A.
Experiments on conventional gate valve
To experimentally investigate the flow conditions, an experimental setup with a recirculation system was fabricated. It included a pipeline with a traditional gate valve. The inflow was taken from the overhead tank under a constant head of 1.83 m. For the experimental model, various trials were taken to measure discharge for the same gate position of the valve and corresponding rotation angles were recorded.
Figure 3a shows the schematic of the experimental setup, and Fig. 3b shows the actual setup with a conventional gate valve. The discharge was measured on a volumetric basis. While carrying out the tests with a conventional gate valve, the fluctuating separation zones were observed. The modified gate valve can be used as a flow measuring device (e. g. in a laboratory) as well as a flow control device (e. g. in industry). While using it for any of the above-mentioned purposes, the calibration would be with respect to the corresponding supply head. If the supply head changes, then the calibration equation will also change accordingly.
Fig. 3a Schematic of experimental setup [3]. b Experimental setup of convention and modified gate valve setup [3]
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For the conventional model, a 65 mm metallic gate valve was taken. Complete closing of this valve requires 13 rotations of the wheel, which results in an angular measure of 46,800. Before fixing the valve, points at 900 intervals are marked along the periphery of the bonnet of the valve. On both the sides of the valve, an acrylic pipe of length equal to the flow development length (i.e., 650 mm) was provided. The transparency of the acrylic pipe helped to observe the flow conditions. For the remaining portion, a non-transparent PVC pipe was used. Hence, the total length of the horizontal pipe of the experimental setup was 6 m.
The experiments were started with a completely open valve and measured the corresponding discharge. Then it was partially closed by rotating it in a clockwise manner through an angular interval of 90°, and the discharge was measured. The same procedure was repeated until the valve was closed up to 8 rotations. On a similar line, the readings were taken while opening the valve at an interval of 90° by rotating the wheel in an anticlockwise direction. This completed one set of readings. 2-sets of such readings were taken. It was noticed from Fig. 4 that, for the same angular position of the wheel, the discharge was not the same. This has given an indication of the problem associated with the traditional gate valve. Due to flow separation that occurs in the conventional gate valve, very high fluctuations are recorded in the flow rate.
B.
Experiments on gate valve with flexible membrane pipe
Discharge through conventional gate valve at an interval of 90° rotation angle in clockwise and anticlockwise direction
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Another model with identical parameters was fabricated by putting an additional flexible membrane pipe inside the gate valve, as shown in Fig. 5a. Figure 5b shows the schematic of the modified shape of the flexible pipe inside the gate valve as a response to the position of the gate. The purpose of using flexible pipe was to avoid the formation of separation zones. Figure 5c shows the actual experimental setup with a close-up view of the transparent acrylic pipe with a flexible pipe duly modified.
Fig. 5a Flexible rubber membrane pipe. b Schematic of flexible pipe inside gate valve. c Actual flexible membrane pipe inside gate valve
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This system consists of a 65 mm gate valve fixed along the acrylic pipe on either side, having a flow development length of 650 mm. This flexible pipe was fabricated with rubber material which is used in cars as a mat sheet.
$$ \begin{aligned} {\text{Length}}\;{\text{of}}\;{\text{flexible}}\;{\text{pipe}}\;{\text{was}} & = {\text{Flow}}\;{\text{development}}\;{\text{length}}\;{\text{on}}\;{\text{either}}\;{\text{side}} + {\text{length}}\;{\text{of}}\;{\text{valve}} \\ & = \left( {650 + 650} \right) + 228.6 \\ & = 1528.6\,{\text{mm}} \\ \end{aligned} $$
As a result, a flexible pipe 1550 mm long was chosen. Initially, the transparent acrylic pipes were connected on either side of the gate valve. Then the flexible pipe was inserted inside this assembly. Due to the additional 100 mm length of flexible pipe, 50 mm of it came outside the ends of the acrylic pipes. This part of the flexible pipe was gently wrapped around the PVC pipe and the solution was applied to make it water tight. Further acrylic pipes were connected to PVC pipes.
The same procedure is followed for the recording of readings. Similar to the previous case, two sets of readings were taken in a clockwise and anticlockwise manner and are presented in Fig. 6. It was observed that the discharge was almost the same for the same position of the gate valve.
C.
Findings of experimental study
Discharge through modified gate valve at an interval of 90° rotation angle in clockwise and anticlockwise direction
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For each set of readings, graphs were drawn to analyse the results. On X-axis angle of rotation of wheel in degree was taken while discharge was taken on Y-axis in litres per second.
Graphical presentation of readings taken for conventional Gate valve showed scattered pattern as discharge varied each time due to formation of fluctuating separation zones. Whereas in case of Gate valve with flexible pipe, the pattern observed was in close proximity. This showed that the relationship between gate position and discharge could be established.
Figure 7 depicts a comparison of discharge vs. wheel rotation angle for conventional and modified valves, for a total of two sets of readings. Figure 7a represents the first cycle of clockwise and anticlockwise running, and Fig. 7b represents the second cycle of clockwise and anticlockwise running. For the same rotation angle, considerable variation in discharge in a conventional gate valve was observed in both cycles. The discharge fluctuations may be attributed to the fluctuating separation zones formed on either side of the gate. Whereas for the modified gate valve, the discharge fluctuations were considerably damped in both cycles.
Fig. 7Comparison of discharge through conventional and modified gate valve for both cases in clockwise and anticlockwise direction
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After complete analysis of the results, it was observed that the use of flexible pipe has considerably improved the performance of the gate valve as a flow measuring device. The modified gate valve was calibrated and the linear equation was obtained by the method of best fit as given below.
$$ y = 6.042 - 0.0005x $$
where \(y\): Discharge in liters per second, \(x\): Angle of Rotation in Degree.
The error between discharge estimated by equation and experimentation was found to be less than ± 2%. Thus, a good agreement was found between the mathematical and experimental models. Whereas the maximum discharge variation in the case of a traditional gate valve was observed to be 12%.