Pump is the core of the fluid industry device, its role is like the heart of the human body, the system for the fluid within the device to provide power to ensure the normal operation of the process. Commonly used pumps, according to the classification of sub-leaf pump, volume pump, special purpose pumps. Among them, the vane pump centrifugal pump in the most widely used.
Centrifugal pumps need to avoid two problems during operation: stop the pump water hammer and below the minimum flow. To solve these two problems, the method is more, but the basic idea is how to configure a suitable system around the centrifugal pump. In these systems
Plays a very important role, and with the understanding of these two types of deepening, the birth of a number of dedicated
Stop water hammer protection and valves
Water hammer is a series of drastic changes in the velocity of the medium in the pressure pipeline caused by the rapid rise and fall of the water hammer phenomenon. Water hammer is very dangerous, you can destroy the pump, piping and other equipment. Pressure pipes in the water hammer for many reasons, such as the rapid closure of the valve, abnormal pump and so on.
The Mechanism of Pumping Water Hammer
When the initial stage, the pipe within the pipeline to rely on inertia to move forward, but the speed gradually reduced to zero; this time, if the pipeline layout there is a high and low gap, the role of the medium in the role of gravity The pump will return to the pump; when the backflow medium reaches a certain speed, the pump outlet
Will quickly close, so that the speed of a large number of media here suddenly becomes zero, causing a sharp increase in medium pressure here - the pump water hammer is generated. A large number of literature pointed out that the main pump water pump is the original pump outlet
Suddenly closed. However, studies have shown that although in some cases the checkout valve at the pump outlet can be canceled, in most cases, to prevent a large amount of media from flowing back into the centrifugal pump, the anti-backflow setting at the pump outlet is required.
Stop water hammer to avoid measures
There are many measures to avoid the risk of stopping the water hammer, such as the installation of water hammer eliminator, pressure relief valve, pressure tank, etc., the following only two kinds of applications, and general valve-related measures.
1, set the slow closing check valve
The slow closing check valve is a check valve that is slowly closed by increasing the actuator and damper. The above figure shows the installation of a slow closing check valve centrifugal pump pump water hammer protection system diagram, then slow closing check valve need to cooperate
(Switch valve) use. When the medium under the action of gravity back, the check valve slowly closed, effectively avoid the sudden closing of the ordinary check valve generated by the water hammer. The disadvantage is that because the shutdown speed is slow, part of the media will inevitably flow back into the centrifugal pump, the pump may cause mechanical failure.
2, set the slow closed only
This is a large water conservancy system in the application of more common, the effect is better way. Slow closed back
By the butterfly valve, the implementation of the structure and hydraulic control system. The above figure is a schematic diagram of a water pump protection system for a centrifugal pump with a slow-closing check valve. The system only need to install the slow closure of the butterfly valve can be, that can play the role of the check valve can play the role of switch valve. When the centrifugal pump is turned on, it is opened by the first step in the first step, to ensure that the pump low load open; when the pump suddenly stopped working, the first step quickly after the close, that can avoid the generation of water hammer, but also Avoid excessive media backflow through the pump, causing pump mechanical failure.
Avoid minimum flow conditions and valves.
The minimum flow rate is to ensure that the pump can work properly. If the pump is working below the minimum flow conditions, it will cause noise and vibration, pump performance will become unstable, and even cause abnormal pump cavitation, reducing pump life. So must take measures to avoid the centrifugal pump in the minimum flow conditions work, the current practice is to set the minimum flow of centrifugal pump loop. But the value of the pump itself is only for those large flow, high head, high-power centrifugal pump set the minimum flow circuit is reasonable. The minimum flow rate allowed by the centrifugal pump is determined by the pump manufacturer or experimentally.
The simplest minimum flow loop only needs to be fitted with an on-off valve in the circuit
, When the pump is about to be in the minimum flow conditions open the valve, connected to the minimum flow loop, to avoid the pump in the minimum flow conditions work.
to sum up
The basic structure of the valve described above and the general valve is no different, but because of the application of the conditions to do the corresponding improvements, making these valves become a solution to these two types of special valves. (According to China's first valve network)