WATER PIPING SYSTEM WITH SLAM MITIGATION FUNCTION OF CHECK VALVE, AND CONTROL METHOD THEREFOR

Abstract

The present invention relates to a water piping system. More particularly, it relates to a water piping system that can alleviate water hammer due to slamming of a check valve by reducing the pressure difference between the front end and the rear end of the check valve by supplying some of fluid at the rear side of the check valve to the front side of the check valve when a pump is stopped, and a method of controlling the water piping system. The present invention includes: a sub-pipe having both ends connected to a front side and a rear side of the check valve, respectively, and supplying some of fluid at the rear side of the check valve to the front side of the check valve to suppress negative pressure and low pressure that is generated at the front end of the check valve when the pump is stopped.

Claims

1. A water piping system having a function of alleviating slamming of a check valve, the system comprising: a pump pressurizing fluid; a main pipe for delivering the fluid pressurized by the pump; a check valve disposed at an outlet port of the pump to prevent backflow of fluid; a sub-pipe having both ends connected to a front side and a rear side of the check valve, respectively, to supply some of fluid at the rear sides of the check valve to the front side of the check valve therethrough when the pump is stopped; and a control valve disposed in the sub-pipe to open and close a flow channel.

2. The system of claim 1, wherein the pump comprises a plurality of pumps connected to each other in parallel, the sub-pipe comprises a plurality of sub-pipes connected to the main pipe and respectively connected to front ends of check valves disposed at outlet ports of the pumps, and the control valve is disposed in each of the sub-pipes.

3. The system of claim 2, wherein the sub-pipes have first ends respectively connected to the front ends of the check valves disposed at the outlet ports of the pumps and second ends connected to a header, and the header is connected to the main pipe.

4. The system of claim 1, further comprising a controller controlling opening and closing of the control valve, wherein the controller closes the control valve after a predetermined period of time passes from the moment when the pump is stopped.

5. The system of claim 1, further comprising: a controller controlling opening and closing of the control valve; a first pressure sensor sensing pressure at the front side of the check valve of the main pipe; and a second pressure sensor sensing pressure at a rear side of the check valve of the main pipe, wherein the controller receives and compares pressures at the front side and the rear side of the check valve sensed by the first pressure sensor and the second pressure sensor, and closes the control valve after a predetermined period of time passes when the pressure at the rear side of the check valve is higher than the pressure at the front side of the check valve as the result of comparing.

6. The system of claim 1, further comprising a differential pressure sensor sensing a pressure difference between the front side and the rear side of the check valve, wherein the control valve closes after a predetermined period of time passes when it is determined that pressure at the rear side is higher than pressure at the front side of the check valve on the basis of the pressure difference sensed by the differential pressure sensor.

7. The system of claim 1, further comprising a flow rate sensor disposed at the rear side of the check valve of the main pipe, wherein the control valve closes after a predetermined period of time passes when it is determined that the pump has been stopped on the basis of flow of fluid sensed by the flow rate sensor.

8. The system of claim 1, wherein the control valve is a mechanical slow closing valve that is closed after a predetermined period of time passes from the moment when the pump is stopped.

9. The system of claim 8, wherein the control valve is a slow closing check valve.

10. The system of claim 1, wherein the control valve includes: a valve body disposed in the sub-pipe connecting a front end and a rear end of the check valve in the main pipe; and an actuator having a disc dividing an inside horizontally to the left and right therein, having both ends connected to the front end and the rear end of the check valve in the main pipe, respectively, and opening and closing the valve body when the disc is moved by a pressure difference between the front end and the rear end of the check valve.

11. The system of claim 10, further comprising a needle valve disposed at a front side of the actuator.

12. The system of claim 1, wherein the sub-pipe connected to the front side of the check valve has an end extending in the main pipe and curved toward the check valve.

13. The system of claim 1, wherein the sub-pipe connected to the front side of the check valve has an end extending in the main pipe and diagonally disposed toward the check valve.

14. The system of claim 1, wherein a pressure tank is connected between a rear side of the control valve in the sub-pipe and the rear side of the check valve.

15. The system of claim 14, wherein the control valve includes: a valve body disposed in the sub-pipe having a front end connected to a front end of the check valve of the main pipe and a rear end connected to the pressure tank; and an actuator having a disc dividing an inside horizontally to the left and right therein, having both ends connected to the front end and the rear end of the check valve, respectively, and opening and closing the valve body when the disc is moved by a pressure difference between the front end and the rear end of the check valve.

16. The system of claim 15, further comprising a needle valve disposed at a front side of the actuator.

17. The system of claim 14, wherein the pump comprises a plurality of pumps connected to each other in parallel, the sub-pipe comprises a plurality of sub-pipes connected to the pressure tank and respectively connected to front ends of check valves disposed at outlet ports of the pumps, and the control valve is disposed in each of the sub-pipes.

18. The system of claim 17, wherein the sub-pipes have first ends respectively connected to the front ends of the check valves disposed at the outlet ports of the pumps and second ends connected to a header, and the header is connected to the pressure tank.

19. The system of claim 14, further comprising a diffuser disposed in the pressure tank and connected to the sub-pipe, wherein the diffuser is connected to the sub-pipe connected to a rear side of the control valve, is annularly disposed around an inner side of the pressure tank, and has a plurality of spray holes formed through a surface thereof.

20. The system of claim 14, further comprising a diffuser disposed in the pressure tank and connected to the sub-pipe, wherein the diffuser is connected to the sub-pipe connected to a rear side of the control valve and has an end curved in an elbow shape.

Description

DESCRIPTION OF DRAWINGS

[0033] FIG. 1 is a view schematically showing a common water piping system of the related art;

[0034] FIGS. 2A, 2B and 2C are a view showing the configuration of a water piping system having a function of preventing slamming of a check valve according to the present invention;

[0035] FIGS. 3A and 3B are a view schematically showing a change in flow of fluid through a main pipe and a sub-pipe by operation of a control valve of the present invention;

[0036] FIG. 4 is a view showing a water piping system equipped with a control valve electrically operated to open/close in accordance with an embodiment of the present invention;

[0037] FIG. 5 is a flowchart showing a process of controlling a water piping system with an electric control valve, as shown in FIG. 4;

[0038] FIG. 6 is a view showing a water piping system equipped with a control valve electrically operated to open/close in accordance with another embodiment of the present invention;

[0039] FIG. 7 is a flowchart showing a process of controlling a water piping system with an electric control valve, as shown in FIG. 6;

[0040] FIG. 8 is a view showing a water piping system equipped with a control valve controlled by a differential pressure sensor in accordance with another embodiment of the present invention;

[0041] FIG. 9 is a view showing a water piping system equipped with a control valve controlled by a flow rate sensor in accordance with another embodiment of the present invention;

[0042] FIG. 10 is a view showing the configuration of a water piping system equipped with an actuator, a valve body, and a needle valve for a control valve in accordance with the present invention;

[0043] FIGS. 11A and 11B are a view showing the configuration of water piping systems equipped with a sub-pipe structure according to an embodiment of the present invention;

[0044] FIGS. 12A, 12B and 12C are a view showing the configuration of water piping systems including a pressure tank in accordance with another embodiment of the present invention;

[0045] FIG. 13 is a view showing the configuration of a water piping system equipped with a pressure tank, and an actuator, a valve body, and a needle valve for a control valve in accordance with the present invention; and

[0046] FIGS. 14A and 14B are a view showing the configuration of a water piping systems including a pressure tank having a diffuser therein in accordance with the present invention.

MODES FOR CARRYING OUT THE INVENTION

[0047] The configuration and operation of a water piping system having a function of alleviating slamming of a check valve according to the present invention are described in detail with reference to embodiments and the accompanying drawings. The water piping system stated herein includes all kinds of fluid piping systems such as common water supply pipes, circulation pipes for heating/cooling and industrial facilities, pipes for agriculture and industries, and petrochemical plants.

[0048] FIG. 2 is a view showing the configuration of water piping systems having a function of alleviating slamming of a check valve according to the present invention. As shown in the figures, a water piping system according to the present invention includes: a pump 2 that pressurizes fluid; a main pipe 10 that delivers the fluid pressurized by the pump 2; and a check valve 4 that is disposed close to the outlet port of the pump 2 in the main pipe 10 to prevent backflow of fluid, and further includes a sub-pipe 20 and a control valve 30.

[0049] The sub-pipe 20 is a pipe for supplying some of fluid from the rear side of the check valve 4 to the front side of the check valve 4 to suppress negative pressure or low pressure that is generated at the front side of the check valve when the pump 2 is stopped. To this end, the sub-pipe 20 has both ends connected to the front side and the rear side of the check valve 4 in the main pipe 10 and is connected to the main pipe 10 in parallel with respect to the check valve 4. The sub-pipe 20 connected to the front side of the check valve 4 in the main pipe 10 may be connected to a portion as close as possible to the check valve 4.

[0050] The control valve 30 is disposed in the sub-pipe 20. The control valve 30, which is provided to open/close the flow channel of the sub-pipe 20, is opened when the pump is operated, and is closed after a predetermined period of time passes when the pump is stopped.

[0051] In water piping systems including a plurality of parallel pumps 2, 2, and 2, as shown in FIG. 2 (b), a plurality of sub-pipes 20, 20, and 20 is connected to a min pipe 10, second ends of the sub-pipes 20, 20, and 20 are respectively connected to check valves 4, 4, and 4 disposed at the outlet ports of pumps 2, 2, and 2, and control valves 30, 30, and 30 are disposed in the sub-pipes 20, 20, and 20, respectively.

[0052] Further, as shown in FIG. 2 (c), first ends of the sub-pipes 20, 20, and 20 may be connected to the front ends of the check valves 4, 4, and 4 disposed at the outlet ports of the pumps 2, 2, and 2, respectively, second ends of the sub-pipes may be connected to a header 22, and the header 22 may be connected to the main pipe 10 through one pipe.

[0053] FIGS. 3 (a) and 3 (b) schematically show a change in flow of fluid through the main pipe 10 and the sub-pipe 20 by the control valve 30. As shown in FIG. 3 (a), while the pump is operated, fluid is discharged under high pressure from the outlet port of the pump and the pressure at the front end of the check valve 4 is higher than the pressure at the rear end of the check valve 4 due to friction resistance between the pipe and the valve. Accordingly, fluid is delivered through the main pipe 10 after pushing a disc 4a in the check valve 4. Further, since the control valve 30 is open, the fluid pressurized by the pump flows to the sub-pipe 20 from the main pipe 10 at the front side of the check valve 4 and then flows back into the main pipe 10 at the rear side of the check valve 4. The ratio of the fluid flowing through the check valve 4 in the main pipe 10 and the fluid flowing to the sub-pipe 20 is a function of the diameters and lengths of the two pipes and the flow speed.

[0054] Further, as shown in FIG. 3 (b), when the pump 2 is stopped, discharging of fluid from the pump is suddenly stopped, so the pressure at the front side of the check valve 4 drops, and accordingly fluid flows backward through the check valve 4 and the disc 4a in the check valve 4 starts to close. As described above, the disc 4a of the check valve 4 is rapidly closed by backflow, in which generation of negative pressure or low pressure is accelerated at the front side of the check valve 4, whereby slamming of the check valve 4 is generated. However, since the sub-pipe 20 and the control valve 30 are additionally disposed in the present invention, the fluid flowing backward at the rear end of the check valve 4 flows through the sub-pipe 20 to the front side of the check valve 4, so it is possible to prevent negative pressure or low pressure, but maintain positive pressure at the front end of the check valve 4. Accordingly, the closing speed of the disc 4a in the check valve 4 is decreased and slamming of the check valve 4 is alleviated.

[0055] However, fluid can be supplied only for a predetermined time to the front end of the check valve 4 through the sub-pipe 20 when the pump is stopped. If a large amount of fluid is continuously supplied to the front end of the check valve 4 through the sub-pipe 20, damage may be caused by reverse revolution of the pump, and all the fluid in the pipes returns to the pump, so a large accident may be caused. Accordingly, fluid may be supplied to the front side of the check valve 4 through the sub-pipe 20 temporarily for a predetermined time such that the check valve 4 can be slowly closed. The time may be experimentally determined as an appropriate value in advance, depending on the size or the operation state of the water piping system. According to experimental values, the closing time of the check valve 4 in a piping system equipped with a pressure tank is very short, within several seconds after a pump is suddenly stopped.

[0056] In order to supply fluid to the front side of the check valve 4 through the sub-pipe 20 for a predetermined period of time when the pump is suddenly stopped, the control valve 30 may be a slow closing valve that automatically closes or gradually closes when a predetermined period of time passes after the pump is stopped.

[0057] To this end, FIG. 4 shows an example of a water piping system equipped with a control valve 30 that is electrically controlled to open and close. As shown in the figure, the control valve 30 may be an electric valve that is automatically electrically controlled, and a controller 100 for controlling the control valve 30 is provided. The controller 100 may be configured to control the parts of the entire water piping system including a pump, or to independently control only the control valve 30.

[0058] FIG. 5 is a flowchart showing a process of controlling a water piping system with an electric control valve 30, as shown in FIG. 4. The controller 100 first operates the pump to deliver fluid through the water piping system so that the fluid flows through the main pipe 10 and the sub-pipe 20 (S1), and opens the control valve 30 (S2). Next, the controller 100 monitors whether the pump is operated in real time (S3). Monitoring whether the pump is operated may be performed by monitoring the number of revolutions of the pump, monitoring a power supply switch, monitoring a power supply sensor, monitoring a flowmeter, monitoring a pressure sensor, and sensing load current of the pump, etc. Opening and closing the control valve 30 may be performed, depending on pressure to prevent malfunction during idling or no-load operation even if the pump is rotated (operated).

[0059] When it is determined that the pump has been stopped as the result of monitoring whether the pump is operated, the controller 100 closes the control valve 30 after a predetermined period of time (input in advance in the controller 100) passes (S4). To this end, the control valve 30 may have a built-in timer to be closed when a predetermined period of time passes after the controller 100 gives a control instruction.

[0060] FIG. 6 shows another embodiment of a water piping system equipped with a control valve 30 that is electrically controlled to open and close. As shown in the figure, in this embodiment, an electric valve 30 such as a solenoid valve and a controller 100 are provided. Further, a first pressure sensor P1 and a second pressure sensor P2 for measuring pressure at the front side and the rear side of a check valve 4 are further provided.

[0061] FIG. 7 shows a flowchart illustrating a process of controlling a water piping system equipped with the electric control valve 30, the first pressure sensor P1, and the second pressure sensor P2, as shown in FIG. 6. The controller 100 first operates the pump to deliver fluid through the water piping system so that the fluid flows through the main pipe 10 and the sub-pipe 20 (S100), and opens the control valve 30 (S200). Next, the controller 100 receives in real time pressure values at the front end and the rear end of the check valve 4 from the first pressure sensor P1 and the second pressure sensor P2 and compares the pressure values (S300).

[0062] The fact that the pressure at the front end of the check valve 4 is higher means that the pump is in operation, while the fact that the pressure at the rear end of the check valve 4 is higher means that the pump has been stopped. Accordingly, the controller 100 keeps the control valve 30 open when the pressure at the front side of the check valve 4 is higher than the pressure at the rear side (when the pump is in operation), and closes the control valve 30 in other cases, for example, when the pressure at the rear side of the check valve 4 is higher than the pressure at the front side (when the pump is stopped) (S400).

[0063] On the other hand, as another embodiment, the control valve 30 may be controlled to open and close by a differential pressure sensor DPS, as shown in FIG. 8. The differential pressure sensor DPS senses a pressure difference between the front side and the rear side of the check valve 4 and closes the control valve 30 after a predetermined period of time passes when it is determined that the pressure at the rear side of the check valve 4 is higher than the pressure at the front side on the basis of the sensed pressure difference.

[0064] Further, as another embodiment, the control valve 30 may be controlled to open and close by a flow rate sensor FS, as shown in FIG. 9. The flow rate sensor FS is disposed at the rear side of the check valve 4 of the main pipe 10 to close the control valve 30 after a predetermined period of time passes when it is determined that the pump has been stopped on the basis of the sensed flow of fluid.

[0065] Although the control valve 30 is an electrically controlled valve in the above description, the control valve 30 may be a mechanically controlled valve. The mechanical control valve 30 is configured to automatically close after a predetermined period of time passes when the pump is stopped, by a mechanical configuration thereof without a specific part such as the controller 100. The control valve 30 should be a mechanical slow closing valve so that the control valve automatically closes after a predetermined period of time with a pump stopped.

[0066] There are various mechanical slow closing valves. For example, the control valve 30 may be a slow closing check valve. In this case, the disc 4a is open while a pump is operated, but when the pump is suddenly stopped, the check valve 4 is closed first and then the control valve 30 in the sub-pipe 20 is closed. That is, a check valve including a hydraulic cylinder that provides a shock-absorbing force opposite to the closing direction of a disc of the control valve may be selected as the control valve 30 so that the disc of the control valve 30 is closed after a predetermined period of time passes. Further, a check valve having parallel-cylinder (Korean Patent No. 10-1487748) by the applicant(s) may be selected as the control valve 30 to further decrease the closing speed of the disc.

[0067] FIG. 10 shows an embodiment of the mechanical slow closing valve. As shown in FIG. 10, the control valve 30 may include an actuator 30b and a valve body 30a such that the valve body 30a is opened and closed by a pressure difference between the front and rear sides of the actuator 30b, and may further include a needle valve 30c.

[0068] The valve body 30a is disposed in the sub-pipe 20 connecting the front end and a rear end of a check valve 4 of a main pipe 10 to each other and the actuator 30b is connected to the valve body 30a. In detail, the actuator 30b has a disc D that horizontally divides the inside thereof to the left and right and, both ends of which are connected to the front and rear sides of the check valve 4 of the main pipe 10, respectively, through a hydraulic hose or a common pipe. Further, the disc D in the actuator 30b is connected to a valve unit that connects/disconnects (opens/closes) the flow channel in the valve body 30a so that when the disc D is moved, the valve unit is operated to open/close the flow channel in the valve body 30a. The structure and the connection relationship of the disc D and the valve body 30a are not limited as long as the valve body 30a can be opened/closed when the disc D is moved. The system may be configured such that when the disc D is horizontally moved, the valve unit is horizontally moved to open the flow channel in the valve body 30a, or such that when the disc D is horizontally moved, the valve unit is rotated to open, using a gear assembly such as a rack and pinion between the disc D and the valve unit. When the valve unit is rotated to open and close, the valve body 30a may be a ball valve or a butterfly valve. According to this configuration, when the fluid at the front and rear ends of the check valve flows to the front and rear sides of the actuator 30b, respectively, the disc D in the actuator 30b is moved to any one side by the pressure difference between the front and rear ends. Further, as the disc D is moved, the valve unit of the valve body 30a connected to the disc D is moved and the flow channel of the sub-pipe 20 is closed.

[0069] The control valve is controlled to open and close, depending on whether the pump 2 is operated. While the pump 2 is operated, the pressure at the front side is higher than the pressure at the rear side of the check valve 4, and when the pump 2 is stopped, the pressure at the front side is lower than the pressure at the rear side of the check valve 4. Accordingly, while the pump 2 is operated, the disc D in the actuator 30b is moved from the front side to the rear side of the check valve 4 (from the left to the right in FIG. 10), so the valve body 30a is opened and the fluid at the front side of the check valve 4 of the main pipe 10 is supplied to the rear side of the check valve 4 through the sub-pipe 20. In contrast, when the pump 2 is stopped, the pressure at the rear side of the check valve 4 becomes higher, so the disc D in the actuator 30b is moved from the rear side to the front side of the check valve 4 (to the left in the figure), thereby closing the valve body 30a.

[0070] A needle valve 30c may be additionally disposed at the front side of the actuator 30b. When the needle valve 30c is provided, it is possible to reduce the speed of the disc D moving from the rear side to the front side by adjusting the amount of fluid flowing to the main pipe out of the actuator 30b when the disc D in the actuator 30b is moved to the front side from the moment when the pump is stopped, by setting the degree of opening in advance, whereby it is possible to achieve the effect of slowly closing the valve body 30a.

[0071] Although the front and rear ends of the actuator 30b are connected to the front and rear ends of the check valve, respectively, in the above description, the front end of the actuator 30b may be connected to the sub-pipe connected to the front end of the check valve and the rear end of the actuator 30b may be connected to the sub-pipe connected to the rear end of the check valve.

[0072] Further, various mechanical slow closing valves such as a needle valve, a spring type valve, a diaphragm valve, and a relief valve may be used as the control valve 30 as long as they can close after a predetermined period of time passes with a pump stopped.

[0073] FIG. 11 is a view showing the configuration of sub-pipe 20 for a water piping system according to the present invention. As shown in FIG. 11 (a), a sub-pipe 20 connected to the front side of a check valve 4 of a main pipe 10 may be curved in the shape of an elbow toward the check valve 4, with an end extending in the main pipe 10. According to this structure, when a disc 4a in the check valve 4 is closed by backflow of fluid, fluid is supplied to the front side of the check valve 4 through the sub-pipe 20, thereby preventing negative pressure or low pressure. Further, the pressure of the fluid flowing backward through the check valve 4 is offset by the pressure of the fluid supplied through the sub-pipe 20 so that the disc 4a is more slowly closed, whereby it is possible to attenuate slamming of the check valve 4. Further, when the end of the sub-pipe 20 curved in the shape of an elbow faces the check valve 4, reverse revolution of the pump is prevented, so it contributes to stabilizing the piping system. On the other hand, as shown in FIG. 11 (b), a sub-pipe 20 connected to the front side of a check valve 4 may have an end extending in a main pipe 10 and diagonally disposed toward the check valve 4.

[0074] FIG. 12 is a view showing the configuration of water piping systems according to other embodiments of the present invention. As shown in the figures, the embodiments, similar to the above embodiments, include a sub-pipe 20 connecting the front end and the rear end of a check valve 4 to each other, and a control valve 30, in which a pressure tank 5 is connected between the rear sides of the control valve 30 of the sub-pipe 20 and the rear side of the check valve 4. The pressure tank 5 is usually provided to prevent water hammer in a water piping system, but, as shown in FIG. 1, it was connected individually to the rear side of the check valve 4 of the main pipe 10 in the related art. In the present invention, the rear side of the pressure tank 5 is connected to the rear side of the check valve 4 of the main pipe 10 and the rear side of the control valve 30 is connected to the upper portion of the pressure tank 5, whereby it is possible to prevent dead water, which will be described below.

[0075] Dead water means a phenomenon in which contamination is generated by fluid remaining for a long period of time in the pressure tank 5 connected to the main pipe 10 to prevent water hammer. In particular, when the water piping system is used for delivering tap water, purified water, or milk, the tap water, purified water, or milk to be supplied to the consumers may be contaminated by dead water, so there is a need for measurements for preventing this problem.

[0076] Accordingly, in the present invention, the fluid in the pressure tank 5 is continuously discharged to the main pipe 10 by connecting the pressure tank 5 to the sub-pipe 20 so that fluid flows into the pressure tank 5 through the sub-pipe 20 when the pump is operated, whereby it is possible to prevent fluid from remaining for a long period of time and suppress dead water. As described above, when the pressure tank 5 is connected to the sub-pipe 20, it is possible to supply the fluid at the rear side of the check valve 4 to the front side of the check valve 4 through the sub-pipe and to prevent dead water, when the pump is stopped, so it is possible to achieve a double purpose.

[0077] FIG. 12 (a) shows a system with one pump 2 is exemplified, in which only one sub-pipe 20 is connected to the pressure tank 5. In water piping systems including a plurality of parallel pumps 2, 2, and 2, as shown in FIG. 12 (b), a plurality of sub-pipes 20, 20, and 20 is connected to a pressure tank 5 and are respectively connected to the front ends of check valves 4, 4, and 4 at the outlet ports of the pumps 2, 2, and 2, and control valves 30, 30, and 30 are disposed in the sub-pipes 20, 20, and 20, respectively. Further, as shown in FIG. 12 (c), first ends of the sub-pipes 20, 20, and 20 may be connected to the front ends of the check valves 4, 4, and 4 disposed at the outlet ports of the pumps 2, 2, and 2, respectively, second ends of the sub-pipes may be connected to a header 22, and the header 22 may be connected to the pressure tank 5.

[0078] FIG. 13 shows an embodiment of a control valve applied to a system in which a sub-pipe is connected to a pressure tank. The control valve used for this embodiment, the same as the control valve shown in FIG. 10, includes an actuator 30b, a valve body 30a, and a needle valve 30c. However, the rear end of the valve body 30a is connected to the pressure tank in this embodiment. Further, the front end of the actuator 30b may be connected to the sub-pipe connected to the front side of the check valve in the main pipe or to the front end of the check valve, and the rear end of the actuator 30b may be connected to the sub-pipe connected to the rear end of the check valve in the main pipe, or the pressure tank, or the rear side of the check valve. The operation of the control valve is the same as that of the embodiment shown in FIG. 10, so the detailed description is not provided here.

[0079] On the other hand, though not shown in the figures, in a system having a main pipe 10 that is a circulation pipe, gas in the main pipe 10 flows to a pressure tank 5 through a sub-pipe 20, so the sub-pipe 20 may be used to discharge the gas in the main pipe 10.

[0080] In most work sites, a check valve, an electric valve (not shown) for controlling flow rate, and a manual shutoff valve (not shown) are installed at the outlet port of a pump, so a large friction loss is caused by the valves and a large pressure difference is generated between the front end of the check valve 4 and the joint of a pressure tank 5 and a main pipe 10. Accordingly, an environment in which fluid can flow to the pressure tank through a sub-pipe where there is little friction loss is made and a large pressure difference is generated when a pump is operated with the electric valve (not shown) for controlling a flow rate closed by about 10 to 50% to control a flow rate, so the technique for preventing dead water can be more effectively used. Further, it may be possible to control the amount of fluid flowing to the sub-pipe 20 by adjusting the degree of opening of the electric valve (not shown) for controlling a flow rate.

[0081] Further, a diffuser 50 connected to the sub-pipe 20 may be additionally provided in the pressure tank 5 so that the fluid supplied through the sub-pipe 20 is uniformly distributed in the pressure tank 5. The diffuser 50, as shown in FIG. 14 (a), is connected to the sub-pipe 20 connected to the rear side of the control valve 30, is annularly disposed around the inner side of the pressure tank 5, and has a plurality of spray holes through the surface thereof. Further, the diffuser 50, as shown in FIG. 14 (b), has an end curved in an elbow shape. In this case, fluid moved down while turning around the inner side of the pressure tank. Further, the diffuser 50 may be formed in various types such as a fixed type or a floating type.

[0082] Although the present invention was described in detail with reference to embodiments, the scope of the present invention is not limited thereto and includes the range substantially equivalent to the embodiments.