Efficient and energy-saving nitrogen generation system

Abstract

The utility model relates to an efficient and energy-saving nitrogen making system, which belongs to the technical field of PSA nitrogen making, and comprises an adsorption tower A and an adsorption tower B which are mutually independently arranged, a pipeline is connected between the adsorption tower A and the adsorption tower B, an automatic valve or a manual valve is arranged on the pipeline, and the efficient and energy-saving nitrogen making system is favorable for improving nitrogen making efficiency and reducing nitrogen making energy consumption.

Description

TECHNICAL FIELD

[0001] The utility model relates to PSA nitrogen making technical field especially relates to a high -efficient energy -conserving nitrogen making system. BACKGROUND

[0002] The current PSA nitrogen making machine will keep some nitrogen with lower purity than target purity in the adsorption tower after each shutdown, so it needs to wait for a period of time to improve the purity of nitrogen in the adsorption tower to the target purity before feeding to the process tank each time, the above-mentioned purity improvement process not only has long duration (generally needs 20 to 40 minutes), but also needs to consume electric energy continuously during the waiting period (because compressed air needs to be injected into the adsorption tower continuously, and the air compressor keeps running to consume electric energy continuously), which not only affects the nitrogen production efficiency, but also causes energy waste, and this problem has been the pain point and difficulty of the gas air separation industry. SUMMARY

[0003] The utility model aims at shortening the starting purity standard time of PSA nitrogen making machine, and reducing the energy consumption caused by starting stage.

[0004] Therefore, the utility model adopts the following technical scheme:

[0005] A kind of high -efficient energy -conserving nitrogen making system, including the A adsorption tower, B adsorption tower and process tank independently arranged, it further includes intake manifold, intake branch pipe, first connecting pipe, emptying branch pipe, emptying main pipe, lower equalizing pipe, second connecting pipe, outlet branch pipe, outlet main pipe, upper equalizing pipe and back flushing pipe;Intake manifold one end three-way connection intake branch pipe, the both ends of intake branch pipe are three-way connection first connecting pipe, the both ends of first connecting pipe are communicated with the bottom of A adsorption tower and B adsorption tower respectively, the both ends of emptying branch pipe are three-way connection first connecting pipe, one end of emptying main pipe three-way connection emptying branch pipe, the other end is communicated with external;The both ends of lower equalizing pipe are communicated with the middle part of A adsorption tower and B adsorption tower respectively, one end of second connecting pipe three-way connection lower equalizing pipe, the other end three-way connection first connecting pipe between the both ends of intake branch pipe and emptying branch pipe;The both ends of outlet branch pipe are communicated with the top of A adsorption tower and B adsorption tower respectively, one end of outlet main pipe three-way connection outlet branch pipe, the other end is communicated with process tank, the both ends of upper equalizing pipe are three-way connection outlet branch pipe on the both sides of outlet main pipe respectively, the both ends of back flushing pipe are three-way connection upper equalizing pipe.

[0006] The first automatic valve is arranged on the air inlet branch pipe on one side of the air inlet main pipe and on the pipeline between the air inlet main pipe and the A adsorption tower, the second automatic valve is arranged on the air inlet branch pipe on the other side of the air inlet main pipe and on the pipeline between the air inlet main pipe and the B adsorption tower, the third automatic valve is arranged on the exhaust branch pipe on one side of the exhaust main pipe and on the pipeline between the exhaust main pipe and the A adsorption tower, the fourth automatic valve is arranged on the exhaust branch pipe on the other side of the exhaust main pipe and on the pipeline between the exhaust main pipe and the B adsorption tower, the fifth automatic valve is arranged on the first connecting pipe between the second connecting pipe and the air inlet branch pipe and the exhaust branch pipe and on the pipeline between the second connecting pipe and the A adsorption tower, the sixth automatic valve is arranged on the first connecting pipe between the second connecting pipe and the air inlet branch pipe and the exhaust branch pipe and on the pipeline between the second connecting pipe and the B adsorption tower, the seventh automatic valve is arranged on the lower pressure equalizing pipe and on the pipeline between the second connecting pipe and the A adsorption tower, the eighth automatic valve is arranged on the lower pressure equalizing pipe and on the pipeline between the second connecting pipe and the B adsorption tower, the ninth automatic valve is arranged on the gas outlet branch pipe on one side of the gas outlet main pipe and on the pipeline between the gas outlet main pipe and the A adsorption tower, the tenth automatic valve is arranged on the gas outlet branch pipe on the other side of the gas outlet main pipe and on the pipeline between the gas outlet main pipe and the B adsorption tower, the eleventh automatic valve is arranged on the upper pressure equalizing pipe between the two ends of the back flushing pipe, and the twelfth automatic valve and the manual valve are connected in series on the back flushing pipe.

[0007] The utility model discloses a nitrogen making system, which comprises an air compressor, an air cooler, an air filter, an air tank, an air inlet main pipe, an air inlet branch pipe, an exhaust main pipe, an exhaust branch pipe, a gas outlet main pipe, a gas outlet branch pipe, an A adsorption tower, a B adsorption tower, a first connecting pipe, a second connecting pipe, a lower pressure equalizing pipe, an upper pressure equalizing pipe, a back flushing pipe, a first automatic valve, a second automatic valve, a third automatic valve, a fourth automatic valve, a fifth automatic valve, a sixth automatic valve, a seventh automatic valve, an eighth automatic valve, a ninth automatic valve, a tenth automatic valve, an eleventh automatic valve, a twelfth automatic valve and a manual valve. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 The utility model discloses a nitrogen making system's structure schematic diagram DETAILED DESCRIPTION

[0009] The technical solutions in the embodiments of the utility model will be clearly and completely described below with reference to the drawings in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all the embodiments.

[0010] As Figure 1The high-efficiency and energy-saving nitrogen production system comprises A adsorption tower 1, B adsorption tower 2 and process tank 3 which are arranged independently, the A adsorption tower 1 and the B adsorption tower 2 are used for decomposing high-purity nitrogen from compressed air, and the process tank 3 is used for receiving the high-purity nitrogen output from the A adsorption tower 1 and the B adsorption tower 2, wherein the high-purity nitrogen in the application refers to the nitrogen with the purity reaching the set target purity.

[0011] The nitrogen production system further comprises air inlet main pipe 4, air inlet branch pipe 5, first connecting pipe 6, air exhaust branch pipe 7, air exhaust main pipe 8, lower equalizing pipe 9, second connecting pipe 10, air outlet branch pipe 11, air outlet main pipe 12, upper equalizing pipe 13 and back flushing pipe 14; one end of the air inlet main pipe 4 is connected with the air inlet branch pipe 5 through a tee joint, and the other end is connected with an air compressor, both ends of the air inlet branch pipe 5 are connected with the first connecting pipe 6 through a tee joint, both ends of the first connecting pipe 6 are communicated with the bottom of the A adsorption tower 1 and the B adsorption tower 2, both ends of the air exhaust branch pipe 7 are connected with the first connecting pipe 6 through a tee joint, one end of the air exhaust main pipe 8 is connected with the air exhaust branch pipe 7 through a tee joint, and the other end is communicated with the outside; both ends of the lower equalizing pipe 9 are communicated with the middle part of the A adsorption tower 1 and the B adsorption tower 2, one end of the second connecting pipe 10 is connected with the lower equalizing pipe 9 through a tee joint, and the other end is connected with the first connecting pipe 6 between the air inlet branch pipe 5 and the air exhaust branch pipe 7 through a tee joint; both ends of the air outlet branch pipe 11 are communicated with the top of the A adsorption tower 1 and the B adsorption tower 2, one end of the air outlet main pipe 12 is connected with the air outlet branch pipe 11 through a tee joint, and the other end is communicated with the process tank 3, both ends of the upper equalizing pipe 13 are connected with the air outlet branch pipe 11 on both sides of the air outlet main pipe 12 through a tee joint, and both ends of the back flushing pipe 14 are connected with the upper equalizing pipe 13 through a tee joint. All the above pipes are arranged outside the A adsorption tower 1, the B adsorption tower 2 and the process tank 3, wherein the first connecting pipe 6 is in inverted U shape, and both ends thereof are fixed to the bottom of the A adsorption tower 1 and the B adsorption tower 2 through flanges, the air inlet branch pipe 5 and the air exhaust branch pipe 7 are arranged horizontally in the U opening of the first connecting pipe 6, and both ends thereof are connected with the first connecting pipe 6 on both sides through a tee joint, the air inlet branch pipe 5 is arranged below the air exhaust branch pipe 7, one end of the second connecting pipe 10 is connected with the top of the first connecting pipe 6 through a tee joint, the air outlet branch pipe 11 is in U shape, and both ends thereof are fixed to the top of the A adsorption tower 1 and the B adsorption tower 2 through flanges, the upper equalizing pipe 13 is arranged horizontally in the U opening of the air outlet branch pipe 11, and both ends thereof are connected with the air outlet branch pipe 11 on both sides through a tee joint, and the back flushing pipe 14 is in inverted U shape and is arranged above the eleventh automatic valve 25.

[0012] The nitrogen making system further comprises a first automatic valve 15, a second automatic valve 16, a third automatic valve 17, a fourth automatic valve 18, a fifth automatic valve 19, a sixth automatic valve 20, a seventh automatic valve 21, an eighth automatic valve 22, a ninth automatic valve 23, a tenth automatic valve 24, an eleventh automatic valve 25, a twelfth automatic valve 26 and a manual valve 27, all of which are pneumatic angular valves, wherein the first automatic valve 15 is arranged on the air inlet branch pipe 5 on one side of the air inlet main pipe 4 and on the pipeline between the air inlet main pipe 4 and the A adsorption tower 1, and the second automatic valve 16 is arranged on the air inlet branch pipe 5 on the other side of the air inlet main pipe 4 and on the pipeline between the air inlet main pipe 4 and the B adsorption tower 2; the third automatic valve 17 is arranged on the exhaust branch pipe 7 on one side of the exhaust main pipe 8 and on the pipeline between the exhaust main pipe 8 and the A adsorption tower 1, and the fourth automatic valve 18 is arranged on the exhaust branch pipe 7 on the other side of the exhaust main pipe 8 and on the pipeline between the exhaust main pipe 8 and the B adsorption tower 2; the fifth automatic valve 19 is arranged on the first connecting pipe 6 between the second connecting pipe 10 and the air inlet branch pipe 5 and the exhaust branch pipe 7 and on the pipeline between the second connecting pipe 10 and the A adsorption tower 1, and the sixth automatic valve 20 is arranged on the first connecting pipe 6 between the second connecting pipe 10 and the air inlet branch pipe 5 and the exhaust branch pipe 7 and on the pipeline between the second connecting pipe 10 and the B adsorption tower 2; the seventh automatic valve 21 is arranged on the lower equalizing pipe 9 and on the pipeline between the second connecting pipe 10 and the A adsorption tower 1, and the eighth automatic valve 22 is arranged on the lower equalizing pipe 9 and on the pipeline between the second connecting pipe 10 and the B adsorption tower 2; the ninth automatic valve 23 is arranged on the gas outlet branch pipe 11 on one side of the gas outlet main pipe 12 and on the pipeline between the gas outlet main pipe 12 and the A adsorption tower 1, and the tenth automatic valve 24 is arranged on the gas outlet branch pipe 11 on the other side of the gas outlet main pipe 12 and on the pipeline between the gas outlet main pipe 12 and the B adsorption tower 2; the eleventh automatic valve 25 is arranged on the upper equalizing pipe 13 between the two ends of the back flushing pipe 14, and the twelfth automatic valve 26 and the manual valve 27 are connected in series on the back flushing pipe 14.

[0013] The operation process of the above-mentioned nitrogen making system is divided into trial operation and normal operation, and correspondingly, the control method of the above-mentioned nitrogen making system is divided into trial control method and normal control method.

[0014] The trial control method comprises trial start-up control method and trial shutdown control method.

[0015] The trial start-up control method is as follows:

[0016] The A adsorption tower 1 and the B adsorption tower 2 are alternately operated once, all the automatic valves are in the closed state before start-up, and the manual valve 27 is kept open during the whole process.

[0017] When the A adsorption tower 1 works, the A adsorption tower 1 is started and the second automatic valve 16, the third automatic valve 17 and the twelfth automatic valve 26 are opened, compressed air is introduced into the A adsorption tower 1 from the bottom along the air inlet main pipe 4, the air inlet branch pipe 5 and the second connecting pipe 6 to refine nitrogen, until the purity and pressure of the nitrogen in the A adsorption tower 1 reach the set value, the tenth automatic valve 24 is opened, the high-purity nitrogen in the A adsorption tower 1 is discharged from the top of the A adsorption tower 1 along the air outlet branch pipe 11 and the air outlet main pipe 12 to the process tank 3, at the same time, the B adsorption tower 2 is analyzed, a small amount of high-purity nitrogen in the A adsorption tower 1 is blown into the B adsorption tower 2 from the bottom along the back blowing pipe 14, the waste gas in the B adsorption tower 2 is blown out of the outside world from the exhaust branch pipe 7 and the exhaust main pipe 8, until the internal pressure of the B adsorption tower 2 is less than the internal pressure of the A adsorption tower 1, the third automatic valve 17 is closed, then the B adsorption tower 2 is pressure equalized, the eleventh automatic valve 25 is opened, the high-purity nitrogen at the top of the A adsorption tower 1 is introduced into the top of the B adsorption tower 2 along the upper pressure equalizing pipe 13, then the fifth automatic valve 19 and the eighth automatic valve 22 are opened, the gas in the middle of the A adsorption tower 1 is introduced into the bottom of the B adsorption tower 2 along the lower pressure equalizing pipe 9, the second connecting pipe 10 and the first connecting pipe 6 in turn, until the internal pressure of the B adsorption tower 2 is consistent with the internal pressure of the A adsorption tower 1, the eleventh automatic valve 25, the fifth automatic valve 19 and the eighth automatic valve 22 are closed, the A adsorption tower 1 is completed, and the second automatic valve 16 and the tenth automatic valve 24 are closed.

[0018] When the B adsorption tower 2 works, the B adsorption tower 2 is started and the first automatic valve 15 and the fourth automatic valve 18 are opened, compressed air is introduced into the B adsorption tower 2 from the bottom along the air inlet main pipe 4, the air inlet branch pipe 5 and the second connecting pipe 6 to refine nitrogen, until the purity and pressure of the nitrogen in the B adsorption tower 2 reach the set value, the ninth automatic valve 23 is opened, the high-purity nitrogen in the B adsorption tower 2 is discharged from the top of the B adsorption tower 2 along the air outlet branch pipe 11 and the air outlet main pipe 12 to the process tank 3, at the same time, the A adsorption tower 1 is analyzed, a small amount of high-purity nitrogen in the B adsorption tower 2 is blown into the A adsorption tower 1 from the bottom along the back blowing pipe 14, the waste gas in the A adsorption tower 1 is blown out of the outside world from the fourth automatic valve 18, until the internal pressure of the A adsorption tower 2 is less than the internal pressure of the B adsorption tower 2, the fourth automatic valve 18 is closed, then the A adsorption tower 1 is pressure equalized, the eleventh automatic valve 25 is opened, the high-purity nitrogen at the top of the B adsorption tower 2 is introduced into the top of the A adsorption tower 1, then the sixth automatic valve 20 and the seventh automatic valve 21 are opened, the gas in the middle of the B adsorption tower 2 is introduced into the bottom of the A adsorption tower 1, until the internal pressure of the A adsorption tower 1 is consistent with the internal pressure of the B adsorption tower 2, the eleventh automatic valve 25, the sixth automatic valve 20 and the seventh automatic valve 21 are closed, the B adsorption tower 2 is completed, and the first automatic valve 15 and the ninth automatic valve 23 are closed.

[0019] The method for controlling the shutdown of the test machine comprises the following steps:

[0020] S1, the twelfth automatic valve 26 is closed;

[0021] S2, closing all automatic valves except the eleventh automatic valve 25 to keep the top of the A adsorption tower 1 and the B adsorption tower 2 at a uniform pressure;

[0022] S3, opening the third automatic valve 17, the fourth automatic valve 18, the fifth automatic valve 19, the sixth automatic valve 20, the seventh automatic valve 21 and the eighth automatic valve 22 to release the waste gas in the A adsorption tower 1, the B adsorption tower 2 and all pipelines to the outside along the exhaust main pipe 8;

[0023] S4, intermittently opening the ninth automatic valve 23 and the tenth automatic valve 24 multiple times to shock the waste gas carried by the high-purity nitrogen in the process tank 3 to the A adsorption tower 1 and the B adsorption tower 2 in a pulse mode and to the outside along the lower pressure equalization pipe 9, the second connecting pipe 10, the first connecting pipe 6, the exhaust branch pipe 7 and the exhaust main pipe 8 with the waste gas in the A adsorption tower 1 and the B adsorption tower 2, so as to improve the purity of the nitrogen in the process tank 3 and to complete the desorption of the A adsorption tower 1 and the B adsorption tower 2 at the same time;

[0024] S5, closing the third automatic valve 17 and the fourth automatic valve 18 and continuously opening the ninth automatic valve 23 and the tenth automatic valve 24 to make the high-purity nitrogen in the process tank 2 flow back to the A adsorption tower 1 and the B adsorption tower 2 until the pressure between the A adsorption tower 1, the B adsorption tower 2 and the process tank 3 is equalized.

[0025] S6, opening the twelfth automatic valve 26 to keep the A adsorption tower 1 and the B adsorption tower 2 at a uniform pressure state.

[0026] After the trial operation, the A adsorption tower 1 and the B adsorption tower 2 can store the qualified nitrogen with the same purity as that of the process tank 3, and the A adsorption tower 1 and the B adsorption tower 2 can output the qualified nitrogen without waiting for the nitrogen purity to rise in the next regular operation.

[0027] The regular control method includes a regular start-up control method and a regular shutdown control method, wherein the regular shutdown control method is the same as the trial shutdown control method, and the difference between the regular start-up control method and the trial start-up control method is that the A adsorption tower 1 and the B adsorption tower 2 continuously work multiple times in the regular start-up control method.

[0028] After each regular operation, the A adsorption tower 1 and the B adsorption tower 2 can store the qualified nitrogen with the same purity as that of the process tank 3, and the A adsorption tower 1 and the B adsorption tower 2 can output the qualified nitrogen without waiting for the nitrogen purity to rise in each subsequent regular operation.

[0029] By adopting the above control method, the above nitrogen production system of the utility model realizes the use effect of “the purity reaching the standard as soon as starting up without waiting”, which shortens the start-up time and saves the energy consumption in the start-up stage.

[0030] The above embodiments are only the preferred embodiments of the present application, and for those skilled in the art, it is obvious that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or basic characteristics of the present application. Therefore, from any point of view, the embodiments should be regarded as non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. A high-efficiency energy-saving nitrogen production system, comprising an A adsorption tower (1) and a B adsorption tower (2) which are independently arranged, characterized in that: It also includes the intake manifold (4), intake manifold (5), the first connecting pipe (6), emptying branch (7), emptying manifold (8), lower equalizing pipe (9), the second connecting pipe (10), out of gas branch (11), out of gas manifold (12), upper equalizing pipe (13) and back flushing pipe (14); One end of the intake manifold (4) is connected to the intake manifold (5), both ends of the intake manifold (5) are connected to the first connecting pipe (6), both ends of the first connecting pipe (6) are connected to the bottom of the A adsorption tower (1) and B adsorption tower (2), both ends of the emptying branch (7) are connected to the first connecting pipe (6), one end of the emptying manifold (8) is connected to the emptying branch (7), and the other end is connected to the outside; Both ends of the lower equalizing pipe (9) are connected to the middle of the A adsorption tower (1) and B adsorption tower (2), one end of the second connecting pipe (10) is connected to the lower equalizing pipe (9), and the other end is connected to the intake manifold (5) and the first connecting pipe (6) between the two ends of the emptying branch (7); Both ends of the out of gas branch (11) are connected to the top of the A adsorption tower (1) and B adsorption tower (2), one end of the out of gas manifold (12) is connected to the out of gas branch (11), both ends of the upper equalizing pipe (13) are connected to the out of gas branch (11) on both sides of the out of gas manifold (12), and both ends of the back flushing pipe (14) are connected to the upper equalizing pipe (13); The first automatic valve (15), the second automatic valve (16), the third automatic valve (17), the fourth automatic valve (18), the fifth automatic valve (19), the sixth automatic valve (20), the seventh automatic valve (21), the eighth automatic valve (22), the ninth automatic valve (23), the tenth automatic valve (24), the eleventh automatic valve (25), the twelfth automatic valve (26) and the manual valve (27) are further included; the first automatic valve (15) is arranged on the air inlet branch pipe (5) on one side of the air inlet main pipe (4) and located on the pipeline between the air inlet main pipe (4) and the A adsorption tower (1), the second automatic valve (16) is arranged on the air inlet branch pipe (5) on the other side of the air inlet main pipe (4) and located on the pipeline between the air inlet main pipe (4) and the B adsorption tower (2); the third automatic valve (17) is arranged on the exhaust branch pipe (7) on one side of the exhaust main pipe (8) and located on the pipeline between the exhaust main pipe (8) and the A adsorption tower (1), the fourth automatic valve (18) is arranged on the exhaust branch pipe (7) on the other side of the exhaust main pipe (8) and located on the pipeline between the exhaust main pipe (8) and the B adsorption tower (2); the fifth automatic valve (19) is arranged on the first connecting pipe (6) between the second connecting pipe (10) and the air inlet branch pipe (5) and the exhaust branch pipe (7) and located on the pipeline between the second connecting pipe (10) and the A adsorption tower (1), the sixth automatic valve (20) is arranged on the first connecting pipe (6) between the second connecting pipe (10) and the air inlet branch pipe (5) and the exhaust branch pipe (7) and located on the pipeline between the second connecting pipe (10) and the B adsorption tower (2); the seventh automatic valve (21) is arranged on the lower equalizing pipe (9) and located on the pipeline between the second connecting pipe (10) and the A adsorption tower (1), the eighth automatic valve (22) is arranged on the lower equalizing pipe (9) and located on the pipeline between the second connecting pipe (10) and the B adsorption tower (2); the ninth automatic valve (23) is arranged on the air outlet branch pipe (11) on one side of the air outlet main pipe (12) and located on the pipeline between the air outlet main pipe (12) and the A adsorption tower (1), the tenth automatic valve (24) is arranged on the air outlet branch pipe (11) on the other side of the air outlet main pipe (12) and located on the pipeline between the air outlet main pipe (12) and the B adsorption tower (2); the eleventh automatic valve (25) is arranged on the upper equalizing pipe (13) between the two ends of the back flushing pipe (14), the twelfth automatic valve (26) and the manual valve (27) are connected in series on the back flushing pipe (14).

2. The energy efficient nitrogen generation system of claim 1, wherein: The A adsorption tower (1) and the B adsorption tower (2) are identical in structure.

3. The energy efficient nitrogen generation system of claim 1, wherein: The first connecting pipe (6) is inverted U-shaped and its two ends are fixed to the bottoms of the A adsorption tower (1) and the B adsorption tower (2) through flanges.

4. The energy efficient nitrogen generation system of claim 3, wherein: The air inlet branch pipe (5) and the exhaust branch pipe (7) are horizontally arranged in the U-shaped opening of the first connecting pipe (6) and their two ends are connected to the two sides of the first connecting pipe (6) through three-way pipes.

5. The energy efficient nitrogen generation system of claim 4, wherein: The air inlet branch pipe (5) is located below the exhaust branch pipe (7).

6. The energy efficient nitrogen generation system of claim 3, wherein: One end of the second connecting pipe (10) is connected to the top of the first connecting pipe (6) through a three-way pipe.

7. The energy efficient nitrogen generation system of claim 1, wherein: The air outlet branch pipe (11) is U-shaped and its two ends are fixed to the tops of the A adsorption tower (1) and the B adsorption tower (2) through flanges.

8. The energy efficient nitrogen generation system of claim 7, wherein: The upper equalizing pipe (13) is horizontally arranged in the U-shaped opening of the gas outlet branch pipe (11) and its two ends are respectively connected to the two sides of the gas outlet branch pipe (11) through three-way pipes.

9. The energy efficient nitrogen generation system of claim 7, wherein: The back flushing pipe (14) is in inverted U shape and is arranged above the eleventh automatic valve (25).

10. The energy efficient nitrogen generation system of any of claims 1-9, wherein: All the automatic valves are pneumatic angle valves.

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