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Measures to Avoid Water Hammer of Multistage Centrifugal Pum
Source:未知|Popularity:0|release date:2020-12-04 16:57:33
Multistage centrifugal pumps have been widely used in mine drainage, energy and chemical industries due to their large flow and high lift characteristics.
Two problems need to be avoided during the operation of multistage centrifugal pumps: water hammer when the pump is stopped and the minimum flow rate is lower. There are many ways to solve these two types of 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 of understanding of these two types of problems, many special valves have been born.
1. Pump stop water hammer protection and valve
Water hammer is a series of sudden pressure alternating rise and fall of water hammer caused by the drastic change of the medium flow rate in the pressure pipeline. Water hammer is very harmful and can destroy pumps, pipelines and other equipment. There are many reasons for water hammer in pressure pipelines, such as rapid closing of valves and abnormal pump stoppages.
2. The mechanism of water hammer when the pump is stopped
When the pump suddenly stops working due to abnormal reasons, such as power failure: In the initial stage, the medium in the pipeline continues to advance by inertia, but the speed gradually decreases to zero; at this time, if there is a height difference in the pipeline layout, the medium will act on gravity When the backflow medium reaches a certain speed, the check valve at the outlet of the pump will quickly close, so that the speed of the large amount of medium arriving here suddenly becomes zero, causing the medium pressure here to rise sharply-stop Pump water hammer is produced. A large number of documents point out that the main cause of water hammer when the pump is stopped is the sudden closing of the check valve at the pump outlet. However, studies have shown that although the check valve at the pump outlet can be eliminated in some cases, in most cases, in order to prevent a large amount of medium from flowing back into the centrifugal pump, the anti-backflow setting at the pump outlet is necessary.
3. Stop pump water hammer avoidance measures
There are many measures to avoid the hazard of water hammer when the pump is stopped, such as the installation of water hammer eliminators, pressure relief valves, pressure regulating tanks, etc. The following only introduces two measures related to general valves that have more applications.
1). Set up a slow closing check valve
Slow closing check valve is a check valve that realizes slow closing by adding actuators and dampers. The above picture is a simplified diagram of the water hammer protection system for centrifugal pumps with slow-closing check valves. At this time, the slow-closing check valve needs to be used with a gate valve (on-off valve). When the medium flows back under the action of gravity, the check valve is slowly closed, effectively avoiding the water hammer caused by the sudden closing of the ordinary check valve. The disadvantage is that due to the slow closing speed, a part of the medium inevitably flows back into the centrifugal pump, which may cause mechanical failure.
2). Set slow closing check butterfly valve
This is a method that is widely used in large pumping systems and has better results. The slow closing check butterfly valve consists of a butterfly valve, an executive structure and a hydraulic control system. The picture above is a simplified diagram of the water hammer protection system for centrifugal pumps with slow-closing check butterfly valves. The system only needs to install a slow-closing check butterfly valve, which can play the role of a check valve and an on-off valve. When the centrifugal pump is turned on, it is turned on in a slow first and then fast step to ensure that the pump is turned on at low load; when the pump suddenly stops working, it is turned off in a fast and slow step first to avoid water hammer. Avoid excessive medium flowing back through the pump, causing mechanical failure of the pump.