How to avoid stopping pump water hammer？Today let us talk this topic together!
The centrifugal pump is the core device of the fluid industry. Its function is like the heart of human body. It provides power for the fluid in each device of the system and ensures the normal operation of the process flow. Commonly used pumps are divided into vane pump, positive displacement centrifugal pump, special purpose pump, etc. Among them, centrifugal pump is the most widely used vane pump.
There are two problems to be avoided in the operation of centrifugal pump: the water hammer to stop the centrifugal pump and the flow below 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. In these systems, valves play a very important role, and with the deepening understanding of these two kinds of problems, many special valves have been born.
Pump stop water hammer protection and valve
Water hammer is a series of water hammer phenomena caused by the sharp change of medium velocity in pressure pipeline. The harm of water hammer is very big, it can destroy the pump, pipeline and other equipment. There are many reasons for the water hammer in the pressure pipeline, such as the quick closing of the valve, abnormal stop of the centrifugal pump, etc.
Mechanism of water hammer in pump stop
When the centrifugal pump stops working suddenly 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 reduces to zero; at this time, if there is a high and low drop in the pipeline layout, the medium will flow backward to the centrifugal pump under the action of gravity; When the backflow medium reaches a certain speed, the check valve at the centrifugal pump outlet will close quickly, so that the speed of a large number of medium arriving here suddenly becomes zero, resulting in the sharp rise of medium pressure here - water hammer of pump stop. A large number of documents have pointed out that the main cause of the water hammer is the sudden closure of the check valve at the outlet of the centrifugal pump. However, some studies have shown that although the check valve at the pump outlet can be cancelled in some cases, in most cases, in order to prevent a large amount of media from flowing back into the centrifugal pump, the anti backflow setting at the pump outlet is necessary.
Measures to avoid water hammer during pump stop
There are many measures to avoid the harm of water hammer, such as the installation of water hammer eliminator, pressure relief valve, pressure regulating tank, etc. the following only introduces two measures that are more widely used and related to general valves.
1. Set slow closing check valve
Slow closing check valve is a kind of slow closing check valve by adding actuator and damper. The above figure is the schematic diagram of water hammer protection system for centrifugal pump with slow closing check valve installed. At this time, slow closing check valve needs to be used with gate valve (on-off valve). When the medium flows backward under the action of gravity, the check valve closes slowly, effectively avoiding the water hammer caused by the sudden closing of the common check valve. The disadvantage is that due to the slow closing speed, part of the media inevitably flows back into the centrifugal pump, so the centrifugal pump may have mechanical failure.
2. Set slow closing check butterfly valve
This is a common and effective method in large-scale water conservancy system. Slow closing check butterfly valve is composed of butterfly valve, executive structure and hydraulic control system. The above figure is the schematic diagram of water hammer protection system for centrifugal pump with slow closing check butterfly valve. The system only needs to install slow closing check butterfly valve, which can play the role of check valve and on-off valve. When the centrifugal pump is started, it is started in the slow and fast steps to ensure that the pump is started at low load; when the pump suddenly stops working, it is closed in the fast and slow steps, which can not only avoid the generation of water hammer, but also avoid too much medium backflow through the centrifugal pump, causing mechanical failure of the centrifugal pump.