Patent Application
20180128412
The present invention relates to a water piping system and, more particularly, to a water piping system that prevents degradation of water quality due to fluid remaining in a pressure tank for a long period of time and removes gas and other impurities in a pressure tank and a pipe, and a method of controlling the water piping system.
In general, when a pump is suddenly stopped or a valve is suddenly closed in a water piping system, transient condition in which the flow rate of fluid rapidly changes is generated, and this phenomenon is called water hammer. Due to the water hammer, the pressure in the pipe rapidly increases or the pressure in the pipe drops under the saturation vapor pressure of water and vapor is produced, and then the pipe line may be broken or damaged by shock waves in the process of column separation and return.
For example, a common piping system shown in
A pressure tank 5 is connected to the main pipe 10 in the related art to attenuate the water hammer. A predetermined amount of fluid is kept in the pressure tank 5, so when the pump 2 suddenly stops, some of the fluid in the pressure tank 5 is discharged to the main pipe 10 before the pressure in the main pipe 10 drops to a predetermined low level or vapor cavity is generated in the main pipe 10. Further, when water hammer is generated due to backflow of the fluid in the main pipe 10, fluid is supplied into the pressure tank 5, thereby attenuating shock.
Fluid flows into/out of the pressure tank 5, depending on the states of the piping system, and the fluid flows inside/outside even if lift changes due to simple stop of the pump or a change in the number of operating parts. A pressure change is very little when the pump normally operates, so inflow/outflow of fluid is very little, so a large amount of fluid very rarely flows inside/outside, for example, in the case of a power failure. Since only some of the entire fluid kept in the pressure tank 5 flows inside/outside, the fluid at the upper portion in the pressure tank does not move and remains in the pressure tank 5 for a long period of time. Further, the water in a pressure tank installed outdoor at a place where temperature is relatively high (around the equator) is higher in temperature and specific volume than fluid that flows in pipes, so it is light. Accordingly, a laminar flow is generated and the fluid remains in the pressure tank 5 for a long period of time. That is, the fluid at the upper portion in the pressure tank 5 hardly flows and only the fluid at the lower portion repeatedly flows inside/outside. When the fluid at the upper portion in the pressure tank 5 remains (stays) for a long period of time, contamination may become worse and causes deterioration of water quality (so called ‘dead water’). The deterioration of water quality results in very serious problems when a piping system is applied to a system for supplying drinkables such as tap water or milk. Further, as for water piping systems for sewage or water containing a large amount of solid, it is required to discharge impurities accumulated in a pressure tank or a connection pipe for the pressure tank and it is also required to clean the inner side of the pressure tank. Further, bubbles in the fluid flowing through a pipe produce air pockets in the pipe, thereby reducing the cross-sectional area of the pipe through which the fluid flows, whereby it may cause unstable flow and water hammer accordingly. Further, pipe systems that are used for local heating or used in plants are generally used or high-temperature or chemical fluid, so installation of air valves is limited, and accordingly, there is a need for removing gas in pipes. There has been no way of discharging dirt, removing gas, and flushing a pressure tank in the related art.
<Prior Art Documents>
(Patent Document 1) Korean Patent No. 10-0868908, titled “Waer hammer preventing system”
(Patent Document 2) Korean Patent No. 10-1538728, titled “Check valve for preventing slam and waterhammer”
The present invention has been made in an effort to solve the problems with water piping systems in the related art and an object of the present invention is to prevent dead water due to fluid remaining in a pressure tank for a long period of time by discharging the fluid. Another object of the present invention is to provide a water piping system that can prevent functional reduction as a water hammer attenuator by having a function of discharging impurities in a pressure tank to the outside and flushing the pressure tank and that can effectively remove gas in a pipe, and a method of controlling the water piping system.
In order to achieve the above object, according to one aspect of the present invention, there is provided a water piping system that includes: a pump pressurizing fluid; a main pipe for delivering the fluid pressurized by the pump; a main valve disposed at an outlet port of the pump; a pressure tank connected to the main pipe; a sub-pipe having a first end connected to a front side of the main valve of the main pipe and a second end connected to the pressure tank so that some of the fluid pressurized and discharged from the pump flows into the pressure tank through the sub-pipe; and a control valve disposed in the sub-pipe to open and close a flow channel.
The pump may be a plurality of pumps connected to each other in parallel, the sub-pipe may be disposed at a front end of a main valve disposed at an outlet port of any one of the pumps, and the control valve may be disposed in the sub-pipe.
The pump may be a plurality of pumps connected to each other in parallel, the sub-pipe may be a plurality of sub-pipes connected to the pressure tank, the sub-pipes may be connected to front ends of main valves disposed at outlet ports of the pumps, respectively, and the control valve may be disposed in each of the sub-pipes.
The sub-pipes may have first ends respectively connected to the front ends of the main valves disposed at the outlet ports of the pumps and second ends connected to a header, and the header may be connected to the pressure tank.
The control valve may be a one-way valve that is opened only when pressure at a front end thereof is higher than pressure at a rear end.
The control valve may be closed after a predetermined period of time passes from the moment when the pump is stopped.
The water piping system may further include a controller controlling opening and closing of the control valve, in which the controller may close the control valve after a predetermined period of time passes from the moment when the pump is stopped.
The system may further include: a controller controlling opening and closing of the control valve; a first pressure sensor sensing pressure at the front side of the main valve of the main pipe; and a second pressure sensor sensing pressure at a rear side of the main valve of the main pipe, in which the controller may receive and compare pressures at the front side and the rear side of the main valve sensed by the first pressure sensor and the second pressure sensor, and may close the control valve after a predetermined period of time passes when the pressure at the rear side of the main valve is higher than the pressure at the front side of the main valve as a result of the comparing.
The system may further include a differential pressure sensor sensing a pressure difference between the front side and a rear side of the main valve, in which the differential pressure sensor may sense a pressure difference between the front side and the rear side of the main valve and may control the control valve to close after a predetermined period of time passes when it is determined that pressure at the rear side of the main valve is higher than pressure at the front side of the main valve.
The system may further include a flow rate sensor disposed at the rear side of the main valve of the main pipe, in which the control valve may be closed 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. The control valve may be a mechanical slow closing valve that is closed after a predetermined period of time passes from the moment when the pump is stopped, and the control valve may be a slow closing check valve.
The control valve may include: a valve body disposed in a sub-pipe having a front end connected to a front end of the main 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 main 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 main valve. The system may further include a needle valve disposed at a front side of the actuator.
The system may further include a diffuser disposed in the pressure tank and connected to the sub-pipe, in which the diffuser may be connected to the sub-pipe connected to a rear side of the control valve, may be annularly disposed around an inner side of the pressure tank, and may have a plurality of spray holes formed through a surface thereof.
The system may further include a diffuser disposed in the pressure tank and connected to the sub-pipe, in which the diffuser may be connected to the sub-pipe connected to a rear side of the control valve and may have an end curved in an elbow shape.
The system may further include a sub-pump disposed in the sub-pipe to force fluid in the sub-pipe to the pressure tank.
The pressure tank may be equipped with a discharge pipe and a discharge valve so that gas or impurities are discharged out of the pressure tank.
According to another aspect of the present invention, there is provided a method of controlling the water piping system described above, the method including: delivering fluid through the main pipe and the sub-pipe by operating the pump; opening the control valve disposed in the sub-pipe; monitoring whether the pump is operated; and closing the control valve when the pump is stopped. The control valve may be closed after a predetermined period of time passes from the moment when the pump is stopped.
According to another aspect of the present invention, there is provided a method of controlling the water piping system described above, the method including: delivering fluid through the main pipe and the sub-pipe by operating the pump; opening the control valve disposed in the sub-pipe; sensing pressure at a front side and pressure at a rear side of the main valve of the main pipe; and comparing the sensed pressures at the front side and the rear side of the main valve and closing the control valve when the pressure at the rear side of the main valve is higher than the pressure at the front side of the main valve, as a result of the comparing. The control valve may be closed after a predetermined period of time passes, when the pressure at the rear side of the main valve is higher than the pressure at the front side of the main valve, as a result of comparing the sensed pressures at the front side and the rear side of the main valve.
According to another aspect of the present invention, there is provided a water piping system that includes: a pump pressurizing fluid; a main pipe for delivering the fluid pressurized by the pump; a main valve disposed at an outlet port of the pump; a pressure tank connected to the main pipe; a sub-pipe having a first end connected to a front end of the pump and a second end connected to the pressure tank so that fluid in the pressure tank is supplied to a front side of the pump through the sub-pipe; and a control valve disposed in the sub-pipe to open and close a flow channel.
According to the water piping system and the method of controlling the system of the present invention, it is possible to prevent dead water due to fluid remaining for a long period of time in a pressure tank and prevent deterioration of fluid quality and deterioration of the function as a water hammer attenuator by discharging impurities in the pressure tank and flushing the pressure tank. Further, it is possible to prevent water hammer due to a friction loss (a decrease in cross-sectional area) and unstable flow that may be caused by air pockets formed by bubbles that are contained in fluid and collect in a pipe.
The configuration and operation of a water piping system according to the present invention is 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 a common water supply pipe, circulation pipes for heating/cooling and industries, pipes for agriculture and industries, petrochemical plants, and pipes for drinkables.
The sub-pipe 20 allows some of the fluid pressurized and discharged from the pump 2 into a pressure tank 5 to discharge the substance in the pressure tank 5 or the gas in the main pipe to the outside, and as shown in
According to this configuration, when fluid is pressurized and discharged from the pump 2, most of the fluid is delivered through the main pipe 10 via the main valve 4, but some of the fluid is delivered through the sub-pipe 20. The fluid flowing through the sub-pipe 20 is supplied under relatively high pressure to the upper portion of the pressure tank 5, whereby it pushes out the fluid in the pressure tank 5. Accordingly, the fluid in the pressure tank 5 is discharged to the main pipe 10. The fluid in the pressure tank 5 is continuously discharged by this operation, so a dead water phenomenon that fluid remains (stays) in the pressure tank 5 for a long period of time is prevented. Further, impurities in the pressure tank are also discharged when the fluid is discharged, so it is possible to prevent the problem of deterioration of water quality in the pressure tank 5.
In this configuration, a discharge pipe 5a and a discharge valve 5b may be disposed at a side (preferably the lower portion) of the pressure tank 5 so that impurities can be easily discharged out of the pressure tank 5. The discharge valve 5b is an electrically controllable valve such as an electric valve and it is possible to smoothly discharge impurities to the outside by opening the discharge valve 5b when fluid is supplied into the pressure tank 5 through the sub-pipe 20. Further, when air flows into the pressure tank 5 and the liquid level in the pressure tank 5 decreases, the air is discharged through an exhaust valve (not shown) at the upper portion of the pressure tank 5, so the liquid level can be maintained at a predetermined height.
Meanwhile, gas in the main pipe 10 flows into the pressure tank 5 through the sub-pipe 20, so the gas in the pipes is removed. Entrained air causes circulation disorder and, cavitation, noise, and vibration of the pump, and the entrained air comes into a free air bubble state at portions with a low flow speed, thereby forming air pockets, so it becomes a factor of circulation disorder in a pipe. Further, the dissolved oxygen in the bubbles in a pipe causes oxidation and corrosion of metallic pipes or devices and increases friction in a pipe by reducing the cross-sectional area of the pipe. Accordingly, it is required to increase the power of a pump and replace pipes, so the maintenance cost is increased and the lifespan of pipes is decreased. Bubbles in a pipe increase in volume and collect at a portion under low pressure (a higher portion of the pipe), so air pockets are formed and the cross-sectional area of the pipe is reduced. Accordingly, the speed of fluid is increased and loss resistance is accordingly increased, and unstable flow is caused. Further, the air pockets temporarily clog the pipe (stop water supply) and some of the air pockets break and generate shock waves, which causes water hammer. Accordingly, air in a pipe should be removed.
On the other hand, air has a characteristic that it comes into a free air bubble state at a flow speed of 0.6 m/s or less in a pipe whereby, at a flow speed greater than 0.6 m/s, it is mixed with flowing fluid and then flows as entrained air through a pipe. In general, the flow speed in a normal state of pipes are designed to about 1˜3 m/s, so it is not easy to sufficiently remove air that flows inside from the outside or has remained from the early operation. Under this condition, when some of or the entire fluid from the pump 2 is sent to the upper portion of the pressure tank 5 through the sub-pipe 20, the fluid decreases in speed and moves down in the pressure tank 5 because the pressure tank 5 has a diameter sufficiently larger than that of the main pipe 10 or the sub-pipe 20, so the air comes into the free air bubble state and is mostly pushed up in the pressure tank 5, and then fluid is discharged to the main pipe. Further, the air pushed up collects at the upper portion and is discharged through an air exhaust unit (not shown), whereby the liquid level in the pressure tank 5 is continuously controlled at a predetermined height.
For example, assuming that the outlet diameter of the pump 2 is 300 mm and the flow speed is 3 m/s, when the entire fluid is sent to the pressure tank 5, only some of the fluid flows into pressure tank 5. However, the diameter of the pressure tank 5 is usually over 1000 mm, so the flow speed (Q=AV, Q: flow rate, A: cross-sectional area, V: flow speed) of fluid from the upper portion to the lower portion in the pressure tank 5 decreases 11.1 times, because the cross-sectional area is in proportion to the square of the diameter, that is, the cross-sectional area increases 11.1 times. Accordingly, the fluid flows from the upper portion to the lower portion in the pressure tank 5 at a speed of about 0.27 m/s that is 1/11.1 times the flow speed of 3 m/s at the outlet of the pump 2. In this process, the air (bubbles) comes into a free air bubble state at the upper portion and only the liquid is discharged through the pipe connected to the lower portion. Meanwhile, the air (bubbles) moved to the upper portion reduces the liquid level, but it is possible to handle the air even though air continuously flows into the pressure tank 5 by discharging the compressed air in the pressure (controlling the liquid level by opening/closing an electronic valve in response to a signal from a liquid level sensor in an automatic control system), so the liquid level is maintained in an appropriate level in the pressure tank 5. Accordingly, the pressure tank 5 performs the function of an air discharge device that is useful for a piping system required to discharge air.
On the other hand, when a sufficient cross-sectional area of the sub-pipe 20 is ensured, fluid flows through the sub-pipe 20 even without specific controlling, so it is possible to easily discharge the substances in the pressure tank 5. However, the cross-sectional area of the main pipe 10 should be sufficiently larger than the cross-sectional area of the sub-pipe 20 in order not to interfere with the flow of fluid through the main pipe 10, so it is preferable to make the cross-sectional area of the sub-pipe 20 as small as possible. However, when the cross-sectional area of the sub-pipe 20 decreases, fluid may not smoothly flow through the sub-pipe 20. Accordingly, when the cross-sectional area of the sub-pipe 20 is relatively small, the main valve 4 that controls the main pipe 10 is normally opened so that fluid can be delivered through the main pipe 10. Further, in order to discharge the substances (fluid, gas, and other impurities remaining for a long period of time) in the pressure tank 5, the main valve 4 is partially or entirely closed so that the fluid flowing through the main pipe 10 is partially or entirely delivered to the pressure tank 5 through the sub-pipe 20. Further, it may be possible to open and close the main valve 4 with a predetermined period so that the substances in the pressure tank 5 is discharged at every predetermined time. Further, when the main valve 4 is closed by 50 to 100%, the fluid flowing through the sub-pipe 20 increases in speed, so it is possible to achieve the effect of flushing the pressure tank 5.
On the other hand, as shown in
In general, water hammer is not generated while the pump 2 is normally operated, so the pressure tank 5 is also in a standby state without performing a specific function, and accordingly, even though flushing is performed, it does not cause a problem with the system. However, pressure drops in the main pipe 10 when the pump 2 is suddenly stopped, so when the fluid in the pressure tank 5 is discharged to the main pipe 10 and then the fluid flows backward in the main pipe 10, fluid flows into the pressure tank 5 to attenuate shock. Accordingly, when fluid flows backward, as described above, it is required to attenuate shock to the fluid flowing into the pressure tank 5 using the pressure in the pressure tank 5, so the fluid supply through the sub-pipe 20 is stopped to maintain the pressure in the pressure tank 5. Further, the entire water in the pipes may flow backward through the sub-pipe 20 and it may cause an accident, so the control valve 30 may be disposed in the sub-pipe 20 to prevent this case.
As described above, the control valve 30 may be a valve that is opened when the pump 2 is operated and is closed when the pump 2 is stopped. To this end, as an embodiment, the control valve 30 may be a one-way valve that is opened only when the pressure at the front end of the control valve 30 is higher than the pressure at the rear end.
The fact that the pressure at the front end of the control valve 30 is higher than the pressure at the rear end means that the pump 2 is in operation, and the fact that the pressure at the rear end of the control valve 30 is higher than the pressure at the front end means that fluid flows backward due to stopping of the pump 2. Accordingly, when the control valve 30 is a one-way valve that is opened only when the pressure at the front end thereof is higher than the pressure at the rear end, the valve is opened and flushing and removal of gas can be performed when the pump 2 is in operation, and the valve is closed and it is possible to attenuate water hammer in the pressure tank 5 when the pump 2 is stopped. The one-way valve may be a check valve, a pneumatic valve, a diaphragm valve, and a relief valve, etc.
The configuration shown in
On the other hand, the control valve 30 may be a slow closing valve that is closed after a predetermined period of time passes from the moment when the pump 2 is stopped in order to attenuate water hammer.
As shown in
Further, as shown in
However, fluid can be supplied only for a predetermined period of time to the front end of the main 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 main valve 4 through the sub-pipe 20, an accident may be generated due to backflow. Accordingly, fluid may be supplied to the front side of the main valve 4 through the sub-pipe 20 temporarily for a predetermined period of time such that the main valve 4 can be slowly closed. The period of time may be experimentally determined as an appropriate value in advance, depending on the size or the operation state of the water piping system.
In order to supply fluid to the front side of the main 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.
There are various slow closing valves, but a mechanical valve may be used herein. 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 controller. A slow closing check valve may be exemplified as the mechanical valve. The slow closing check valve includes a hydraulic cylinder that provides a shock-absorbing force opposite to the closing direction of a disc. Accordingly, the disc is opened when the pump is in operation and is closed when the pump is stopped because fluid flows through the sub-pipe 20, in which the disc is slowly closed by the shock-absorbing force from the hydraulic cylinder. 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.
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 from the moment when a pump is stopped.
Such one-way valves are all mechanical valves and the control valve 30 may be an electrically controlled valve such as an electric valve or a solenoid valve for more precise control.
According to this configuration, the controller 100 monitors whether the pump 2 is operated in real time, and opens the control valve 30 while the pump 2 is operated and closes the control valve 30 when the pump 2 is stopped.
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.
The fact that the pressure at the front end of the main valve 4 is higher means that the pump is in operation. Accordingly, the controller 100 keeps the control valve 30 open when the pressure at the front side of the main 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 main valve 4 is higher than the pressure at the front side (when the pump is stopped) (S400).
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
As another embodiment, 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 ends of the actuator 30b, and may further include a needle valve 30c, as shown in
The valve body 30a is disposed in a sub-pipe 20 connecting the front side of a main valve 4 of a main pipe 10 and a pressure tank 5 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 ends of the main 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 (not shown) 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 main valve flows to the front and rear ends 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.
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 main 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 main 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 main valve 4 (from the left to the right in
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 with the pump stopped, by setting the degree of opening in advance, whereby it is possible to achieve the effect of slowly closing the valve body 30a.
Although the front and rear ends of the actuator 30b are connected to the front and rear ends of the main 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 main valve and the rear end of the actuator 30b may be connected to the sub-pipe or the pressure tank connected to the rear end of the main valve.
Further, as another embodiment, the control valve 30 may be controlled to open and close by a flow rate sensor FS, as shown in
When there is no or little flow of fluid through the sub-pipe 20, as shown in
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
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.
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 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.
On the other hand, another embodiment of a water piping system for preventing dead water is shown in
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2015-0132357 | Sep 2015 | KR | national |
This application is a continuation application of international application PCT/KR2016/010274, filed on Sep. 12, 2016, now pending, which claims foreign priority from Korean Patent Application No. 10-2015-0132357 filed on Sep. 18, 2015 in the Korean Intellectual Property Office, the disclosure of each document is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/KR2016/010274 | Sep 2016 | US |
| Child | 15864779 | US |
