GB2050577A

GB2050577A - Changeover Device for Pressurised Fluid Containers

Info

Publication number: GB2050577A
Application number: GB8015269A
Authority: GB
Original assignee: Messer Griesheim GmbH
Current assignee: Messer Griesheim GmbH
Priority date: 1979-05-10
Filing date: 1980-05-08
Publication date: 1981-01-07
Also published as: DE2918791C2; DE2918791A1; FR2456273A1; GB2050577B; NL8002482A; FR2456273B1; IT8021842A0; CH647310A5; AT381158B; ATA203980A; IT1131437B

Abstract

A changeover device (1) (fig. 1) connects two gas cylinders (B1,B11) in parallel and changes over automatically and without interruption from one cylinder (B1) to the other cylinder (B11) after the first cylinder (B1) is emptied, so that a constant gas flow to the consumer (V) is ensured. The aim of the invention is to device the changeover device (10) so that it changes over only upon the optimum emptying of the cylinder (B1). To achieve this the back pressure region of the pressure-reducer (64) provided in the outlet pipe (62) is connected back to the changeover device (10). In this way the changeover pressure is controlled as a function of the work pressure of the consumer (V) so that an optimum emptying of the cylinders (B1,B11) is obtained at all times. <IMAGE>

Description

SPECIFICATION Changeover Device for Pressurised Fluid Containers The present invention relates to a changeover device for the alternate withdrawal of a liquid or gaseous medium from pressurised fluid containers such as gas cylinders, tanks etc., wherein the changeover from the one fluid source to the other is effected by the fluid itself having a chamber accommodating a piston and with which supply channels and outlet channels combined in a common pipe are associated, also with pressure relief valves and at least one nonreturn valve connected to the chamber.

A changeover device conforming to the above defined category can be seen to be already known from German Patent 812,139. By means of such a changeover device, gas can be withdrawn from a cylinder and supplied to a consumer. Just before this cylinder is emptied, the changeover device changes over to the full cylinder connected in reserve. By this means it is ensured that a continuous gas flow to the consumer can be made without interruption of service.

Starting from this prior art, it is the aim of present invention to devise the changeover device in such a way that the changeover of the device occurs as a function of the work pressure of the consumer, so that by this means an optimum emptying of the cylinder connected in each case is always ensured.

In order to achieve the stated aim it is proposed according to the invention to arrange in the outlet pipe a pressure-reducer, the back pressure region of which is connected by a branch pipe to the pressure relief valve.

It is provided according to the invention that each branch pipe is connected through the pressure relief valve to one of the outlet channels.

It is particularly advantageous if the outlet channel (back pressure space of the regulator) is connected to an annular space which is formed between a connector for the supply channel and the end face of the piston occupying its respective closing position.

In the preferred embodiment of the invention it is further provided that the two outlet channels are connected to a further chamber in which an auxiliary piston is provided slidingly. In this case it is particularly advantageous if the auxiliary piston is constructed as a nonreturn valve and for the actuation of the pressure relief valves.

Lastly it is further advantageous if radial seals are provided for sealing both the piston and the auxiliary piston.

The description of a preferred embodiment of the changeover device according to the invention given hereinbelow serves for further explanation in conjunction with the accompanying drawing.

In the sole drawing the changeover device according to the invention is designated by the reference numeral 10. As may be seen, said changeover device has a symmetrical construction with reference to the vertical axis, so that it is sufficient if only one half of this device is described hereinbelow.

As shown in the drawing, the changeover device 10 exhibits a housing 12, in the upper region of which a cylindrical chamber 14 is arranged. The open end face of the chamber 14 is closed by a connector 1 6 which is screwed gas-tightly into a screwthreaded bore 1 8 of the housing 1 2. The connector 1 6 is connected to a gas pipe 20, which leads to gas cylinder (not shown) or to another gas container. The gas cylinder is designated symbolically in the drawing by the designation B I or B II.

The gas pipe 20, and hence the cylinder (B I or B II) communicates through a central passage bore 22 in the connector 1 6 with the chamber 14. The chamber 14 limited on the left and right in the housing 12 by the two connectors 1 6 serves to accommodate and guide a piston 24, the sliding stroke of which is defined within the chamber 14 by the two connectors 1 6.

In order to prevent the gas flowing into the changeover device during service from the cylinder B I from entering the region of the chamber 14 t associated with the cylinder B II, the piston 24 is equipped at its circumference with radial ring seals 26, by which the chamber 14 is subdivided into two mutually sealed chamber regions.

On the end face 28 of the piston 24 there is provided centrally a stud 30 which is accommodated gas-tightly by the corresponding passage bore 22 of the connector 1 6 (left or right-hand) depending upon the position of the piston 24 in the chamber 14. Radial ring seals 32 let into the wall of the passage bore 22 ensure gas-tight closure of the gas pipe 22 with reference to the chamber 14 in the position of engagement of the stud 30 in the passage bore 22.

As is illustrated particularly by the left-hand position of the piston 24, the connector 1 6 is conformed internally so that it forms an annular space 34 in conjunction with the end face 28 and particularly here with its bevelled external region. The annular space 34 communicates through an outlet pipe 36 in the central section of the housing 12 through a further annular space 37 with a transverse bore 38 of a further screwthreaded connector 40 screwed into the housing. Said screwthreaded connector serves to accommodate a pressure relief valve 42 which is of construction known per se and exhibits in its interior A valve piston 46 loaded by a spring 44 and with a valve rod 48 connected thereto.In the closed position of the pressure relief valve, the valve piston 46 rests upon a valve seat 50 as shown on the right-hand side.

The valve rod 48 of the pressure relief valve 42 projects into a central bore 52 of the screwthreaded connector 40. Said central bore is enlarged in the region of its exit from the screwthreaded connector and serves to accommodate a stud 54 of an auxiliary piston 56 which is arranged with sliding mobility in a second chamber 58 of the housing 12.

From the second chamber 58, which is defined in its magnitude by the screwthreaded connectors 40, two tapping bores 60 also start, which combine to form a common outlet pipe 62.

According to the invention there is provided in said outlet pipe 62 a pressure-reducer 64, by which the incident cylinder pressure (front pressure) is reduced to the required work pressure (back pressure) of the consumer V in manner known per se. In that part 62a of the outlet pipe 62 following the pressure-reducer 64, considered in the direction of flow of the gas, there is provided a branch pipe 66 which according to the invention is connected to both the pressure relief valves 42.

In the illustrated position of the changeover device the cylinder B I is connected to the consumer V, whereas the cylinder B II is connected in reserve. The gas flowing from the cylinder battery B I passes through the passage bore 22 and the chamber 14 into the outlet pipe 36 and from there through the annular space 37 and transverse bore 38 (of the screwthreaded connector 40) into the second chamber 58 which it leaves through the outlet pipes 60 and 62. The auxiliary piston 56 occupies its left-hand closing position and-acting as a nonreturn valve-prevents any back flow of the gas through the left-hand tapping bore 60 into the left-hand closed control region of the changeover device 10.The gas-tight closure of said left-hand control region is effected by the radial ring seals 26, 32, which are associated not only with the piston 24, but also with the auxiliary piston 56.

The gas supplied to the consumer V is reduced to the required work pressure (=back pressure) by the pressure-reducer 64. This work pressure therefore prevails in the pipe section 62a and hence also in the branch pipe 66.

According to the invention the branch pipe 66 is connected to the pressure relief valve 42. Since in the present case the left-hand valve 42 is open, the gas expanded to the work pressure passes through the channels 52, 38, 36 into the annular space 34, so that the work pressure likewise prevails there at the (left-hand) end face 28 of the piston 24. Dictated by the surface constitution of the mutually abutting end face of the connector 16 and end face 28 of the piston, gas also passes into this "interstice". The pressure prevailing in the region of the annular space 34 and of the "interstice" corresponds in its value to the work pressure (back pressure) prevailing in the branch pipe 66.The pressure force generated by the back pressure does not correspond to the value P=pxf, but is reduced by the factor F ( < 1). The fact F takes into consideration the fact that the pressure cannot attack on the total end face because of the surface constitution of the end face, and simultaneously includes frictionai forces. But the higher and work pressure chosen, the greater does the factor F (o1) 1) also become.

When in the course of time the cylinder pressure B I decreases, then at a certain point the situation is reached in which the pressure force acting upon the right-hand side of the valve piston becomes smaller than the pressure force acting upon the left-hand side of the valve piston (attacking the end face of the stud 30), resulting from the cylinder pressure B II, including the pressure force continuing to attack the end face 28, resulting from the work pressure/back pressure. When this total force prevails, the changeover from cylinder battery B I to B II therefore occurs. The piston 24 and auxiliary piston 56 are now moved into their right-hand limit position by the gas flowing in from B II.

The auxiliary piston in the right-hand limit position, likewise acting as a nonreturn valve, here again prevents any return flow of the gas into the right-hand channels 52,38,36. The residual gas remaining on the right-hand side as result of the changeover can be supplied through the pressure relief valve 42 opened by the auxiliary piston 56 without loss through the branch pipe 66 to the consumer V.

By means of the changeover device according to the invention it is advantageously possible to empty a cylinder (cylinder, tank etc.,) optimally before the changeover from the cylinder just emptied to the still full one occurs.

In this case optimum emptying does not mean that the gas is virtually totally withdrawn from the cylinder. On the contrary, the degree of emptying is a function of the work pressure at the consumer (back pressure) and also especially of the gas volume/h required.

In order to supply a specific volume of gas to the consumer, this is a function of the passage pipe of the pressure-reducer (Nm3/h), a specific back pressure is required which-to enable the required volume of gas to be supplied-must again be smaller by a specific amount than the front pressure, so that the pressure-reducer exhibits an adequate pressure gradiant from front to back pressure.

This optimum changeover from the one cylinder (B I) to the other (B II) will be further explained by two examples: Example 1 Cylinder pressure (initial pressure): p112=1 50 bar Diameter of piston 24: d1=2 cm Diameter of studs 30: d2=0.5 cm Back pressure and pressure-reducer: pHD=4 bar required: Changeover pressure: p,=! bar from d, we obtain f,=3.14 cm from d2 we obtain f2=0.1 9 cm2 therefore the area f2 of the end face 28 (=ring surface) f3=f1-f2=2.95 cm2 P1=p1xf1=1 50x3.1 4=471.0 da N P2=p2xf2=1 50x0.1 9=28.5 da N PHD=PHDXf3XF=4x2.95x0.4=4,7 da N (the factor F is-as already stated-an imperical value which must be taken into consideration because the back pressure pHD is not fully effective at the end face 28, since of course this said end face abuts against the connector 1 6 and frictional forces are also present. The factor F becomes correspondingly greater for a greater back pressure).

Accordingly the total force P9=P2+PHD=285+47 Pg=332 N is active on the "changeover side".

Condition for the changeover: Pg=P1(Pg=332 N 33.2 da N) (P, is reduced by the falling cylinder pressure p1, starting from its initial value 4710 N, until it falls below the value Pg=332 N=changeover).

From this we obtain in accordance with P=pxf Pg 33.2 da N pu=p1 =-= =10.6 bar f, 3.14 cm2 The cylinder battery B I can therefore be "run down" in the case of a required back pressure 4 bar down to a cylinder pressure p,=10.6 bar before the changeover occurs.

Example 2 The values p112, d, and d2 remain unchanged. Only the back pressure PHD=16 bar: whilst the factor F is also increased to 0.8.

P,,=p,,xf,xF=16x2.95x0.8=37.7 da N Pg=P2+pHD=285+377 (P2 by example 1) Pg=66.2 da N Pg 66.2 da N p1 = =21 bar f, 3.14cm2 For a back pressure of 1 6 bar the changeover now occurs at pU=21 bar.

It emerges from the two examples given hereinbefore that for a rising back pressure its difference from the changeover pressure becomes smaller.

It is therefore advantageously ensured by the control of the changeover device according to the invention that, as a function of the back pressure (=work pressure at consumer) respectively selected or required, the changeover from the one cylinder battery to the other is "co-determined" by the value of the back pressure, so that optimum emptying of the cylinder etc., under the relevant existing conditions is always ensured.

Claims

1. Changeover device for the withdrawal of fluid from pressurised fluid containers, wherein the changeover is effected by the medium withdrawn, with a chamber which is connectable to two pressure containers and which which two outlet channels are associated which combine to form a common outlet pipe and with a control piston in the chamber which exhibits at both ends shut off elements for the pressure container supply and the associated outlet channel characterised in that a pressure-reducer is arranged in the outlet pipe, and that from the back pressure region of the pressurereducer there are two pipes each of which leads into a pipe entering one of the front pressure regions and that pressure relief valves and a nonreturn valve are arranged in connection with each of the said two pipes.

2. Changeover device according to Claim 1, characterised in that each outlet channel is connected to an annular space which is formed between a connector for the supply channel and the end face of the piston when the piston occupies respective closing position.

3. Changeover device according to Claim 1 or Claim 2 characterised in that the two outlet channels are connected to a further chamber in which an auxiliary piston is slidingly arranged.

4. Changeover device according to any of Claims 1 to 3, characterised in that the auxiliary piston is constructed as a nonreturn valve and also arranged to actuate the pressure relief valves.

5. Change over device according to any preceding claim characterised in that radial seal elements are provided for sealing both the piston and the auxiliary piston.

6. Changeover device for withdrawal of fluid from pressurised fluid containers substantially as hereinbefore particularly described and as illustrated in the accompanying drawing.