Difference between self-priming pumps and submersible pumps

Self-priming pump: The principle of a self-priming pump relies on a unique impeller and separation disc to force the separation of gas and liquid, thereby enabling the pumping process. Its shape, volume, weight, and efficiency are similar to those of a pipeline pump. Vertical self-priming pumps do not require auxiliary equipment such as foot valves, vacuum valves, or gas separators. No filling is required when normal production starts; it has a strong self-priming capability and can replace the submersible pumps that are currently widely used. It can be employed as a circulation pump, a pump for transporting liquids in tank trucks, a self-priming pipeline pump, or a portable pump. Submersible pump: The submersible pump solves the problem of transporting liquids at low levels. However, due to the use of a long shaft, combined with the unbalanced radial forces on the impeller and the cantilever structure of the entire shaft, significant deflection occurs at the impeller end during rotation. The longer the shaft, the greater the deflection. To solve this problem, a bearing is installed on the shaft. However, since the entire shaft is flexible, the bearings are subject to unilateral wear on a continuous basis; the amount of wear is significant, the bearings vibrate violently, and the wear rate increases, which results in a high frequency of damage to the submersible pump. Moreover, the shaft should not be made too long, generally staying within 2 meters. The bearings of submersible pumps are cooled and lubricated by the medium transported by the pump. If the pumped medium does not cool the bearings nor lubricate them (a situation that occurs when the pump is running without fluid or when the inlet is blocked by debris), bearing wear can occur, and in severe cases the motor may be damaged as well. And the repair and installation of submersible pumps are very troublesome. Especially when transporting corrosive media, it is difficult to complete the task without lifting equipment. The advantage of submersible pumps is that they can go deep below the medium to be transported, enabling transfer at low levels. Its structural feature is the use of a long-axis cantilever structure. The submersion depth should be kept within 2 meters as much as possible; exceeding this limit results in a significant drop in efficiency. But the major problem with submersible pumps is that the entire shaft is flexible; during the transfer of the medium, the bearings are constantly subjected to unilateral wear. Excessive wear leads to vibration in the bearings, which in turn exacerbates the wear on the bearings, creating a vicious cycle. Therefore, the failure rate of submersible pumps remains very high. Moreover, most of the components with high wear are located below the conveying medium, making disassembly and maintenance extremely inconvenient. The development and introduction of self-priming pumps can be considered an innovation in the existing transportation systems. Firstly, this pump eliminates the long shaft of submersible pumps, getting rid of all those troublesome bearings as well. Secondly, the main components of the self-priming pump are all above the ground level, with no mechanical parts located beneath the medium being transported. Therefore, daily maintenance and repairs become very fast and convenient. Then there is a significant increase in head; the suction lift of self-priming pumps can reach around 7 meters (higher with special designs), representing a qualitative improvement compared to submersible pumps. Another advantage, or feature, of self-priming pumps is that once the pump chamber is filled with the liquid to be pumped, the medium can be drawn into the pump directly while the pump is running without load (the idling time does not exceed 7 minutes). It prevents accidents caused by improper operation that lead to motor burnout due to idling, **reducing usage risks and improving the efficiency of the pump.

However, the self-priming height of a self-priming pump decreases as the specific gravity of the medium being transported increases; for media with high specific gravity and that are located at a significant distance above the ground surface, it is recommended to use submersible pumps

Comparison between vertical self-priming pumps and submersible pumps: 1. The self-priming pump has a vertical design; compared to submersible pumps with similar specifications, it has **less weight and occupies less space. Since the shaft is installed vertically, leakage at the shaft seal is unlikely. 　　2. The self-priming pump eliminates the need for a long shaft, which also removes the problem related to bearings; this leads to an **extended maintenance period** and reduces vibration as well. 　　3. All the parts that may be damaged and require repair are on the ground, which greatly facilitates maintenance. The pump inlet is merely a hollow tube, so no foot valve is required. If the inlet is blocked by debris, it can be cleared by pulling out the hollow tube, whereas an submersible pump requires the entire pump to be lifted out in order to be cleaned. 　　4. When purchasing a submersible pump, it is necessary to determine the pumping depth. If the depth of the liquid does not match the length of the pump shaft, a different pump will be required. In contrast, a vertical self-priming pump can pump at different depths by simply using hollow tubes of varying lengths, without the need to replace the pump itself. 　　5. The air pump can continue to operate for a considerable period of time, which helps in detecting problems early and taking measures to prevent damage to the motor, thereby reducing losses caused by improper operations and ensuring better safety. 　　6. The submersible pump must be installed directly above the liquid. This self-priming pump can be installed either above or beside, and it can even use vacuum-resistant hoses to draw up liquids that cannot be reached by straight pipes, offering high mobility.

Self-priming pump draws in liquid; submersible pump backs up

The impeller of a self-priming pump is above the liquid surface, while the impeller of a submersible pump is below it.

It’s obvious from the pump’s name – it’s self-priming: lol

Self-priming pumps are easy to maintain, whereas submersible pumps are not.

Self-priming pumps can self-primed, while submersible pumps experience backflow. This is the difference in their water absorption principles

Prefer self-priming over submersible operation :victory: