Solve the problem that the fire pump cannot supply water and how to determine the flow rate of the fire pump
Nov 29, 2022
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The fire pump has become the most widely used fire pump because of its simple structure, convenient use and maintenance, and high efficiency. However, sometimes the centrifugal fire pump cannot lift water, which is very troublesome. The cause of the failure of the fire pump to lift water is now analyzed.
The speed of the fire pump is too low
(1) Human factors. Due to the damage of the original motor, a considerable number of users randomly equipped the fire pump with another motor to drive it. As a result, the flow rate was low, the head was low, and even the water could not be pumped.
(2) The transmission belt is worn. There are many large-scale isolated fire pumps that use belt transmission. Due to long-term use, the drive belt is worn and loosened, and slipping occurs, thereby reducing the speed of the fire pump.
(3) Improper installation. The distance between the centers of the two pulleys is too small or the two shafts are not parallel, the fire pump transmission belt is installed on the tight side, resulting in too small wrap angle, the calculation error of the diameter of the two pulleys, and the large eccentricity of the two shafts of the fire pump driven by the shaft, etc. Both will cause changes in fire pump speed.
(4) Mechanical failure of the fire pump itself. The fastening nut between the impeller and the pump shaft is loose or the pump shaft is deformed and bent, causing the impeller to move more, directly rubbing against the pump body, or the bearing is damaged, which may reduce the speed of the fire pump.
(5) Improper maintenance of fire pump power machine. The motor loses its magnetism due to the burning of the windings, the number of winding turns, wire diameter, and wiring method changes during maintenance, and the failure of the fire pump or maintenance to completely eliminate factors will also change the speed of the fire pump.
The second way to solve the fire pump failure:
Some users have measured that although the vertical distance from the water reservoir or water tower to the water surface of the fire pump is slightly smaller than the lift of the fire pump, the water capacity is still small or cannot be lifted. The reason for the fire pump is often that the pipeline is too long, there are many bends in the water pipe, and the resistance loss of the water flow in the pipeline is too large. The reason is often that the pipeline is too long, there are many bends in the water pipe, and the resistance loss of the water flow in the pipeline is too large. In general, the resistance of the 90-degree elbow is greater than that of the 120-degree elbow, and the head loss of each 90-degree elbow is about 0.5 to 1 meter, and the resistance of each 20-meter pipe can cause a head loss of about 1 meter. In addition, some users also choose the diameter of the inlet and outlet pipes of the fire pump at will, which also has a certain impact on the lift.
(1) Some users do not fill enough water before starting the fire pump; sometimes it seems that the filled water has overflowed from the vent hole, but the air is completely discharged without turning the pump shaft, resulting in a little air remaining in the water inlet pipe or pump body middle.
(2) The horizontal section of the inlet pipe that is in contact with the fire pump shall apply a descending slope of more than 0.5% against the direction of water flow, and the end connected to the inlet of the fire pump shall be the highest, and shall not be completely horizontal. If it is tilted up, air will remain in the water inlet pipe, which will reduce the vacuum in the water pipe and fire pump, and affect water absorption.
(3) The packing of the fire pump has been worn out due to long-term use or the packing is too loose, causing a large amount of water to spray out from the gap between the packing and the pump shaft sleeve. As a result, the external air enters the fire pump from these gaps. The inside of the pump, which affects the pumping of water.
(4) The water inlet pipe has been underwater for a long time, and the pipe wall has corroded holes. After the fire pump works, the water level continues to drop. When these holes are exposed to the water surface, air enters the water inlet pipe through the holes.
The flow value of the stabilized pump depends on many factors, the main ones are:
(1) Type of system When the stabilized pump is used in a self-spray system, consider the water volume of a sprinkler; and when it is used in a fire hydrant system, consider the water volume of a fire hydrant.
(2) When there is an air pressure water tank and an air pressure water tank, the flow rate of the pressure stabilizing pump is not greater than the water volume of a nozzle or a fire hydrant. When there is an air pressure water tank, the water supply and pressure guarantee of the system are implemented by the air pressure water tank, and the flow rate of the pressure stabilizing pump only needs to meet the flow requirements of the air pressure water tank, that is, the flow rate of the pressure stabilizing pump should take into account the pressure of the air pressure water tank. Factor for adjusting the volume of the tank. At this time, the flow rate of the pressure stabilizing pump should be calculated and determined according to the calculation formula of the total volume of air and water in the tank of the air pressure water supply equipment and the volume of water in the tank. The water output of the water pump should be not less than 1.2 times the hourly flow of the pipe network when the tank is at the average pressure.
There is no provision in the "High Regulations" that the air pressure water tank must be equipped, but without the air pressure water tank, the voltage stabilizing pump starts frequently and is easy to be damaged; with the air pressure water tank, the problem of the pressure stabilizing pump starting frequently can be alleviated, and the voltage stabilization work of the system can be alleviated. The guarantee of the situation can be better reflected. However, the cost of the air pressure water tank needs to be increased. In general, the volume of the air pressure water tank provided with the equipment does not need to be too large, and the volume should be less than 50L. Shanghai has compiled a standard atlas of pressure-stabilizing pumps for supporting air-pressure water tanks.
(3) System scope The quasi-high-pressure water supply system (or called the high-pressure water supply system) with a stabilizing pump can range from indoor to indoor and outdoor. Indoor quasi-high pressure water supply system, the pipe is made of steel pipe, and the interface is connected by thread, flange or welding. The leakage of the pipe network system mainly occurs in the sealing part of the water pump, and its quantity is relatively limited. In the indoor and outdoor quasi-high pressure water supply system, since the outdoor pipes are made of cast iron, the interface adopts socket connection, and the interface seal adopts rubber ring. Immediately after the construction of the pipeline, the soil is covered, and sometimes the interface is reinforced with concrete enclosure. Even if there is leakage, it is difficult to take remedial measures. All these show that when the quasi-high pressure water supply system is used indoors and outdoors, there should be enough room for the flow rate of the stabilizing pump.
The speed of the fire pump is too low
(1) Human factors. Due to the damage of the original motor, a considerable number of users randomly equipped the fire pump with another motor to drive it. As a result, the flow rate was low, the head was low, and even the water could not be pumped.
(2) The transmission belt is worn. There are many large-scale isolated fire pumps that use belt transmission. Due to long-term use, the drive belt is worn and loosened, and slipping occurs, thereby reducing the speed of the fire pump.
(3) Improper installation. The distance between the centers of the two pulleys is too small or the two shafts are not parallel, the fire pump transmission belt is installed on the tight side, resulting in too small wrap angle, the calculation error of the diameter of the two pulleys, and the large eccentricity of the two shafts of the fire pump driven by the shaft, etc. Both will cause changes in fire pump speed.
(4) Mechanical failure of the fire pump itself. The fastening nut between the impeller and the pump shaft is loose or the pump shaft is deformed and bent, causing the impeller to move more, directly rubbing against the pump body, or the bearing is damaged, which may reduce the speed of the fire pump.
(5) Improper maintenance of fire pump power machine. The motor loses its magnetism due to the burning of the windings, the number of winding turns, wire diameter, and wiring method changes during maintenance, and the failure of the fire pump or maintenance to completely eliminate factors will also change the speed of the fire pump.
The second way to solve the fire pump failure:
Some users have measured that although the vertical distance from the water reservoir or water tower to the water surface of the fire pump is slightly smaller than the lift of the fire pump, the water capacity is still small or cannot be lifted. The reason for the fire pump is often that the pipeline is too long, there are many bends in the water pipe, and the resistance loss of the water flow in the pipeline is too large. The reason is often that the pipeline is too long, there are many bends in the water pipe, and the resistance loss of the water flow in the pipeline is too large. In general, the resistance of the 90-degree elbow is greater than that of the 120-degree elbow, and the head loss of each 90-degree elbow is about 0.5 to 1 meter, and the resistance of each 20-meter pipe can cause a head loss of about 1 meter. In addition, some users also choose the diameter of the inlet and outlet pipes of the fire pump at will, which also has a certain impact on the lift.
(1) Some users do not fill enough water before starting the fire pump; sometimes it seems that the filled water has overflowed from the vent hole, but the air is completely discharged without turning the pump shaft, resulting in a little air remaining in the water inlet pipe or pump body middle.
(2) The horizontal section of the inlet pipe that is in contact with the fire pump shall apply a descending slope of more than 0.5% against the direction of water flow, and the end connected to the inlet of the fire pump shall be the highest, and shall not be completely horizontal. If it is tilted up, air will remain in the water inlet pipe, which will reduce the vacuum in the water pipe and fire pump, and affect water absorption.
(3) The packing of the fire pump has been worn out due to long-term use or the packing is too loose, causing a large amount of water to spray out from the gap between the packing and the pump shaft sleeve. As a result, the external air enters the fire pump from these gaps. The inside of the pump, which affects the pumping of water.
(4) The water inlet pipe has been underwater for a long time, and the pipe wall has corroded holes. After the fire pump works, the water level continues to drop. When these holes are exposed to the water surface, air enters the water inlet pipe through the holes.
The flow value of the stabilized pump depends on many factors, the main ones are:
(1) Type of system When the stabilized pump is used in a self-spray system, consider the water volume of a sprinkler; and when it is used in a fire hydrant system, consider the water volume of a fire hydrant.
(2) When there is an air pressure water tank and an air pressure water tank, the flow rate of the pressure stabilizing pump is not greater than the water volume of a nozzle or a fire hydrant. When there is an air pressure water tank, the water supply and pressure guarantee of the system are implemented by the air pressure water tank, and the flow rate of the pressure stabilizing pump only needs to meet the flow requirements of the air pressure water tank, that is, the flow rate of the pressure stabilizing pump should take into account the pressure of the air pressure water tank. Factor for adjusting the volume of the tank. At this time, the flow rate of the pressure stabilizing pump should be calculated and determined according to the calculation formula of the total volume of air and water in the tank of the air pressure water supply equipment and the volume of water in the tank. The water output of the water pump should be not less than 1.2 times the hourly flow of the pipe network when the tank is at the average pressure.
There is no provision in the "High Regulations" that the air pressure water tank must be equipped, but without the air pressure water tank, the voltage stabilizing pump starts frequently and is easy to be damaged; with the air pressure water tank, the problem of the pressure stabilizing pump starting frequently can be alleviated, and the voltage stabilization work of the system can be alleviated. The guarantee of the situation can be better reflected. However, the cost of the air pressure water tank needs to be increased. In general, the volume of the air pressure water tank provided with the equipment does not need to be too large, and the volume should be less than 50L. Shanghai has compiled a standard atlas of pressure-stabilizing pumps for supporting air-pressure water tanks.
(3) System scope The quasi-high-pressure water supply system (or called the high-pressure water supply system) with a stabilizing pump can range from indoor to indoor and outdoor. Indoor quasi-high pressure water supply system, the pipe is made of steel pipe, and the interface is connected by thread, flange or welding. The leakage of the pipe network system mainly occurs in the sealing part of the water pump, and its quantity is relatively limited. In the indoor and outdoor quasi-high pressure water supply system, since the outdoor pipes are made of cast iron, the interface adopts socket connection, and the interface seal adopts rubber ring. Immediately after the construction of the pipeline, the soil is covered, and sometimes the interface is reinforced with concrete enclosure. Even if there is leakage, it is difficult to take remedial measures. All these show that when the quasi-high pressure water supply system is used indoors and outdoors, there should be enough room for the flow rate of the stabilizing pump.
