JPH05172102A - Control method for flow adjusting valve equipped in parallel - Google Patents

Abstract

PURPOSE:To reversibly change over a small type flow adjusting valve and a large type flow adjusting valve to adjust flow of fluid without generating hunting and the like at the time of changing over flow control. CONSTITUTION:Valve openings of a small type flow adjusting valve 1v and a large type flow adjusting valve 2v interposed in a first pipe passage 1 and a second pipe passage 2 can be opened and closed in a range of 0-100% by respective positioners 1p, 2p. When the upper limit of the small type flow adjusting valve 1v is detected by the upper limit switch LS1, the large type flow adjusting valve 2v in a closing state is gradually opened to be transferred to control the large type flow adjusting valve 2v at the opening exceeding the flow control impossible range. In the opposite way, when the lower limit of the large type flow control valve 2v is detected by the lower limit switch LS2, the large type flow adjusting valve 2v is gradually closed to be transferred to control by only the small type flow adjusting valve 1v. It is thereby possible to adjust flow of fluid at the range avoiding the flow control impossible range of the large type flow adjusting valve 2v.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve control method for controlling the opening degree of a valve, and more particularly, a valve of a flow control valve installed in each of parallel pipelines in a chemical plant, a boiler or the like. The present invention relates to a method for controlling a parallel flow rate control valve that controls the opening to control the flow rate of fluid.

[0002]

2. Description of the Related Art For example, an input signal to a valve positioner output from one regulator is divided into two, and this valve positioner controls the opening of one flow control valve by one of the two divided input signals. There is known a control method of juxtaposed flow control valves, which is a so-called split range control method, in which the control is performed and the opening of another flow control valve is controlled by the other.

First, an example of such a split range control method is shown in FIG. 4 of its control system diagram, FIG. 5a of a strip range characteristic diagram of a small flow control valve, and a strip range characteristic diagram of a large flow control valve. 5b and FIG. 5c which is an explanatory diagram of the valve capacity change according to the strip range control method, the description will be made below. The reference numerals 1 and 2 shown in FIG. 4 branch at a certain position and merge at the downstream side thereof. , The second conduit, and of the first conduit 1 and the second conduit 2, one of the first conduits 1 has a small capacity small flow rate control valve 1
v, and the second flow path 2 on the other side is provided with a large flow rate control valve 2v having a larger capacity than the small flow rate control valve 1v.

The opening of the small flow rate control valve 1v is controlled by a control signal from a positioner which is set so as to operate the input signal from the controller 3 between 0 and 50%, as shown in FIG. 5a. , 0 to 100%, and the large flow rate control valve 2v receives the input signal from the controller 3 by 5
The opening is controlled by the control signal from the positioner set to operate between 0% and 100%, as shown in FIG.
As shown in, the control is performed between 0 and 100%.

Therefore, as shown in FIG. 5c, the small flow rate control valve 1v is controlled when the input signal from the controller 3 is 0 to 50%, and when the input signal exceeds 50%, the small flow rate control valve 1v is controlled. The opening degree of is maintained at 100%,
The large flow rate control valve 2v is controlled, and the control of the small flow rate control valve 1v is started from the control of the small flow rate control valve 1v with 50% of the input signal as a boundary.
Since the valve capacity is changed by switching to the v control, the flow rate of the fluid flowing downstream from the confluence of the first conduit 1 and the second conduit 2 is adjusted.

[0006]

However, as shown in FIGS.
As indicated by a broken line in each of the drawings b and 5c, there is a flow control uncontrollable region in a region where the opening degree of the flow control valve itself is small. In the feedback adjustment control in this region, the flow control valve causes a hunting phenomenon, so that the flow rate of the fluid cannot be correctly controlled by the valve opening control of the flow control valve by the controller.

More specifically, when the flow rate control valves have a small opening, the control continuity is lost and the ON-OFF state occurs, so that the two flow rate control valves are controlled in the split range control as described above. Even if it does so, the flow control uncontrollable region in the small opening region of the large flow control valve does not disappear, and in the case of the above-mentioned conventional example, as shown in FIG. 5, in the vicinity of 50% of the input signal. The flow rate of the fluid cannot be controlled.

Therefore, an object of the present invention is to stabilize the control without switching from a small flow control valve to a large flow control valve and vice versa when switching control from a large flow control valve to a small flow control valve. Another object of the present invention is to provide a control method for a parallel flow rate control valve capable of adjusting the flow rate of a fluid.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. Therefore, the gist of the control method for a parallel flow control valve according to the present invention is, on the one hand, a large-capacity large flow control valve. On the other hand, on the other hand, the flow rate of the fluid at the confluence of the small flow control valves having a smaller capacity than the capacity of the large flow control valve is inserted, In the control method of parallel flow rate control valves that control by adjusting, the valve positioner that sets each control area of the large and small flow rate control valves enables control operation in all areas, and control by the small flow rate control valve When the small flow rate control valve reaches the upper limit opening, the large flow rate control valve that is closed is gradually and forcefully opened, and the large flow rate control valve is opened after the opening becomes equal to or larger than the flow control uncontrollable opening degree. While shifting to the control of the flow rate control valve, When large flow control valve in the control becomes lower opening, characterized in that it shifts to the control of small flow regulating valve only by gradually forcing close the large-sized flow control valve.

[0010]

According to the method for controlling a parallel flow rate control valve according to the present invention, both the large and small flow rate control valves can be controlled by the valve positioner so that the degree of opening can be controlled in all regions. When the small flow rate control valve reaches the upper limit opening during the control, the large flow rate control valve that is closed is gradually opened while the small flow rate control valve is opened according to the degree of opening of the large flow rate control valve. After the valve is closed and the valve opening of the large flow control valve becomes larger than the flow control uncontrollable opening, the control of the small flow control valve is switched to the control of the large flow control valve. At this time, the small flow rate control valve also receives the same control signal at the same time, so it operates at the same opening as the large flow rate control valve, but since the small flow rate control valve has a small capacity, it actually controls the large flow rate control valve. Has been switched to.

On the contrary, when the large flow rate control valve reaches the lower limit opening during the control by the large flow rate control valve, the large flow rate control valve is gradually and forcibly closed so that only the small flow rate control valve is controlled. The small flow rate control valve is switched to a large opening automatically by the adjustment operation of the controller to compensate for the flow rate of the large flow rate control valve that is forcibly closed.

[0012]

Embodiments of the present invention will be described below with reference to FIG. 1 of a control system diagram of a parallel flow rate control valve, FIG. 2 of a large flow rate control valve signal changeover switch circuit diagram, and opening degree of a parallel flow rate control valve. With reference to FIG. 3 which is an explanatory diagram of the detection procedure, the same parts and those having the same function as those of the conventional one will be described with the same reference numerals.

That is, as in the prior art, reference numerals 1 and 2 are first and second pipelines that branch at a certain position and join at the downstream side thereof, and the first pipeline 1 and the second pipeline 2 respectively. Among them, a small capacity small flow rate control valve (hereinafter referred to as a small valve) 1v is provided in one first pipeline 1 and a large capacity flow control with a larger capacity than the small valve 1v is provided in the other second pipeline 2. Valve (hereinafter referred to as large valve) 2
v are respectively interposed.

The small valve 1v includes an upper limit opening detecting limit switch LS for detecting an upper limit opening of the small valve 1v.
₁ is attached, also a large valve 2v, the lower limit opening detecting limit switch LS ₂ for operating at a flow rate controllable lower opening by the large valve 2v is attached.

Further, the small valve 1v is set to operate between 0 and 100% by an input signal from the controller 3, and the opening degree of the small valve 1v is controlled between 0 and 100%. A small valve positioner 1p is provided. Further, the large valve 2v is provided with a large valve positioner 2p for controlling the flow rate of the fluid between the lower limit opening and the upper limit opening capable of controlling the flow rate of the large valve 2v by an input signal from the controller 3. There is a controller 3 and a positioner for large valves 2
A switching circuit 4 for switching the controller output signal output from the controller 3 is interposed between p and p.

For details of the changeover circuit 4, a changeover switch 41 to which the output signal of the controller outputted from the controller 3 is inputted and which has two switching positions A and B, and one terminal of the changeover switch 41. An output signal from A is input, and a signal gradual generator 42 that inputs the output to the large valve positioner 2p and an output signal from the other terminal B of the changeover switch 41 are input, and the output is the same as the large valve. And a signal gradual stop 43 input to the positioner 2p for
The controller output signal is inputted to the signal gradual generator 42 or the signal gradual stop 43 by switching the changeover switch 41 to the A position or the B position.

The signal gradual generator 42 receives the controller output signal when the selector switch 41 is switched,
The value of this output signal approaches the same value as that of the controller output signal that is input gradually after t hours, and within the time of t time, when it becomes the same value as the changed controller output signal, and after t time, adjust immediately. The output of the same value as the meter output signal is continuously output to the large-valve positioner 2p, and the signal gradual stop unit 43 reversely takes the inputted controller output signal to zero for about t hours and elapses t time. After that, zero output is continuously output to the large valve positioner 2p.

By the way, the changeover switch 41 having the changeover positions A and B is changed over by a large valve signal changeover switch circuit as shown in FIG. That is, the configuration of this switch circuit is such that the upper limit opening detection limit switch LS
₁ and limit switch for lower limit opening detection LS ₂ and relay R
And a timer T is interposed.

The operation is as follows. When adjusting the flow rate in the control range of the small valve 1v with a small flow rate, the relay R is de-energized, the changeover switch 41 is switched to the terminal B side, and the large valve 2v is fully closed. It has become. As the required flow rate increases due to automatic adjustment, the controller output signal increases,
As shown in FIG. 3, the small control valve 1v actuates the upper limit opening detecting limit switch LS ₁ and the relay R is de-energized so that the timer T is also de-energized and the contact T ₁ of the timer T is closed. Therefore, the relay R is excited. That is,
The changeover switch 41 is switched to the terminal A side.

Then, the large signal valve 2v is started to be opened by the signal gradual generator 42, and the opening degree increases as the output from the signal gradual generator 42 passes through the uncontrollable region. Since the valve 2v is forcibly and gradually opened and is not fed back, the flow rate of the fluid flowing through the large valve 2v is gradually increased in a stable state.

On the other hand, since the controller 3 gradually lowers the controller output signal in order to guarantee this increase, the small valve 1v
Is gradually decreased, and the input signals to the small valve 1v and the large valve 2v become the same value within the time t, or when the time t has elapsed, the input becomes the same as the input of the signal gradual generator 42. Moves to the large valve 2v. In this case, the flow rate of the fluid at the confluence of the first conduit 1 and the second conduit 2 is the total amount of the fluid flowing out from the small valve 1v and the large valve 2v.

However, at this time, when the opening degree of the large valve 2v is still in the uncontrollable range, as shown in FIG. 3, the limit switch LS ₂ is still in operation, and therefore, as shown in FIG. In addition, the contact point T of the timer T becomes
_{When 1} is separated, the relay R is in the non-excited state. This is that the changeover switch 41 returns to the terminal B side, and the control of the small valve 1v is continuously performed. The effect is that control is not transferred to the large valve 2v in the large valve uncontrollable region.

Next, when there are fewer active required flow rate output adjusting meter 3 is decreased, the lower limit opening detecting limit switch LS ₂ is actuated by a large valve 2v, from FIG. 2, the contact T ₁ already Since the contacts of the limit switch LS ₂ are also separated because they are separated, the relay R is demagnetized and the changeover switch 41 is changed over to the terminal B side.

Then, due to the operation of the signal gradual stop 43, the large valve 2v slowly operates in the fully closing direction over a period of t hours, while the controller 3 operates in order to compensate for the flow reduction due to the closing operation of the large valve 2v. Increase the controller output signal value. Then, after t time, the output signal from the signal gradual stop 43 becomes zero, so that the large valve 2v is fully closed and only the small valve 1v is controlled.

As described above, while slowly passing through the flow control uncontrollable region of the large valve 2v, in the region beyond the flow control uncontrollable region, the control of the small valve 1v is changed to the parallel control of the large valve 2v and the large valve 2v. Since the control is switched to the control of only the small valve 1v, stable flow rate control can be performed without interrupting the process adjusting operation.

In the above description, the limit switches LS ₁ and LS ₂ are used to detect the upper limit opening of the small valve 1v and the lower limit opening of the large valve 2v. It is also possible to control all within the electric signal range by extracting the upper limit value and the lower limit value from the input signal to the head as signals of the open upper limit and closed lower limit of the control valve.

[0027]

As described above in detail, according to the control method of the parallel flow rate control valve according to the present invention, when the small valve reaches the upper limit opening during the control by the small valve, the valve is closed. The large valve is forcibly opened gradually, and control is transferred to the large valve at a position above the valve opening that exceeds the flow control uncontrollable range.Conversely, the large valve opens the lower limit opening during control with the large valve. In this case, the large valve is gradually closed forcibly to switch to the small valve control, which avoids the flow control of the fluid in the region where the flow control is not possible, and changes from the small valve to the large valve and vice versa. When switching the control from a large valve to a small valve, hunting does not occur, stable flow rate control of fluid is possible, and it is extremely effective for improving the operational stability of chemical plants, boilers, etc. There is.

[Brief description of drawings]

FIG. 1 is a control system diagram of a parallel flow rate control valve according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a large valve signal changeover switch circuit according to an embodiment of the present invention.

FIG. 3 is an explanatory view of an opening degree detection procedure of the parallel flow rate control valves according to the embodiment of the present invention.

FIG. 4 is a control system diagram showing a conventional split range control method.

5A is a strip range characteristic diagram of a conventional small valve, FIG. 5B is a strip range characteristic diagram of a large valve, and FIG. 5C is a valve capacity variation explanatory diagram by a conventional split range control method. ..

[Explanation of symbols]

A, B ... Changeover position of changeover switch, LS ₁ , LS ₂ ... Limit switch, 1, 2 ... Pipe line, 1p, 2p ... Positioner, 1v, 2v ... Valve, 3 ... Controller, 4 ... Changeover circuit, 4
1 ... Changeover switch, 42 ... Signal gradual generator, 43 ... Signal gradual stop

Claims (1)

[Claims] 1. A flow rate of a fluid at a confluence point of a pipe line, in which a large-capacity large-scale flow control valve is provided on one side and a small-size flow control valve having a smaller capacity than the large-scale flow control valve is provided on the other side. In the control method of the side-by-side flow control valves that controls the valve opening of these large and small flow control valves by controlling the opening degree, the valve positioner that sets each control area of the large and small flow control valves When the small flow rate control valve reaches the upper limit opening during control by the small flow rate control valve, the large flow rate control valve that is closed is gradually and forcibly opened to When the opening becomes equal to or larger than the flow control uncontrollable opening, control is transferred to the large flow rate control valve, and when the large flow rate control valve reaches the lower limit opening during control by the large flow rate control valve, By gradually forcibly closing the flow control valve, only the small flow control valve A method for controlling a parallel flow rate control valve, characterized by shifting to control.