Valve and centrifugal pump safe operation

Overview Pumps are the heart of the fluid industry and act as the heart of a human body to power the fluid within the various devices in the system to ensure that the process is operating properly. Commonly used pumps, divided by the main leaf vane pumps, positive displacement pumps, special purpose pumps. Among them, the vane pump centrifugal pump is the most widely used. Centrifugal pump operation need to avoid two problems: stop water hammer and less than the minimum flow. There are many ways to solve these two problems, but the basic idea is how to configure a suitable system around the centrifugal pump. Valves play a very important role in these systems, and with the deepening awareness of these two types of problems, many specialized valves were born. Stop pump water hammer protection and valve water hammer is a series of dramatic pressure changes caused by the drastic changes in the medium flow velocity in the pressure pipe water hammer phenomenon. Water hammer is very dangerous and can destroy pumps, pipelines and other equipment. Water hammer in the pressure pipe has many causes, such as the rapid closure of the valve, abnormal stop pump and so on. Pump stop water hammer mechanism When due to non-normal reasons, such as power outages, the pump suddenly stopped working: initial stage, the medium in the pipeline to rely on inertia to continue, but the speed gradually reduced to zero; At this time, if the pipe layout there is high and low drop , The medium will flow back to the pump under the action of gravity; when the backflow medium reaches a certain speed, the check valve at the pump outlet will close quickly, so that the mass of medium arriving there suddenly becomes zero, causing the medium Pressure rises sharply - stop pump water hammer. A large number of literatures point out that the main reason for stopping the water hammer is that the check valve at the outlet of the water pump suddenly closes. However, studies have shown that, in some cases, the check valve at the pump outlet can be eliminated, but in most cases a backflow prevention setting at the pump outlet is necessary to prevent large amounts of media from flowing back into the pump. Stop pump water hammer to avoid measures to avoid stopping pump water hammer hazards many measures, such as the installation of water hammer eliminator, relief valve, pressure regulator tank, the following only describes two more applications, and general valve-related measures. 1, set the slow closing check valve Slow closing check valve is a through the implementation of institutions, dampers and achieve a slow closure of the check valve. The picture above shows a simplified diagram of a centrifugal pump with a slow closing check valve and a water hammer protection system. At this time, the slow check valve needs to cooperate with the gate valve (on-off valve). When the media under gravity flow backwards, the check valve closed slowly, effectively avoiding the common check valve due to the sudden closure of the water hammer. The disadvantage is that due to the slow closing speed, a portion of the media inevitably flows back into the centrifugal pump and the pump can therefore cause mechanical problems. 2, set slow stop butterfly valve This is a large-scale water conservancy system in the more common, the effect is better. Slow closing butterfly valve butterfly valve, the implementation of the structure and hydraulic control system. Pictured above is a schematic illustration of a centrifugal pump with slow-closing butterfly valve installed to stop the water hammer protection system. The system can be installed only slowly closed butterfly valve, which can play the role of check valve can play the role of switching valve. When the centrifugal pump is turned on, it starts slowly and quickly after the first step to ensure that the pump low load to open; when the pump suddenly stop working, its first fast and slow steps to close, you can avoid the production of water hammer, but also Avoid excessive media flow back through the pump, causing pump mechanical failure. Avoid minimum flow conditions and valve minimum flow is to ensure that the pump can work normally flow. If the pump is operated below the minimum flow rate, it will cause noise and vibration, the performance of the pump will become unstable, and even cause abnormal cavitation of the pump, reducing the service life of the pump. Therefore, measures must be taken to prevent the centrifugal pump working under the minimum flow conditions. At present, it is common practice to feed the centrifugal pump to set the minimum flow circuit. But from the pump's own value, only for those large flow, high lift, high-power centrifugal pump set the minimum flow circuit is reasonable. The minimum allowable flow rate for a centrifugal pump is calculated or experimentally determined by the pump manufacturer. The simplest minimum flow circuit requires only one on-off valve, such as a gate valve, to be opened in the circuit. Operate the valve when it is assumed that the pump is about to be in the minimum flow condition, turn on the minimum flow circuit, and prevent the pump from operating at minimum flow conditions. Summary The basic structure of the valve described above is no different from the general valve, but because of the corresponding improvements according to the application of the conditions, making these valves to be dedicated valves to solve these two problems.