Application of Foam Fire Truck Foam System in Fire Extinguishing

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Foam fire pump is equipped with a means, the foam tank, the foam tank mixing and generation system and sets, fighting foam may be sprayed flammable, combustible liquid fires, fire-fighting foam mainly to aqueous fire fighting vehicle fire supplemented . Foam fire is made by providing an improved foam fire extinguishing system based on the tank, and the hydraulic system having a tank fire in the main equipment, the foam tank is provided according to different types of foam are mixed, a foam proportioner , pressure balance valve, foam liquid pump, foam gun and so on. Fire fighting foams especially suitable for petroleum and its products and other flammable liquid fire, fire fighting can be used independently, and can supply water to fire foam mixture.

Foam fire truck

The air bubble ratio mixing system is used to extinguish the foam, and the water and foam liquid are mixed in a certain proportion (specific foam type) , and the mixture is sent to the foam generating device by the water pump. At present, foam fire-fighting vehicle foam systems equipped with troops mainly include ring-pumped foam proportioning systems and automatic pressure-balanced proportional mixing systems.

(I) Ring Pump Foam Proportioning System

Ring pump proportional mixing system. Ring pump proportioning system has been made on a foam fire is widely used, it works as shown in FIG.

Pump schematic structural foam proportioning system of FIG. 1 ring

The ring pump proportional mixer is generally installed between the outlet pipe and the inlet pipe of the fire pump. The foam pipe forms a circulating flow, so it is also called a ring pump type negative pressure foam proportioner. Its working principle is to use the water flow from the pump outlet. The negative pressure generated at the entrance and exit of the venturi suctions the foam stock from the foam metering control valve into the on-board water pump. According to the set ratio, the foam stock and water are mixed into a foam mixture with good fire extinguishing capability. The liquid is then pumped out through the pump outlet along the pipeline to an onboard fire monitor or fire gun. According to the different adjustment methods, the ring pump proportional mixer is divided into two types of manual adjustment and automatic adjustment.

A. Manually adjusting the negative pressure foam proportioner requires manually adjusting the handle of the metering control valve to adjust the opening of the metering control valve according to the amount of water pumped out of the pump so as to ensure a fixed foam ratio. Due to the inconvenience in installation and use of this type of foam proportioner, and the inaccurate adjustment of the foam ratio, it is becoming less and less used in the application of fire engines and is gradually being phased out. However, at present, there are still some foam fire engines equipped. Manually adjust the foam proportioner. When fighting a petrochemical fire, it is necessary to pay attention to the adjustment method and the precautions for use of such mixers.

Figure 2 Manually adjust the structure of the negative pressure foam mixer

Manual vacuum foam proportioner adjusted during use, the foam was mixed with the correct ratio of water will directly influence the extinguishing effect, and the mixing ratio depends on the correct degree of pressure generated when the liquid flow through the foam proportioner The degree of vacuum and quantitative hole size. Therefore, in the course of use , in addition to a reasonable match between the foam supply volume and the flow rate of the foam injection device , it must be noted that the pressure in the suction line of the pump should be less than 0.049 MPa to ensure proper operation of the foam proportioner. Therefore, the foam proportioner cannot directly use the water in the fire hydrants and the water directly supplied by other vehicles . Instead, the water in the fire hydrants and the water supplied by other vehicles should be injected into the water tank to reduce the pressure and then supply the water pump . Otherwise , the vacuum is damaged. Effects liquid absorption.

The ring pump type negative pressure foam proportioner has certain requirements for the pressure of the working fluid, the quantity of the sucked foam liquid and the pressure of the output mixed liquid. It controls the inlet pressure of the foam proportioner according to the working pressure calibrated by the foam injection device. For example, the working pressure PQ4, PQ8 air foam gun is 0. 7 MPa, PP24, PP32, PP48 foam gun operating pressure range of 0. 8 ~ 1. 2 MPa, thus requiring foam proportioner inlet pressure is also 0. 7 MPa and 0.8 to 1. 2 MPa . For inhalation volume of foam, according to the specifications required air bubble jet device, be achieved by adjusting the position of the valve body proportioner. Such as: the type PH32 proportioner spool five holes of different diameters quantitative, PH48, PH64 type proportioner has four holes quantitative, they are adjusted by turning the handle the position of the spool, indicated with an arrow on the handle, signs together with the valve cover fixed on the valve body, with a number attached. Because of the different manufacturers , sometimes the sign on the sign means different things. For example, Shanghai, Gela Man International Fire Equipment Co. of PH32 proportional mixer, on its signs marked "25", "50", "100", "150", "200" and "off", etc. these figures shows an air supply amount of foam, the "off" position of the valve means closed; the subject of the proportional mixer PH32 signs Tianjin, China fire equipment factory is "4", "8", "16 "," 24 "," 32 "and" oFF "and other words, these figures represent the flow of the foam mixture. The general foam injection equipment is differentiated by the foam mixture flow rate. What needs to be known here is that the supply of air foam is equal to the flow rate of the foam mixture multiplied by the foaming multiple of 6.25 . In fact, the above two calibrations are the same.

The ring pump negative pressure foam proportioner can be divided into PH32 , PH48 and PH64 according to the maximum mixed liquid flow per second . " P " stands for foam , " H " stands for mixing , and the following number is the main parameter , which represents how many liter of maximum mixed liquor flow is provided per second. For example PH32 type represents the maximum amount of mixture supplied to 32L / s.

In order to specify the correct operation of the foam proportioner when the fire engine uses foam to extinguish fire , the following steps explain its operating procedure :

1 When using foam to extinguish the fire , remove the fire hose and air foam gun as required , connect the hose end to the water pump outlet , and then connect the air foam gun to the other end or adjust the foam gun nozzle to the desired position ;

2 Place the air foam gun open/close handle on the "mixed fluid or water" position or open the foam gun ball valve as required ;

3 Open the water inlet valve of the water tank ;

â‘£ starting the engine, engaging the power take off, the pump low speed;

5 Open the pressure water ball valve handle to the proportional mixer ;

⑥ increase the engine throttle, the pump outlet pressure reaches the air bubble guns or foam nominal pressure value of the working pressure cannon, proportioner rotating adjustment handle, the pointer refers to the air bubble guns calibration fluid or air bubble foam mixture Quantitative hole location. For example, when using a single PQ8 air bubble gun with 6% foam liquid , point the pointer to the quantitative hole position with 8 L/s mixture volume or 50 L/s air foam volume ; if using PP32 foam gun , then point the pointer to the position of the dosing hole where the volume of liquid mixture is “ 32 L /s ” or the amount of air foam is “ 200 L /s ”. If 3% foam liquid is used , the value of the pointer will be halved accordingly.

It is worthy of special attention that if the flow rate of the shooting equipment does not correspond to that of the manual proportional mixer, no qualified foam can be injected.

7 Open the foam liquid inlet ball valve . The air bubble proportioner continuously inhales the foam liquid.

B. Automatic adjustment of negative pressure foam ratio mixers are generally controlled by a programmable logic controller ( PLC ). The effluent flow meter measures the amount of water discharged from the pump and transmits this value to the regulator. The regulator adjusts the rear motor according to the required foam mixing ratio (typically between 1% and 10% ). When the foam diversion valve opens, water pressure from the centrifugal pump will enter the syringe and return to the suction side of the pump. The foam liquid flows from the foam tank into the foam proportional control valve and finally into the syringe where the water flow and the foam will be mixed with each other according to the principle of the syringe. Close the foam drain valve to close the inlet flow and foam ratio mixing system.

Automatically adjust the foam volume of the negative pressure foam proportioner automatically increases or decreases with the flow rate at the outlet, so that the foam ratio is always maintained within the set range. The foam proportioner of this type has the advantages of accurate control, simple operation, reliability and stability, and a manual emergency operation mode to ensure the safety of the system. This type of foam proportioner is becoming more and more popular in fire engine applications with superior performance and easy operation. The automatic foam proportioner is generally composed of a control unit, a display unit, a metering control valve, a flow rate meter, and a Venturi tube.

Automatically adjusted negative pressure foam proportioner for fighting petrochemical fires, such as using semi-fixed foam system for injecting foam and spraying foam to extinguish fire, etc. It is not necessary to specify the flow rate of the sprayer and the foam generator relative to the manual proportional mixer. The quantity does not need to be calculated by calculating the flow of fire extinguishing agent, and the problem that the flow rate of the fire extinguishing agent and the proportional mixer cannot be matched is avoided, and the qualified and stable foam ratio is ensured.

(B) Automatic Pressure Balanced Proportional Mixing System

The automatic pressure balanced proportional mixing system is a mixing method in which the foam liquid is forcibly pressed into water to form a mixed liquid. There will be no impact on the system pressure water flow. The mixing ratio is controlled by the foam liquid flow metering and pressure adjustment integrated module. The mixing precision is high, the allowable foam liquid flow range is large, and the system stability is good at the same time. It depends on the pressure of the outlet water pressure and the use of special foam liquid pump pressure feeding two ways. At present, foam fire trucks that use a positive pressure type automatic proportional mixing system mostly use a foam liquid pump pressure feeding method. This method has high requirements for accurate monitoring and control . The advantages are precise proportional control , high cost of defects , and high application on high-end foam fire engines. Its working principle is shown in Figure 3 .

Fig. 3 Structure of Automatic Pressure Balanced Proportional Mixing System

(III) Precautions for use

( 1 ) When using a foam fire engine to inject foam, the driver must first verify the type and proportion of the vehicle foam. For a vehicle with a manual foam proportioner, the manual adjustment valve must correspond to the flow rate of the foam injection device. When the foam type is 3% , the value of the manual adjustment valve pointer is halved accordingly ; when fighting a petrochemical fire accident, the foam fire truck should be Choose the pump flow rate greater than 100L /S as much as possible . The foam ratio mixer is best to choose the automatic proportioning mixer ; the foam should be the best choice for the low multiple foam type 6% . The foam ratio of the fire truck should be set correctly, for example, the bubble model is 6% . The fire truck foam ratio should be set to 6% .

( 2 ) Positive-pressure foam proportioner adopts independent foam pump for foam injection. The foam injection pressure needs to be higher than the water pressure from 0.1 to 0.2 MPa to ensure the working pressure of the entire fire protection system ; at the same time, the flow rate is also It requires precise control based on the foam ratio. In actual use, it is necessary to increase pressure relief valve to timely and accurately overflow the excess pressure and flow of the foam pump, to avoid the pressure of the foam injection pipeline being too high, and to have an impact on the entire fire protection system; when the foam liquid is externally sucked, the foam empty bucket is replaced. Before closing the manual ball valve installed at the external suction foam mouth to prevent the air from entering, the external suction fails.

( 3 ) In addition to ensuring the pressure difference between the water inlet and the outlet of the water pump, the negative pressure foam proportioner must ensure the height difference between the foam liquid level and the metering valve position. In order to ensure that the foam can be inhaled reliably and quickly, especially when the foam is externally suctioned, the height of the foam bucket must not be too low. Otherwise, the foam liquid may be difficult to inhale. In severe cases, the foam ratio may not reach the preset ratio.

( 4 ) The disadvantages of the manual or semi-automatic foam proportioner are that, on the one hand, it is necessary to confirm the total flow rate of the foam spray device and on the other hand, the flow rate limit of the foam proportioner. E.g., 50,000 cubic meters of oil storage tanks, must confirm the number of foam generators, each generator flow, if there foam generator 10, the flow rate of each generator is 8L / S, and the mixing ratio of the vehicle The flow rate of the mixture can not be adjusted to 80L /S, so that the fire truck of the manual or semi-automatic foam proportioner can not accurately extinguish the tank.

( 5 ) Foam fire trucks equipped with automatic pressure balanced proportional mixing system should pay attention to the matching of the flow rate of the water pump and the foam pump, and understand whether the maximum foam flow rate of the foam pump according to the foam ratio meets the maximum flow rate of the water pump. For example, there is an industrial foam fire, bubble foam proportioner system automatic hydraulic pump foam, fire pumps which supply when the outer water pressure, flow rate up to 18,927 l / min, and the foam pump rated flow of 1022L / Minutes, when a 6% type foam liquid is used, the amount of foam required by the foam pump does not reach the maximum water supply of its pump.

The information in this article comes from the Internet and was reorganized and edited by China Rescue Equipment Network.

Material: brass

Surface finish: Polishing (mirro), chromed plated (mirror)

Surface roughness: Rz 3.2

Casting minimum tolerance: +/-0.2mm

Inspection: Slide caliper, microcaliper, projector, 100%

Certification: CE,ACS,Watermark
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