What is a multi-purpose pump control valve? What are the operating characteristics of the pump need to control the valve? Pump control valve can achieve these controls? And it with the traditional gate valve, butterfly valve, check valve and uniform, Valve in the principle, function, etc. What is the difference in the quality of the author in this article to multi-function piston pump control valve (hereinafter referred to as the control valve), for example, through its analysis of the structure, main functions, working principle, The view of the problem for readers to read. First, the structure of the control valve structure shown in Figure 1 (the icon is open). The main features of the control valve structure is to cancel the valve seat in the middle of the positioning mechanism and the upper valve spring, and the valve flap on the underside of the design of the baffle to minimize the media overcurrent mechanical loss and valve Vortex loss in the lower dome. To the cylinder piston as a driving element, under the pressure of the media itself driven by the valve for up and down movement, to achieve the valve open or closed. Pistons, opening and closing pieces, together with the cylinder body arranged on the valve body, streamlined, wide valve body cavity, not only head loss than similar products to reduce more than 30%, and has good cavitation resistance. Servo system with solenoid valve commutation mechanism (hereinafter referred to as solenoid valve) and pressure pipe to form the servo system, take the pressure water at both ends of the control valve as the driving source, through the electric signal instruction, pressure water at either end can achieve the pump control valve in setting Time and speed of the implementation of the pump on or off. Second, the pump operating characteristics and control valve features, working principle 1. Pump start characteristics and control a) Centrifugal pump zero flow start characteristics and control (ie, valve start) Centrifugal pump in the zero flow conditions The minimum shaft power is 30% - 90% of the rated shaft power, so the start-up feature of the centrifugal pump is zero-flow start-up (ie valve start). After the pump reaches the rated speed, the control valve slowly opens at the set speed. Working principle: When the pump is started (before), the pressure water flows through the solenoid valve with delay to the upper chamber of the piston in the cylinder, while the lower chamber of the piston opens to the atmosphere through the solenoid valve at the lower end of the cylinder. At this time, the control valve is in the closed state. Motor compensation start over, the pump is running, the solenoid valve to perform commutation instructions, cut off the pressure on the cavity of the piston cavity, the lower end of the cylinder closed to the atmosphere loop, while the pressure water through the solenoid valve into the cylinder piston lower chamber, open the piston Upper chamber open to the atmosphere of the loop, the piston cavity of the water through the solenoid valve discharge valve, the control valve at a set speed slowly open to complete and meet the centrifugal pump at zero flow axis power minimum starting characteristics to ensure that the pump unit Safe operation. b) axial flow pump start the flow characteristics and control (ie, fully open valve start) axial flow pump in zero flow conditions, the maximum shaft power for the rated shaft power of 140% to 200%, so the axial flow pump start Characteristics should be large flow start (that is, fully open valve start). Working principle: The control valve to meet the axial flow pump fully open valve to start the working principle is the centrifugal pump off the valve to start the reverse run, the solenoid valve first work, the valve fully open, the pump restart. See a), do not go into details. Axial flow pump before the start, when the valve inlet pressure is zero, the control valve using the valve outlet side of the media pressure valve opens, and start the centrifugal pump is the use of the valve inlet side of the medium pressure valve opens. One of the key features of the pump control valve is its ability to open or close the control valve at either end of the valve. c) control the start of the mixed flow pump features mixed flow pump in the zero flow conditions shaft power between the above two pumps, rated power of 100% to 130%, so mixed flow pump start-up characteristics should also be the two pumps Between the general can choose to start the pump and control valve slowly open simultaneously. How it works: working principle and control of zero-flow centrifugal pump start feature the same, as long as you cancel the delay can be set solenoid valve. 2. Stop the pump and its control a) Control the zero flow of the centrifugal pump to stop the pump (stop the pump after the valve is closed) For the centrifugal pump, firstly slowly close the control valve and then stop the pump. The importance of this is: The rated flow rate is gradually reduced to zero and the speed gradient is very small. This can effectively prevent the occurrence of pump water hammer and pump reverse. The pump shaft power is gradually reduced from the rated power to the minimum operating power, which is in favor of unit safety. Working principle: When the pump needs to be stopped, as long as the control power supply of the solenoid valve is cut off first, the solenoid valve executes the commutation command to close the pressure water source in the lower piston cavity and the circuit in the upper cavity of the piston and open the pressure water source in the upper cavity of the piston Piston through the atmosphere of the lower chamber loop, that is, the pressure of imported water as the driving source, slowly close the control valve, and other control valve is fully closed, the limit switch to stop the pump command operation, the whole process of automatic control. Control valve slow closing time can be adjusted by the throttle valve in the range of 5 ~ 60s or according to user needs to choose. b) Controlled axial flow pump, mixed flow pump stop pump axial flow pump, mixed flow pump stop pump function and working principle is the same as above, not redundant. 3. Change the device characteristics (ie, flow stepless adjustment function) to change the characteristics of the device belongs to the scope of regulation of the pump operating conditions, the most commonly used is throttling method, also known as valve regulation method, the use of open large or small valve opening ; Change the resistance coefficient ξ in the pump device, so that the water supply characteristics of the pipeline H = F (Q) changes in order to achieve the purpose of regulating the flow. Control valve from fully closed to fully open, the valve opening can be infinitely adjusted by the opening of the display shows the opening, and to memory and stability. Working principle: a) The flow is controlled by pressure water injection into the lower cavity of the piston and the circuit of the upper cavity of the piston communicating with the atmosphere is opened. Meanwhile, the pressure water injection pipe on the upper cavity of the piston and the circuit communicated with the atmosphere of the lower cavity of the piston are closed, At this time the valve slowly open, to set the flow, the control circuit that is required by the instructions on the piston, the lower chamber and the atmosphere connected to the circuit closed at the same time the piston, the lower chamber pressure water into the pipeline open, then the piston, Under the total pressure on both sides of the same, the piston is at rest, the entire cylinder into a closed state, stabilizing the valve opening, and the opening of the display shows the opening. b) The flow from the big small is a) the reverse operation, not redundant. The above control circuit instructions can be performed by the limit switch can also be set to implement a small electric control box, both to achieve automatic control. 4. Accidental sudden stop pump water hammer control accidental sudden stop pump generally refers to the power supply network failure or lightning protection trip and so on to stop the pump, the probability of such stop pump less than 1% of the total number of stop pump, but therefore The water hammer generated is devastating to the pipe network and water supply unit and should be taken seriously. a) stop the physical phenomenon of water hammer hammer This article is not to discuss the water hammer in the pipeline, just to facilitate the control valve to reduce the impact of water hammer function and working principle of narrative, reference Rokoffsky water hammer formula to stop pumping water Hammer physical phenomenon for a simple statement. Where H - the water hammer when generating water hammer (m water column); C - water hammer wave propagation velocity, if not for the time being to consider the media, wall material elastic coefficient and wall thickness, take approximately C = 1000m / s; g - Gravitational acceleration, 9.81m / s; Vo - Media velocity before water hammer occurs (m / s); Vt - Media velocity (m / s) when water hammer occurs. From Equation 4-1, we can see that the necessary condition for the water hammer to occur is the velocity of the fluid. The size of the water hammer depends on the magnitude of the gradient. Stop the pump flow rate from V0 to zero, the first floor due to fluid inertia, the water layer is compressed, the pressure rise (ie, water hammer pressure), followed by the role of inertial forces in turn one layer, a layer ... ... stagnation, The pressure increases, is compressed, there are microscopic high-pressure zone and low pressure zone, their interface is called water hammer wave (this time booster wave), booster wave until the end of the pipe end disappears. Then the reverse layer, a layer ... ... spread to the first level when the water hammer liquid level (in this case complex pressure wave), the time required for this round trip process t can be expressed by the following formula: Where L - the length of the water pipe (M). If the valve closing time is T OFF, the water hammer under T OFF L / 500s is the indirect water hammer, ΔH is less than the direct water hammer. This is because, when an indirect water hammer occurs, the pressurization process that is developing in front of the valve is weakened by the pressure wave of the pressure wave. The size of ΔH is related to the degree of interference and the number of interferences. It can be seen from the above description that the control valve can not avoid the occurrence of water hammer when the pump suddenly stops pumping unexpectedly. However, according to the length of the water supply pipeline, the direct water hammer can be converted into an indirect water hammer to minimize ΔH by adjusting the valve closing time, Ensure the safety of water pipelines and pump units. b) the valve closing time adjustment At present, the pump control valve closing time adjustment methods commonly used in two ways to point out that this article refers to the adjustment method is one of the functions of the pump control valve, although with this type of function Check valves or other valves are not necessarily pump control valves, so as not to be misleading as detailed in the "Conclusions" section of Chapter III of this document. c) Two-stage valve closing (that is, the valve is closed after the valve is closed quickly) This type of valve closing can prevent the water hammer of the pump from stopping. As for the valve closing time, it should also match the length of the pipe, taking into account the water pump Reverse speed and the amount of water back to meet the elimination of stop pumping water hammer requirements. d) Uniform Shut-off Valve This shut-off valve is characterized by the ability to adjust different shut-off times depending on the length of water supply pipe and the number of reciprocating pressure wave round trips, and satisfies the conditions of T OFF> L / 500s. Drastically weakened suddenly stop pumping water hammer hydraulic hitting force than the two-stage valve is wide, enough to meet the GB / T50265-97 "pumping station design specifications" on the anti-speed should not exceed 1.2 times the rated speed, sustained Time should not exceed 2min request. Pump control valve of the above two methods are automatically controlled by the solenoid valve. 5. Select the pressure source of mobility Large solenoid valve servo mechanism designed to bidirectional at the same time by the pressure distribution by the one-way valve from a higher pressure in the infusion tube water pressure into the solenoid valve. Whether the water pressure on the inlet side or the outlet side of the pressure water, the valve can be implemented separately on or off. Because of the existence of this feature, the pump control valve to meet the start of a variety of pumps, pumps and other operating characteristics may be demanded. The important point is: when the transmission medium is turbid water, can not be used as a driving source for external pressure source, as long as a servo line to achieve all the features of the control valve. 6. Energy-saving Over-current medium to control the energy consumption in the smallest pump control valve is an important issue. We sampled some of the diameter of the control valve experiment, the following experimental formula for the reader reference: drag coefficient ξ determined by the following formula: when DN ≤ 250 ξ = 14.68 × V1.1339 (7-1) When DN> 250 ξ = 10.97 × V1.1339 (7-2) Where ξ - resistance coefficient; V - medium flow rate (m / s). The local head loss hf is determined by the following equation: hf = ξ × V2 / 2g (7-3) or: hf = 0.749 × V0.8661 (7-4) hf = 0.56 × V0.8661 (7-5) where hf - local head loss (m water column); V - medium flow rate (m / s); g - gravitational acceleration g = 9.81 (m / s2). After testing, the kind of pump control valve head loss than the same type of hydraulic control valve to reduce energy consumption by more than 30%. Third, the conclusion With the control of pump operation characteristics of the valve is called the pump control valve, which is obvious. Section a), b), c) of Section 1 "Pump Start-up Characteristics and Controls" in Chapter 2 of this article; Section a), b) in Section 2 "Stopping pumps and their control" Section "a), b) of" Changing the characteristics of the installation "; Section b) in Section 4" Control of Suddenly Abnormally Stopped Pumping Water Hammer "; the eight functions described here are those required by the operating characteristics of the pump , But also pump operation characteristics of the valve to control the content, but also the necessary function of the pump control valve. These necessary functions are defined by the difference between the pump control valve and the various types of check valves or other valve qualities. Why does not have the necessary function can not be called a pump control valve? This can be illustrated by the following example: If you do not have the first section 2) a) to stop the pump after the first shut-off function, the centrifugal pump, stop pump Have suddenly stopped the pump unexpectedly, accounting for more than 99% of the total stop pump normal stop pump, and can avoid the water hammer and pump reversal of the safety of safety out of order, how dangerous. Without the functions of Section 2 and Section 3, the valve can only be opened if the pump is started, and the valve is closed when the pump is shut down. Obviously this is when the pump is working on the control valve and the control valve is lost "Essence, more difficult to understand as a pump control valve. If you do not have the function of step 3 regulation of flow, once the pump operating conditions due to the resistance is small, the flow is too large, not only the pump deviate from the highest efficiency zone energy consumption, but also because of excessive shaft power overload damage to the unit . Therefore, the pump control valve should have the above eight necessary functions is inevitable.