. Pump according to one of claims 1 to 7, characterized in that the sealing means comprise a hollow cheek ring, centrally disposed and having a shallow cavity of large width in the middle part of its outer periphery, passages starting from the cavity and ending at the internal periphery of the ring at different points, as well as means for bringing a sealing fluid under pressure to the cavity, the solid packing rings constituting sealing means, in the one and the other direction from the central hollow cheek ring, having a cross section in the general shape of a chevron, and all the chevron shaped rings of this kind being aligned so that their concave face is oriented towards the cheek ring dug. 9. Pump according to claim 8, characterized in that the hollow cheek ring is made of metal and the solid packing rings are made of a fluorocarbon polymer, of nylon or of another plastic resin with low coefficient of friction , with reinforcement by a fine solid filler with a higher melting point. 10. Pump according to claim 9, characterized in that the fine solid filler material consists of graphite, molybdenum disulfide, carbon black, glass fibers or metals in fine powders. 11. Pump according to one of claims 1 to 10, characterized in that the adjustable connection means comprise a tapped end section provided at the rear end of the housing, and an annular sleeve externally threaded so as to correspond to the end section threaded, so that the front part of this sleeve can come into contact with the trim cap after being firmly set in place but before full cooperation with the threaded section. 12. Pump according to one of claims 1 to 11, characterized in that the annular jacket has parts limited to one and the other end, which have a reduced internal diameter just sufficiently greater than the external diameter of the housing to ensure between them a narrow sliding assembly, low pressure seals being formed in these parts by means of O-rings located in circumferential grooves provided in one of the cooperating surfaces of this sliding assembly. 13. Pump according to one of claims 1 to 12, characterized in that the annular passage is of a depth less than 6.35 mm, being more particularly between lo, 58 and 4.76 mm. 14. Pump according to one of claims 1 to 13, characterized in that the inlet connection is located in front of the rear end peripheral seal, while the outlet connection is located in the rear of the front extreme peripheral sealing ring. 15. A method of manufacturing the pump according to claim 1, characterized in that the two chambers provided in the one-piece housing are subjected to a high pressure autofrettage treatment after the completion of a rectification of the surfaces of the two chambers. 16. Use of the pump according to claim 1, for each of the individual pumps of a multiplex pump, the control mechanism consisting of a common crankshaft controlled by the intervention of a gear train by an electric speed motor. variable. 17. Use according to claim 16, characterized in that the electric motor is a direct current shunt motor, the speed of which is adjusted by modifying the armature voltage. 18. Use according to claim 17, characterized in that an automatic, sensitive and reaction control circuit is applied to adjust the voltage of the armature of the motor, thereby allowing the engine speed to be maintained.