Pump control valve application examples and water hammer protection features

Water hammer control is an important part of the design of a water distribution system. The formation of water hammer is related to the rapid closing / opening of the valve. Due to the difference between the valve closing / opening time Ts and the water hammer wave length T, the direct water hammer and the indirect water hammer are two forms. When Ts? T, the valve closed, the reflected water hammer wave has not yet reached the valve, the valve has been closed, the water hammer wave generated by the pressure increase without interference, this water hammer is called direct water hammer, Valve open state and the closed state on the contrary, with ordinary check valve water supply system often have a direct water hammer. When Ts? T, during the valve closing process, the reflected water hammer wave arrives at the valve, the valve has not been fully closed, the water hammer wave caused by the pressure increase has been disturbed, the water hammer peak is reduced, this water hammer is called Indirect water hammer. Under the same conditions, the direct water hammer is more harmful than the indirect water hammer, and the hardest one is to break the water flow to close the water hammer. Zhuzhou South Valve Manufacturing Co., Ltd. production of multi-function pump Control Valve is through the control valve is closed, resulting in the formation of indirect water hammer conditions to achieve the water hammer pipe protection system. A theoretical calculation of the water hammer wave booster pressure water supply system water hammer wave peak P is the pump lift and the water hammer pressure value of the value of the added value of △ P superposition namely: P = P1 + △ P (1) (1) direct Water hammer pressure increase △ P According to the RKS formula, you can calculate the pressure increase in direct water hammer in the water supply system △ P (2) △ ​​P-direct water hammer pressure increase, Kpa; V0- Average flow rate in pipe, m / s; V- Average flow rate in pipe after water hammer, m / s; (3) where K is the modulus of elasticity of water in N / m2; K is 2.04 × 10 5 N / cm2 E: Elastic modulus of pipe wall material, N / m2, steel pipe or reinforced concrete pipe, EO = 2.04 × 107N / cm2 D: diameter of water supply pipe, = K / ρ, the speed of sound transmission in a boundaryless liquid medium of density ρ, elastic modulus K, for water, CO = 1425 m / s. From equation (2), it can be seen that after the pipe material and the medium it delivers are determined, the pressure increase ΔP of the direct water hammer is a function of pipe diameter and flow rate, ΔP = f (V, 1 / D) The direct pressure of the water hammer value △ P increases with the flow rate increases, with the increase of diameter decreases. Therefore, in engineering design can reduce the flow rate that is to increase the diameter to reduce the harm of water hammer. (2) Calculation of the indirect water hammer pressure increase △ P1 The calculation of the indirect water hammer pressure increase is more complicated [2] [3], and can be calculated according to the fluid mechanics formula. △ P, = T / Ts · △ P "- Indirect water hammer when the water pressure value, Kpa; due to the occurrence of indirect water hammer, Ts? T, from (4) shows that △ P"? △ P, under the same conditions, indirect water hammer than direct water hammer Water hammer pressure peak should be small. When the valve is closed (open) time Ts, water hammer wave length T is determined, you can press (4) directly calculate the indirect water hammer pressure value. In the actual selection of pump multi-function valve, when the diameter is greater than DN800, generally Ts = (1.3-1.5) T, Ts≯2.0T appropriate. When the pipe diameter is small, the pipe is not long, Ts can be appropriately increased, the valve closing time Ts can be 2-10 times the water hammer phase T = 2L / C, the actual water hammer pressure P limited within the safe range. By adjusting the valve opening and closing action time (3 ~ 120s), so that the calculation of water hammer pressure peak value is less than 1.5 times the pump working pressure. This is different from the liquid-controlled slow-closing valve, liquid-controlled slow-closing valve through the fast off, slow off the two stages achieved in the fast off stage, the closing angle of about 60-80%, while the time is very short, 1 -2s; in the slow phase, the closing angle is small. Closure time is too long, easily lead to a large number of water pressure in the back of the pipeline, the pump reversal speed exceeds the allowable value, or cause the pressure pipe in the water column was quickly pulled off, some pipe vacuum, and even cut off to close the water hammer. 2 Multi-function pump control valve water hammer control process Multi-function pump control valve is a new type of hydraulic control valve, a valve can simultaneously replace the current pump pressure water pipe electric butterfly (valve) valve, check valve and water hammer to eliminate It can basically realize the function of the existing liquid-controlled slow-closing valve, that is, the two-stage valve-closing process can effectively realize the slow opening (quasi- soft starting) when the pump is on and the quick closing / slow closing when the pump is stopped Prevent water hammer accidents, but it does not have any electrically controlled power or external hydraulic system. In the valve body design also uses a wide body streamlined design, effectively reducing the water flow resistance. Multi-function water pump control valve water hammer protection process: Before the pump starts, the valve outlet pressure on the role of the main valve plate, the main valve plate is closed, while the diaphragm controller connected to the pressure on the upper chamber water, the lower chamber and the valve Imported low-pressure interlinked. Pump starts, the valve inlet pressure gradually increased, while pressure water through the valve inlet side of the connecting tube slowly into the diaphragm controller cavity, the main valve plate to achieve a slow opening, the opening speed can be adjusted by the control valve. When the pump is shut down, the pressure at the inlet of the valve is reduced. When it approaches zero flow, the main valve plate closes rapidly under its own gravity. As the pressure at the inlet of the valve is reduced, the pressure water at the outlet of the valve enters the upper chamber of the diaphragm controller through the connecting pipe, the lower chamber water is pressed back to the inlet of the valve through the connecting pipe at the inlet of the valve, the slowly closing valve plate is slowly closed, Adjust by control valve. The closure of the main valve plate and the slow closing flap valve comply with the two-phase closing rule of the water supply system, so it can effectively reduce the water hammer pressure peak. Accessory pipe attachment design: micro check valve is to ensure that the valve opening time is greater than the motor start-up time, so that light motor start; valve opening time pressure conditions can be set according to the scene. The control valve can adjust the water flow speed between the upper and lower chambers of the diaphragm controller so as to adjust the slow closing time. The valve can also be manually operated during the normal operation of the water pump to open and close the valve. The filter is to ensure the cleanliness of the water in the upper and lower chambers of the diaphragm controller. Because the valve in the opening process of water is reciprocating access, itself has the role of backwash, it can also be used for poor media conditions. The opening of the main valve plate of the multifunctional pump control valve is determined by the impact force of the water flow in the pipe. When the flow velocity is high, the opening degree of the main valve plate is large, and the valve plate opening degree is small when the flow velocity is reduced; when the flow velocity approaches zero, shut down. The whole process is consistent with the two-stage closing principle of eliminating water hammer, so removing the water hammer works well. Multifunctional pump control valve slow closing valve plate is closed in the diaphragm controller after the pressure difference between the lower chamber to achieve, that is, after the main valve plate is closed, the slow closing valve plate can only be closed, so there will be no slow closing and The phenomenon of speed synchronization. 3 Application Examples Ankang Railway Waterworks Reconstruction Project: Designed pump head 80m, terrain elevation 68.4m, design flow 850m3 / h, pipe diameter DN400, pipe length 6.0km, design flow rate 0.50-1.20m / s, C = 980.4m / s, the water hammer wave length T is 12.2s, Ts = 2.25T = 30s, in theory, the peak value of indirect water hammer is 1.34Mpa. After installation of multi-function pump control valve, 0.98Mpa; install the normal check valve to stop the water hammer pressure peak was 1.88MPa. According to the field test, JD745X-10DN400 multi-function pump control valve was installed. When the slow closing time was 30s, the peak value of stopping pump pressure was 0.95MPa, less than 1.20Mpa, while the original configuration was electric butterfly valve and micro- Is 1.2 ~ 1.4MPa. After stopping the pump the maximum reversal speed of the pump 600r / min, the same as the original configuration. After many practical use of proof, multi-function pump control valve has a good water hammer protection.