Analysis of fire pump inspection methods in fire water supply system

Abstract: The method of using the fire pump speed for self-checking is analyzed. Self-checking methods can be divided into normal-speed self-checking methods and low-speed self-checking methods. The low-speed self-checking methods include soft starter methods and frequency conversion methods. Through the comparison and analysis of these two self-checking methods of fire pumps, the technical requirements for fire pump self-checking are pointed out, which provides certain technical basis and guarantee for the application of fire pump self-checking methods. ​
Keywords: Fire pump self-inspection method (automatic inspection) normal speed self-inspection low-speed self-inspection
0. Preface
Fire water supply is an important part of the water fire extinguishing system, and the fire pump is the key equipment in the fire water supply. In the fire water supply system, the reliability of the fire pump water supply directly determines the success of fire extinguishing.
Building fire water supply equipment has a common feature in operation, that is, these equipment rarely operate at ordinary times, but they need to be reliably put into use once a fire is extinguished. However, since these equipment have not been used for a long time, the normal operation of the equipment may not be guaranteed when putting out a fire. Among them, fire pumps are no exception. In order to enhance the reliability of fire pump water supply, the Shanghai Engineering Construction Standard “Design Regulations for Water Fire Extinguishing Systems for Civil Buildings” (DGJ08-94-2001) raised the issue of self-inspection of fire pumps for the first time in China. The regulations stipulate that fire pumps in super high-rise buildings and first-class high-rise public buildings should be equipped with self-checking devices. In addition, the “Code for Fire Protection Design of Buildings” that is being revised also states that fire water supply equipment must have automatic inspection functions.
The self-inspection of the fire pump is the automatic inspection. It automatically starts the fire pump within a set time period and checks the operation of the fire pump. The purpose of fire pump self-inspection is to increase the reliability of the fire pump and ensure the overall reliability of the fire water supply system. The use of timed self-checking devices for fire pumps is conducive to understanding the actual performance of fire pumps in a timely manner, solving the problem of fire pump corrosion and sticking, maintaining good working conditions of fire pumps, and is also conducive to intelligent fire protection system management. It has certain significance in improving the safety and reliability of fire water supply system.
1. Fire pump self-checking method
1.1 Normal speed self-test method
The normal speed self-test method is also called the power frequency self-test method. It regularly runs the fire pump at rated speed for a period of time and then automatically stops the pump. Figure 1 and Figure 2 show the pipeline design of normal speed self-checking mode. In order to ensure that the operating pressure of the fire pump does not cause damage to the system during self-test, the original inlet and outlet pipes of the fire pump must be adjusted and improved.
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When the fire pump absorbs water from the fire pool, a bypass pipe should be installed on the water outlet pipe. During the self-inspection, open the solenoid valve on the bypass pipe, and the water effluent from the fire pump self-inspection operation is discharged from the bypass pipe to the fire pool. After the self-inspection is completed, close the solenoid valve and restore the original normal working state. In the way fire pumps draw water from the municipal water supply network, overpressure during self-check operation should also be considered. At this time, a bypass is set up on the inlet and outlet pipes of the fire pump, and the solenoid valve is opened during self-test so that the outlet water returns to the inlet pipe. After operating overpressure, discharge it from the pressure relief valve of the system to an outdoor open ditch. At the same time, in order to prevent secondary pollution of municipal water supply, a backflow preventer must be installed on the water suction pipeline of the fire pump.
1.2 Low-speed self-test method
The low-speed self-inspection method is also one of the methods for regular inspection of fire pumps. The fire pump operates in a unique low-speed mode during self-test, and it does not require major changes to the fire water supply network (see Figure 3). In the low-speed self-test mode, the fire pump rotates at a lower speed and its outlet pressure is smaller. According to different control methods, it can be divided into soft starter method and frequency conversion method.

1.2.1 Soft starter method
It uses a soft starter to control the self-test of the fire pump and does not consider pressure reduction starting. Within the preset period, perform self-test of the fire pump according to the preset soft starter operation mode. This operation mode uses a soft starter to control the starting phase of the fire pump, that is, the fire pump’s scheduled soft start technology (SSD). It is shorter, generally around 10 s. The entire process is implemented using programmable control technology (PLC) to ensure that the fire pump is always in a good state of readiness.
In the recommended general atlas for building products in Shanghai, “XZW Series Fire Self-inspection and Stabilized Water Supply Equipment, XW Series Fire Voltage Stabilizing Equipment Installation” (2000 Shanghai S/T-102), the soft starter is used for fire self-inspection. method.
1.2.2 Frequency conversion method
This method is to start the inspection subroutine by the inspection cycle clock in the microcomputer controller (PCL), and output a lower frequency from the frequency converter to drive the fire pump. Usually, the rotation speed generated by controlling the frequency of the fire pump is around 300 r/min. Because its speed is much lower than the rated speed of the fire pump, there will be no large pressure increase in the system, and the fire water supply system can use the original pipeline. During the inspection process, the frequency converter starts feeding power from zero Hz, and the fire pump starts relatively smoothly. There is no mechanical impact on the fire pump. The speed of the fire pump keeps the impeller rotating but does not discharge water in a critical state, which will not cause system pipe failure. Network overpressure. The settings of the backflow preventer are the same as in Figure 2.
2. Analysis and comparison of two self-inspection methods of fire pumps
2.1 Technical
The fire pump self-test method provides a method for daily testing of fire pumps in fire water supply systems. During the fire pump self-inspection, it can not only prevent the fire pump from being corroded and stuck, but also provide alarms for motor overload, short circuit, overvoltage, phase loss, undervoltage, overheating, etc. The self-inspection of fire pumps can be regarded as a technological progress to improve the management level of the system.
In the two fire pump self-checking methods, both can reflect the maintenance effect of self-checking on the fire pump. However, the low-speed self-checking method only runs a preliminary stage in the startup of the fire pump and cannot fully reflect the actual operation of the fire pump in the future. working conditions. In addition, after the results of the fire pump self-inspection are fed back to the fire control center, further manual judgment is required. Therefore, the fire pump self-inspection method cannot completely replace manual maintenance and management of fire pumps.
2.2 Analysis of self-test methods
The normal speed self-test method simulates the actual working conditions of fire water supply within a certain period of time. What it detects is the entire process of starting and normal operation of the fire pump. The pipeline design needs to be improved. The most important thing is to prevent the solenoid valve on the bypass pipeline from malfunctioning. It must be opened during self-check and closed in time after the self-check is completed.
The low-speed self-test method does not require changes to the fire pump pipeline, but it only detects one stage of the fire pump’s normal working conditions. Fire pumps can be divided into direct start and indirect start. Larger power needs indirect start. Indirect starts include Y/△ step-down start, auto-coupling step-down start, soft starter start, etc. During the operation of the fire pump, the start of the soft starter is only an early stage of the operation of the fire pump, followed by normal operation. The frequency conversion method also failed to run to the power frequency stage. However, the low-speed self-check method still plays a certain role in preventing corrosion of fire pumps. Relatively speaking, it has the characteristics of low-frequency drive, low-speed rotation, and low-power operation of the equipment.
2.3 Comparison of self-test methods
​ Among the fire pump self-checking methods, both the normal speed self-checking method and the low-speed self-checking method play a certain role in the maintenance of the fire pump. From the perspective of maintenance and management, they can all be used in fire water supply systems. Relatively speaking, the normal speed self-test method can reflect the actual operating conditions of the fire pump. From the perspective of the causes of fire pump failure, the failure caused by long-term use of the fire pump is mainly due to the engagement problem of the pump unit shaft. There are few problems when the motor is not started completely, so it is not of great significance to overemphasize the operation of the fire pump in complete working conditions. The normal speed self-check method is suitable for the situation where the fire pump absorbs water from the fire pool. The layout of the pipeline should be reasonably considered in the design. The method in Figure 2 has certain problems during operation. It can quickly cause overpressure and is not very suitable for application in engineering. The normal speed self-checking method and the low-speed self-checking method each have their own characteristics. Although the low-speed self-test method does not comprehensively test the operating conditions of the fire pump, it has no special requirements for the design of the fire pump pipeline and can basically be applied to the technical requirements of the fire pump self-test. It is more suitable for situations where the fire pump absorbs water directly from the municipal pipe network.
The comparison of the main features of the two self-test methods is shown in Table 1.
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Through analysis and comparison, it can be seen that when the fire pump absorbs water from the fire pool, the normal speed self-test method or the low-speed self-test method should be selected (see Figure 1 and Figure 3); when the fire pump absorbs water from the municipal water supply pipe network, it should be selected The low-speed self-test method can use either the frequency conversion method or the soft starter method (see Figure 3).
3. Technical requirements for fire pump self-inspection
Fire pump self-inspection is a new technology in fire water supply systems. No matter which self-inspection method is used, certain technical requirements are required to ensure it is perfect and reliable.
(1) All fire pump self-test methods must be controlled by PLC. The self-test cycle is generally set at 10 to 15 days, and the running time of each self-test should be 5 to 10 minutes. The fire water supply system should be comprehensively tested once a year, and the fire pump should also be tested for water discharge (normal working conditions). This is because the best working conditions for fire pump self-test are those that can truly reflect the actual operating conditions of the fire pump.
(2) The fire self-inspection method should have the function of automatic switching in case of fire, and ensure that the fire pump shall not automatically stop the pump after it is started. When the fire pump is running for fire extinguishing, it should not respond to the self-check signal.
During the self-inspection of the fire pump, if a fire protection operation command is encountered, the ongoing self-inspection action should be immediately interrupted, the solenoid valve on the bypass line should be closed in a timely manner and confirmed, and the self-inspection should be forcibly stopped. The system automatically transfers the fire pump to normal (power frequency) working conditions, allowing the fire pump to reach the rated speed, ensuring that the water output from the fire pump can meet the flow and head requirements of the system.
(3) In the fire water supply system equipped with fire self-inspection, from the perspective of reliability, a pressure relief valve must be installed. Regardless of whether it is the normal speed self-checking method or the low-speed self-checking method, there may be overpressure problems in the system. If the solenoid valve is not opened or the soft starter or frequency converter is not operating properly, the pump may be stuffy. A common set of pressure relief valves can be installed in the system.