Technical requirements for pressure tanks for variable frequency water supply equipment

With the rapid development of human society, the emergence of new technology products is widely used in the water supply and drainage field (such as: inverters, programmable controllers, touch screens (human-machine interface), fuzzy controllers, etc. The water supply equipment has a revolutionary technological leap. At the same time, the application of new products has made the water supply and drainage equipment various in structure and control. When the excellent "constant pressure variable" function of the variable frequency water supply equipment is accepted, " "Constant pressure" is more obvious in the life water supply equipment. Therefore, the frequency conversion water supply equipment is more in the form of "water pump group + frequency conversion electric control cabinet". Then, does the variable frequency water supply equipment need a pressure tank as part of the equipment?

Generally speaking, unlike the regular supply of production water, the domestic water consumption curve has a large change curve and has obvious time characteristics. Therefore, the domestic water supply equipment should have “more water, more electricity consumption; less water consumption and less power consumption”. Energy saving features. Generally speaking, the frequency conversion water supply equipment is in the normal water use stage, the water pump generally works in the high speed section (also the high efficiency area), and the power consumption of the water pump is basically uncontroversial; the water consumption is low and the nighttime water consumption is small (or no water, but the total network When there is a certain leakage), the pump will enter the low-speed operation, the working condition deviates from the high-efficiency area, and the energy saving effect is not good. Even if the pipe network is completely sealed and leak-free, the frequency conversion water supply device without the pressure tank is operated by the low speed of the pump to ensure the constant flow of the pipe network. Pressure, that is, even if the user does not use water, the pipe network has no water flow. In order to ensure the pressure of the pipe network, the pump must also maintain a certain low speed operation. At this time, all the electric energy consumed by the pump is wasted? Our weightlifter stayed in the state of holding the barbell for three seconds after lifting it up. Although there was no work at this time, the athlete still needs to contribute.

In order to reduce the energy consumption of the pump when the water supply equipment has a small flow rate or zero flow rate, the domestic variable frequency water supply equipment must be equipped with a constant pressure air tank, which is supplemented by the pressure tank when the water flow is small or zero flow.

So, what role does the pressure tank play in the variable frequency water supply equipment?

First, the pressure tank is the precondition for the pump to enter the sleep pressure tank - using the Boeile (RobertBoyle) gas law:

PV/T=n;

(P-pressure, V-barrel tank gas volume, T-temperature);

The principle that the product of gas pressure (P) and volume (V) is equal to a constant at a certain temperature, using the property of minimal compressibility of water, storing water in the tank with an external force, the gas is subjected to a compression pressure, and when the external force disappears, the pressure is compressed. Gas expansion removes water.

It is well known that the end of the life pipe network is difficult to make dripping water. Therefore, the water supply equipment or system without the pressure tank maintains the system pressure by the pressure water of the pipe network itself. Since the compression ratio of water is much smaller than that of gas, when the pipe network has a small flow leakage, the pressure can be greatly reduced, and the pump can be started frequently. If the power frequency pump supplies water directly to the user, it is necessary to equip the pressure tank to relieve the frequent start of the pump. Due to the application of frequency conversion, the equipment controls the water pump for supply (variable constant pressure). The zero-flow frequency control pump low-speed guarantees the pipe network "constant pressure". With this point, the variable frequency water supply equipment of the pressure tank is no longer provided. There must be a water pump to work continuously or frequently to ensure the pressure of the pipe network for 24 hours. Therefore, The pressure tank is a prerequisite for ensuring that the pump rests normally and prolongs sleep.

Second, the volume of the pressure tank determines the time of the pump sleep (a) the volume of the pressure tank determines the amount of water to replenish the pipe network within a certain pressure range; the volume of the pressure tank in the case of a certain leakage flow rate (L/S) of the pipe network The size determines the length of the pump restart interval, the larger the volume, the longer the interval time; therefore, the choice of a slightly larger pressure tank can extend the sleep time of the pump.

(b) Correctly understand the size of the pressure tank.

Excessive volume of pressure tanks will increase capital investment, inconvenient maintenance, and long inflation time. Example: The constant pressure value of the life pipe network is P1=0.5MPa, the lower limit of pressure (pump restart pressure) P2=0.35MPa. Under normal conditions, it is assumed that the pipe network leaks 5L/h, and the pump stops working at night for 7h (22 :00-5:00) Calculate, the leakage is 35L. Then, if the pressure tank has a regulating water volume of more than 35L in the pressure range of P1?P2=0.15MPa, the pump can be guaranteed to sleep for 7 hours. Therefore, it is more suitable to use a pressure tank with a water volume of about 35 to 50L. If you choose a pressure tank that regulates the water volume much more than 50L (within the above pressure range), although the pump has a longer working interval, it has begun to enter the water phase for more than 7 hours, and it is meaningless to extend the sleep time. In contrast, the matching small pressure tank and the oversized volume pressure tank have the same interval time as the water pump, and therefore, the volume arrangement of the pressure tank is too large.

It should be pointed out that the "Code for Design of Building Water Supply and Drainage" GBJ15-88 does not stipulate the starting frequency of the water pump for life frequency variable speed water supply equipment. Therefore, the volume of the pressure tank is not 7 hours or 5 hours during the period of low water consumption. Or the amount of water to be adjusted calculated in 4 hours; it should be adjusted according to local conditions, and should be reasonably arranged according to various aspects such as system flow, pump power, and building area.

In summary, for the living frequency water supply equipment, how to properly configure the pressure tank in the case of very little water is an important factor to prolong the sleep time of the pump, reduce the pump loss, and prolong the life of the pump.