US3238887A - Cryogenic liquid pump - Google Patents

Description

March 8, 1966 E. T. voLZ CRYOGENIC LIQUID PUMP Filed March 26, 1964 INVENTOR ERICH T.VOLZ WM@ Z2@ ATTORNEY United States Patent O 3,238,887 CRYDGENIC LIQUID PUMP Erich T. Volz, Buffalo, NSY., assigner to Union Carbide Corporation, a corporation of New York lFiled Mar. 26, 1964, Ser. No. 355,035 Claims. (Cl. 10S-153) This invention relates to apparatus for pumping a volatile liquid having a boiling point temperature at atmospheric pressure materially below 273 K., and more particularly to a reciprocating pump for pumping a liquelied gas having a normal boiling point below 233 K., such as liquid oxygen, nitrogen, and .the like, to an ultrahigh pressure, for example, 10,000 p.s.i.

Pumps heretofore proposed for pumping liquefied gases to high pressures have involved difficulties due to the physical properties of the highly volatile liquids. For example, liquefied gases have greater compressibility than water, and thus present greater heat of compression problems. However, these difficulties have been largely overcome when the desired discharge pressure was below about 3,000 p.s.i. On the other hand, the previously known pumps are either inefficient or unworkable in the ultra-high pressure range above about 5,000 p.s.i. This is because special problems, in addition to strength considerations, arise which tend to decrease .the efficiency of the heretofore known pump-s in this ultra-high Ipressure discharge range, and these difficulties could eventually make the pumps inoperative. These unique problems are due to the increased pressure drop across the leakage path between the pum-p plunger and surrounding cylinder, greater plunger forces and therefore higher plunger friction, and the larger amount of heat added to the liquefied gas during compression. The latter fact leads to vapor ashoff from the liquid trapped in the clearance space; that is, the portion of the pumping chamber not taken up or filled by the plunger at the end of the discharge stroke, after the pressure in the pumping chamber has been released. Vapor fiashoff in this unfilled portion of the pumping chamber limits the amount of liquid that can enter the pumping chamber during the suction stroke, and may cause .the pump to become vapor bound and lose prime. The heretofore proposed pumps have relatively large clearance spaces, which were tolerable with discharge pressure below about 3,000 p.s.i., but cannot be tolerated when a pump must operate in the ultra-high pressure range.

Another limitation of .the heretofore known immersion pumps is the requirement of a relatively high pressure differential between the pumping chamber and the surrounding liqueed gas, to open the suction valve. This characteristic becomes critical in ultra-high pressure operation since ,the increased vapor ashoff results in a higher pressure in the pumping chamber at the end of the discharge stroke. Thus, to maintain the same pressure differential across the suction valve, it is necessary to supply the liquefied gas in the surrounding container at a relatively higher pressure. This requirement may increase the operating costs of the system.

An additional problem not sufficiently overcome by the previously proposed systems for pumping volatile liquids to high pressures is the substantial transmission of heat from the atmosphere through the pump mounting assembly into the container. This heat leak is partly due to conduction and also results from splashing of the liquefied gas against the pump mounting assembly, with resultant wetting of the warm parts of this assembly, thereby increasing the liquid evaporation rate. Because of this wetting, the heat leak lproblem is particularly acute when the immersion pump-liquid container assembly is subject .to considerable vibration and movement, or when fice the pump is mounted substantially horizontally in the container. In the latter case, the pump mounting assembly is either directly immersed in the liquefied gas, `or in relatively close proximately thereto.

Still another disadvantage of the presently used immersion pumps is the slow plunger speed necessary to prevent excessive generation of frictional heat and to avoid the previously discussed excessive pressure drop across the Isuction valve. A relatively slow plunger speed required a larger diameter pump cylinder or body to achieve a given pumping rate, and this in turn necessitates a massive pump body resulting in a high rate of heat transmission into the liquid both inside and outside the pump and requiring a large opening in the container wall for pump installation. The percentage of the liquid which leaks between the plunger and cylinder wall also increases at slow plunger speeds. Finally, the forces imposed on the plunger and driving mechanism for a given pumping rate are higher at slower speeds, which adds to the expense and massiveness of the entire assembly.

One object of the present invention is to provide a highly efficient immersion pump for pressurizing liquefied gas to an ultra-high pressure;

Another object of the present invention is to provide a reciprocating-type pump having a minimum clearance space;

A still further object is to provide a reciprocating-type immersion pump which requires a relatively low pressure differential between the pumping chamber and the surrounding liquefied gas, to open the suction valve;

Another object is to provide a compact immersion pump- Iwhich operates at a relatively high plunger speed but is characterized by low frictional heat and low suction valve pressure drop thereby achieving low cost, high efficiency and operation dependability.

These and other objects and advantages of this assembly will be apparent from the following description and the accompanying drawings in which:

FIG. 1 is a view of a partial vertical section through a pump illustrating a preferred embodiment of the pump inlet valve assembly of the present invention.

FIG. 2 is a cross-sectional view illustrating an alternate inlet valve assembly construction.

FIG. 3 is a fragmentary view of a partial section of a pump inlet valve assembly taken along line 3 3 of FIG. 2.

The reciprocating pump of this invention comprises an enlongated pump body having a pumping chamber at one end and an opening at the other end. An inlet or suction valve controls the inlet port, which is situated near the end of the pumping chamber Opposite the Open end of the pump body. A discharge valve is also provided to control a discharge outlet passage communicating with the pumping chamber for discharge of ultrahigh pressure liquid therethrough. A reciprocating plunger extends through the pump body opening, the plunger having an inner end portion with a recessed section or cavity which covers at least most of the inlet valve at the end of each discharge stroke. Alternately, the suction valve could be positioned within the pump inlet head so as not to protrude into the pumping chamber. In such case, the plunger inner end portion would not have the aforementioned recessed section or cavity. Thus, the clearance space in the pump of the present invention is appreciably reduced by having the plunger fill up a major part of the clearance space between the suction valve and the pumping chamber inner wall at the end of the pump stroke, after the plunger has pumped the liquefied gas to an ultra-high pressure and forced it through the discharge valve-controlled outlet passage. In the preferred embodiment of this invention, a platetype suction valve is used since it permits a smaller clearance volume than prior art valves, requiring less clearance space while also providing a desired total opening area. Furthermore, a plate type suction valve employed in the manner to be described will provide a 'tighter seal than prior art ball-type suction valves and yet also reduce suction valve pressure drop. For example, it is estimated that the pressure drop inherent in the present invention will be about 2/3 of the suction valve pressure drop of the pumps disclosed in the aforementioned applications using multple ball type inlet valves. Thus, it can be seen that the present invention provides a reciprocating pump having a substantially smaller clearance volume than the heretofore proposed pumps; that is, less than about 4 percent and preferably about 2.5 percent of the pumping chamber working volume. This may be accomplished by separately and in combination providing a plunger with la recessed inner end pontion which Kcovers at least most =of lthe plate-type inlet valve assembly at the end of the discharge stroke, thus filling up most of the relatively smaller clearance space. One advantage of minimizing this space may be illustrated by the fact that for an immersion pump operating at 10,000 p.s.i. discharge pressure and F. subcooling, it is estimated that there will be a 3 percent loss in volumeric efficiency for each 1 percent increase in clearance volume.

Referring to the drawings, and specifically to FIG. 1, the pump comprises an elongated body 10 preferably in the form of a barrel having a pumping chamber 12 in one end thereof, preferably the bottom, and an opening in the top or other end thereof. Mounted in the pumping chamber 12 is an inlet valve assembly 14 which controls an inlet port 16 in the bottom of pump body 10. A discharge valve 18 controls an outlet passage 2() from the pumping chamber 12. Discharge valve 18 is preferably a ball valve which is urged to its seat 22 by a spring 24 which is retained by a cap 26. From the side of the discharge valve 18, a discharge conduit 28 discharges the pumped liquefied gas from the pump. Ball valve 18 is preferably metallic because of hardness and impact requirements. Suitable metals include stainless steel, nickel steel and hard surfaced aluminum.

The pump is provided with a reciprocating pump element, the inner working or pumping portion of which is a plunger 32 which enteres the end of the working or pumping chamber 12 which is opposite the head 34 and has an inner end that interfits with the inlet valve assembly to substantially fill the pumping chamber at the end of a discharge stroke. The inner end of the plunger 32 preferably has a recessed part or cavity machined therein, which partially encloses a plate valve 36 at the end of the discharge stroke. The inner end surface of plunger 32 at this point of the pumping cycle is in close proximity with the inner surface of the head 34 and thereby minimizes the clearance volume within the pumping chamber. It is to be noted that in this embodiment of the present invention, the clearance space or volume consists of essentially only that part of the space Within the recessed cavity which is not filled by the plate valve 36 and is usually expressed as a percentage of the total pumping chamber working volume.

Plate valve 36 preferably comprises a substantially flat top portion or valve plate 36a (which is preferably circular but may be rectangular; and either hollow or solid) attached to a stem 36b. Stem 36b has an outer cross-sectional dimension only slightly smaller than the inner cross-sectional dimension of head 34 and guides plate valve 36 by slideably contacting the inner surface of head 34. Since stem 36b and the interior of head 34 will usually have a circular cross-section, there respective dimensions referred to above will be diameters. This type of construction of stem 36b enables the pump to be operated horizontally inasmuch as the reciprocating motion of the plate valve will be adequately guided in all attitudes.

Plate valve 36 is lifted on the suction stroke of plunger 32 by the pressure differential across the valve, and closes on the discharge stroke. The valve seat surface 36e mates tightly with head 34. Both the valve 36 and head 34 are constructed of hardenable material having good low-temperature ductility and impact properties, such as nitrided AISI Type 304 stainless steel. Head 34 is preferably retained within pump body 10 by externally threaded ring nut 34a. While the valve 36 may be retained from above by a cage, it is preferable that stem 36b have an enlarged end 36f to act as a valve-stop, the valve lift being determined by the length of stem 36b extending downward past head 34 when the valve 36 is seated on head 34.

While the valve seating surface 36e is preferably flat as shown in FIG. l, it may be beveled and seat against a `sharp edge of head 34; or valve seating surface 36e may be beveled and seat against a like-beveled surface on head 34. In all these arrangements, the valve 36 is at least partially enclosed within the lower end of plunger 32 in order to reduce the pump clearance to an absolute minimum. Alternately, in those embodiments wherein the plunger would not have a recessed cavity, the plate valve would be partially enclosed within head 34.

As shown in FIGURE l, stem 36b is preferably constructed in the form of a hollow cylindrical shank having an outer diameter only slightly smaller than the inner diameter of head 34. Stem 36b has a plurality of openings 36g therethrough uniformly positioned around it near the valve plate 36a such that fluid may flow into the hollow interior of stem 36b and through the openings 36e into the pumping chamber 12 when the plate 36a is lifted on a suction stroke.

The valve-stop 36]c is preferably constructed of an internally threaded valve nut which is threadedly engaged to the lower end of stem 36b as shown. Valve-stop 36f may alternately comprise a radial extending pin which would engage the lower end of head 34 to restrict upward motion of the plate valve.

To minimize friction between the movable plate valve 36 and the fixed head 34, a self-lubricating cylindrical bushing 34b may be provided in an annular space within head 34 such that the inner surface of bushing 34b will be contacted by the outer surface of stem 36b. Bushing 34h may be retained in place by means of an internally-located snap ring 34C.

FIGURES 2 and 3 show an alternate stem configuration which comprises three or more radial web members 3611 which slideably Contact the inner surface of head 34. These web members 36h need not be solid members but may be formed of perforated material or have the unessential intermediate sections cut away as shown in FIG- URE 2 if desired to minimize the mass of the valve stem.

FIGURES 2 and 3 also show a valve cage configuration in the form of tabs 34a` extending radially inward from the upper end of head 34 to enclose the valve plate 36a and serve as a valve stop to control upward movement of the valve plate 36a. This type of cage configuration or alternately something similar may be substituted for the valve stop 361c of FIGURE 1. Likewise, the valve stop configuration of FIGURE 1 may be substituted in FIGURE 2 in place of cage 34o. With this type of valve cage configuration, the inner end portion of plunger 32 would have a reduced end which ts within the central space between the tabs 34C in the manner disclosed in U.S. -application Serial No. 143,521, filed October 3, 1961 which matured into Patent No. 3,136,136.

It is contemplated that various modifications of the pumping apparatus may be made without departing from the spirit and scope of the invention herein described.

What is claimed is:

1. In a reciprocating pump for liquefied gases comprising an elongated pump body having a pumping chamber therein adjacent one end and an opening at the other, an inlet valve controlled port near the end of said pumping chamber, a reciprocating plunger extending through said opening in the pump body and having an inner pumping end portion constructed and arranged to intertit with an inlet valve assembly when at the end of a discharge stroke, a discharge valve and a discharge valve-controlled port near the end of said pumping chamber, the combination therewith of yan improved inlet valve assembly which comprises a plate valve positioned to control ow through the inlet port, said plate valve comprising a top portion, a stem attached to the top portion and extending through the inlet port and having an outer cross-sectional dimension only slightly smaller than the inner cross-sectional dimension of the inlet port such that said stem guides said plate valve by slideably contacting the sides of said port, and valve stop means to control the valve lift of said plate valve.

2. A valve assembly according to claim 1 wherein said valve stop means is provided by an enlargement at the end of said stem opposite the top portion of said plate valve, the valve lift of said plate valve being determined by the length of said stern extending beyond said inlet port when said inlet port is closed by said plate valve.

3. A valve assembly according to claim 1 wherein said valve stop means is provided by a cage extending into said pumping chamber constructed to retain the top portion of said plate valve.

4. A valve assembly according to claim 1 wherein said stem is constructed of a hollow cylinder having an outer diameter only slightly smaller than the inner diameter of said inlet port, such cylinder having a plurality of openings positioned around it near the top portion of said plate valve such that fluid may ow into the hollow interior of said stem and through said openings into said pumping chamber when said plate valve is lifted on a suction stroke.

5. A valve assembly according to claim 1 wherein said stem comprises at least three radial web members the outer surfaces of which contact the sides of said inlet port, said web members being oriented longitudinally of said inlet port and constructed such that fluid may flow between each web member into said pumping chamber when said plate valve is lifted on a suction stroke.

References Cited by the Examiner UNITED STATES PATENTS 3,016,717 1/1962 Gottzmann 103-l53 X 3,083,648 4/1963 Putnam 103-153 X 3,136,136 6/1964 Gottzmann 103-153 X DONLEY I. STOCKING, Primary Examiner.

Claims (1)

1. IN A RECIPROCATING PUMP FOR LIQUEFIED GASES COMPRISING AN ELONGATED PUMP BODY HAVING A PUMPING CHAMBER THEREIN ADJACENT ONE END AND AN OPENING AT THE OTHER, AN INLET VALVE CONTROLLED PORT NEAR THE END OF SAID PUMPING CHAMBER, A RECIPROCATING PLUNGER EXTENDING THROUGH SAID OPENING IN THE PUMP BODY AND HAVING AN INNER PUMPING END PORTION CONSTRUCTED AND ARRANGED TO INTERFIT WITH AN INLET VALVE ASSEMBLY WHEN AT THE END OF A DISCHARGE STROKE, A DISCHARGE VALVE AND A DISCHARGE VALVE-CONTROLLED PORT NEAR THE END OF SAID PUMPING CHAMBER, THE COMBINATION THEREWITH OF AN IMPROVED INLET VALVE ASSEMBLY WHICH COMPRISES A PLATE VALVE POSITIONED TO CONTROL FLOW THROUGH THE INLET PORT, SAID PLATE VALVE COMPRISING A TOP PORTION, A STEM ATTACHED TO THE TOP PORTION AND EXTENDING THROUGH THE INLET PORT AND HAVING AN OUTER CROSS-SECTIONAL DIMENSION ONLY SLIGHTLY SMALLER THAN THE INNER CROSS-SECTIONAL DIMENSION OF THE INLET PORT SUCH THAT SAID STEM GUIDES SAID PLATE VALVE BY SLIDEABLY CONTACTING THE SIDES OF SAID PORT, AND VALVE STOP MEANS TO CONTROL THE VALVE LIFT OF SAID PLATE VALVE.

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