Why does fire rescue need secondary water supply?

The secondary water supply system is an independent and completely closed system that can draw water from any open source of water (oceans, rivers, lakes, and even fire hydrants) to a large number of water-repellent areas in the fire department without external power supply. In general, the High Capacity Pumping System ( HVP ) can pump more than 3000 meters and supply water at a rate of 30,000 liters / minute (or even higher). You may ask why this system is still needed since there are pumps on the fire truck. At this point, it is necessary to explain the difference between a fire truck pump and an HVP system.

The problem is that a standard fire truck pump can only pump 7.5 meters of water because it uses an engine-driven centrifugal pump. When the fire pump is completely carry water to 7.5 meters high, it can only use 80% of the energy to lift the water, and the remaining 20% of the power used to fill fire hoses. Therefore , if only the fire pump is used to subdivide the water over a distance of more than 3,000 meters , 11 fire engines and 22 fire fighters are required to extinguish the fire. The HVP can lift water vertically or horizontally for 60 meters with almost no pressure loss. The boost pump in the system can raise the pressure to 12 bar or more. The HVP system can also concentrate fire-fighting foam ( foam- forming foam fire extinguishing agent and film-forming fluorin-protein foam fire extinguishing agent ) in a large amount of pumped water and maximize the use of foam by digital adjustment of the balance pressure.

The HVP system uses floating pumps placed in water. These floating pumps do not need to lift water, and 100% of their energy is used to "push" water into the area of ​​the fire. This means that with only one HVP system, 42,000 liters / second of water can be pumped and transmitted at a distance of 3,000 meters or more. The HVP system uses 10 ” or 12 ” large-diameter nitrile rubber hoses, which can greatly reduce the friction loss in the hose. 12 a "pass water hoses, hose 20 is equivalent to 75 mm diameter. The smaller the diameter of the hose, the greater the friction loss, this is the advantage of the large-diameter hose!

The friction loss of the hose is a nightmare for firefighters. As long as the water passes through the fire hose, frictional losses will occur. Factors such as distance, diameter, and flow rate (l / min) can cause frictional losses. When the water passes through the fire hose, the water stream oscillates after rubbing against the inner surface of the hose, counteracting the energy generated by the pump (in mPa megapascals). Therefore, the pressure at the other end of the hose will decrease. The more water flowing through the hose per minute, the greater the shock and friction. In terms of proportion, the surface area of ​​the small-diameter hose is larger than that of the large-diameter hose, so the pressure loss of the latter is much smaller.

Hose friction loss considerations

1. As the flow ( l / min ) increases , the friction loss increases

2, the total friction loss varies with the length of the hose - the longer the length , the higher the loss

3, friction loss is almost independent of pressure

4. Friction loss is related to the type of hose, inner material, weaving technology, quality and age

5. Each time the flow of water is doubled , the friction loss increases by a factor of four . The diameter of the hose is reduced by half , and friction loss increases 32 times at the same amount of water .

When a catastrophic explosion occurs, fire-fighting pipelines and/or pumping stations are often implicated or damaged, so they cannot rely on local infrastructure to provide water. Firefighters need water to fight the fire. If there is no water, the fire fighting capability and the bubble will not be able to talk about, and the firefighters will be in an extremely dangerous situation. When a fire accident occurred in the Bangsfield oil depot in Dalian or the United Kingdom, the fire chief did not work and an alternative source of water must be found. Many fire-fighting departments have fire-fighting water trucks, but their tank storage capacity is relatively small, only about 16,000 liters . The fire engine's water cannon volume is estimated to be only 10,000 liters to 200,000 liters / minute , even for large water cannons . Fire water tanks can only supply water for 1.5 minutes, after which they have to continue to supply water. When a fire broke out in Dalian, a certain brand of HVP continued to supply water for 105 hours and provided 7 million liters of water for fire extinguishing. With so many water volumes, how many water tanks would be needed if using fire water tanks! Therefore, the alternative to the fire main is to take water from open sources (oceans, lakes and rivers). The difficulty lies in how to transport water from the source to the fire area. The HVP system is to solve this problem.

The HVP system is not fixedly installed on fire engines. It is a stand-alone device consisting of a hook-hand system and is installed near water sources. After deploying the HVP system by hooking hands , the fire trucks will return to the base and transport other hook-hand devices, such as safety rescue facilities. During the HVP operation, there is no need to use a fire truck chassis.

In these cases, it is important to use large diameter fire hoses. However, 10 or 12 diameter hoses are difficult to handle due to weight or size factors . Large-diameter hoses are usually towed out of the fire hose box in a standard manner at a speed of 40 km / h. Recycling the hoses requires mechanical assistance, so the HRU needs a hydraulic drive shaft to allow the hoses to rewind into the fire hose box. The firefighters order the paired hoses into sheets. This part of the operation is relatively easy, the recovery speed is 2 km / h, and the spreading speed is much later, after all, the fire is over when the hose is recycled.

Another feature of HVP is its simplicity of operation. Fire scenes where firefighters are located are often daunting and the HVP system that simplifies operations is crucial. Therefore, the HVP system should be completely digitally manipulated by the computer. At a pressure of 12 bar, the large flow of 42,000 liters of water per minute is actually very complicated: if the inlet and outlet pressures do not match, the pump volute and the impeller will generate cavitation, resulting in damage to the pump body, or even damaging the pump during fire extinguishing. . HVP use CANBUS system can balance outlet pressure, pump temperature, and the engine monitoring, analysis conditions such as oil pump, the oil pressure, temperature and pressure of the hydraulic oil. In the event of an accident during the operation, the HVP system will automatically send a message to the command center and the field commander so that the on-site personnel are in danger and can take timely measures.

In addition to assisting fire fighters, HVP can also be used for water treatment in flooded areas, subways, and cellars. In cities, these functions are mainly the responsibility of the fire department. The HVP can be equipped with a special bleeder pump. More than 45,000 liters of water per minute will be pumped away. This is particularly suitable for pumping water in subways and cellars, not to mention flooded urban and rural areas.

This article is copyrighted by "Consumer Frontier", so it is edited and edited by China Rescue Equipment Network.