How to calculate mercury head in water.
Today, the pumping machine suddenly went on strike, and I want to buy a pumping machine for well water online. The vertical height of the water tower from the ground is 16 meters, and the water depth is 5 meters (I defended 3 meters, saying that the water depth is 8 meters. ）。I found that the mercury merchants with a head of 30 meters were afraid to sell to me. I wanted to buy a 928 yuan mercury (220V, power 1100W, head 30 meters), the merchant said that this could not be used, and recommended a deep-water mercury (220V, 750W, head 75 meters, **780 yuan) to me. Although it is relatively preferential, I am very puzzled by this, why is the mercury of water with a head of 30 meters installed at a water tower of less than 24 meters? !
I checked some relevant information and shared it with my friends:
First, the head of the pump.
1. The head of the pump refers to the height at which the pump can lift water. It also refers to the amount of energy required per unit weight of liquid to pass through the pump. It is an important working performance parameter of the pump, and it is also called "pressure head".
2. The head marked on the water mercury nameplate refers to the head that can be generated by the pump itself, and it does not include the loss head caused by the friction resistance of the pipeline water flow. Be careful! So when choosing a water pump, don't ignore it. Otherwise, you may not be able to pump water.
Yang Cheng's calculation formula:h=(p2-p1)/ρg+(v2²-v1²)/2g+z2-z1
Note: h is the head, unit (m).
P1 and P2 are the pressure of the liquid at the inlet and outlet of the pump, in units (Pa).
v1 and v2 are the flow rates of the fluid at the inlet and outlet of the pump, in units (m s).
z1 and z2 are vertical heights in (m).
is the density of the liquid, in kilograms and meters
g is the acceleration due to gravity in units (m s).
There are too many parameters involved in the formula, and it is so complicated (to calculate pressure, density, gravitational acceleration, etc.), if you are interested, you can turn to the physics book yourself. I also have a headache when I see it.
Let's take a brief look at the label on the mercury nameplate.
As shown in the figure: under the voltage of 220V, using a 25mm (1 inch) water pipe, the water pump can be from the water source surface to the center of the pump outlet vertical height of 30 meters, the pumping speed is 3 cubic meters per hour (that is, 3 tons), and the power consumption is 11 degree.
3. Horizontal loss head.
The normal head and horizontal conveying are 10 meters, and the pipeline loss is about 15 meters lift (if there is no elbow, the loss of the elbow will be counted separately!) ）。
Measurement of the actual headWhen purchasing a pump, the loss head should be taken into account in the total head (i.e., the nameplate head of the mercury in water). The loss head should be based on the length of the pipeline, the water mercury bottom valve, the accessories, etc., and the loss value is generally in the range of 10%-20% of the actual head.
Assuming that the actual head needs 24 meters, then the loss head is 24 meters * 02＝4.8 meters, that is, the head on the mercury nameplate of the water we buy and sell should not be less than 24+48＝28.8 meters.
4. Elbow loss head.
According to the experimental results, installing an elbow in a pump results in a 5% 10% head loss. For the installation of multiple elbows, the loss will be more pronounced. Therefore, the number and size of elbows, as well as the cross-sectional area and length of the pipe, need to be considered when designing and using pumps, so as to minimize head loss.
However, in practice, the elbow can not be used, in order to reduce the impact of the elbow on the pump head, it is recommended to take the following measures:
1>.Optimize the installation position and number of elbows to minimize the use of elbows.
2>.The use of reducer joints, the use of large radius elbow, reduce the shrinkage effect of the elbow, reduce frictional resistance.
3>.Increase the cross-sectional area of the pipe (thicken the pipe) to reduce frictional resistance and local pressure loss.
Through the above measures, the influence of the elbow on the head of the pump is reduced as much as possible, and the effective operation and long-term stability of the pump are ensured.
Generally, we pump mercury to the water tower, normally there are at least 3 elbows, (well to the ground, ground to the upstairs, upstairs to the water tower), these elbows have to lose 15% 30% of the head. That is to say, if it is a head of 30 meters, it may lose a head of 9 meters, then 30 9 21 meters will not be able to hit a 24-meter water tower (not counting other losses). So today I still met a conscientious merchant! In this regard, I also hope that when you encounter relevant professional problems, you should consult the merchant more and do not be self-righteous. After all, professional things still have to be done by professional people!
In addition, because I changed it myself, my hands were dirty, so I didn't use diving mercury to take pictures. This figure uses the diagram on the Internet, and the head of this machine is: suction lift + head.
I hope this article will be helpful to those who can't call an electrician and are anxious to change the mercury in water by themselves.