NO793908L - HOEYTRYKKSYLINDER. - Google Patents

Description

The invention relates to a high-pressure cylinder for a high-pressure pump of the reciprocating type with a so-called 'plunger piston'.

Pumps with rod pistons have positive fluid delivery characteristics, but most units are not recommended for use at pressures above 1400 kg/cm 2 in particular. Even at lower pressures, the flexible sealing rings, which are usually used in such equipment, will only have a limited lifetime and they will naturally be destroyed more quickly at higher pumping speeds and/or when working in connection with chemically active substances. At operating pressures significantly above 14 00 kg/cm, fatigue failure in the cylinder unit's steel components will also present problems, and such failure possibilities will also limit the lifetime of the equipment.

There are many areas of application in connection with high pressure and/or corrosive substances where the use of a reciprocating pump with a plunger piston or rod piston would be of interest, if one could increase the life of the equipment and reduce the otherwise prohibitive maintenance costs.

One purpose of the present invention is to provide a high-pressure cylinder which has a long service life. Another purpose of the invention is to provide a high-pressure cylinder which has sufficient fatigue resistance and lifetime to be used commercially at a pressure well above 14,00 kg/cm 2 .

Another purpose of the invention is to provide sealing rings for such a high-pressure cylinder. which sealing rings work even at very high pressures and have sufficient wear resistance and corrosion resistance so that the equipment has a long service life even in connection with pumps that handle chemically active substances.

The starting point for the invention is that there is a need for pumps of the reciprocating rod piston type, which pumps can be used even under very demanding conditions and have a sufficient service life. A particular purpose of the invention is to provide so-called multiplex pumps which can be operated economically for the delivery of regulated quantities of fluid under very high pressures and without significant pulsations.

According to the invention, a high-pressure cylinder device is therefore provided as stated in claim 1. For the device to. get maximum fatigue resistance, which is off. vital importance with respect to achieving long life when working under high pressures, the unitary cylinder housing is subjected to cold drawing treatments, including the use of internal pressure sufficient to effect partial liquefaction or cold working of at least the inner layer of metal around the bores which serve as working pressure- chambers.

In its simplest form, the pressure seal used can be made up of several massive but flexible sealing rings with good lubrication, supported on the outside by a simple spacer ring made of a hard, mainly inflexible material. The lifetime • of even such a simple packing device will be significantly improved by using forced liquid cooling using a jacket around the unitary housing, and the improvement achieved is worth the effort when operating under high pressures and/or pump speeds. However, the most effective pressure packing device is, especially when the aforementioned high pressures are concerned, a pressure packing of the general type described in US Patent No. 3,834,715.

The invention shall be described in more detail with reference to the drawing.

In the drawing, a plunger piston rod 1 is shown in a position just before the forward position (shown with dashed lines and denoted by 2). The rearmost position of the piston rod is also shown with dashed lines - and is denoted by 2'. The piston rod is made of tungsten carbide or another hard, wear-resistant material'. The rear part of the rod 1, which is easily accessible for connection to a suitable drive mechanism, is provided with a ring collar 4.

The rod's 1 working section works inside a powerful, . cylindrical and uniform housing 5 where the main pressure chambers are formed by two axial bores 6 and 7. The bore 6 is located in the front part of the housing 5 and has a length that is greater than the stroke length of the rod 1, and a diameter that is only slightly greater than the rod diameter. In order to obtain a good sliding fit, the bores 6 and 7 are coaxial and made with a highly polished wall surface (for example no more than 0.0004 mm), preferably the surface of the bore is made with a fineness of around 0.0002 mm. The surface of the rod 1 working section is also very smooth and smooth, at least as smooth and smooth as the bores and advantageously better (for example no more than 0.00005 mm). The bore 7 has a significantly larger diameter than the bore 6, so that there is room for the gasket 10, which provides a pressure seal between the rod 1 and the housing 5.

The seal 10 is in the design example of the type that can be pressurized and includes a ring 12 and other special elements which enable a seal better than the minimum requirements mentioned above. In addition to a number of yielding gasket rings which are necessary, the gasket 10 thus includes several gasket rings 11, 13 and 14 on each side of the ring 12, so that the gasket includes two separate gasket ring sets. The front packing ring set includes three individual packing rings 11 which are V-shaped in cross-section, while the rear packing ring set includes four such packing rings 11, all oriented with the concave end surfaces towards the ring 12. In the preferred embodiment of the packing, each packing ring set includes at least two such packing rings 11 which is arranged between a central follower ring 13 and an end follower ring 14, both of which have flat end surfaces on the ends facing away from the sealing rings.

The sealing rings 11, 13 and 14 are made of an inert plastic material, for example a fluorinated hydrocarbon polymer such as Teflon, reinforced with a finely divided, higher melting solid filler material which has better thermal conductivity and heat resistance, for example graphite, molybdenum disulphide, metal in powder form, glass fibres, incense and the like. Advantageously, the follower rings 13 and 14 can be made of Teflon reinforced with copper powder, while the sealing rings 11 are made of graphite-added Teflon, so that a balanced combination is thereby achieved with regard to lubrication, flexibility and thermal stability.

The gasket 10 is terminated at each end with simple spacer rings 15 and 16 respectively. These are, in the same way as the ring 12, made of metal or another hard, inelastic material which can provide support for the flexible gasket rings and help to hold them furnished,

while maintaining concentricity in the cylinder, including the piston rod. In addition, the rear spacer ring 16, which represents an important element even with a minimum solution for the gasket, serves as a free, sliding contact element against the last ■ flexible gasket ring in the gasket (i.e. the follower ring 14 in the present case). This ensures an even transmission of forward axial forces to absorb any slack that may occur in the gasket as a result of compression set, floating or other dimensional changes in the gasket rings.

Such axial forces are provided by means of the tensioning screw 18 which is screwed into a threaded portion 9 at the rear end of the housing 5. The components are dimensioned so that the end surface 19 of the tensioning screw 18 makes contact with the follower ring 14 well before the screw is fully screwed in.

Its tightening plug 18 at the rear end of the housing 5 is usually more important in connection with a gasket construction that satisfies the minimum requirements than in the preferred, pressurizable type shown in the drawing. In a simpler construction, it may be desirable to be able to exert a sufficient axial force by means of the tightening screw in order to thereby be able to press the sealing rings together enough to provide the desired seal, while in

a pressurizable gasket achieves the desired gasket pressure. by means of an introduced pressure fluid, i.e. that the tensioning screw's main function will only be to ensure the maintenance of a good matching of adjacent sealing rings so that proper interaction between them is achieved.

The purpose of the ring 12 . is to distribute the pressure fluid properly in the interior of the seal. For this purpose

In the middle part of the ring 12, a relatively wide, shallow groove 22 is formed, from which several channels 24 (only two are shown) enter the rod 1. The pressure fluid must be supplied from the outside of the cylinder and in the housing 5 there is therefore a radial bore 8 for supplying such pressure fluid.

A mantle body 30 is arranged concentrically around the housing 5, the wall of which is substantially thinner than the wall of the housing 5, but still thick enough to provide constructive rigidity under the influence of the mechanical forces acting. The inner diameter of the mantle 30 is essentially the same over the middle portion of the mantle and is only a small fraction of an inch larger than the outer diameter of the housing 5 (disregarded here from the extended head portion 28 of the housing), so that around most of the housing a narrow annulus 32. At 31 and 33, the inner diameter of the mantle 30 is reduced so that the mantle has short inner sections where the inner diameter is only slightly larger than the outer diameter of the housing 5, so that a good sliding fit is obtained. At the front end, the mantle 30 is provided with an extended part or a head part 34 which is provided with an extended bore for receiving the head part 28 of the housing. the housing 5 from the rear end thereof, first bringing two elastic 0-rings 21 into place in grooves 20 in the housing, which 0-rings form the necessary seals when the mantle has been brought into place, as can be seen from the drawing. In the mantle 30, there are two threaded bores -35 and 36. Both lead inside the annular space 32, respectively at the rear and front end thereof, and they are used as inlet and outlet connections for coolant to be supplied to the annulus. The mantle 30 also has a bore 38. This is concentric with the aforementioned narrower bore 8 in the housing 5-, and serves to provide access to the bore 8, i.e. that pressure fluid can be supplied from an external source. After the mantle 30 has been brought into place around the housing 5, the cylinder inner unit is completed by connecting certain elements, as will be apparent from the following arrangement: 1) The mantle 30 is inserted into the cover element 40 to the position shown, in which the head part 34 is almost entirely occupied in a bore 4 2 , while a smaller bore 44 encloses the mantle at the back of the head. 2) The nose part of a connecting element 50, which contains a fluid channel 52 from a valve chamber not shown, is introduced into a bore 29 in the housing 5, so that the conical end surface 54 of the nose is brought into contact with a planar ring shoulder

3 at the bottom of the bore 29.

3) The seal between the element 50 and the housing 5 is made tight and the mantle 30 is simultaneously fixed in place by inserting it into the threaded holes 54 in the cover element 40. shown threaded bolts which also pass through corresponding bores 55 in the flange 56. The flange 56 presses against a conical shoulder 58 on the element 50. 4) A coolant supply (not shown) is connected to the inlet 35 and a suitable outlet system for the coolant is connected to the outlet 36. 5) Finally< *>the pressure fluid source is connected to the seal, so that it can be pressurized. This happens by a ring "60 being threaded onto the casing 30 and brought to such a position that a radial threaded bore 61 in the ring 60 aligns with the bore 38 and the bore 8 „ A coupling element 66, which has an extended head 68 which is slightly smaller than the bore 38, is introduced into the bore, so that the end surface 69 rests against the bottom ;-39 in a small depression at the outer end of the bore- 8.;A nipple nut 70 is threaded onto the coupling element and;screwed into the threaded bore 62, whereby the inside of the nut- wide shoulder 67 presses against the coupling element and provides a high-pressure seal between the end surface 69 and the surface 39. Between the mantle 30 and the coupling element 66, a low-pressure seal is provided by means of an O-ring 65 located in a groove 63 in the coupling element's head 68. As mentioned in US patent document no. 3 834 715, it is; a good rule of thumb to introduce a pressure fluid into the seal with a back pressure essentially equal to the pressure of the working fluid. In most cases, optimal properties are achieved when the back pressure l igger within t 10% of the working pressure of the pump elements. Excellent results can sometimes be obtained with more than 10% difference in the back pressure, especially on the minus side. Much depends in this connection on the particular combination of variables in the particular situation, for example pump speed, number, type and design of sealing ring elements in the packing device, the general working pressure levels, etc. Another important thing in connection with the present invention is the clear improvements that are achieved with regard to the fatigue resistance in connection with high pressures. Attention is therefore directed in particular to the mention given below of the factors that are important in that connection. Mostly, this is about drafts in connection with the construction and manufacture of the main cylinder housing, because it is this element that is exposed to the greatest extent to maximum fatigue stress when it comes to high-pressure pumps with reciprocating rod pistons. Fundamental to the achievement of improved fatigue properties is the use of a uniform cylinder housing for both the rod piston and the gasket, in combination with a simple jacket for guiding a coolant to remove heat developed in the housing. Other factors that are important in connection with the invention are the construction materials and the method chosen for the cylinder housing. It has been found that a very good construction material is steel alloys with high tensile strength, especially those containing significant amounts of chromium and some nickel. Preferably, the concentration of chromium should be at least approx. 10% by weight, and the nickel content should be at least. about. 4% by weight. Such materials offer the additional advantage that they have excellent corrosion resistance, which of course further contributes to the achievement of a long service life even under difficult working conditions. Regardless of which alloy is chosen, it should be in a highly refined form, free of impurities, so that even small discontinuities, which can serve as a starting point for unwanted stress concentrations, are avoided. The blank from which the cylinder housing is thus manufactured should be manufactured using a technique of the vacuum arc or electro-slag remelting type. Such steel alloys that contain 11-19% chromium and approx. 3-9% nickel as main additives represent good choices. Excellent results have also been achieved using similar alloys which contain a small amount of molybdenum and which are quenched by suitable heat treatment. Such an alloy containing approx. 13% chromium, approx. 8% nickel and approx. 2% molybdenum along with 0.05% carbon and other minor components have been found to be ideal. ;When manufacturing the cylinder housing, it is very important to give the high-pressure drilling chambers a smooth, polished wall surface. It is also desirable to avoid sharp corners in* the high-pressure chambers. In order to achieve maximum fatigue resistance, the high-pressure chambers in the housing should be subjected to -"'cold working sufficient to achieve an initial cold flow of the metal boundary layers in the bore, after which the bore walls should not be disturbed by machining, honing, polishing, etc. In devices of the type that are shown in the drawing, where the outer diameter of the gasket 10 is much larger than the diameter of the piston pin, as will be understood, the cold working must take place in two stages due to the large differences in the internal pressures which are necessary to achieve cold flow in the area of the bore 6 compared to the area at the drilling 7.

In other words, when manufacturing a cylinder housing of the type in question here, one first drills the bore 6 through the entire housing 5 and carries out the necessary honing and polishing of at least the necessary front part, with subsequent cold working in using a very high pressure. The bore 7 is then provided, honed, and polished and then subjected to a second cold working, with a lower pressure, i.e. the pressure necessary for the area around the bore 7. Before the final cold working, the other machined parts are naturally provided parts, such as the radial bore, etc.

One of the most promising areas of application for the invention is use in connection with the delivery of catalysis solutions to polymerization reactors that work with

2 very high pressures, i.e. pressure from approx. 1750 - 350.0 kg/cm . With such use, it is highly desirable to have a smooth delivery with a precisely controllable amount and with minimal pressure pulsations. At lower pressures, it appears that a combination of two cylinder arrangements as described above, using a suitable phase-adjusted drive mechanism, will be sufficient, but at pressures of 1750 kg/cm 2 and more, the compressibility of the liquids will emerge as an important factor, and it is then preferred to use a combination of three or more cylinders.

As an example, it can be mentioned that three identical cylinders of the type that are. shown in the drawing, each with a piston rod with a diameter of 9.5 mm, were driven from a common crankshaft which gave a 10 cm stroke for each piston rod, there being a 60° difference in phase angle for the strokes between cylinders 1 and 2 and cylinders 2 and 3. This unit was tested in connection with pumping a dilute solution of organic peroxides in hexane solvent, supplied with a suction pressure of approx. 10 kg/cm<2> and delivered with a reactor pressure of approx. 2100 kg/cm 2. A direct current motor with variable speed was used, connected to the crankshaft through a reduction gearbox which enabled crankshaft speeds of 10-200 revolutions per minute. minute. The experiment was very successful. Very accurate delivery quantities were achieved, and the pulsation in the delivery pressure was hardly more than 3%, especially in the middle speed range of the crankshaft, from approx. 40-120 revolutions per minute, which incidentally represents the most interesting area in practice.

A particularly well-suited motor in this connection is a direct current shunt motor,• where the speed can be varied by changing the armature voltage, while the field voltage is kept constant. The speed of such motors can be regulated very accurately using commercially available electrical sensing and feedback circuits. For example, mention must be made here of speed control equipment marketed by the Reliance Electric Company under the trade mark

MAXPAK SOLID STATE DC V»C DRIVE.

Although pump units built in accordance with the present invention have not been in use so far that their ultimate fatigue life has been determined, it can still be stated that no failure has been found so far. It is clear that the average lifetime of the pressure seals has been significantly increased as a result of using the forced cooling of the cylinder housing around the seal area.

Claims (1)

"1. Device including cylinder, rod piston and piston seal, with good corrosion resistance and fatigue resistance firmness when used as a high-pressure pump element, . characterized in that it includes 1) a cylindrical rod piston of a hard high-modulus material which has an accessible section at the back provided with a device for connection to a suitable drive mechanism which can give the rod piston a back and forth movement, 2) a thick-walled, uniform cylinder housing of high tensile strength and of a corrosion-resistant metal alloy around the working section of the rod piston, which housing has a smooth internal bore slightly larger than the diameter of the rod piston and extends axially from a point near the front end of the housing and rearward a distance slightly longer than . the stroke length of the rod piston, and behind this bore a similar, coaxial bore with a significantly larger diameter, 3) ... a pressure packing device which completes the annular space in the aforementioned coaxial bore around the rod piston and includes several massive packing rings with good lubrication and flexibility, as well as a follow-up ring of a hard and mainly non-flexible material at the rear end, 4) an adjustable device at the rear end of the housing for exerting a thrust force against the follower ring, which then in turn transfers a pressure force against the sealing rings, and 5) a jacket that concentrically surrounds the housing, but is thinner walled and has an inside diameter only a small fraction of an inch greater than the outside diameter of the housing, so that a narrow annulus is formed around the housing, with circumferential sealing rings between the jacket and the housing at each end, and with a pair of openings through the mantle for connecting inlet and outlet connections for passing a refrigerant through the annulus. 2. Device according to claim 1, characterized v- e d that the cylindrical rod piston is made of tungsten carbide. 3. Device according to claim 2, kara'k teri se. r.t in that the outer surface of the rod piston is honed to achieve a smooth surface finish of no more than 0.0004mm. 4. Device according to claim 3, characterized in that the surface finish is no more than approx. 0.00005mm. 5. Device according to claim 1, characterized. in that the device for connecting the rod piston and the drive mechanism includes a collar-shaped element which is shrink-fit around the accessible rear part of the rod piston. 6r> Device according to claim 1, characterized in that the metal alloy in the housing is a steel alloy with high fatigue resistance, containing at least approx. 10% by weight chrome and at least approx. 4 wt% nickel. 7. Device according to claim 6, characterized in that the alloy also includes a significant amount of molybdenum and is quenched by suitable heat treatment. 8. Device according to claim 1, characterized in that the metal alloy in which the housing is made has been vacuum-arc remelted to eliminate discrete contaminants and resulting discontinuities. 9.. Device according to claim 1, characterized in that each of the aforementioned two boreholes in the housing is subjected to high-pressure cold machining after otherwise necessary machining, including honing of the borehole walls. 10. Device according to claim 1, characterized in that the packing device includes a centrally located ring with a shallow groove with a significant width in the middle part of the outer circumference, from which there are channels to the inner periphery in several places, and an ano arrangement for providing a pressure fluid in the groove, and in that at least one of the massive sealing rings in the sealing device in each direction from the central ring has a mainly V-shaped cross-section, all such V-shaped rings being lined up so that its concave end surfaces are aligned towards the central ring. 11. Device according to claim 10, characterized in that the central ring is made of metal and that the massive sealing rings are made of a fluorocarbon polymer, nylon or another low-friction plastic resin reinforced with powdered filler material with a higher melting point. 12. Device according to claim 11, characterized in that the filling material is selected from the group which includes graphite, molybdenum disulphide, cow ear wax, glass fiber and finely powdered metals. 1-3. Device according to claim 1, characterized in that the adjustable device includes a short end section at the rear end of the housing, with internal r threading, and in that a hollow screw is screwed into the threaded end section so that its front part can make contact with the follower ring after it is screwed in well, but before it is screwed in completely. 14. Device according to claim 1, characterized in that the mantle has sections at each end with a smaller internal diameter, i.e. just sufficiently larger than the outer diameter of the housing to provide a tight sliding fit between the components, and that in the said sections there is arranged low-pressure seals in the form of O-rings placed in circumferential grooves in one of the two opposite circumferential surfaces. 15. Device according to claim 1, characterized in that the annular space has a depth of less than approx. 6.3 mm. 16. Device according to claim 15, characterized in that the depth of the annulus is between approx. 1.5 mm and approx. 4, 5 mm. 17. Device according to claim 1, characterized in that the inlet connector is arranged slightly in front of the sealing ring arranged at the rear end, and that the outlet connection is arranged slightly behind the sealing ring arranged at the front end. 18. Multiplex reciprocating rod piston pump, where each of the individual pump elements is made in accordance with claim 1, and where the drive mechanism is a common crankshaft which is driven through a suitable gearbox by means of an electric motor with variable speed. 19.. Multiplex rod piston pump according to claim 18, characterized in that the electric motor is a direct current shunt motor whose speed can be regulated by regulating the armature voltage. 20. Multiplex rod piston pump according to claim 19, can be actuated by an automatic feedback sensor and control circuit which is used for the regulation of the armature voltage in the motor, whereby it is possible to hold the motor speed within very small tolerances.