The basic relationship of cavitation of stainless steel chemical pump, how to prevent cavitation
When the liquid is at a certain temperature, when the pressure is reduced to the vaporization pressure at that temperature, the liquid produces vapor bubbles. This phenomenon of generating bubbles is called cavitation. The bubbles generated during cavitation, when flowing to a high pressure, their volume is reduced to burst. This phenomenon of bubbles disappearing in the liquid due to pressure rise is called cavitation collapse.
DFP type stainless steel self-balancing chemical pump
The cavitation conditions of the stainless steel chemical pump are determined by the pump itself and the suction device. Therefore, to study the conditions for the occurrence of cavitation, we should consider both the pump itself and the suction device. The basic relationship of cavitation for stainless steel chemical pumps is
NPSHc≤NPSHr≤[NPSH]≤NPSHa
NPSHa=NPSHrNPSHc——The pump starts cavitation
NPSHaNPSHaNPSHrNPSHc-pump without cavitation
In the formula, NPSHa——the device cavitation margin is also called effective cavitation margin, the larger the cavitation margin, the less likely it is to cavitation;
NPSHr——Pump NPSH, also called necessary NPSH or pump inlet dynamic pressure drop, the smaller the cavitation resistance, the better the performance;
NPSHc——Critical NPSH, which refers to the NPSH corresponding to a certain drop in pump performance;
[NPSH]——Allowable NPSH is the NPSH used to determine the pump operating conditions, usually [NPSH]=(1.1～1.5)NPSHc.
When the stainless steel chemical pump is in operation, if the partial area of the overflow part (usually somewhere behind the inlet of the impeller blade) for some reason, the pressure of the pumped liquid drops to the liquid vaporization pressure at the current temperature, the liquid will be This place begins to vaporize, producing a large amount of steam, forming bubbles. When the liquid containing a large number of bubbles passes through the high-pressure area in the impeller, the high-pressure liquid around the bubbles causes the bubbles to shrink sharply and even burst. While the bubbles are condensed and ruptured, the liquid particles fill the cavities at a very high speed. At this moment, they generate a strong water hammer and hit the metal surface with a very high impact frequency. The impact stress can reach several hundred to several thousand. Atmospheric pressure, the impact frequency can reach tens of thousands of times per second, and the wall thickness will be broken down in severe cases.
The process in which bubbles are generated in the pump body of the stainless steel chemical pump and the bubbles burst to damage the flow parts is the cavitation process in the water pump. After cavitation occurs, the pump will not only cause damage to the flow parts, but also produce noise and vibration, and cause the performance of the pump to decline. In severe cases, the liquid in the pump will be interrupted and the pump will not work properly.
Measures to prevent cavitation in stainless steel chemical pumps
To prevent cavitation, NPSHa must be increased, so that NPSHaNPSHr can prevent cavitation from occurring as follows:
1, reduce the geometric suction height hg (or increase the geometric backflow height);
2. Reduce the suction loss hc. For this reason, try to increase the pipe diameter and minimize the pipe length, elbows and accessories, etc.;
3, prevent long-term operation under large flow;
4. At the same speed and flow rate, a double-suction pump is used. Because the inlet flow rate is reduced, the pump is not prone to cavitation;
5. When cavitation occurs in the stainless steel chemical pump, the flow should be reduced or run at a reduced speed;
6. The condition of the suction pool of the stainless steel chemical pump has an important influence on the cavitation of the pump;
7. For pumps operating under severe conditions, cavitation-resistant materials can be used to avoid cavitation damage.
