GB2151307A

GB2151307A - Pressure surge reducers

Info

Publication number: GB2151307A
Application number: GB08431503A
Authority: GB
Inventors: Christian Welzel
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1983-12-14
Filing date: 1984-12-13
Publication date: 1985-07-17
Also published as: FR2556816A1; IT8423092A1; IT8423092A0; IT1176921B; DE3345667A1; GB8431503D0

Abstract

The invention relates to pressure surge reducers for use in pipelines. A plurality of pressure vessels (2) are disposed around a support pipe (1) which is installed as part of the pipeline. Each pressure vessel is independently connected to the support pipe (1) by a discrete feed line (7), and has a gas cushion (4) which absorbs and thereby reduces pressure surges of the fluid in the pipeline. The reducer may be preassembled for direct installation in a pipeline, the support pipe (2) constituting a length of the pipeline itself. <IMAGE>

Description

SPECIFICATION Pressure surge reducers The invention relates to a pressure surge reducer for fluid pipelines. It has typical application in water pipelines connected to pumping stations, but also has use in other fields.

The invention is particularly concerned with surge reducers in a body of fluid coupled to that in the pipeline, is acted on by a cushion of gas, normally under pressure.

Pressure surges occur in the operation of pipelines through a sudden change in the quantity flowing through e.g. when feed pumps are switched off or suddenly break down, or rapid opening and closing of shut off devices. Under such circumstances, the pressure in the pipeline oscillates up and down about the normal operating pressure creating a pressure wave which must be dissapated in the line Typically, the wave is reflected at the line end or at closures and runs back as a negative wave to theisource.

After the next run back and forth it comes positive again etc. This oscillation is absorbed above all by the roughness f the pipeline and gradually dies down. The pressure surge must on no account exceed the permissible stress of the pipe line. To ensure this pressure surge reducers are disposed on the pipeline, frequently alongside nozzle non-return valves and/or immediately behind pumping stations.

A simple form of surge reducer is a surge tank connected above a pipeline containing a body of the fluid in the line. The energy of the wave is dissapated in the tank by the raising and lowering of the fluid level in the tank.

Currently, a particularly frequently used type of pressure surge reducer is the so called air vessel. These are pressure containers which are connected with the pipeline via a feed line and in normal instances are half filled with the fluid which is conveyed in the pipeline. The other half of the air vessel confines a cushion of gas, normally air, under pressure. On negative pressure surges, fluid is automatically delivered from the container to the pipeline, whereas conversely in the case of positive pressure surges fluid is taken up by the container, with a reduction in the volume of the cushion of pressure gas. In both cases respectively a reduction in the pressure peak occurs.A disadvantage of these air vessels is that in the case of larger pipelines they require considerable resources in construction and installation, since a compressor station is to be provided to maintain the gas cushion.

This requires continuous expenditure for maintenance and care of the compressors, which is a great problem particularly in the case of water pipes in many developing countries because of the insufficient availability of suitable specialist personnel.

In German Patent Specification No.25 49 367 a device is proposed to relieve a fluid pipeline of pressure surges, which is provided with a relief valve connected to the pipeline and closeable by a mechanism which is able to be charged with a pressure gas under the pressure prevailing in the pipeline. The pressure gas is enclosed within a storage container in a flexible bellows, and is thereby separated from an inert sealing liquid, which fills up the remainder of the storage container.

The storage container is connected via a feedpipe with a blocking container, connected to the pipeline and partly filled with the fluid of the pipeline and partly with the inert sealing liquid. A sudden increase in pressure in the pipeline causes a corresponding rise in pressure in the blocking container and via the sealing liquid also in the storage container, so that the pressure gas bellows is compressed.

Via the increase in gas pressure, the relief valve is then actuated. Not only is this an expensive mode of construction but the device has the particular disadvantage that with positive pressure surges fluid escapes from the pipeline and that in practice, no account is taken of negative pressures surges since the relief valve only reacts to excess pressure.

The present invention is directed at a pressure surge reducer for a fluid pipeline, which can react quickly both to positive and to negative pressure surges, possesses a high degree of operational security and can operate practically without maintenance. To this end, a surge reducer according to the invention comprises at least two pressure vessels, each vessel having a discrete feedline for connection to a said pipeline and means for defining in the vessel a gaseous cushion for accommodating changes in fluid pressure transmitted thereto through the respective feed line. Typically, each gaseous cushion is separated from fluid in the respective vessel by an elastic casing at least part of which will normally have a bellows construction.

In preferred embodiments of the invention, each vessel has a valve for controlling the amount of gas in said cushion, and a manometer for indicating the pressure therein. In another preferred feature each vessel comprises a tubular body with a flange-mounted cover at one end thereof. Thus, such a valve is conveniently mounted on a line coupled to the cushion through the cover.

Surge reducers according to the invention may be designed for direct incorporation into a pipeline,by including a support pipe upon which the vessels are mounted, and to which their respective feed lines are connected. The support pipe can thus be fitted into and as part of the section of pipeline. This enables the surge reducer to be assembled elsewhere as an integral construction, thereby simplifying installation. The construction may also include an assembly stand which can further facilitate installation. The cross-section of the support pipe should preferably be at least as large as that of the pipeline. Typically, the support pipe is of the same material quality, and has the same internal and external diameters. The total effective volume of the pressure vessels will normally constitute at least 1%, normally 1% to 2% of the pipeline section in which it is to be effective.The required volume for a particular application can though be more accurately determined in a surge calculation.

In an integral construction of the type described above, the sum of the cross section of the pressure vessels is preferably at least equal to that of the support pipe, and the feed lines extend from the support pipe to an angle in the range 30' to 45,, to the axis of the support pipe. Each vessel may conveniently have a longitudinal axis aligned parallel to that of the support pipe, and such axes may be disposed in a region to one side of a plane containing the axis of the support pipe. The connections of the feed lines to the support pipe can be spaced both around and along the support pipe.

In the use of a surge reducer according to the-embodiment of the invention, a cushion of pressure gas enclosed within a pressure vessel in an elastic cover is acted upon by the pressure of a fluid pipeline. With a positive surge, each gas cushion is compressed, so that a correspondingly greater volume is available for the fluid in the pipeline and the fluid pressure is reduced. Conversely negative pressure surges, which under certain circumstances may result from for example, the collapse of the pipeline are reduced by the expansion of the gas cushions and additional fluid being passed into the pipeline. According to the invention, at least two, preferably three pressure vessels, which operate independently of each other, are provided in order to achieve security for the pipeline even if an individual pressure vessel were to break down.Further, this division favours a rapid fluid exchange between the pressure vessels and the pipeline and hence a rapid reduction of the pressure peak.

In order that positive and negative pressure surges are taken up equally, the pressure vessels in normal operating condition are in each case filled half with fluid from the pipeline and half with gas under pressure within the elastic cover. The pressure gas cushion in each pressure vessel may be filled from the outside via a filling valve, and may be monitored by means of a manometer. When a pressure vessel is damaged, the gas filling merely has to be renewed so that otherwise the apparatus operates without maintenance.

Where the pressure vessels are arranged around a support pipe the vessels may be connected with each other and/or with the support pipe by means of additional fastening elements (apart from the line connection), further facilitating preassembly of the reducer in the factory prior to the transportation as one unit to the place at which it is to be installed. Such an unit merely has to be inserted with its piece of support pipe into the pipeline system and connected therewith; e.g.

by the welding of two circular seams. Matching of the cross section of the support pipe to that of the pipeline can ensure that the surge reducer practically does not adversely increase the flow resistance of the pipeline as a whole.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings wherein: Figure 1 is a plan view of a pressure surge reducer according to the invention, Figure 2 is a section taken on line A-A in Figure 1, Figure 3 is a view on line B-B in Figure 2, and Figure 4 is a view, partly in section, of a pressure vessel as shown in Figures 1 to 3.

The pressure surge reducer illustrated has three pressure vessels 2 which operate independently of each other, and which are connected with the piece of support pipe 1 via discrete feed lines 7. The pressure vessels 2 are constructed substantially as tubular bodies, which preferably have a larger diameter than the piece of support pipe 1. Their dimensioning depends upon the calculation of the pressure surge, which has to be plotted for each case of operation of the pipeline or pipeline section which is to be protected. At their head end they are connected in each case with a feed line 7 via a reducing piece 3, and have on their rearward end a flangemounted cover 8, e.g. a welding neck flange.

Through the cover 8, in each case, an elastic gas-tight casing 4 of rubber or synthetic material, can be filled with pressure gas, preferably nitrogen (as it is harmless in a drinking water system), by means of a feed line 13 which is provided with a filling valve 14. A manometer 12, is connected to the pressure gas casing 4, whereby the gas filling can be monitored from the outside at any time.

In normal state, in which the pressure gas cushion is below the operating pressure of the pipe line, each pressure vessel 2 is approximately half filled with the fluid 11 of the pipe line and half-filled with the elastic casing 4.

As shown in Figure 4 the casing 4 is preferably constructed, at least to a partial extent, as a bellows 6, in order to promote a fast compression or expansion of the casing 4 in the case of a pressure surge. For this purpose, it is also advantageous to provide the inner surfaces of the wall of the pressure surge vessels 2 with a smooth coating (e.g. epoxy resin) which reduces friction. So as not to have to dismantle the entire pressure surge reducer and hence have to interrupt the transportation of fluid, in the case of a necessary repair to the pressure containers 2 which are practically maintenance-free, each pressure vessel 2 may be isolatable from the piece of support pipe 1 by a stop valve 5 in the feed line 7. In addition, discharge connecting pieces and safety valves may be provided (not shown).The axes of the pressure containers 2 are preferably aligned parallel to the axis of the piece of support pipe 1 and lie in a geometric half space, which is limited by a plane in which the axis of the piece of support pipe 1 lies. In this way a compact construction is achieved. The feed lines 7 open expediently in the piece of support pipe 1 at those positions which are arranged in angular displacement and/or at an axial distance behind each other, and also have a cross section which in total is at least as great as the cross section of the piece of support pipe 1. They are inclined at an angle of approximately 30 to 45 to the axis of the piece of support pipe 1 (in the opposite sense to the conveying direction of the pipe-line, which is indicated by arrows in Figure 2).These steps favour a quick reception of a pressure surge by the pressure containers 2, as the flow resistances are kept to a minimum. The pressure vessels 2 are firmly connected with each other and with the piece of support pipe 1 by fastening elements 10, so that the entire pressure surge reducer can be fully preassembled at the factory and transported as a complete unit.

An additional feature for the transporting and subsequent installation at the site of construction (anchoring) is the mounting of the entire arrangement firmly on a flat assembly stand or steel section frame 9,not shown in Figure 1. Also the support pipe is selected to be of the same material quality and the same dimensions as in the pipe-line itself which is to be secured. In this way the same expenditure is required for assembly at the construction site as for the fitting (e.g. welding) of a normal piece of pipe into the pipeline.

Additional security against pressure surge for a pipeline section is the provision of a second pressure surge reducer, the pressure vessels of which are aligned exactly in reverse; i.e., with the feed lines 7 inclined to the pipeline axis in the conveying direction of the pipeline. In this way, the pressure waves moving ahead and the reflected pressure waves are attenuated equally well, which is particularly important for the first amplitudes.

Advantages of pressure surge reducers according to the invention result from their suitability for complete pre-fabrication at the factory and the elimination of a compressor station, whereby a considerable expenditure in assembly and testing at the construction site is avoided. Conventional commercial-and therefore favourably priced-pipes may be used for the pressure vessels 2 and as the support pipe 1. The apparatus is simple reliable in operation and practically maintenance free. Proper functioning may be monitored from the outside without difficulty.

Claims

1. A pressure surge reducer for a fluid pipeline comprising at least two pressure vessels, each vessel having a discrete feed line for connection to a said pipeline and means for defining in the vessel a gaseous cushion for accommodating changes in fluid pressure transmitted thereto through the respective feed line.

2. A surge reducer according to Claim 1 wherein each gaseous cushion is separated from fluid in the respective vessel by an elastic casing.

3. A surge reducer according to Claim 2 wherein at least a part of the casing has a bellows construction.

4. A surge reducer according to any preceding Claim wherein each vessel has a valve for controlling the amount of gas in said cushion, and a manometer for indicating the pressure therein.

5. A surge reducer according to any preceding Claim wherein each vessel comprises a tubular body with a flange-mounted cover at one end thereof.

6. A surge reducer according to Claim 4 or Claim 5 wherein the valve on each vessel is mounted on a line coupled to the cushion through the cover.

7. A surge reducer according to any preceding Claim wherein each gaseous cushion is defined by a mass of nitrogen.

8. A surge reducer according to any preceding Claim having three said pressure vessels.

9. A surge reducer according to any preceding Claim wherein the inner surface of each vessel comprises a smooth finished coating to reduce friction.

10. A surge reducer according to any preceding Claim wherein the vessels are mounted on a support pipe adapted for incorporation into a said pipeline, and to which the feed lines are connected.

11. A surge reducer according to Claim 10 wherein the source ofthe cross-sections of the pressure vessels is at least equal to the crosssection of the support pipe.

12. A surge reducer according to Claim 10 or Claim 11 wherein the feed lines extend from thesupport pipe at an angle in the range 30 to 45 to the axis of the support pipe.

13. A surge reducer according to any of Claims 10 to 12 wherein each vessel has a longitudinal axis aligned parallel to that of the support pipe.

14. A surge reducer according to Claim 13 wherein said axis of the vessels are disposed in a region containing or to one side of a planecontaining the axis of the support pipe.

15. A surge reducer according to any of Claims 10 to 14 wherein the connections between the feed lines and the support pipe are disposed in at least two spaced planes perpendicular to the axis of the support pipe.

16. A surge reducer according to any of Claims 10 to 15 including an assembly stand upon which the support pipe and pressure vessels are mounted.

17. A surge reducer according to any of Claims 10 to 16 installed on a pipeline section with the support pipe an integral part thereof.

18. A surge reducer according to Claim 17 wherein the total effective volume of the pressure vessels constitutes at least 1% of the pipeline section.

19. A surge reducer according to Claim 17 or Claim 18 wherein the material quality and the diameter of the support pipe are substantailly the same as those of the pipeline section.

20. A pressure surge reducer substantially as described herein with reference to the accompanying drawings.