02 Nov 2020
The working principle of musical fountain pump.
Before starting the pump, fill the pump and the inlet pipe with water. After the pump is running, under the action of the centrifugal force generated by the high-speed rotation of the impeller, the water in the impeller channel is thrown around and pressed into the volute. The impeller inlet creates a vacuum. The water in the pool is replaced along the suction pipe under the external atmospheric pressure to supplement this space. Then the inhaled water is thrown out by the impeller through the volute and enters the outlet pipe. It can be seen that if the impeller of the centrifugal pump rotates continuously, it can continuously absorb water. Constantly rising from low to high or far. Therefore, it is called a centrifugal pump. Therefore, the installation of centrifugal pumps generally needs to be installed on the surface of the pool below.
2. General characteristics of centrifugal pumps
The flow direction of water along the centrifugal pump is sucked along the axial direction of the impeller, and flows out perpendicular to the axial direction, that is, the direction of water flow in and out is 90° with each other.
Since the centrifugal pump forms a vacuum suction by the impeller inlet, it is necessary to fill the pump and suction pipe with water before starting, or use a vacuum pump to exhaust air to form a vacuum, and the pump casing and suction pipe must be strictly sealed. There must be no air leakage, otherwise a vacuum will not be formed and water will not be sucked up.
Since it is impossible to form an absolute vacuum at the impeller inlet, the suction height of the centrifugal pump cannot exceed 10 meters, plus the loss along the way caused by the water flowing through the suction pipe, the actual allowable installation height (the height of the pump axis from the suction water surface) is much smaller than 10 meters. If the installation is too high, no water will be absorbed; in addition, because the atmospheric pressure is lower in mountainous areas than in plains, the installation height of the same pump in mountainous areas, especially in high mountainous areas, should be lowered, otherwise it cannot suck up water.
3. The scope of use of centrifugal pumps:
1. Urban water supply 2. Sewage system 3. Civil engineering, construction system 4. Agricultural water conservancy system 5. Power station system 6. Chemical system 7. Petroleum industry system 8. Mining and metallurgical system 9. Light industry system 10. Ship system
Special pump for fountain
The working principle and characteristics of fountain pump
1. The working principle of fountain pump
The working principle of the fountain professional pump is different from the centrifugal pump. It mainly uses the thrust generated by the high-speed rotation of the impeller to lift water. The lift generated by the blades of the fountain pump against the water can push the water from below to above.
The blades of the fountain pump are generally immersed in the pool of the water source. Due to the high-speed rotation of the impeller, under the action of the lift generated by the blades, the water is continuously pushed upwards, causing the water to flow out along the outlet pipe. The impeller rotates continuously, and the water is continuously pressed to a high place.
2. General characteristics of professional fountain pumps
As the name implies, the fountain pump is a special axial flow submersible pump designed according to the actual needs of fountains and waterscapes. The direction of the axial flow of water in the fountain pump is suction and outflow along the axial direction of the impeller, so it is also called shaft Flow pump. (Currently fountain pumps are divided into 304 stainless steel submersible pumps and cast iron submersible pumps)
High lift, large flow, high efficiency, suitable for waterscapes, fountains, a unique submersible pump, which is different from general irrigation submersible pumps and sewage submersible pumps. In order to meet the frequent opening and operation of the water feature fountain for a long time, or the use of frequency conversion technology to make the water column high and low, the requirements for the bearing are also higher, and the high-efficiency hydraulic components and imported polymer fiber bearings are used. Quiet and high temperature resistant, high efficiency and long life without maintenance.
No need to fill water before starting, easy to operate.
The safety factor is higher, the protection device of the fountain special pump is more sensitive, the internal insulation of the pump is more reliable, and the waterproof performance is higher. Of course, the construction must be strictly in accordance with the industry specifications. The cable needs to be waterproof, and the underwater connector needs to be installed with an underwater junction box , And potting glue. Wait for the glue to harden before contacting with water. Each water feature fountain must be equipped with a professional fountain control cabinet separately, with leaking treasure, circuit breaker, grounding, etc. installed in the cabinet!
About the selection principle of waterscape fountain pump:
The flow and dust of the selected pump are basically the same as the design flow and design head of the fountain system, and when the working point changes, the pump always works in a high-efficiency range, which will not cause cavitation or overload the power machine
The size and number of pumps are mutually restricted. Larger selection of pumps results in higher efficiency, fewer installations, and costs for equipment, civil engineering, and management can be reduced accordingly, so the selection should be reasonable and appropriate.
Use pumps with good cavitation performance as much as possible. This has a great impact on simplifying the pump room structure, reducing investment in pumping stations, and ensuring the safe operation of the unit. If you must choose a centrifugal pump, you must use a more complex, reinforced concrete A dry-chamber pump house composed of a mixed structure of soil and masonry (this requirement can be met due to different regional environments, and more factors need to be considered, such as the geographical climate with more rain and the climate with more salt near the sea , More cautious)
Defects in the use of centrifugal pumps in waterscape fountains:
Large flow loss
The installation of the centrifugal pump requires a closed basement without moisture, or a machine room with a high waterproof and drainage coefficient. Under this condition, the complexity of pipeline installation can be imagined. The hydraulic loss is caused by the impact of the liquid in the pump, eddy current and surface friction. The loss of impact and vortex is caused by the change of the direction of the liquid flow. Surface friction will always occur when the liquid flows through the flow channel in contact. The energy loss caused by this is mainly determined by the length, size, shape, and surface of the flow channel. The degree of roughness, and the flow rate and characteristics of the liquid. 2. Volume loss. Volume loss is the result of a part of the liquid that has gained energy flowing in and out of the pump. The volumetric efficiency of the pump is generally 0.93-0.98. Therefore, the sealing ring and sealing structure of the centrifugal pump have higher requirements, and the construction difficulty is often proportionally increased. 3. Mechanical loss: Mechanical loss refers to the friction loss between the side of the impeller cover and the liquid in the pump casing, as well as the friction loss of the pump shaft in the movement of mechanical parts such as packing, bearings and balance devices. Generally, the former is dominant.
Because centrifugal pumps often have longer pipelines, slow pressure transmission, and large losses, (10 meters of horizontal pipelines are equivalent to one meter of head, and a discounted head of 5% for right-angle elbows)
The selection of centrifugal pumps increases the loss of flow and head, so the number and power of water pumps will be greatly increased, including the construction of civil works, which will increase the cost accordingly.
Serious cavitation phenomenon
According to the working principle of the centrifugal pump, the liquid flow flows into the impeller under the pressure difference (Pa-Pk) formed between the suction pressure Pa and the lowest pressure Pk at the impeller inlet. The lower the pressure Pk at the impeller inlet, the lower the suction capacity. The larger the value, but if Pk decreases to a certain limit value (currently, the saturated vapor pressure Pt of the liquid at the delivery temperature is usually the close value of the liquid vaporization pressure), cavitation will occur. When the cavitation develops to a certain degree, a large number of bubbles will be produced, which will block the flow channel, causing the flow rate, lift and efficiency of the pump to decrease significantly.
Produce vibration and noise.
Due to the particularity of the centrifugal pump installation, when the motor is operating in a closed space, the vibration and noise generated will be doubled.
The installation is complicated and the civil construction cost is high (need to be closed underground dry room or closed underground dry pump room)
Low safety factor
Many people think that the lack of direct contact between the pump and the water increases the safety hazards of the waterscape operation, so the surrounding environment is ignored in the construction. Because the machine room and the pump pit are under the ground, if the waterproofing is not in place during the construction, In addition to natural factors, such as heavy rain and snow, water can easily penetrate into the machine room from the ground and around the wall. The junction box of the centrifugal pump has no waterproof insulation device, so it is very particular about the installation environment and must be dry. The drainage system of the pump room should be good, (the drainage has a hidden danger of blockage). For example, in a long-term damp environment, the corrosion degree of the cable will greatly increase. (Generally, the cables in the machine room are not waterproof cables). Just imagine in a dark and humid environment without installation Does the probability of leakage in the control cabinet increase correspondingly? When people step into the leakage area, is the probability of electric shock greater?
The above summary: centrifugal pumps are more suitable for transporting liquids, and the transported liquids do not need to be recycled. However, the water resources of fountain water features need to be considered for energy conservation and environmental protection. Therefore, it must be necessary to achieve continuous operation of the outlet and return water and maintain a balance. Circulating water system. No matter how large a company can afford to consume water resources every day, imagine if the designed waterscape fountain wastes thousands or even tens of thousands of cubic meters of water every day. Will the owner run his waterscape every day? And now it is the urban waterscape The water fall in the middle of the water, the small water feature is just a decoration right after it is finished, and it can't run at all. The biggest problem is that the water return in the water system is not timely, making the water feature unable to run continuously! ------So the water feature fountain design The construction needs to find a professional company for design and construction, and the construction is strictly in accordance with the regulations. The construction of dangerous voltages must be multi-protected. Because of the specific use of the professional fountain pump, if it is not purchased in the industry, there is no experience, and the general submersible pump is often used as a fountain pump. Come to use, greatly increase the hidden danger of safety!
Originally published 02 Nov 2020, updated 02 Nov 2020.