【 Weak current College 】 fire pump main standby switch method comparison

Fire pump main standby switch is to ensure that fire standby pump operation. Its switching method lies in the choice of control signals. This article by two fire pump main standby switch method comparison, analysis, presented in fire water supply system uses a pressure signal control methods better than current signals, and suggested that the fire pump main standby switch uses the pressure signal control method.
Keywords: fire; fire standby pump; switch; compare
Fire is fire water supply system of the heart. In fire water supply system, set fire standby pump can increase overall system security, and help to improve the overall reliability of the fire water system. Based on national standards for the building design fire protection standard (GBJ16-87), in addition to the outdoor fire water consumption not exceeding 25L/s in factories, warehouses, and seven to nine layers of unit residential, fixed fire-fighting pump should be equipped with standby pump, its working capacity should not be less than one main pump. The tall buildings design fire protection standard (GB50045-95) article also stipulates in 7.5.3, fire water system should be set the alternate fire pump. Fire pump main standby switch is fire standby pump into an important means of human work, and also the fire water system reliable and safe operation of important aspects.

1, fire pump main standby switch method
From the fire pump start signal acquisition and control perspective, the design of main standby switch has two methods. The key is to control the signal source selection, it can be divided into current signal control and pressure signal control method. Usually the main fire pump is required press the standby pumps each alternate approach to design.
Current signal control method is now in the fire protection design fire pump main standby switch of commonly used methods. It through the pump motor current signal feedback, to determine whether a fire pump. When the motor circuit (power off), excessive current, the power automatically switches to another pump motors, stopped the first fire pump work, start another pump is working.
Pressure signal control method is in the fire pump water mains pressure gauge with electric node on the set, as in Figure 1, the fire pump main spare switch is determined by the pressure gauge signals to judge. When the fire pump control box received the action directive, immediately start any fire pumps, fire pumps working electrical pressure gauge indicate that the node does not achieve the set pressure value, the control box will automatically switch to another fire pump to start work.
Of course, the electric fire pump control principle that can be optionally specified a fire pump-pump or the alternate pump. Current signal control method in the current domestic uses the earliest, most, while the pressure signal control method in the sprinkler system to start the application, the pressure signal control methods on the fire water system of automatic control provides a reliable way.

2. main standby switch methods

2.1, fire pump failure cause analysis

Fire pump failures the end result is a fire pump can not be normal water. Result in fire pump failure of main reasons can be divided into two categories, one category is motor failure, another kind is the pump failure.
In motor failure, power issues, such as the power supply is not functioning properly due to power failure, the voltage is too high or too low, and so on; the motor itself, such as damage due to the motor to run; motor overload problems, motor-driven pump shaft power is too large or pipe plug, form the current is too large to stop working, and so on.
In pump failure may be due to the water pump bearings, impeller and other issues. According to the experience of engineering practice, motor failure probability to a pump failure probability is high.

2.2, fire pump main standby switch methods of analysis

Using current signal control method, its advantages are promptly reflected motor failure. But motor failure is also the main pump units. But this method does not indicate whether the water pump is real.
Using pressure signal control methods that can truly reflect the actual fire pump work its switching signal credibility is high. Regardless of fault or the fault of pump motor, so long as the fire pump outlet pressure did not reach a certain pressure value, you need timely switch master alternate fire pump. However, the pressure signal control method has its drawbacks. When the fire water system of the actual yield is large, fire pump outlet pressure drop, causing fire pump pressure switch signal malfunction, stop a fire pump switch to another fire started. Water pump in the switch, restart the need for a certain period of time. So, inevitably causing fire water supply interruptions, delays in the fire. In addition, the pressure signal control methods may also be considered in the circuit design of the motor circuit, overload, overvoltage, phase, undervoltage, overtemperature protection function.
From system view, the fire pump and motor pump unit as a whole, judging the final effect of the water supply is whether water pump units, should use pressure signal control of main standby switch method is more reasonable. In the fire water system water exceed the design value, you can control circuit to expand on the fire pump electrical capacity of design, ensure all fire pump power consumption and electricity consumed in the fire control pump of fire during all fire power consumption is only one part of the overall fire power supply system would not result in a greater impact. This outlet pressure decrease, the timely start another fire pumps, regardless of the original fire pumps shut down problems.

From the perspective of reliability, fire pump water supply system of reliability is concerned with the reliability of structure. Setting the main fire pump spare block diagram of reliability can be represented as a series of pump and motor unit and unit, and the relationship between the parallel relationship between the distance 1.
The entire line of reliability can be simply expressed as R. R = 1 a (1 a R1) X (1 a R2) = 1 a (1 a R1aXRlb) X (1 a R2aXR2b). From Figure 2 that can also be directly seen, enhancing the fire pump and motor reliability of equal importance. If only 1 Motors (1B or 2B) to determine a reliable water supply system is not perfect. Using the reliability of the entire system is in the firePump outlet manifold set signal, this is a reliable and meaningful.
Note that in the fire pump outlet pressure value is set, you should consider the early fire extinguishing with high pressure water tank of water. Therefore, for temporary high-voltage indoor fire water supply system, the set pressure value should be greater than the usual network of water pressure. The other main pumps starting fire, the need to set a certain delay before Judge electric pressure values the pressure gauge nodes, determine whether you need to switch to another fire standby pump. And that will power the node set in fire pump pressure outlet valve after (according to the direction of flow) of fire water supply mains, to spray system to set the fire pump outlet check valve and hydraulic alarm valve group so as to ensure reliable pressure signal.

2.3, two control methods
Current signal control and pressure signal control methods are fire pump main standby switch. Fire pump control requirement is consistent with, and two methods for signal acquisition, the ultimate control of the effect is different.
Reasonable choice fire pump main standby switch manner is of great significance. It is the reliability of the fire water system play an important role in the guarantee. Pressure signal control method to BA real control, especially suitable for automatic sprinkler system.

2.4, pressure signal control problems
In pressure signal control method of design, the need to pay attention to the following questions to ensure that the fire pump master alternate switching reliability.
(1) electric node gauges yishe in fire pump water mains, it should not be set before the fire pump valve (according to the direction of flow). Pressure set value should be greater than the fire water tank of water and high pressure value.
This is because the pressure signal location should be capable of faithfully reflect fire pumps and systems of water supply and operating conditions. If the gauge is located in the fire pump outlet valve and valve before, you accidentally close the fire pump while running, you can display the normal water pressure, the water cycle and the system is not working properly. Hence, uses the pressure signal control switch can also be adjusted pipeline fire pump is not working properly in the water cycle, the timely start another pump water supply pipe.
(2) in the signal control judgment of circuit design, the switches need to set a time delay. This is mainly due to the fire pump startup needs a start time and the current elapsed time, time delay judgment needs to be greater than the above two factors, the General can take 1 ~ 2min. In this way, electric pressure signal control node value is true.
(3) pressure signal control method of switching can be optionally specified fire pump or the alternate pump, you can also switch on a regular basis.
(4) fire control in addition to automatic control, you should have in place (manually) control functions. Fire control pump of the signal necessary to fire control centers to monitor, control and building automation.
In fire power of design to consider adequate fire pump power capacity. The fire control pump of the switch, it is recommended that you do not stop the first fire pump power supply, i.e. the most disadvantageous when two sets of fire control pump power supply design, so that the situation is conducive to meet fire protection water supply system in the overload condition of operating conditions, and to reduce fire pump in the interval of time when you switch, as soon as possible, let the fire pump running, improving fire protection water supply.

3. conclusions
(1) fire pump main standby switch is the key to the selection of the control signal. Toggle the main fire pump is an alternate method of the current signal control and pressure signal control.
(2) in fire water supply system, the pump works uses a pressure signal control methods better than current signal control method. Pressure signal control method cannot truly reflect the condition of the fire-fighting water supply, and reliability of the switching signal is higher. Recommendations in the relevant fire normative explicitly fire pump master alternate switching pressure signal control method.
(3) in the pressure signal control methods used, the switch signal electric pressure gauges should be set in the node fire pump outlet manifold valve or the valve after hydraulic alarm. At the same time, the circuit design of the need to set a time delay to determine pressure gauge electro node value.