Valves and centrifugal pumps safe operation procedures and characteristics of centrifugal pumps

Valves and centrifugal pumps safe operation procedures and characteristics of centrifugal pumps

Pump is a liquid industrial production device, its role like the heart of the human body, for the system in the equipment in the liquid increase power, to ensure the normal operation of the production process. Common pumps are divided into axial piston pumps, positive displacement pumps, special function pumps, etc. Wherein, the centrifugal pump in the axial piston pump is used as.
Pump is a liquid industrial production device, its role like the heart of the human body, for the system in the equipment in the liquid increase power, to ensure the normal operation of the production process. Common pumps are divided into axial piston pumps, positive displacement pumps, special function pumps, etc. Wherein, the centrifugal pump in the axial piston pump is used as.
Centrifugal pump operation must prevent several problems: stop pumping water hammer and less than low flow. There are many ways to deal with these two problems, but basically the concept is how to tightly around the centrifugal pump equipped with a set of appropriate system software. Valves play a vital role in all kinds of systems, but as these two kinds of difficult understanding increases, many valves appear.
Stop pump water hammer protection and valve
Water hammer is a series of water hammer phenomena caused by the drastic change of medium flow velocity in a type II pressure vessel. Water hammers can be particularly harmful, destroying pumps, pipes and other machinery. There are many factors caused by the water hammer in the working pressure pipeline, such as the efficient closure of the valve, abnormal stop of the pump and so on.
Stop pumping water hammer principle
When abnormal reasons, such as power off, the pump stops working: at the beginning, the material in the pipeline continues to move forward with the help of inertial force, but the speed slowly decreases to zero; At this time, if the pipeline design has many ups and downs, the material under the action of gravity will be pump countercurrent; When the countercurrent material reaches a certain rate, the pump outlet check valve will quickly shut off, so that the rate of many media arriving here suddenly becomes zero, causing a substantial rise in the working pressure of the material here – caused by the stop pump water hammer. Many references emphasize that the key to stop pumping water hammer is the sudden closure of the centrifugal pump outlet check valve. But studies have shown that although the check valve at the pump outlet can be closed in some cases, in the vast majority of cases, in order to avoid a lot of material countercurrent into the centrifugal pump, the pump outlet anti-countercurrent setting is necessary.
Stop pumping water hammer prevention countermeasures
There are many countermeasures to prevent water hammer damage from stopping the pump, such as the assembly of water hammer remover, pressure reducing valve, transformer tank, etc. The following is only a detailed introduction of two kinds of commonly used countermeasures related to universal valves.
1. Set the slow closing check valve
Slow closing check valve is a kind of check valve that realizes slow cancellation by adding actuator and shock absorber. Xinhua News Agency reporter set a schematic diagram of centrifugal pump stop pump water hammer protection system with slow closing check valve. At this time, slow closing check valve needs to be applied with stop valve (cut off valve). When the substance under the action of countercurrent, the check valve slowly closed, effectively prevent the general check valve suddenly closed caused by the water hammer. Its disadvantage is that due to the slow shutdown, a part of the material inevitably countercurrent into the centrifugal pump, and the pump may cause equipment failure.
2. Set the slow closing disc valve
This is a common and effective method used in all kinds of water conservancy systems. The slow closing disc valve is composed of butterfly valve, operating structure and hydraulic transmission system. Xinhua News Agency reporter set the centrifugal pump stop pump water hammer protection system diagram with slow closing disc valve. This system only needs to assemble the slow closing disc valve, which can play the function of the check valve and cut off the valve. When the centrifugal pump starts, it is opened according to the process of first slow and then fast, to ensure that the pump starts with low load; When the pump stops working, it is turned off by the first fast and then slow process, which can not only prevent the formation of water hammer, but also avoid too much material countercurrent according to the pump, resulting in centrifugal pump equipment failure.
Prevent low flow operating conditions and valves
Low flow is to ensure that the pump can operate normally platform flow. If the pump is working under the condition of less than low flow, it will cause noise and vibration, the characteristics of the centrifugal pump will become unstable, and even cause abnormal cavitation of the centrifugal pump, reducing the service life of the pump. Therefore, effective measures must be taken to prevent centrifugal pumps from working under low flow conditions. At present, a widespread practice is to set a low flow control loop for centrifugal pumps. However, in terms of the use value of the centrifugal pump itself, it is only reasonable to set a low flow control loop for those centrifugal pumps with high flow, high head and high power. The minimum allowable flow rate of centrifugal pump is determined by the pump manufacturer or the test.
Super simple total flow control loop * must be assembled in the control loop a cut-off valve, such as a stop valve, when you feel that the pump will be in a low flow working condition to open the valve, access to low flow control loop, to prevent the pump in low flow conditions.
summary
The basic structure of the valve recommended above is the same as that of the universal valve, but because of the corresponding improvement according to the working condition of the application, this valve becomes to deal with these two kinds of problems.
After motor maintenance, before laying the connecting shaft, check whether the rotation orientation of the motor is correct or not. 2) Check whether the pump inlet and outlet pipes and attached pipes, flanges and valves are assembled correctly, whether the anchor screws and grounding wires are in place, and whether the connecting shaft is installed. 3) Open the brake to check whether there is any problem with rotation. 4) Check whether there is any problem with the oil quantity of the grease, provide oil without oil, and check the oil characteristics of the grease (fat). 5) Open each cooling circulating water valve, and check whether the pipeline is smooth. Pay attention to the cooling circulating water can not be too big or too small, too much exchange will cause waste, too small the actual effect of refrigeration
The normal operation mode of centrifugal pump is shown as follows:
1. Check the centrifugal pump before operation
1) After motor maintenance, check whether the rotation orientation of the motor is correct or not before laying the connecting shaft.
2) Check whether the pump inlet and outlet pipes and attached pipes, flanges and valves are assembled correctly, whether the anchor screws and grounding wires are in place, and whether the connecting shaft is installed.
3) Open the brake to check whether there is any problem with rotation.
4) Check whether there is any problem with the oil quantity of the grease, provide oil without oil, and check the oil characteristics of the grease (fat).
5) Open each cooling circulating water valve, and check whether the pipeline is smooth. Pay attention to the cooling circulating water can not be too big or too small, too much exchange will cause waste, too small refrigeration effect is not good. General cooling water flow into strips can be.
6) Open the channel valve of the centrifugal pump, close the outlet valve of the centrifugal pump, and then open the on-off valve of the barometer.
7) Check the tightness of the condensate pump and the opening degree of the skeleton seal.
Note: The heat conduction oil pump should be heated evenly before starting.
2. Operation of centrifugal pump
1) Open the channel valve, turn off the outlet valve, and run the motor.
2) When the pump outlet working pressure exceeds the operating temperature, check the normal operation of all places, slowly open the outlet valve.
3) When running the motor, if it cannot run or there is abnormal sound, the power supply should be turned off immediately for check, and the common faults can be removed before running.
4) During operation, note that people do not have to face the coupling device to prevent flying out and causing injuries.
3. Actual operation of centrifugal pump shutdown
1) Gradually turn off the centrifugal pump outlet valve.
2) Disconnect the switching power supply of the motor.
3) Turn off the barometer switch valve.
4) When stopping, do not stop cooling circulating water immediately. When the humidity of the centrifugal pump drops to 80¡æ, the water can be cut off.
5) Turn off the channel valve and empty the pump housing according to the demand.
4. Actual operation and maintenance of centrifugal pump after operation
When the centrifugal pump runs normally, the pump operator needs to carefully inspect the following points:
1) Check the condensate pump outlet working pressure, total flow, electrical flow, etc., no overload work, and accurately record the electrical flow, working pressure and other data.
2) Listen to the sound, distinguish the running sound of the condensate pump and the motor, and distinguish whether there is any abnormality.
3) Check the vibration of the condensate pump, motor and pump seat. If the vibration is serious, change the pump for inspection.
4) Check the ambient temperature of the motor housing, the ambient temperature of the bearing seat of the condensate pump, the ambient temperature of the bearing seat shall not exceed 65 degrees, and the ambient temperature of the motor shall not exceed 95 degrees.
5) Ensure the normal condition of grease oil and liquid level meter of grease bag. Grease tank liquid level instrument, if there is a ruler as the standard; There is no scale to see the window (oil level meter), the oil quantity should be maintained in the middle of 1/3 ~ 1/2, in the conventional oil quantity, the grease leakage shall not exceed 5 drops/minute, the working pressure of refueling, to indicate the equipment as the standard.
6) Check the tightness of the condensate pump and the flange, the wire plug, the cooling circulating water, the sealing oil connector is not leaked.
7) Check the reserve status of the standby pump, and brake once a day.
5. Practical operation of conversion of centrifugal pump
In order to ensure that in the conversion pump, the total flow, working pressure and other data almost do not change, no ups and downs, more suitable for two people together with the actual operation.
1) Do a good job of the preparatory work before running the pump.
2) One person first opens the standby pump, and gradually opens the outlet valve after the normal and stable operation of the centrifugal pump. At this time, with the opening of the pump outlet valve, the working pressure of the centrifugal pump outlet valve decreases slightly, but the electrical and mechanical flow increases. At the same time, another person slowly shuts down the outlet valve of the centrifugal pump, and then completely shuts down the outlet valve of the centrifugal pump when the flow of the pump to be operated is sufficient and too large. Turn off the power, and then do the normal pump shutdown treatment.