Note: Descriptions are shown in the official language in which they were submitted.
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1 BACKGROUND OF THE INVENTION
2'
3 Severe pipeline damage could result from pressure surges in
i a liquid pipeline, which could occur when there is any sudden
change in velocity of the liquid, as when starting or stopping
6 a pumo. Such surges have been relieved in some instances by
7 operation of valve which open whenever they occur. Since many
8 pipeline surges never reach dangerous levels, the diversion of
9 liquid at every occurence is a needless waste and may require
a reservoir of enormous capacity. Particularly where a closed
11 tank is required, this could be very costly.
12
13 OBJECTS OF THE INVENTION
14
It i9 an object of this invention to provide a liquid
16 surge relieving system which operates to relieve only those
17 pressure surges which are beyond a limit to be safely accommodatec .
18 by the pipeline.
19 It is a further object of this invention to provide a surge
relieving system which provides controlled flow from the pipeline
21 of a quantity of liquid which is then brought to a controlled
22 stop.
23 It is a further object of this invention to provide a pipe-
24 line surge control system which diverts just that quantity of
liquid necessary to eliminate the dangerous peak of a pipeline
26 surge and then dissipates the energy of that quantity of liquid.
27 It is a further object of this invention to provide a com-
28 plete surge relief system which is compact in construction and
29 which may be installed as a unit.
Other objects and advantages of this invention will become
31 apparent from t~e description to follow, particularly when read i
32 conjunction with the accompanying drawing.
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1 BRIEF SUMMARY OF THE INVENTION
3 In carrying out this invention, there is provided for a
i liquid pipeline, a surge relief valve, which may be of the type
having a flexible tube which is constricted around a circular
6 barrier by hoop tension and by pressure of a surrounding pilot
7 gas. When the surge relief valve is opened, the pipeline liquid
8 is diverted through the relief pipe to a closed receptacle which
9 is pre-charged by a gas at a pressure level sufficient to cushion
the impact and, as is desirable in some cases, to maintain the
11 fluid in liquid state. Means are provided within the closed
12 receptacle to dissipate the energy of the surging liquid and
13 bring it to a controlled stop as soon as possible.
14 In operation of the system, the pilot gas is set at a pre-
determined pressure level which is well in excess of normal
16 pipeline pressure, but within the range that can safely be handle
17 by the pipeline. Hence, pipeline liquid is diverted to the close
18 receptacle only in the event of dangerous surges, and only in a
19 volume to prevent the surge from generating the pressure peak
which exceeds the safe design level. In a preferred embodiment~
21 the relief line is connected to a pipe within a closed receptacle
22 which pipe has a plurality of apertures along its length through
23 which the liquid flows as it moves along. When the surge has
24 passed, and pipeline pressure subsides, a return line returns the
25 ¦ 1iquid so di rted to the pipeline.
27
28
29
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113~4S
1 BRIEF DESCRIPTION OF THE DRAWING
2- 1
¦ FIG. 1 is a more or less schematic view of the surge relief
4 system of a preferred embodiment;
5 I FIG. 2 is an end view of the system assembly;
6 , FIG. 3 to 10 illustrate other embodiments of this invention.
7 l
8 I DESCRIPTION OF PREFERRED EMBODIMENTS
I
. 9 1 Embodiment of FIGS. 1 and 2
, 10 .
; 11 Referring now to the drawing with greater particularity,
12 1 the surge relief system 10 of this invention is adapted for op-
13 eration in conjunction with a liquid transporting pipeline
14 12, and is installed in a branch or surge relief line 14 in open
15 ¦ communication therewith. Surges frequently occur when the flow-
16 1 ing liquid is subjected to sudden changes in flow conditions,
17 as when a pump (not shown) is activated or deactivated. ~.'hen
18 such surges exceed a predetermined designed pressure level of
19 ¦ safe pipeline operation, the system 10 is conditioned to relieve
20 ¦ them.
21 The pressure is relieved through a valve 16, ~hich is bi.ased
22 toward open position by pxessure of li~uidin the pipeline, and
23 may be of the expansible tube type, such as is that shown in
24 Bryant U.S. patent No. 3,272,470, granted September 13, 1966.
Specifically the surge relief valve 16 may comprise a cylindrical
26 body shell 18, which is clamped between two closure plates 20,
27 as by means of studs 22~The closure plates are, in turn, secured
28 by a conventional means to complementary flanges 24 in the pipe-
2 line branch 14 with the output thereof directed to a storage
3 reservoir 26.
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. I 113~3745
1 A slotted core 28 is carried within the valve body 18 and
2 includes spaced, circumferential rows of inlet and outlet slots
3 30 and 32 on opposite sides of an intermediate barrier 34. A
flexible, expansible tube 36 is stretched around the cylindrical
sealing surface 38 of the barrier, normally to prevent flow from
6 the slots 30 to the outlet slots 32. A gas, such as Nitrogen
7 from a suitable source 39, is regulated by a regulator 40 to a
8 predetermined pressure Pj to be maintained in the jacket 41
9 surrounding the expansible tube 36. The jacket pressure Pj is
well above normal pipeline pressure Pl, but within the safe
11 design limits of the pipeline, and will enable the valve 16 to
12 open and relieve a surge when that pressure is exceeded. A
13 restraining sleeve 42 with perforations therein limits the ex-
14 pansion of the rubber tube 36, while the spaceous chamber 43
lS around the sleeve provides plenty of volume for compression of
16 the control gas, whereby the surge relief valve 16 will open
17 quickly to pipeline pressure asserted against the interior of
18 the flexible tube 36 when it reaches a level which is in excess
19 of the jacket pressure Pj.
Extending into the reservoir 26 is an energy-attenuating
21 tube 44, which is connected directly to the branch line 14,
22 as by a suitable flange connection 46. The attenuating tube 44
23 is preferably centered within the reservoir 26, as by means of
24 arms 48,and is provided with several rows of apertures, which may
2~ be in the form of slots 50, spaced arcuately around the cylin-
26 drical surface thereof.
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. . 1 113~745
1 As shown in FIG. 2, the surge relief pipe 14 has a U-bend
2 between the relieving valve 16 and the closed receptacle 26
3 and, for greater accessibility, the axis of the reservoir 26 is
i displaced from the vertical plane of the axis of the valve 16.
The U-bend dissipates some energy of the diverted liquid by
6 ¦imposing friction losses on it; the rapid reversal tends to
1 7 equate thrust forces; and the bend enables a more compact
8 structure. In addition, the centrifugal force tends to throw the
¦liquid to the outside wall of the pipe. This, together with the
laying over of the relief pipe 14 at an angle tends to generage a
11 rotation in the stream and elongation of the rapidly moving
12 ¦front, converting the "piston slug" to a wedge.
13 It is highly desirable to have more slot area in the sparge
14 tube 44 than is needed to accommodate maximum liquid flow, so that
gas is drawn into the sparge tube 4A to reduce the pressure of the
16 fluid, creating a greater pressure differential to increase flow
17 from the valve 16.
18 In any event, when the surge relief valve 16 opens, the
19 diverted liquid flowing into the sparge tube will flow, drop and
be projected, through the apertures 50 whereby energy thereof is
21 attenuated until it reaches a state of quiescence in the reservoir
22 1 26.
23 In addition, the reservoir 26 is precharged with a gas, such
24 as air or nitrogen, from the source 39, regulated by regulator
2 at 51 to a predetermined pressure level Pc to cushion the impact
2 of the arriving waves and, in the case of some liquids such as a
2 volatile liquid, to maintain a pressure sufficient to prevent it
2 from becoming gaseous. The closure cap 52 at the end of the
2 attenuator tube 44 entraps gas in the imperforate end portion
3 to provide a further cushion.
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113B745
The surge relief system 10 is designed to relieve only
2 ¦ dangerous surges; most surges will be acocmmodated in the pipe-
3 ¦ line itself. Even with dangerous surges, only that amount
4 ¦ of pipeline liquid is diverted to the reservoir 26 which is
S ¦ attributable to that portion of the surge beyond the safe limits
of the pipeline, taking into consideration a margin of safety.
7 That is, if it is determined that the pipeline can safely handle
pressures at a given level though well above normal pipeline pres-
sures, the surge reliever 16 is set so that it will not open
10 ¦ until that level is reached. Then, only that volume of liquid
11 necessary to contain the peak pressure within a safe design
12 ¦ level needs to be accommodated in the attenuation tube 44 and
13 cushioned by the precharge pressure Pc~ which is determined by
14 pipeline design parameters, and may be atmospheric pressure or
higher.
16 ¦ Particularly with the loop 14a in the branch line 14 dispos-
17 ¦ ing the reservoir 26 adjacent to the surge relief valve 16, the
18 entire system lO is extremely compact and may be assembled and
19 shipped on a single platform or skid (not shown).
After a surge is attenuated and subsides in the pipeline 12,
21 it is desirable to restore the capability of the system lO and
22 transfer diverted liquid from the reservoir back to the pipeline
23 12 in order to return the reservoir to full, or near-full,
24 capacity. For this purpose, a small return line 54 is provided
with an on-off valve 56 in the event that it is desired to monito
2 the return manually. In addition, or in the alternative, a simpl
2 check valve 58 may be installed in the line for automatic liquid
2 return when pressure in the reservoir and branch line 14 down-
2 stream of the surge relief valve 16 exceeds that in the pipeline
3 12 after the surge subsides. In either event, since the liquid
33 in the reservoir 26 and branch line 14 augmented by the compresse
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. . 1138745
1 gas cushion, is usually well above pipeline pressure, it will
2 return to the pipeline lO without need of a pump when pressure
3 therein subsides, to normal or near normal level. With the
4 automatic liquid return enabled by the check valve 58, a float
5 valve 60 is also provided so that, when liquid ceases flowing,
6 it will close to prevent loss of the precharged qas in the
7 chamber 26.
8 For complete drainage of the reservoir 26, a liquid drain
9 line 62 is opened from the bottom of the reservoir 26 with a check
valve 64 or the liXe provided to effect flow.
11
12 The Embodiment of FIG. 3
13
14 In this embodiment, the surge wave is relieve~ by directing
a quantity of liquid from the surge relief valve 16, through
16 relief pipe 66, and the energy of the liquid as so diverted is
17 attenuated by impacting in a jet against the end of a cylindrical
18 tank 6P. An obvious disadvantage of this embodiment resides in
19 the unidirectional thrust im~osed on the system by the impacting
20 jet.
21
2 The Embodiment of FIG. 4
23
2 ~nidirectional thrust can be avoided by directing the jet
2 tangentially of the cylindrical tank 70. This generates a swirl-
2 ing mass around the tank 70, dissipating energy while avoiding
2 jet impact. If the relief pipe 72 is located near the top of
2 the tank 70, the liquid will follow a generally spiral path
2 until it reaches the bottom.
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. 113~745
1The Embodiment of FIG. 5
3In FIG. 5, the gas or buffer G contained in the closed end 74
4 of the energy dissipating chamber 75 is separated from the liquid
5 in the surge by means of a piston 78 or the like. This would
6 avoid gas entrainment in the liquid and resultant loss of the
7 cushioning gas when the liquid is returned to the pipeline. The
8 energy of the diverted flow is dissipated in compressing the gas
9 on the opposing side of the piston 78. If desired, the gas
10 cushion may be augmented or replaced by a spring 8~.
11
12 The Embodiment of FIG. 6
13
14 Here, energy is again attenuated by compressing a gas G
hich is separated from the pipeline liquid by a diaphragm 82
16 sealed across the closed chamber 84. In addition, the diaphragm
17 may be elastic to further dissipate energy in stretching.
18
19 The Embodiment of FIG. 7
21 In this embodiment, a series of accumulators P6 open to the
22 closed chamber 88, each with a bladder 90 or the like charged
23 ith a gas under pressure. Hence, the surging liquid flows into
24 he accumulators 86 to compress the gas in the bladders 90, thereby
25 dissipating energy. In addition, the chamber 88 may be pre-charged
26 with a cushioning gas.
27
28
29
31
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113B745
1 The Embodiment of FIG. 8
3 In this case the energy is attenuated by providing the
i closed chamber 92 with a series of bends 94 which impose friction
losses on the diverted liquid. In addition the chamber may be
6 of progressively increasing cross-section to further dissipate
energy.
8 Also as shown in FIG. 8 the system of this invention is not
9 limited to an expansible tube valve, as illustrated in FIG. l,
10 and any embodiment shown will operate with any flow blocking
11 device that opens at a predetermined pressure level. For example,
12 a device 96 with a rupture disc 98 which ruptures at a given pres-
13 sure to allow full flow will answer the needs of the system.
14 However, without the expansible tube of FIG. l to modulate the
15 flow, some other means, such as a bundle of tubes lO0 to impose
16 friction losses may be required to lessen the impact against the
17 closed chamber 92.
18
19 The Embodiment of FIG. 9
21 In this embodiment the closed chamber 102 is angled upward
22 so that impact of the surging liquid is with a sloping wall.
23 This has much the same effect as the dissipation of ocean waves
25 breaking up on a beach.
33
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1~387~5
1 The Embodiment of FIG. 10
3 Finally, the FIG. 10 embodiment overcomes the disadvantage of
4 unilateral thrust by forming the closed chamber 104 as a "Y" to
S divide the stream at 106 and 108, to ~et two streams into a tank
6 110 from opposite directions, to produce a mutually cushioning
7 effect.
8 While this invention has been described in conjunction with
9 preferred embodiments thereof,it is obvious that other modifi-
cations and changes may be made by those skilled in the art
11 without departing from the spirit and scope of this invention,
12 ¦ a~ defined the claims appended hereto.
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