What happens when a chemical pump reverses? What should I do if the chemical pump reverses?

　　I. Reasons for chemical pump reversal

　　The reversal of chemical pump can be divided into active reversal and passive reversal.

　　Active reversal refers to the reversal of the motor-dragging chemical pump unit, which is mainly caused by the reversal of the phase sequence of the main wiring of the motor, and this kind of situation generally occurs in the debugging or start-up phase of the chemical pump unit.

　　Passive reversal, refers to the chemical pump drag motor reversal, that is, the liquid in the pump outlet pipeline backflow, causing the chemical pump reversal, and drive the motor reversal. This kind of situation is generally due to the sudden loss of motor power or pump shutdown when the export valve is not closed completely, due to the liquid level difference caused by the liquid backflow caused by the valve may also be too fast to close the water flow impact.

　　Second, the hazards of chemical pump reversal

　　1 pump damage

　　Chemical pump reversal will cause significant damage to the chemical pump itself, first of all, the chemical pump unit for a long period of time reversal, will be on the packing seals or mechanical seals with rotational requirements caused by greater damage. Secondly, the chemical pump reversal will have rotational requirements of the chemical pump structural components (such as bushings lock nut, impeller lock nut, etc.) have an impact, once the pump reversal, these parts are easy to loose, affecting the internal structure of the pump and the normal operation of the components. Again, once the chemical pump passive reversal, a short period of time will produce a large axial thrust and additional torque, thus the pump bearings, balance disk, balance drum, shaft, impeller and other major parts of the axial and radial forces, these axial and radial forces, may lead to damage to the chemical pump bearings, the destruction of the balance of components, and in severe cases will cause the pump shaft bending or fracture.

　　In addition, the multi-stage pump reversal may reach the critical rotational speed of the pump rotor to cause resonance, resulting in damage to the pump unit. For axial flow chemical pumps, its reversal may reach the flyaway speed. Pump in the operation of a sudden power outage of water through the pump backflow, the pump reverse rotation, the maximum speed of the pump is called the maximum speed of the flyaway speed called. The unit will cause the main shaft swing increase and vibration intensification, resulting in wear and tear of the shaft tile, causing other structures vibration surface damage to the equipment, if the escape speed reaches its maximum value and exceeds the allowable time, will cause permanent deformation of the rotor parts of the damage.

　　2 Damage to the motor

　　Chemical pumps in reverse will produce a large torque, will cause the motor wind blade on the balance block and stator wear, resulting in motor bearing damage, stator winding damage, rotor wind blade damage. Chemical pump passive reversal will also make the motor into a power state, thus causing damage to the motor and the pump unit corresponding to the electrical wiring.

　　Chemical pump reversal of the motor damage by the pump and motor connection. If the pump and the motor using a belt connection, chemical pump reversal on the motor may be less because of belt slippage. If the pump and motor coupling connection, chemical pump reversal may first cause damage to the coupling without damaging the motor. If the pump and motor using direct connection, gear box connection, hydraulic coupling connection, then the chemical pump reversal may cause greater damage to the motor.

　　3 piping damage

　　Chemical pump passive reversal is often accompanied by the production of water hammer. Stop pump water hammer is one of the water hammer phenomenon, refers to the pump unit due to a sudden power failure or other reasons caused by the open valve state of natural parking, in the pump and piping system, due to sudden changes in the flow rate caused by a series of sharp pressure alternately rise and fall of the hydraulic shock phenomenon of the solid water hammer effect is extremely destructive, stop the pump water hammer is a more serious type of water hammer effect. The production of water hammer, will make the pipeline pressure increases dramatically, more than the normal pressure of the pipeline several times, dozens of times or even greater. This larger pressure fluctuations will cause strong vibration of the chemical pump unit piping system, at the same time will destroy the pipeline valves, pressure gauges, flow meters and other ancillary equipment, and will even contribute to the pipe burst and other accidents.

　　Third, the chemical pump reversal prevention

　　1 design precautions

　　Selection of relatively small torque of inertia of relatively large pump units or chemical pump units installed on the inertia flywheel, can reduce the degree of chemical pump reversal. Inertia flywheel installed in the rotating part of the pump unit, you can avoid stopping the pump when the speed of the pump drops sharply, preventing the separation of the water column, thereby reducing the water hammer pressure. This can reduce the impact of the pump stopping water hammer, thus effectively preventing the reversal of the chemical pump. Installation of inertia flywheel method for horizontal pumps, and the requirements of the field pipeline can not be too long in the pipeline design, appropriate increase in the diameter of the pipeline, wall thickness, in order to reduce the liquid flow rate in the pipeline; change the longitudinal cross-section of the pipeline layout; reduce the length of the pipeline and so on can be guarded against the water hammer effect, so as to reduce the impact caused by the reversal of the chemical pump. In practice, try to avoid large height differences. If used in high-rise buildings, segmented water supply can be used to reduce the height of a single pump outlet section of the pipeline.

　　2 pipeline auxiliary devices

　　Slow-closing check valve (check valve) instead of ordinary check valves, in order to prevent backflow of media in the pipeline at the same time to reduce the pumping water hammer, to prevent the chemical pump reversal has a significant effect. Slow closing check valve with slow opening and closing and eliminating water hammer technical characteristics, to achieve a light load pump and prevent the generation of water hammer when the pump stops turning off the slow closing check valve by slowing down the way to eliminate water hammer, to prevent the chemical pump reversal, its high sensitivity, simple and feasible, safe and reliable, good sealing, more common in practice, mainly used in small and medium-sized pumping stations.

　　Liquid-controlled slow-closing butterfly valve, in the power outage can be predetermined time and angle, divided into fast, slow off the two-stage closure, can effectively reduce the pressure fluctuations in the pipeline network to eliminate the liquid in the pipeline network of water hammer hazards, control pump reversal, thereby protecting the pumps and pipeline network system, safe and reliable operation, and can also be used as a main valve pumps, a valve on behalf of the two valves (gate valves and backstop valves.) Liquid-controlled slow-closing butterfly valve easy to operate, safe and reliable, in the case of larger flow, higher head, longer pipeline, but also can produce good results, has been widely used in the higher security requirements of the pumping station.

　　In the pump export pipeline is not long, the pump head is low, you can cancel the check valve, and in the pipeline at the exit of the installation of flap, can effectively prevent the chemical pump in the shutdown reversal. In the chemical pump start, due to the impact of the medium, the clap door automatically open; and in the chemical pump shutdown, due to self-weight and the role of the medium backflow pressure, the clap door automatically closed to prevent the pipeline medium backflow, caused by the chemical pump reversal. The structure of the gate is simple, inexpensive used in irrigation pumping stations.

　　3 operation precautions

　　In the chemical pump debugging and start the pump, the first way to observe the direction of rotation with a point motor to determine the motor steering and chemical pump rotation in the same direction. If the steering is opposite, any replacement of the two motor main power supply access to the position of the wire can be.

　　In the chemical pump unit operation, the unit for inspection, observation of chemical pump unit operation and unit-related electrical equipment conditions, thereby reducing the high temperature, overpressure protection and other reasons for power failure, to prevent the chemical pump passive reversal. In the chemical pump unit shutdown, to do first close the export valve and then shut down the chemical pump power. Close the exit door slowly for several times. If the chemical pump using frequency control, in the shutdown frequency can be gradually reduced through the pump speed to prevent the pump from stopping the introduction of emergency, so as to prevent the chemical pump reversal.

　　Chemical pump unit reversal problem will have a significant impact on its safe operation. Accidents caused by chemical pump reversal are common. People should pay attention to the harm caused by the problem. In practical application, according to the actual situation, should fully consider the chemical pump reversal problem, as far as possible to use economical, safe and feasible precautions to improve the reliability of chemical pump unit operation.