1. Working principle of centrifugal slurry pump:
The main flow-passing components of the centrifugal slurry pump include the suction chamber, impeller, pressure chamber, etc. The impeller is the most important working component of the pump and the heart of the slurry pump.
Before the centrifugal slurry pump works, fill the pump with liquid first, and then start the centrifugal pump. The centrifugal pump relies on the action of the rotating impeller on the liquid to transfer the mechanical energy of the prime mover to the liquid. Due to the centrifugal force, when the liquid flows from the impeller inlet to the outlet, its speed energy and pressure energy are increased. The liquid discharged by the impeller passes through the discharge chamber, and most of the speed energy is converted into pressure energy, and then transported out along the discharge pipeline. At this time, a vacuum or low pressure is formed at the impeller inlet due to the discharge of liquid. The liquid in the suction pool is forced into the impeller inlet under the action of liquid surface pressure (atmospheric pressure). As a result, the rotating impeller continuously sucks in and discharges liquid.
2. Main parts of centrifugal pump:
Centrifugal pumps are composed of many parts. According to the working state of each component during operation, it can be roughly divided into three major types: rotating components, fixed components and transfer components.
1. Impeller
The impeller is the core part of a slurry pump, just like the human heart.
The closed impeller is composed of front and rear cover plates, blades, back blades, etc.; the semi-open impeller is composed of cover plates, blades, and back blades. Closed impellers can achieve better efficiency and reduce wear on the front guard plate; semi-open impellers are only used on small-diameter pumps and in some special circumstances. These special circumstances include: prone to clogging; slurry containing Foam.
Back blades of a certain height are also designed on the front and rear cover plates of the impeller. The number of back blades is more than the number of main blades, usually more than twice. The front back blade can reduce the backflow from the high-pressure side of the impeller outlet to the low-pressure area of the impeller inlet through the gap between the impeller and the front guard plate, improving the efficiency of the pump; the back blade can reduce the pressure at the shaft seal, which is beneficial to improving the seal's durability. Working effect and lifespan; the front and back blades can also prevent particles from entering the gap between the impeller and the guard plate, preventing these particles from causing excessive damage to the guard plate; another function of the back blades is to reduce the impact on the slurry during transportation. Axial force on the impeller.
2. Sheath (pump body)
The flow rate of the slurry in the sheath of the slurry pump is much lower than that of the clean water pump. This is to reduce the wear of the sheath by the slurry, but this increases the size of the sheath.
The profile of the sheath is usually semi-spiral or annular, and the gap between the sheath tongue and the impeller is relatively large, which is designed to obtain a reasonable service life.
Failure modes of sheath: excessive wear, heating, cavitation, corrosion
3. Shaft seal
The shaft seal structure of slurry pump includes three categories: packing seal, auxiliary impeller seal and mechanical seal.
Different shaft seal types have different application conditions, so it is very important to choose the seal type reasonably.
1) Packing seal
Packing seal is the most commonly used and simplest and most reliable shaft seal structure. Packing seals also have different structures. The standard packing seal structure of the slurry pump is such that a front water seal ring is set, and clean shaft seal water (or flushing water, cooling water) with a certain pressure and flow rate evenly enters the packing and the sealing ring through the water seal ring. The gap between the shaft sleeve prevents the slurry liquid from flowing into the packing. Shaft seal water has three important functions: cooling, lubrication and flushing.
The shaft seal water pressure is usually about 35KPa higher than the pump outlet pressure. The flow rate depends on different shaft diameters and the maximum speed of different pumps. The flow rate has specific numerical requirements in the installation instructions of the pump.
2) Vice impeller seal
The auxiliary impeller seal relies on the pressure generated by the auxiliary impeller that is synchronized with the main impeller to prevent the high-pressure slurry in the pump chamber from leaking outward.
There are several packing or rubber lip seal rings behind the auxiliary impeller. They play a sealing role during pump start-up and shutdown. The auxiliary impeller seal does not require shaft seal water (except in special circumstances). The packing or sealing ring is lubricated by grease.
Under normal operating speed, there will be no contact between the packing or sealing ring and the shaft sleeve. The function of the auxiliary impeller can prevent the slurry inside the decompression cover cavity, forming the so-called gas-liquid interface. The auxiliary impeller seal is used at work sites where there is no water source or dilution of the slurry is not allowed. Under appropriate conditions of use, it will have a very ideal sealing effect and can achieve no leakage. At the same time, it does not require shaft seal water.
3) Mechanical seal
In the 1990s, mechanical seals began to be promoted and applied in the field of slurry transportation. The mechanical seals configured on slurry pumps are different from ordinary clean water pumps in structure and materials, and fall under the requirements of slurry mechanical seals:
1. Wear-resistant. The environment in contact with the slurry requires that the dynamic and stationary rings of the mechanical seal and the parts in contact with the slurry must have good wear resistance.
2. Earthquake resistance. The working conditions of the slurry pump are harsh, the rotor balance accuracy is low, and the pump shaft vibrates heavily. The mechanical seal's dynamic and static rings must have reliable compensation performance, and single spring and multi-spring designs are usually used.
4. Outer shell of slurry pump
The double-shell slurry pump has a radially split outer shell made of cast iron, which is composed of a pump body, a pump cover and connecting parts.
The pump body and pump cover bear the pressure of the pump chamber and the force of the pipeline. Therefore, they have high requirements for strength. The pressure-bearing capacity of the pump body and pump cover determines the maximum working pressure of the pump and the number of stages that can be connected in series.
5. Transmission part
At present, the drive shaft and bracket of horizontal slurry pumps are all cantilever type. The pump shaft has a large diameter, good rigidity and short cantilever. It will not bend or vibrate under harsh working conditions. The bracket is divided into two types of lubrication (thin oil lubrication and grease lubrication).
A thin oil lubricated bracket is used. The bearing is directly installed in the horizontally opened bracket. It is easy to disassemble, inspect and adjust. It is also equipped with a water cooling system, which improves the working conditions of the bearing and allows the bearing to run at a lower temperature, which greatly improves the performance of the bearing. Improved bearing life.
Using a grease-lubricated bracket, first assemble the bearing assembly and place the assembled cylindrical bearing assembly in the bracket body. Depending on the power transmitted, heavy-duty single-row or double-row tapered roller bearings and cylindrical roller bearings are selected as bearings, which can withstand the maximum axial and radial loads of the pump. There are sealed end caps, labyrinth sleeves and labyrinth rings at both ends of the bearing assembly, which can effectively prevent slurry and other dirt from entering the bearing, ensuring that the bearing can operate safely and have a high lifespan.
Post time: Feb-22-2024