Diesel engine fire pumps are the heart of the fire water supply system. In the fire water supply system, setting up a fire standby pump can increase the safety of the entire system and help improve the reliability of the entire fire water supply system.
1. Main and standby switching methods of diesel engine fire pumps
From the perspective of the acquisition and control of the fire pump start-up signal, there are two main methods for the main and standby switching of fire pumps in the design. The key is the selection of the control signal source, which can be divided into current signal control method and pressure signal control method. Usually, the main and standby pumps of fire pumps must be designed in a mutually standby manner. The current signal control method is a common method for the main and standby switching of fire pumps in current fire protection design. It judges whether the fire pump is working by feedback of the motor current signal of the water pump. When the motor is short-circuited (power off) and the current is too large, the power supply automatically switches to the motor of another water pump unit, stops the first fire pump, and starts the other fire pump. The pressure signal control method is to set an electric node pressure gauge on the water outlet main pipe of the fire pump, and the switching of the main and standby of the fire pump is judged by the signal of the pressure gauge. When the fire pump control box receives the action command, it will immediately start any fire pump. If the pressure indicated by the pressure gauge of the electrical node after the fire pump works fails to reach the set pressure value, the control box will automatically switch to another fire pump and start working.
Of course, in the principle of electrical fire pump control, one fire pump can be arbitrarily designated as the main pump or the backup pump. The current signal control method is currently the earliest and most widely used in China, while the pressure signal control method has begun to be used in foreign automatic sprinkler fire extinguishing systems. The pressure signal control method provides a reliable way for the automatic control of the fire water supply system.
2. Comparison of main and backup switching methods
(1) Analysis of the causes of fire pump failure The final result of the fire pump failure is that the fire pump cannot supply water normally. The main causes of fire pump failure can be divided into two categories, one is motor failure and the other is water pump failure. Among motor failures, there are power supply problems, such as power failure caused by abnormal power supply, too high or too low voltage, etc.; motor problems, such as failure to run due to motor damage; motor overload problems, the water pump shaft driven by the motor has too much power or the pipeline is blocked, resulting in excessive current and stopping work, etc. In the case of water pump failure, it may be caused by problems such as water pump bearings and impellers. According to the experience of engineering practice, the probability of motor failure is higher than that of water pump failure.
(2) Analysis of the main and standby switching method of fire pumps The advantage of the current signal control method is that it can reflect the motor failure in time. And the motor failure is also the main failure of the water pump unit. However, this method cannot indicate whether the fire pump actually discharges water. The pressure signal control method can truly reflect the actual working conditions of the fire pump unit, and the switching signal has a high credibility. Whether it is a motor failure or a water pump failure, as long as the pressure of the fire pump outlet pipe does not reach a certain pressure value, it is necessary to switch the main and standby fire pumps in time. However, the pressure signal control method also has its disadvantages. When the actual water output of the fire water supply system is large, the pressure of the fire pump outlet pipe drops, which is easy to cause the fire pump pressure switching signal to malfunction, stopping the work of one fire pump and switching to the start of another fire pump. It takes a certain amount of time for the water pump to switch and restart. In this way, it is bound to cause the interruption of fire water supply and delay fire fighting.
In addition, the pressure signal control method can also consider the motor's short circuit, overload, overvoltage, phase loss, undervoltage, overheating and other protection functions in the circuit design. From the perspective of the system, the fire pump and the motor are regarded as the entire fire pump unit. It is more reasonable to use the main and standby switching method controlled by the pressure signal to judge the final effect of its water supply, that is, whether the water pump unit is out of water. When the water consumption of the fire water supply system exceeds the design flow, it can be adjusted in the control circuit to expand the design of the power capacity of the fire pump to ensure the power consumption of all fire pumps. The power consumption of the fire pump during the fire is only a part of the total fire power consumption, which will not cause a major impact on the entire fire power supply system. In this way, after the pressure of the outlet pipe is reduced, another fire pump can be started in time without considering the shutdown of the original fire pump.
