JPS634202B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a valve operating method, and particularly to a valve operating method in a piping system in which two or more valves are connected in series. If the secondary pressure of the valve is low and the amount of pressure reduction is large, the first
As shown in the figure, a method is used in which two or more valves 1 to 3 are connected in series to reduce the pressure. These two or more valves 1
If valves 3 to 3 are operated at the same opening degree, the valves on the downstream side tend to cavitate. In order to perform proper valve operation, the valves should be opened and closed so that the cavitation coefficients of all valves are equal. For this purpose, as shown in Figure 1, the upstream side, downstream side,
Pressure detectors M ₁ to M ₄ are provided between each valve 1 to 3, and their output signals are input to the control device D to determine the target valve differential pressure from the secondary pressure of each valve 1 to 3, and the valve It is conceivable to operate the actuators A ₁ to _{A 3} and control the opening degrees of the valves 1 to 3 to achieve the differential pressure, but this method requires a large number of pressure detectors,
Furthermore, since the differential pressure of each valve is controlled independently, there is a risk that the control may become unstable. Therefore, an object of the present invention is to provide a method of valve operation that can reduce the number of pressure detectors used and perform stable valve control. Therefore, in a piping system including two or more valves connected in series, pressure detectors are provided in the upstream and downstream parts of the piping system to detect the pressures in the upstream and downstream parts, and One of the valves included in the system is operated by an operation command or operation signal from an external operator, its opening is detected by a valve opening detector, and the valve opening is detected by a valve opening detector. Using the detection signal, the characteristics of each valve, and the equal cavitation conditional expression, a microcomputer calculates the valve opening of each valve so that the cavitation coefficient is equal to that of the externally operated valve. Controls the opening of valves other than those operated from the outside. Hereinafter, an embodiment of the valve operating method of the present invention will be described with reference to FIGS. 2 and 3. In Fig. 2, 1, 2 to K to n are valves installed in series in the piping system, and valve K among them is designed to open and close in response to an external operation signal _S1 . . In addition, A ₁ to _{A o} are valve actuators that operate each valve, M _u is an upstream pressure detector installed in the upstream part of the piping system, M _d is a downstream pressure detector installed in the downstream part of the piping system, and M 〓 is This is a valve opening degree detector that detects the opening degree of valve K. Further, C is a microcomputer, and the microcomputer C includes a pressure signal input device C ₁ , a valve opening signal input device C ₂ , an arithmetic storage device C ₃ ,
Equipped with valve opening signal output device _C4 . As shown in Fig. 2, in a piping system in which valve 1, valve 2...valve n are connected in series from the downstream side of the piping system, the absolute pressure in the upstream part of the piping system is Hn, the absolute pressure in the downstream part is Ho, Valve i located i-th from the downstream side
Let θi be the opening degree, λi be the loss coefficient, and Vi be the cavitation coefficient. When detecting pressure as a gauge pressure, the average atmospheric pressure set in the arithmetic storage device _C3 of the microcomputer C is added to the gauge pressure to approximately obtain the absolute pressure. In addition, since the valve characteristic unique to each type of valve, that is, the relationship between the valve opening degree and the valve loss coefficient, is determined, the valve characteristic for valve i is expressed as λ _i = fi (θi), and this relationship is expressed as a function. Alternatively, it may be stored in the arithmetic storage device _C3 of the microcomputer C as a table. Further, it is assumed that R=Hn/Ho. Next, a procedure for making the cavitation coefficients of valves other than valve K operated by external operation signal _S1 equal to the cavitation coefficient of valve K will be explained. First, the opening degree θk of valve K is detected by the valve opening degree detection device.
The loss coefficient λk of the valve K is determined by the valve characteristic λk=f stored in the arithmetic storage device _C3 of the microcomputer C by detecting it with M and inputting it to the valve opening signal input device _C2 of the microcomputer C. Calculated from _k (θk) (1). The loss coefficient of valve i is The calculation is performed by the arithmetic and storage unit _C3 of the microcomputer C using the following formula. Further, the corresponding valve opening degree θi is calculated from θi=fi ^-1 (λi) (3), and this value is output using the valve opening degree signal output device _C4 of the microcomputer C. When the valve opening degree is manipulated by the valve actuator Ai to match this valve opening degree θi, the cavitation coefficient of valve i becomes equal to the cavitation coefficient of valve K, and its value is Vi=1/(n√−1) (4) becomes. This relationship holds true for any i-th valve, so the opening degrees of all valves are found using equations (1), (2), and (3), and using that information, all valves are can be manipulated to equalize the cavitation coefficients. The above formula can be confirmed from the formula below. First, if the velocity head is C, the following equation holds true. C=(Hn−Ho)/ _o Σ ^j=1 λj (5) Substituting equation (2), Cavitation coefficient of valve 1 located at the most downstream position
Substituting equations (2) and (6) into the basic equation that defines V ₁ , we get Also, the cavitation coefficient Vi of valve i (2≦i≦n) is becomes. That is, when the loss coefficient calculated by equation (2) is used, the cavitation coefficient for all valves becomes (n√-1) ^-1 , which is the same value for all valves. Now suppose that four valves K ₁ , K ₂ , K ₃ and K ₄ are connected in series, the pressure on the downstream side is Ho, and the valve K _{1 is}
and the pressure between valve K ₂ is H ₁ , the pressure between valve K ₂ and valve K ₃ is H ₂ , the pressure between valve K ₃ and valve K ₄ is H ₃ , and the upstream pressure is H ₄ , d ₁ , d ₂ , d ₃ and d ₄ are the differential pressures before and after the valve, respectively, and c is the velocity head, i.e.
V ² /2 g meters, λ is the loss coefficient, k is the cavitation coefficient, and x=R ^(i-2) /n. Now let us choose valve K ₃ and use the above formula (2)
From (5), the following Table 1 is obtained. However, this is a case where Ho = 20 meters and H ₄ = 60 meters, and valve K ₃ is selected, so λ _i = λ ₃ (H ₄ /Ho) ^(i-3)/n = λ ₃ R ^{(i-3 )/n} . In addition, if valve K ₁ is selected, the following table 2
get. Here, λ _i =λ ₁ (H ₄ /Ho) ^(i-1)/4 = λ ₁ R ^(i-1)/4 .

【table】

【table】

[Table] As can be seen from Tables 1 and 2 above, the cavitation coefficients Vi can be made substantially the same. Further, according to the present invention, when performing so-called constant pressure control in which the pressure Ho in the downstream part of the piping system is made to match the predetermined pressure target value Ho' using valves 1, 2;...valve n, Ho is Ho' is maintained approximately equal to Ho', so instead of inputting the detected pressure Ho of the downstream pressure detector Md to the microcomputer C, the pressure target value Ho' is set as a constant in the microcomputer C, thereby achieving the above embodiment. Equivalent operations can be performed. FIG. 3 shows an example in which downstream pressure constant control is performed on a piping system in which three valves are connected in series. In FIG. 3, a constant pressure control device _G1 outputs a valve opening/closing signal _S1 so as to reduce the deviation between the detected pressure Ho and the pressure target value Ho', and the valve 1 operates in response to the signal _S1 . This constant pressure control device G ₁
The microcomputer C determines the opening degrees of the valves 2 and 3 in accordance with the opening degree θ ₁ of the valve 1 operated by the microcomputer C so as to satisfy the equal cavitation condition. That is, the microcomputer C obtains the opening degree θ ₁ of the valve 1 via the valve opening degree detector M, determines the loss coefficient λ ₁ of the valve 1 based on equation (1), and then sends it to the target pressure setting device C ₅ . Set pressure target value
Using the upstream pressure Hn input via Ho' and the upstream pressure detector Mu, the formula is The loss coefficients λ ₂ and λ ₃ of valves 2 and 3 are determined using equation (3), and the valve openings θ ₂ and θ ₃ are determined using equation (3) and outputted from the valve opening signal output device C ₄ . valve actuator
Valve ₂ and valve ₃ are operated via A 2 and A 3 . When the downstream pressure is controlled to be constant in this way, there is no need to input the pressure detection signal from the downstream pressure detector Md into the microcomputer C, and there is no need to provide a signal transmission line for this purpose. Similarly, when the upstream pressure is controlled to be constant, a line for transmitting the upstream pressure detection signal to the microcomputer C becomes unnecessary. As described above, according to the present invention, the cavitation coefficients of all valves can be made equal using detection signals from pressure detectors of at most two valves connected in series. Also, based on the opening information of the valves K operated by up to two pressure signals and external operation signals, the openings of the remaining numerous valves are determined in a manner dependent on the openings of the valves K. Controllability is also improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional valve operating method in a piping system including two or more valves connected in series. FIG. 2 is a block diagram of a valve operating method according to an embodiment of the present invention in a piping system including two or more valves connected in series, and FIG. FIG. 2 is a block diagram of an embodiment applied when 1, 2~K~n...Valve, _A1 ~ _Ao ...Valve actuator, Md...Downstream pressure detector, Mu...
Upstream pressure detector, M〓... Valve opening detector, C...
...Microcomputer, C ₁ ...Pressure signal input device, C ₂ ...Valve opening signal input device, C ₃ ...Arithmetic storage device, C ₄ ...Valve opening signal output device, C ₅ ...
Target pressure setting device, G ₁ ... Constant pressure control device.

Claims (1)

[Claims] 1. In a piping system including two or more valves connected in series, pressure detectors are provided in the upstream and downstream parts of the piping system to detect the pressure in the upstream and downstream parts,
In addition, one of the valves included in the piping system is operated from the outside, and the valve opening degree is detected by a valve opening degree detector, and the detection signals from those detectors, the characteristics of each valve, etc. Using the cavitation conditional expression, a microcomputer calculates the valve opening of each valve that has a cavitation coefficient that is substantially the same as that of an externally operated valve, and then uses that information to A valve operating method characterized by controlling the opening degree of a valve. 2. In a piping system including two or more valves connected in series, a pressure detector is installed in the upstream or downstream part of the piping system to detect the pressure in either the upstream or downstream part, and One of the valves is operated from the outside, the valve opening is detected by a valve opening detector, and the detection signal from those detectors, the characteristics of each valve, and the equal cavitation conditional expression are used to detect the valve opening from the outside. A microcomputer calculates the opening degree of each valve so that the cavitation coefficient is substantially the same as that of the operated valve, and a constant pressure control target value is set as a constant in the microcomputer, and this information is used to calculate external A valve operating method characterized by controlling the pressure to be constant by operating the opening of a valve other than the operated valve.