1. Basic working principle of high-temperature pumps
High-temperature centrifugal pumps usually rely on motors to drive the pump shaft and impeller to rotate at high speed. After the medium enters the center of the impeller, it is thrown toward the outer edge of the impeller under the action of centrifugal force. The speed energy is converted into pressure energy through the volute or guide vane, and finally enters the pipeline system from the pump outlet.
The basic principle is similar to that of ordinary centrifugal pumps, but three key control links are added under high temperature conditions:
Controlling medium vaporization: An increase in temperature will cause an increase in the saturated vapor pressure of the medium. If the pump inlet pressure is insufficient, the liquid may vaporize at the impeller inlet, causing cavitation.
Compensation for thermal expansion: The pump body, pump shaft and sealing components expand in different amounts after being heated, and the rotor needs to be kept centered through reasonable structural gaps, support methods and material combinations.
Isolate the effects of high temperature: Use cooling chambers, heat dissipation structures, extended bearing brackets or external flushing systems to reduce the transmission of high temperatures to bearings and mechanical seals.
Therefore, whether the high-temperature pump can operate stably depends not only on the pressure generated by the impeller, but also on the inlet conditions, thermal alignment, seal cooling and material temperature resistance.
2. What technical parameters need to be confirmed for high-temperature pumps?
When buyers make inquiries, it is recommended to provide at least the following parameters:
Design flow rate and normal flow rate, unit is m³/h;
Rated head or inlet and outlet pressure, unit is m or MPa;
Normal temperature, maximum operating temperature and start-stop temperature difference;
Media name, density, viscosity, corrosiveness and solid particle content;
Inlet pressure, device steam Erosion allowance NPSHa and site altitude;
Continuous operation time and start-stop frequency;
Pump installation method, nozzle direction and basic conditions;
Motor power, voltage, frequency, explosion-proof level and protection level;
Mechanical seal, magnetic drive or other sealing requirements;
Material, execution standards and inspection document requirements.
Among them, the maximum temperature cannot be filled in only according to the normal operating temperature. A short-term temperature rise may occur when the equipment is started, stopped or during process fluctuations. Reasonable margins should be reserved for materials, seals and bearing systems during selection.
3. Why is cavitation prone to occur under high temperature conditions?
The following must be met when selecting:
Device cavitation margin NPSHa ＞ The pump must have cavitation margin NPSHr + safety margin.
The following measures can be taken to improve the cavitation problem:
Increase the liquid level or inlet pressure of the storage tank;
Shorten the suction pipeline and reduce elbows, valves and local resistance;
Increase the suction pressure Inlet pipe diameter;
Reduce the installation height of the pump;
Select a low NPSHr impeller or reduce the pump speed;
Avoid clogging of the suction filter and insufficient opening of the inlet valve.
For hot water, heat transfer media and high-temperature chemical liquids close to the boiling point, NPSH verification should be a necessary step in pump selection.
4. How to choose materials and seals for high-temperature pumps?
Mechanical seal selection should focus on the sealing surface material, the temperature resistance range of the auxiliary sealing ring and the flushing and cooling scheme. Ordinary rubber seals may harden, lose elasticity or age rapidly at high temperatures. Depending on the risk of the medium and site requirements, you can choose:
Single-end mechanical seal: suitable for clean, less dangerous media;
Double-end mechanical seal: suitable for flammable, toxic or media that are not allowed to leak;
Bellows mechanical seal: suitable for high temperature and obvious thermal cycle conditions;
Magnetic drive structure: used for media with higher requirements for leakage control.
The specific sealing scheme should be determined in conjunction with API 682 or project technical specifications, and cannot be judged solely based on temperature.
5. Frequently asked questions about high-temperature pumps
1. What is the reason why the high-temperature pump has flow but insufficient pressure?
It may be that the impeller rotates in the wrong direction, the speed is insufficient, the system resistance changes, the impeller is worn, the inlet is entrained or the medium is vaporized. The judgment should be made based on the flow rate, inlet and outlet pressure and motor current.
2. Why does the mechanical seal leak soon after operation?
Common causes include sealing materials that are not temperature resistant, insufficient cooling or flushing flow, pump shaft deflection, poor thermal alignment, cavitation vibration, and long-term operation of the pump at low flow rates.
3. Does the high-temperature pump need to be preheated before starting?
When the delivery temperature is high or the pump body is large, it is usually necessary to gradually preheat to avoid thermal deformation, seal damage or rotor jamming caused by excessive local temperature differences. The actual preheating speed should be implemented in accordance with the equipment instructions and process requirements.
VI. Feiyue High Temperature Pump Product Solutions
During the project selection stage, it is recommended that customers provide media data sheets, flow rates, lifts, maximum temperatures, inlet pressures, operating systems, material requirements and sealing standards. Through pump type matching, NPSH verification, material selection, seal configuration and motor power verification, the risks of cavitation, leakage and thermal deformation can be reduced and the continuous operation reliability of the high-temperature conveying system can be improved.
