JPH0981247A - Pressure control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute effective pressure control even for a pipeline system having a large flow rate change range in a pressure control device to be used for a water feeding/distributing field in water treatment facilities. SOLUTION: The pressure control device is provided with a pressure gauge 5 for measuring the pressure of water distribution, a flow meter 6 for measuring a flow rate, pressure reducing valves 2, 3 arranged in series in a pipeline system to adjust the pressure of water distribution, an initial cavitation coefficient reference table storing initial cavitation coefficient data, and a controller 4 for finding out the cavitation coefficients of the valves 2, 3 from the measured signals of the pressure gauge 5 and the flow meter 6, calculating the cavitation coefficient ratios of the valves 2, 3 by referring to the initial cavitation coefficient reference table and controlling the valves 2, 3 so that the calculated cavitation coefficient ratio of the valve 2 is equal to that of the valve 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure controller used for water supply and water distribution in a water treatment facility.

[0002]

2. Description of the Related Art In a conventional pressure control device in a water treatment facility, in order to solve the problem of cavitation, many valves are arranged in series to deal with the problem. In some cases, the valve opening ratio of each valve is determined as a function of the flow rate so that the valves connected in series have the same cavitation coefficient, and the valves are controlled.

[0003]

With the conventional control method as described above, good pressure control cannot be performed in the case of a large flow rate fluctuation range or a piping system in which the flow rate changes abruptly. Further, the limit of cavitation of a valve differs depending on the valve type and the like, and controlling with the same cavitation coefficient cannot be said to be optimum control.

The present invention has been made in view of the above points, and an object thereof is to provide a pressure control device capable of performing good pressure control even in a piping system having a large flow rate fluctuation range.

[0005]

[Means for Solving the Problems]

(1) The present invention is a pressure control device used for water supply and distribution in a water treatment facility, a pressure gauge for measuring distribution pressure, a flow meter for measuring flow rate, and a pressure reducing valve for adjusting distribution pressure. And the first, which is arranged in series in the piping system,
A second pressure reducing valve, an initial cavitation coefficient reference table in which data of the initial cavitation coefficient is stored, and the cavitation coefficients of the first and second pressure reducing valves are obtained from the measurement signals of the pressure gauge and the flowmeter, and the initial cavitation is also performed. The cavitation coefficient ratio of the first and second pressure reducing valves is calculated by referring to the coefficient reference table, and the calculated cavitation coefficient ratio of the first pressure reducing valve and the second cavitation coefficient ratio are calculated.
It is characterized in that a control unit for controlling the first and second pressure reducing valves is provided so that the cavitation coefficient ratio of the pressure reducing valve becomes equal.

(2) The fundamental cause of the occurrence of cavitation is the local pressure drop due to the abrupt change of the flow path contraction and expansion flow direction. The degree of cavitation is calculated from the cavitation coefficient and is represented by the following formula (from the Japan Water Works Association, 1990 Guidelines for Water Supply Facilities, Commentary). Although there are simpler calculation formulas, this formula is more strict.

Σ = (H ₂ +10) / {H ₁ −H ₂ + (v ² / 2g)} (1) σ: Cavitation coefficient H ₁ : Primary valve pressure H ₂ : Secondary valve pressure v: Velocity (m / s) g: Acceleration of gravity Valves cause their own cavitation phenomenon depending on the structural shape and the like depending on the type. Therefore, in order to perform the operation without the occurrence of cavitation, it is necessary to consider the characteristics of each valve.

A numerical value of the initial cavitation coefficient (σc) is known as an index showing the limit of cavitation of the valve. To prevent cavitation from occurring in the valve, it is necessary that σ> σc. In other words, “σ / σc> 1” is sufficient (the cavitation coefficient ratio SS is SS = σ / σc).

In the pressure control device of the present invention, when the flow rate of the pipe changes, the valve opening of each valve is controlled in order to keep the pressure constant. At that time, the control device that issues a command to the valve controls each valve. The constant pressure control is performed while the valve opening ratio is determined so that the cavitation coefficient ratio (SS) is maintained uniform. As a result, safe constant pressure control can be realized even when the flow rate fluctuation is large.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of the present invention. 1 is a reservoir for storing drinking water. 2 is a pressure reducing valve for adjusting the distribution pressure, and 3
Is a pressure reducing valve connected in series with the pressure reducing valve 2. Reference numeral 4 is a control device that issues a valve opening command so that the pressure reducing valves 2 and 3 have an opening ratio according to the pressure and the flow rate. This control device 4 has a pressure gauge 5
And the operation amount of the pressure reducing valves 2 and 3 is calculated from the signal of the flow meter 6, and each valve issues a command to the pressure reducing valves 2 and 3 so that the generation of cavitation is most suppressed. The pressure reducing valve 2 of the present embodiment is a cone valve, and the pressure reducing valve 3 is a butterfly valve.

In the apparatus constructed as described above, it is the pressure reducing valve 2 that suppresses the occurrence of cavitation most.
It is when the cavitation coefficient ratios (SS) of 3 become equal. FIG. 2 shows functional blocks of the control device 4 in FIG. 1 and 2, the cavitation coefficients of the pressure reducing valves 2 and 3 are calculated from the data input from the pressure gauge 5 and the flow meter 6, and the cavitation coefficient ratio (SS ) Is calculated, and an operation command is issued to the pressure reducing valves 2 and 3 so that the cavitation coefficient ratios SS become equal.

[0012]

EXAMPLE FIG. 3 is a graph of the initial cavitation coefficient of the valve adopted this time, FIG. 4 is the result of the constant water distribution pressure water supply control in the system adopting the control method of the present invention, and FIG. 5 is the conventional cavitation coefficient match. The results of the control of constant water pressure for water distribution are shown. At high flow rates,
Since the system is less likely to cause the problem of cavitation, the one shown in the figure is near the portion where cavitation occurs, which is the limit of the system, where the flow rate gradually decreases. 4 and 5, 11 is a cavitation coefficient ratio of a cone valve, 12 is a cavitation coefficient ratio of a butterfly valve, 13 is a flow rate, 14 is water distribution pressure, 15 is a cone valve opening, and 16 is a butterfly valve opening characteristic. Are shown respectively.

According to FIG. 4 (control method of the present invention), the pressure reducing valve 2 and the pressure reducing valve 3 are well controlled in a coordinated manner, and the flow rate is 1.
It can be seen that the generation of cavitation is suppressed up to 5.05 m ³ / min. However, in FIG. 5 (conventional cavitation coefficient matching control), 20.09 m ³ / m
Cavitation has already occurred in.

In the control system of the present invention (FIG. 4), the critical cavitation coefficient is not reached even after the initiation cavitation has occurred, and fatal damage to the pressure reducing valve and the like is avoided even in severe operating conditions beyond the limit. I am able to. On the other hand, in the conventional method (Fig. 5), the pressure reducing valve 3
The cavitation coefficient ratio (SS) of No. 1 rapidly decreases, and there is a high possibility that the pressure reducing valve will be fatally damaged.

In this embodiment, an example of a typical cone valve and butterfly valve has been shown, but the present invention is not limited to this, and similar effects can be obtained by controlling other valves.

[0016]

As described above, according to the present invention, it is possible to perform constant pressure control while determining the valve opening so as to keep the cavitation coefficient ratio of each valve for adjusting the water distribution pressure uniform. This enables good and safe pressure control even in a piping system where the flow rate fluctuation range is large.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an entire embodiment of the present invention.

FIG. 2 is a block diagram showing functions of a control device of the present invention.

FIG. 3 is a graph showing a valve initial cavitation coefficient.

FIG. 4 is a characteristic diagram showing the results of constant water distribution pressure water supply control in a system to which the present invention is applied.

FIG. 5 is a characteristic diagram showing a result of constant water distribution pressure water supply control in conventional cavitation coefficient matching control.

[Explanation of symbols]

 1 ... Reservoir 2, 3 ... Pressure reducing valve 4 ... Control device 5 ... Pressure gauge 6 ... Flow meter

Claims (1)

[Claims] 1. A pressure control device used for water supply and distribution in a water treatment facility, comprising a pressure gauge for measuring distribution pressure, a flow meter for measuring flow rate, and a pressure reducing valve for adjusting the distribution pressure. The first and second pressure reducing valves arranged in series in the piping system, the initial cavitation coefficient reference table in which the data of the initial cavitation coefficient is stored, and the first and second measurement signals from the pressure gauge and the flow meter. While calculating each cavitation coefficient of the pressure reducing valve, the cavitation coefficient ratio of the first and second pressure reducing valves is calculated by referring to the initiation cavitation coefficient reference table, and the calculated cavitation coefficient ratio of the first pressure reducing valve and the first cavitation coefficient ratio are calculated. And a control unit for controlling the first and second pressure reducing valves so that the cavitation coefficient ratio of the two pressure reducing valves becomes equal.