Under the big issue of stabilizing high-pressure fire water supply system, there are many articles to be done that need to be further explored. We have already talked about the difference between stable high-pressure water supply system and high-pressure, temporary high-pressure water supply system, characteristics, and the flow of the regulator pump, etc. This article would like to stress that the head of the regulator pump to determine and set pressure for colleagues to explore . Polycarbonate Solid Sheet ,Solid Polycarbonate Roofing Sheets,Clear Solid Polycarbonate Sheet,4Mm Solid Polycarbonate Sheet NINGBO CHAOMEI PLASTIC CO.,LTD , https://www.pcban88.com
The pressure pump head and pressure settings to determine the three cases to distinguish: (1) steady high-pressure fire water supply system, the pressure pump and fire pump share the pressure tank; (2) steady high-pressure fire water supply system , Pressure pump set air pressure tank; (3) steady high-pressure fire water supply system, there is no pressure regulator pump and water tank.
As for the fire water supply system to replace the fire water tank to replace the pressure tank, and its water regulation capacity of 18m3, 12m3, 6m3, or "Sprinkler Systems Design Code" (GBJ45-85) revised version of the draft for review Specified 2.4m3, are not discussed in this article, the article refers to the pressure tank water regulation capacity of 450L and below the pressure tank.
In the first case, when the pressure pump and fire main pump share the pressure tank, the pressure tank is not used to replace the fire tank, and only serve the water quantity and pressure required for fire protection before starting the fire main pump; and through the water level and pressure sensor Control the start-stop pump and fire pump start-up, the pressure tank in the main three pressure settings, as shown in Figure 1.
VX ?? water storage capacity;
VS ?? Regulated water volume;
VΔΡ ?? Buffered water volume;
V0 ?? fixed water volume;
P0 ?? starting pressure;
P1 ?? minimum working pressure;
P2 ?? maximum working pressure, fire extinguishing fire main pump start pressure;
P3 ?? Regulated water volume lower limit pressure, pressure regulator fire pump start pressure;
P4 ?? Regulated water volume upper limit pressure, pressure regulator fire pump to stop pressure;
h0 ?? starting water level;
h1 ?? fire water storage volume lower limit water level;
h2 ?? fire water storage capacity of the upper limit of water level;
h3 ?? Regulated water volume lower limit water level;
h4 ?? Regulated water volume upper limit of water level.
P2 is the starting pressure of the fire main pump, P3 is the starting pressure of the stabilizing pump, P4 is the pressure of stopping the pump of the stabilizing pump, according to the experience of China's relevant design institute P3-P20.02MPa, P4-P30.05MPa. The water levels corresponding to the pressure values ​​of P2, P3 and P4 are h2, h3 and h4. h2 water level line under the water regulation volume, according to "Code for fire protection of high-rise buildings," the provisions of 450L, h2 ~ h3 section of the water volume of buffer water volume, h3 ~ h4 section of the volume of water for the regulator volume.
In this case, the pressure setting of the pressure regulating pump is P3 and P4, and P3 is the lower pressure setting value of the pressure regulating pump, that is, the starting pressure of the pressure regulating pump; P4 is the upper limit of the pressure setting of the pressure regulating pump, that is, Pump stop pump pressure. P3 and P4 are greater than P2, greater than the head of fire main pump. The opinion of the domestic technical community is consistent with the relative relationship of the above pressure setpoints and the relevant requirements have been incorporated into the relevant provisions of the Code of Practice for Design of Pneumatic Water Supply (CECS 76:95) (see specification item 4.3.4). If you want to explore, but also limited to P3 and P4 pressure set value higher than P2 how much the problem.
The second case when the system is equipped with a pressure tank, and the pressure tank does not store the fire required before starting the fire pump water, pressure tank settings, its only purpose is to: (1) control the start and stop pump ; (2) to ease the regulator pump start and stop too often; (3) buffer due to stop pumping caused by water hammer on the system pressure shock.
In this case, the conventional approach is to start the pressure regulator pump pressure, that is, the pressure lower limit slightly higher than the head of the fire pump, pump stop pump pressure, that is, the upper limit of pressure by the pressure tank working pressure ratio, that is Air pressure tank to adjust the volume to determine, but also determined by empirical coefficient values, the method is similar to the first case, shown in Figure 2. The water levels corresponding to P3 and P4 are h3 and h4, and the water volume in the area between h3 and h4 is the buffered water volume. There are also fire main pump start pressure value set in the pressure tank, and if so, Figure 2 is converted into the form of Figure 1.
Note: Figure 2, the letter meaning the same as Figure 1
This practice has long been unquestioned and licensed for the following reasons: (1) The function of the regulator pump is to provide one-sidedness and surface-level understanding of the water pressure stability of the fire service water distribution network. (2) Think fire pumps, including fire main pumps and booster pumps, do not need to account for efficiency and energy consumption as life pumps do. At the same time for the sake of stability, that the pump head high, high pressure pipe will not be harmful, good for fire fighting. (3) According to the fire design flow calculation main fire pump head, then calculate the pressure pump set pressure value and lift, more convenient. (4) There is no study on the technical aspects of fire protection.
However, the situation is changing. With the increasing emphasis on the steady-pressured water supply system, some problems have been newly recognized as a result of the application of the centralized and stable high-pressure water supply system: (1) high pump head and high pipe network pressure are not Good thing. Long-term operation of the pipe network under high pressure, easy to aggravate the leakage, causing pipe fittings displacement and other issues. (2) The number of main fire pump start-up less, you can not need to account for the efficiency and energy consumption, as the life of the pump, and pump the situation is different, start and stop frequently, without regard to pump efficiency and energy consumption is not appropriate .
Therefore, it is necessary to meet the most unfavorable fire extinguishing facilities fire water pressure and water requirements under the premise of determining the pump lift and pressure settings.
When the fire main pump work: fire design flow Qs; the most unfavorable fire extinguishing facilities when the required water pressure Hx; the most unfavorable fire extinguishing facilities and fire main pump elevation difference ΔΗ; pipe network through the fire design flow The required head loss along the way is Hy; the local head loss required for the flow through the fire design flow is Hj, then the head of the fire main pump is:
H = Hx + ΔH + Hy + Hj (1)
When the regulator pump work: Regulator pump flow 1L / s or 5L / s; the most unfavorable fire extinguishing facilities when the required water pressure is still Hx; the most unfavorable fire extinguishing facilities and pump elevation difference is ΔH ', when the pump for the laying of the lower position, and fire main pump in the fire pump room, ΔΗ' and ΔH values ​​quite close; pipe network through the steady flow required head loss along the way Hy '; pipe network The local head loss required to pass the regulated flow is Hj '; then the head of the regulated pump is:
H '= Hx + ΔH' + Hy '+ Hj' (2)
Comparing equations (1) and (2), Hx = Hx, ΔHΔΗ '. Head loss along the way and local head loss are determined by the flow rate, the pump flow is much smaller than the fire main pump flow, so Hy '"Hy, Hj'" Hj, or H'H. The conclusion is that H '≠H, to meet the most unfavorable fire extinguishing facilities on the premise of fire water pressure, the pump lift head does not equal to the head of the main fire pump, pump head can be lower than the head of the main fire pump. This conclusion will bring designers several serious concerns:
(1) not easy to understand. Generally considered the main fire pump head is the pressure of fire, but do not understand the different design flow allows for different fire pressures. Therefore, on the surface, it is not easy to understand that the pressure head of the pump is lower than the head of the fire main pump, but in essence, both of them are premised on meeting the water pressure requirements of fire water for the most unfavorable fire extinguishing facilities. The difference is that the fire main pump flow, regulator pump flow is small, even if all in order to meet the same place, the same purpose, the same purpose of hydraulic pressure requirements, and due to fire design flow and the difference between the value of the constant flow rate, so that the two pumps lift Different. However, even if the two pumps have different heads, there is no problem in terms of ensuring the fire hydrant pressure requirements.
(2) There are doubts about the operation of the pipe network. In actual operation, when the pressure tank is pressure P4 and the highest water level h4, the pressure regulating pump stops pumping. When there is leakage in the pipe network and the water level drops to h3, Pump starts; when the pressure pump starts, the water level of the pressure water tank rises, when it rises to h4, the pressure pump stops pumping; when the fire water supply network fire extinguishing facilities start to discharge water for fire fighting, the water level inside the pressure water tank drops to h3 , Even if the regulator pump starts, and the water level continues to drop to h2 or pressure drops to P2, the fire main pump starts, and fire design flow water supply, then the main fire pump lift head above the pump P4, pump regulator In the fire main pump work does not work, so the pump head lift level or not, will not affect the normal operation of the fire water supply network.
The pump head and the fire pump to determine the head of the difference between the existence of the shortcomings:
(1) double calculation, fire design flow calculation of the main lift pump head to the regulator flow regulator pump head, compared to only calculate the head of the fire pump to be complex, often not accepted by the design department.
(2) regulator device styling products have come out. Regulators in these products specifications, performance can not be as specific as possible to know the most unfavorable fire water supply project fire extinguishing facilities elevation, pipe network form, pipe length and pipe size, so the pressure pump head lift by fire main pump head And set. To accurately determine the pressure pump head and pressure set point only in specific projects can be done. The difference between the pressure pump and fire pump head lift in the general project can be ignored, when the pipe network is small, especially when the pressure is low. In other cases, it is important to pay attention to, it is also very necessary, such as: centralized high-pressure water supply system of its pipe network, long pipe, high water pressure, when the fire water supply network under long-term high pressure operation, Is unfavorable and it should be said that it is safer to allow it to operate adequately but not too high under stressful conditions. In particular, the environmental conditions in some projects are not satisfactory, such as poor soil quality, bearings and abutments Not fully in place, the interface is not ideal, too much evasion of the pipeline in the construction, the pipeline segment has more elbow to withstand the weaknesses of the internal water pressure to reduce the head lift pump to make it below the head of the fire main pump to To alleviate the problem of high pressure in fire service water supply network, it should be said that it is a very effective measure, the only downside is
Regulator pump pressure setting and head determination technology
figure 1
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