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Why does the fire pump idling and how does the frequency conversion fire pump work?

2020-09-16
 In the operation of the fire pump, the idling of the fire pump is not allowed. The majority of users do not understand the cause of the idling phenomenon and do not know how to solve it well. In fact, the fire pump will not cause damage in a short period of time (less than 1 minute).

The working principle of variable frequency fire pumps How to achieve variable frequency energy saving and power saving is to use the frequency converter to change the speed of the water pump to adjust the flow and pressure of the water pump. The frequency converter generally has a closed-loop control function, which can automatically control the operation according to the pressure signal to achieve a constant pressure Water supply.

Frequency conversion energy saving of frequency conversion fire pump

According to fluid mechanics, P (power) = Q (flow) ╳ H (pressure), flow Q is proportional to the first power of speed N, pressure H is proportional to the square of speed N, and power P is proportional to the cube of speed N If the efficiency of the water pump is constant, the speed N can be reduced proportionally when the required adjustment flow drops, and the shaft output power P decreases in a square relationship at this time. That is, the power consumption of the water pump motor and the speed are approximately in a square ratio relationship. For example: a water pump motor has a power of 55KW. When the speed drops to 4/5 of the original speed, its power consumption is 28.16KW, which saves 48.8% of power. When the speed drops to 1/2 of the original speed, its power consumption The amount is 6.875KW, saving 87.5% of electricity.

The power factor compensation of the frequency conversion fire pump saves energy

Reactive power not only increases the line loss and the heating of the equipment, but more importantly, the reduction of the power factor leads to the reduction of the active power of the grid. A large amount of reactive power is consumed in the line, the efficiency of the equipment is low, and the waste is serious. The formula P=S ╳COSФ, Q=S╳SINФ, where S-apparent power, P-active power, Q-reactive power, COSФ-power factor. It can be seen that the larger the COSФ, the greater the active power P, and the power factor of the ordinary water pump motor is Between 0.6 and 0.7, after using the variable frequency speed control device, due to the effect of the internal filter capacitor of the frequency converter, COSФ≈1, thereby reducing reactive power loss and increasing the active power of the grid.

The soft start energy saving of the frequency conversion fire pump

Since the motor is a direct start or Y/D start, the starting current is equal to (4-7) times the rated current, which will cause serious impact on the electromechanical equipment and the power supply grid, and will also require too high grid capacity, resulting in The damage to the baffle and valve during high current and vibration is extremely unfavorable to the service life of equipment and pipelines. After using the frequency conversion energy-saving device, the use of the soft start function of the frequency converter will make the starting current start from zero, and the value does not exceed the rated current, which reduces the impact on the power grid and the requirements for power supply capacity, and extends the service life of the equipment and valves. . Save equipment maintenance costs.

The reasons for the idling of the fire pump are: the inlet medium of the fire pump is insufficient or the inlet pressure is not enough, or the water inlet pipe of the fire pump is blocked, or the air in the fire pump cavity is not exhausted. When the fire pump is idling, the impeller does not touch or seldom touches the medium, it cannot work effectively, and the liquid cannot be sent out normally. These are all useless work. Since there is no effective work, the load on the motor is very small, and the current generated is also very small. There will be no impact on the motor. The idling of the fire pump is indeed fatal to the pump. Idling fire pumps are prone to cavitation, causing damage to the pump body and flow parts; idling fire pumps with mechanical seals or packing seals will not be lubricated by liquid, resulting in dry grinding and rapid damage; idling The rotor parts and pump body of the fire pump will heat up, and there will be no liquid cooling, and the narrow gaps (such as the sealing ring) are easy to be seized by the effect of heat expansion and contraction; the idling multi-stage fire pump balance plate is not lubricated by water, the balance plate Will be burnt to death and damaged soon.

It is recommended to improve the design of the fire pump to a higher level during the early warning and maintenance of the fire pump idling:

1. Treat each gap position of the fire pump and expand it under allowable conditions to prevent seizure;

2. Special process treatments, quenching and tempering, heat treatment, etc. are carried out on the shaft of the fire pump to increase the hardness, and use materials with low flexibility to prevent large swings and seizures during idling;

3. Use mechanical seals and filler cavities that do not need to be lubricated by liquid media;

Fourth, use enclosed self-lubricating bearings that do not require oil.

The pump cavity of the horizontal self-priming fire pump has an increased volume compared to other fire pumps, and there is a place where water can be stored. Before the self-priming fire pump works normally, the cavity must be filled with liquid. There is a period of self-priming before operation. During this time, air is continuously discharged to the pump body. This period of time is part of the idling.

Set up idling induction system. The fire pump is monitored in real time through modern equipment. When the fire pump is idling, it immediately alarms and automatically shuts down to protect the safety of the unit.