Hydrodynamic Experiment of Large-scale Hydraulic Butterfly Valves

The butterfly valve is installed at the front side of the unit, which not only serves to cut off the water flow in the normal maintenance stage but also ensures that the dynamic water flow is cut off under the condition that the body structure is stable in the emergency state, so as to prevent the accident from further expanding; Therefore, the test of butterfly valve mainly focuses on the dynamic water closing experiment stage; At the same time, as the last key experiment of butterfly valve assessment, the result of the experiment directly affects the project parties' evaluation of butterfly valve manufacturing and installation quality.
 
The butterfly valve of this project is manufactured by a valve factory in Changsha, Hunan; For butterfly valve equipment in the project construction stage, the main task undertaken by our company is the installation and commissioning of butterfly valves (static without water, static with water and dynamic with water). This paper will focus on the analysis of phenomena and data of butterfly valves in the process of dynamic water closing experiment.
 
Equipment features and parameters
 
Chukasi Hydropower Station uses penstock to divert water, and the steel pipe is in the form of one pipe with two machines, that is, the main pipe with a diameter of 6,200mm is divided into two independent diversion pipes with a diameter of 3,500mm at the branch pipe, and a butterfly valve with the same diameter is installed between the downstream side of the branch pipe and the upstream side of the volute inlet of the unit. On the downstream side of the butterfly valve, a Francis turbine generator set of HLA551 h-LJ-261 is installed, with a total capacity of 52,000 kW.
 
The main features and parameters of the butterfly valve are as follows:

The layout of the butterfly valve: horizontal;
Valve body diameter: 3500mm;
Design pressure: 0.82 MPa;
The rated water head: 48.4m;
Rated flow rate: 61m3/s;
Operation mode: open-double hydraulic cylinder jacking; Close-double hammer under heavy pressure;
Operating oil pressure of relay: 16mpa;
Valve pressure leveling mode: using the body bypass valve to level the pressure;
Type of bypass valve: diameter of the bypass pipe is 350 mm, bypass valve-hydraulic needle valve,
Operating oil pressure—16mpa;
On/off time: the main valve is opened-—60 s~120 s adjustable; Main valve closing —60 s~120 s adjustable; Opening and closing of bypass valve—within the 30s.
 
Debugging butterfly valves

First of all, the control situation of the butterfly valve is explained: the butterfly valve control hydraulic system shares a set of hydraulic sources with the unit governor, and its automatic control mainly depends on the hydraulic control valve group in the butterfly valve hydraulic control cabinet. To put it bluntly, it is a two-position three-way electromagnetic directional valve, and its principle is: when the butterfly valve is not needed to be operated, the solenoid valve is in a power-off state (the pressure oil is on the pressure port P of the solenoid valve); When the butterfly valve needs to be opened, the solenoid valve is energized, the spool is reversed, the pressure oil is introduced into the servomotor to open the cavity, and the butterfly valve is opened; When the butterfly valve needs to be closed, the solenoid valve is powered on again, the open oil port of the servomotor is connected with the oil return pipe, the servomotor loses pressure, and the valve is closed under the action of the heavy hammer.
 
Static debugging without water
 
purpose
 
This commissioning is the first action experiment after the butterfly valve is installed, so the main purpose of this experiment is to check whether the installation of the butterfly valve body is qualified (mainly including the connection quality of the butterfly valve, the adjustment of the main valve expansion joint, the assembly quality of pipe joint of control system, electrical control logic, the action of each control valve group, the adjustment of valve action time, whether each position annunciator is normal, remote control operation, etc.).
 
Commissioning preparation
 
One of the first conditions before commissioning is that the hydraulic control system has been debugged and has normal working conditions. Other major preparations are as follows:
 
(1) the inside and outside of the valve body should be cleaned, especially the valve plate area should be carefully checked for foreign bodies;
(2) The maintenance seal of the butterfly valve needs to be confirmed whether it is in the exit position, otherwise, it should be manually withdrawn;
(3) Designate the forbidden area in the experimental area and set up safety warning signs;
(4) Prepare cotton yarn and other necessary materials, and prepare for leakage treatment of hydraulic pipeline;
(5) Set up necessary operations or check platforms and channels;
(6) Other necessary safety measures.
 
Experimental method

During the first action, first, adjust the pressure of the control system to the lowest action pressure of the butterfly valve, and then manually jog the control valve to make the butterfly valve open slightly; Observe that there is no abnormal sound and other abnormal phenomena. Then continue to open the butterfly valve to 50% opening. If there is no abnormal phenomenon, all butterfly valves can be opened. After fully opening, all manual valves are closed, and the valve plate is locked in the fully open position by manual locking of the butterfly valve. After that, technicians enter the valve body to check whether the valve plate seal and hinge are normal. After the inspection, the personnel will withdraw, lockout and manually control the valve to open. Then close the butterfly valve. If the process is normal, it indicates that the valve can enter the next debugging process. The next step is to increase the pressure of the hydraulic system to 80% and open and close the butterfly valve again. If the system is normal, raise the system pressure to the rated pressure and switch again. (When the main valve acts, the bypass needle valve can be synchronously tested.)
 
Finally, adjust the opening and closing time of the butterfly valve. According to the technical documents, temporarily adjust the opening time of the main valve to 90 s and the closing time to 110 s. It should be noted that adjusting the closing time of the main valve is divided into two steps. The first step is to release all the flow regulating valves in the hydraulic pipeline and then adjust the flow-regulating valves on the butterfly valve servomotor body, and the time is adjusted to 105s; The second step is to adjust the flow regulating valve in the pipeline to 110s; The purpose of this is that, because the strength of the hydraulic pipeline is lower than that of the relay, the hydraulic pipeline may burst in work. This is to ensure that the butterfly valve can still have a safe closing speed when the hydraulic pipeline bursts, so as to prevent water hammering in the penstock.
 
Static debugging with water

Water static commissioning mainly examines the water sealing situation of each sealing part and connecting part of the butterfly valve during operation or after many times of operation. The experimental process is consistent with the waterless static experiment process, so it will not be repeated here.
 
The purpose of water dynamic debugging
 
The purpose of this commissioning is mainly to check whether the design and manufacture of butterfly valves are qualified, specifically to verify whether the butterfly valves can be reliably closed under extreme conditions. And whether the butterfly valve body (expansion joint, foundation bolt, bypass pipe) and upstream and downstream steel pipes are in a normal state.
 
Commissioning preparation
 
Considering that there may be vibration and slight displacement during the dynamic water shut-off experiment, on the basis of the preparation for static commissioning, additional preparations are as follows:
(1) Set up an observation frame independent of the butterfly valve body (the observation frame is made of light section steel), and set up a dial indicator at the selected position at the same time;
(2) In order to reduce the potential safety hazard caused by the water hammer when the butterfly valve is closed by moving water, turn on Unit 2 to no-load operation during the experiment of Unit 1;
(3) Before the experiment, reconfirm whether the static closing time of the butterfly valve is 110s;
(4) Pressure gauge is installed at the pressure tap of the butterfly valve servomotor, and the position of the measuring point is shown in Figure 1 (the point number without an arrow is the number of measuring points in the vertical direction of this position).
 
Experimental method
 
The dynamic water closing test of the butterfly valve will be carried out under four working conditions: no-load, 25% load, 50% load and (25 MW)100% load. Before the experiment, the butterfly valve plate is in the fully open position, and after the unit runs stably, the butterfly valve is closed by operating the close button. In order to ensure safety, technicians should be arranged on standby at the gate control cabinet of the water inlet of the dam and the governor of the unit when the butterfly valve carries out the dynamic water experiment, and emergency operations can be carried out when necessary.
 
The main observation items during the dynamic water experiment are: when the butterfly valve opening is 20%, 50%, 75% and 100%, respectively record the time points (accurate to S), the upstream and downstream pressures of the butterfly valve (read from the pressure transmitter), the opening pressure of the hydraulic servomotor, the pressure at the end of the volute, the vibration amplitude at the turbine head and bearing, the valve body and bypass pipe, the displacement of the butterfly valve foundation, etc.
 
Experimental phenomena and results
 
(1) experimental phenomena:
① No-load state of the unit: at this time, the opening of the movable guide vane of the turbine is 16%, the main valve body of the butterfly valve has no obvious vibration and displacement during the process from full opening to full closing, and the bypass valve (especially the top of the needle valve) slightly vibrates. At the same time, when the butterfly valve plate is close to full closing, the sound of high-speed water flow in the channel can be heard, and the valve closing time is shortened from 110 s to 88 s.
 
② The unit is loaded with 25% load: at this time, the opening of the movable guide vane of the hydraulic turbine is 37%. During the process from full opening to full closing of the butterfly valve, the main valve body vibrates slightly, and the bypass valve (especially the position far away from the butterfly valve) vibrates strongly. At the same time, when the butterfly valve plate is close to full closing, the sound of high-speed water flow in the channel can be heard (the sound is louder than that in no-load condition), and the valve closing time is shortened from 110 s to 58 s.
 
③ The unit is loaded with 50% and 75% respectively: at this time, the opening of the movable guide vane of the hydraulic turbine is 51% and 66% respectively. During the process of the butterfly valve fully opening to fully closing, the main valve body vibrates strongly, and the bypass valve (especially the position far away from the butterfly valve) vibrates violently. At the same time, when the butterfly valve plate is close to fully closing, the sound of high-speed water flow can be heard in the flow channel (with the increase of load, the sound gradually becomes a harsh buzzer), and the valve closing time is reduced from the original 10%.
 
Note: As the unit is loaded at 75%, the vibration of the bypass valve is too strong when the butterfly valve is closed by moving water, and a water hammer occurs in the flow passage. For safety reasons, the bypass valve should be reinforced and the butterfly valve closing time adjustment scheme should be considered first. After the treatment is finished, the butterfly valve closing experiment at 100% load should be continued (the treatment scheme will be reflected in the following description).
 
④ The unit is loaded with 100% load: at this time, the opening of the movable guide vane of the turbine is 51% and 66% respectively. During the process from full opening to full closing of the butterfly valve, the main valve body vibrates strongly, and the bypass valve (especially the position far away from the butterfly valve) vibrates violently. At the same time, when the butterfly valve plate approaches full closing, the sound of high-speed water flow can be heard in the channel (with the increase of the load, the sound gradually becomes a harsh buzzer), and the valve closing time is shortened from the original 110 s.
 
(3) Analysis of experimental data: When the butterfly valve is closed under no-load, 25% load, 50% load and 75% load, the time compression rates are 20%, 34.5%, 50% and 59% respectively; At the same time, the corresponding pressure increase rates in the channel are 11.5%, 17.3%, 18.2% and 19.2% respectively. According to this trend, if the dynamic water shut-off experiment under 100% load is carried out before treatment, the time compression rate will exceed 65% and the pressure increase rate will exceed 20%. When the butterfly valve is closed by dynamic water, the vibration of the butterfly valve body will be intensified, and the maximum vibration will be a 2.2 displacement analysis. According to the finite element analysis results, the maximum deflection of the main beam of the hydraulic plane steel gate is 2.58 mm, which mainly occurs in the web area of the main beam between the inner web of the No.3 longitudinal beam and the No.2 side beam. However, under the front water-stop mode, the maximum deflection of the main beam of the gate is 3.21 mm, which mainly occurs in the middle of the main beam. When the front water stop is set, the deflection of main beams 1#~4# tends to increase; The deflection of the 1# main beam is the largest under the backwater stop, and it is larger than that of the 1# main beam under the front water stop. The reason is that 1# main beam directly bears water pressure under this water stop. When the rear water stop is installed, the deflection of main beams 2#~4# also shows an increasing trend, but the maximum deflection is smaller than that of the front water stop. In a word, the deflection deformation of the main beam is better than that of the front water stop when the DTH plane steel gate at the inlet of the reservoir discharge culvert is set to stop the water.
 
Conclusion
 
To sum up, the stress of each component of the down-the-hole plane steel gate at the entrance of the discharge culvert of Santunhe Reservoir meets the requirements of the code under two water-stop arrangements, but there is excessive stress and concentration in some areas, so reinforcement measures must be taken for such areas. The stress distribution of the steel gate panel and 2#~4# main beams is even and the maximum stress is smaller than that of the front water stop when the backwater stop is adopted. The stress distribution of the lower side beam and 1# main beam in front water stop mode is better than that in rear water stop mode; The deflection of 2#~4# main beams under the rear water stop arrangement is smaller than that of the front water stop. From the above analysis results, it can be seen that the DTH plane steel gate at the entrance of the S reservoir discharge culvert should be arranged in the way of back sealing, so that the steel gate has better stress-bearing capacity and deformation resistance.