WO1991002160A1

WO1991002160A1 - A piston pump or compressor for handling both gas and wet gas, and a suction emptying system for lpg gas cylinders equipped with such a pump

Info

Publication number: WO1991002160A1
Application number: PCT/DK1990/000197
Authority: WO
Inventors: Peder Lorenzen
Original assignee: Kosan Crisplant A/S
Priority date: 1989-08-04
Filing date: 1990-08-03
Publication date: 1991-02-21
Also published as: EP0592393A1; DK162854C; DK382689D0; DK162854B; AU6171490A; DK382689A

Abstract

A piston pump or compressor having a pump cylinder (2) and a cylinder head (7) with suction valve (8) and exhaust valve (10) is arranged and oriented in such a manner that the pump cylinder (2) has its cylinder 'head' (7) turned downwardly, this head thus forming the bottom of the cylinder (2). The exhaust valve (10) is placed such that it communicates with the lowermost cylinder space portion, whereby any collection of liquid in the cylinder (2) will be forced out already by an initial downstroke of the piston, without any impact on the pump at the end of the downward working stroke. The pump is also well suited for handling pure liquid and gaseous liquid, and on that background a highly simplified suction emptying for LPG gas cylinders is disclosed.

Description

A piston pump or compressor for handling both gas and wet gas, and a suction emptying system for LPG gas cylinders equipped with such a pump.

The present invention relates to a piston pump or compressor for handling potentially wet gases or liquids containing gas. Traditionally there is a rather sharp distinguishing between liquid pumps and gas compressors, and in usual designs the relevant two types of devices are well suited for handling liquid and gas, respective¬ ly, but very ineffective or directly unusable for handl¬ ing gas and liquid, respectively. In particular, piston compressors for gas normally are not only unsuited for handling liquids, but even subject to destruction if handling gases having a considerable content of liquid, inter alia because a given discharge capacity for com¬ pressed gas conditions a design of the discharge valve system which is quite different from the design of the same valve system for use with liquids, which are by definition not noticeably compressible.

In gas compressors it should be endavoured to keep the so-called dead space, i.e. the remaining cylinder space above the piston top at the end of the working stroke of the piston, as small as possible, because otherwise the piston, by its following suction stroke, will not initiate any effective suction until the com¬ pressed gas in the dead space has expanded to the suc¬ tion pressure after a certain displacement of the pis¬ ton. Similar conditions occur by the handling of LPG gas and corresponding gases, where the gas is discharged from the pump without any considerable compression; if the gas holds just a minor fraction of the gas in its liquid phase, then this gas liquid will deposit on the piston top and evaporate immediately at the beginning of the suction stroke, whereby the suction becomes ineffec- tive. Moreover the compressor or the gas pump may be mechanically overloaded if the amount of liquid gas at the end of the working stroke is larger than the volume of the dead space, because the non-compressible liquid will then be beaten against the cylinder head and the associated valve system.

By way of" example, see TJS-A-1,901,478, it has been attempted to provide an ammonia pump with an upper cyl¬ inder head, in which the valve system is mounted in an intermediate cylinder head that is arranged so as to be liftable as a whole against the action of a strong spring, if the piston at the end of its working stroke forces a collection of liquid against the cylinder head, such that this gives rise to the formation of a long, annular liquid discharge slot. Such a design, however, will be quite expensive.

It is the purpose of the invention to provide a compressor or a pump, which is mechanically simple and yet capable of handling both dry and wet gases.

The invention is based on the very simple consider¬ ation that the said problem with respect to the impact of the liquid against the upper cylinder head is due to the fact that this cylinder head, traditionally, is a 'top head', i.e. located at the top of the upward work¬ ing stroke of the piston, while in principle the problem will be eliminated if the pump is turned upside down such that the cylinder head will now be a 'bottom head' . Hereby the fraction of liquid, if any, will collect at the bottom head, immediately adjacent to the discharge valve, and during the now downwardly directed working stroke of^*the piston the increasing pressure of the gas will act upon the discharge valve through the collection of liquid in a non-impacting manner; when the required discharge pressure has been built up underneath the piston the discharge valve will open as usually, but now it will be the liquid which is the first to be dis- charged, viz. influenced by the overlying cushion of pressurized gas. By a suitable positioning of the dis¬ charge valve the entire amount of liquid will then have been driven out long ago, when the 'piston top' carries out the last phase of its working stroke. Thus, apart from its general orientation in the space, the pump can be designed in a quite simple and even traditional man¬ ner.

On this background the invention is primarily char¬ acterized by the matter stated in the characterizing clause of claim 1.

The invention also comprises a suction emptying system for LPG gas cylinders, inasfar as with the use of the disclosed pump it has been found possible to simpli¬ fy the traditional suction emptying systems quite dras¬ tically. In these systems the task is to suck out pos¬ sible remnants of liquid LPG gas from the gas cylinders prior to these being refilled, since prior to at least a volumetrically controlled filling it is required to make sure that there is no liquid gas left in the cylinder, the cylinder not being allowed to be entirely filled with gas liquid. The sucked out gas liquid should be conveyed to a collector tank, and it is inevitable that the sucked out liquid product will in some phase become partly gaseous, just as it is desirable to continue the sucking until there is only pure gas left. As mentioned it is not only traditional gas compressors, which are unsuitable for the handling of liquids, but also tradi¬ tional liquid pumps that are unsuited for handling gases, and the invention is now further based on the fact that the pump according to the invention can very well be designed to handle not only gas or wet gas, but also pure liquids and gas holding liquids. Just hereby it will be conditioned that in a suction emptying system it will be possible to replace the otherwise used sepa¬ ration tanks and associated valve equipment by a simple pump according to the invention, since by means of the latter it is possible to arrange for a direct pumping over of the collected gas liquid from the gas cylinders to a storage tank until the pumping product has become dry gas. The pump can well be an efficient gas compres¬ sor, i.e having a dead space of small dimensions, and the suction emptying may thus, if desired, be continued for achieving a sub pressure in the suction system.

In the following the invention is explained in more detail with reference to the drawing, in which:-

Fig. 1 is a sectional view of a pump according to the invention.

Fig. 2 is a corresponding sectional view of another embodiment of the pump, and

Fig, 3 is a schematic view of a suction emptying system for LPG-cylinders.

The pump shown in Fig. 1 has a pump cylinder 2, which, in a non-illustrated machine structure, is mounted obliquely depending from a crank housing, from which a piston rod 4 having a piston 6 is moved up and down in the cylinder 2. At the lower end of the cylinder is mounted a 'top cylinder head' 7, which is provided with an intake valve 8 and a central discharge valve 10. The latter is mounted or provided in such a manner that an annular seat surface thereof extends through the lowermost area of the space inside the the cylinder head 6, this being truncated outside of the end facet con¬ stituted by the discharge valve 10. The valve design will not be described in more detail, as the valve it¬ self as well as the cylinder head may be designed fully conventiona1ly.

It-will be easily understood that the disclosed pump will be able to work with both gases and liquids, and that -in working with wet gases there will be no impact problems at the end of the working strokes of the piston, as any,possible liquid collection underneath the piston during and just after the suction stroke will be present at the bottom portion which communicates with the discharge valve 10, i.e the liquid collection will be forced out from the cylinder as soon as the piston, by its downward working stroke, has built up the cylin¬ der pressure at which the discharge valve 10 opens.

In Fig. 2 a pump cylinder 2 with vertical orienta¬ tion is shown. The intake valve 8 is mounted centrally in the cylinder bottom, shaped as a conically upstanding disc, which is sloping from its middle portion downward¬ ly towards a surrounding, lower annular area, underneath which the discharge valve 10 is mounted, shaped as a horizontal annular plate member supported by an underly¬ ing spring 12 as indicated. Also here the lowermost portion of the cylinder space is located immediately adjacent to the discharge valve itself, such that gas liquid collected at the bottom will leave the cylinder as soon as the piston initiates its working stroke from above. This embodiment may operate with relatively very large flow through areas in the intake and discharge valves.

It will be appreciated that in the pumps according to both Figs. 1 and 2 it is possible to provide dead spaces of a very small size.

Fig. 3 illustrates a suction emptying system for LPG gas cylinders. Several gas cylinders are placed upside down in connector sockets 16, which are flow connected with a collector tank 18, the lower end of which is connected with the suction side of a pump 20 according to the invention. The discharge side of this pump is connected with a storage or filler tank 22, and as mentioned the pump will be usable for direct transfer of rest gas from the cylinders 14 to the tank 22, ir¬ respectively of the pumping medium consisting of both pure gas liquid, gas holding gas liquid and pure gas.

For comparison it can be noted that in conventional suction emptying systems it has been common practice to make use of the system shown in dotted lines in Fig. 3, the system comprising two containers 24 with switch over valves 26, a gas pump 28 and a liquid trap 30. The valves 26 can be set such that by means of the gas pump 28 gas is sucked into one of the containers 24 from the cylinders 14, while gas liquid from the other container is pressed into the tank 22, the gas pump 28 hereby being able to work solely with dry gas. In connection with the invention it is fully acceptable that the cor¬ responding pump works also with pure liquid and liquid containing gas, and on that background it is possible to replace the entire sub system illustrated in dotted lines by i^xe simple pump according to the invention.

The pump shown in Fig. 2 may well be mounted in an inclined position, even inclined almost down to a hori¬ zontal position, so it is well suited for use in a plural cylinder pump in the form of a hanging V or . The same, of course, applies to the pump according to Fig. 1.

Claims

C L A I M S :

1. A piston pump or compressor for handling both pure gas and liquid containing gas, comprising a pump cylinder having a movable piston and a cylinder head with associated intake and discharge valve means, char¬ acterized in that the pump cylinder is oriented with its cylinder head located at the bottom and that the dis¬ charge valve is designed and mounted so as to communi¬ cate with the lowermost sub space of the pump cylinder.

2. A pump or compressor according to claim 1, char¬ acterized in that the cylinder is mounted in an inclined position and that an edge area of the discharge valve, which is placed centrally in the cylinder head, is located at the lowermost area of the cylinder space.

3. A pump or compressor according to claim l, char¬ acterized in that the cylinder is mounted in a vertical¬ ly hanging position and that the intake valve at the bottom of the cylinder is shaped with a surface which is outwardly and downwardly sloping, the discharge valve being arranged as an annular plate valve extending along the outer, lower edge of the intake valve.

4. A suction emptying system for LPG gas cylinders, characterized in that between a suction conduit, which is connected to the gas cylinders, and a storage or filler tank for the liquid LPG gas there is arranged, substantially solely, a pump according to any of the claims 1, 2 or 3.