How to choose the pressure tank of frequency conversion water supply equipment?
With the rapid development of science and technology brought about by the progress of human society, the emergence of new technology products and extensive replacement of water supply and drainage fields (such as: frequency converter, frequency converter sequence controller, touch screen (human-machine interface), fuzzy controller, etc., make at the same time The application of new products also makes water supply and drainage equipment various in structure and control mode. When the excellent “constant pressure variable” function of frequency conversion water supply equipment is accepted by people, the more obvious the expression of “constant pressure” in domestic water supply equipment . So the frequency conversion water supply equipment adopts the form of “water pump unit + frequency conversion electric control cabinet” in the structure. So, does the frequency conversion water supply equipment need a pressure tank as a part of the equipment?
Basically, unlike the regular and quantitative supply of production water, the change curve of domestic water consumption is continuous and has obvious time characteristics. Therefore, domestic water supply equipment should have the energy-saving characteristics of “more water and more electricity; less water and less electricity” . Generally speaking, in the normal water use stage of the frequency conversion water supply equipment, the pump generally works in the high-speed section (also in the high-efficiency area). There is basically no dispute about the pump; the low water consumption and the low water consumption at night (or no water is used, but the pipeline network is always When there is a certain leakage), the water pump enters the low-speed operation, and the working conditions change in the high-efficiency area, and the energy-saving effect is not good; even if the pipe network is completely sealed and leak-free, the variable frequency water supply equipment without air pressure tank can be operated at low speed to ensure the constant pipe network. Therefore, even if the user does not use water and there is no water flow in the pipe network, in order to ensure the pressure of the pipe network, the pump must maintain a certain low operation. At this time, all the electrical energy consumed by the pump is wasted-this is our weightlifter After the barbell is raised, keep the posture for three seconds. Although there is no work done at this time, the athlete still needs to work hard.
In order to reduce the rated value of the water pump when the water supply equipment has a small flow or zero flow, the life frequency conversion water supply equipment must be equipped with an air pressure tank. When the flow is small or zero, the air pressure tank is adjusted and supplemented.
So, what role does the air pressure tank play in the frequency conversion water supply equipment?
1. The pressure tank is the proper condition for the pump to enter sleep
Pneumatic Tank-Using Robert Boyle’s Law of Gas:
PV / T = n;
(P-pressure, V-gas volume of the pressure tank, T-temperature);
At a certain temperature, the product of gas pressure (P) and volume (V) is equal to the principle that the product of gas pressure (P) and volume (V) is equal to a constant. Using the extremely small compressibility of water, the water is stored in the tank with external force. The gas is compressed and the pressure increases, and when the external force disappears, it compress Gas expansion can remove water.
Absolutely, it is very difficult for the end valves of the life pipe network to drip and not leak. Therefore, for water supply equipment or systems without air pressure tanks, the pressure of the pipe network itself maintains the system pressure. Since the compression ratio of water is much smaller than that of gas, when the pipe network is as small as a power frequency pump to directly deliver to the user, it is necessary to equip the air pressure tank to reduce the start of replacement of the water pump. Through the application of frequency conversion, the equipment controls the water pump to supply according to demand (when the flow rate is zero, the low speed of the frequency conversion control water pump ensures the “constant pressure” of the pipe network. To take advantage of this, the frequency conversion water supply equipment without the air tank must have a water pump 24 hours a day. Stop work or restart to ensure the pressure of the pipe network. Therefore, the air pressure tank is an alternative to ensure the normal rest of the pump and extend the sleep time.
2. the volume of the pressure tank determines the sleep time of the pump
(A) The volume of the air pressure tank determines the amount of water that can be added to the pipe network within a certain pressure range; when the pipe network has a certain connection flow rate (L/S), the volume of the air pressure tank determines the length of the pump restart interval. The volume, the longer the rest time; therefore, choosing a larger air pressure tank can prolong the sleep time of the pump.
(B) Correctly understand the size of the pressure tank.
A pressure tank with too large volume will increase capital investment, inconvenient maintenance, and long inflating time. For example: the variable frequency constant pressure change of the domestic pipe network P1 = 0.5MPa, the lower pressure limit (the pump restart pressure) P2 = 0.35MPa, under normal circumstances, assuming that the pipe network leaks 5L/h, the pump stops working at night and presses it for 7h (22: 00-5: 00) Calculate, the leakage is 35L, then, if the pressure tank is at P1? P2 = 0.15MPa The adjusted water volume in the pressure range is greater than 35L, which can guarantee the pump sleep for 7 hours. Therefore, it is more appropriate to replace a pressure tank with a water volume of about 35-50L. For example, if you replace the air pressure tank with the adjusted water volume greatly exceeding 50L (within the above pressure range), although the intermittent working time of the water pump is shortened, it has already entered the water use stage after 7 hours, and it is meaningless to extend the sleep time. According to the ratio, the matched small pressure tank and the oversized pressure tank have the same interval time for the water pump. Therefore, the volume of the pressure tank may be too large.
It should be pointed out that the “Code for Design of Water Supply and Drainage for Buildings” GBJ15-88 does not specify the starting frequency of water pumps for domestic variable-speed water supply equipment. Therefore, the volume of the pressure tank does not follow 7 hours, 5 hours, Or choose the adjusted water volume calculated in 4 hours; it should be based on local conditions, and reasonable layout should be considered according to the system flow, pump power, building area and other aspects.
In summary, for life frequency conversion water supply equipment, how to reasonably configure air pressure tanks with very little water is an important factor in extending the sleep time of the pump, reducing pump loss, and extending the life of the pump.