Negative pressure in high-flow, high-head multistage pumps is a concern that can negatively impact the pump's performance and lifespan. Here are some suggestions for addressing this situation.

1. Identify the cause of negative pressure: First, determine the source of the negative pressure. It could be due to pump design issues, piping system problems, or improper operation. Check if the pump is installed correctly, if there are any leaks or blockages in the piping, and if the flow rate and head are within the pump's rated range.

2. Adjust operating parameters: Appropriately adjust the pump's speed, flow rate, and head to ensure they operate within the normal range. Excessively high head or flow rate can lead to negative pressure. By adjusting these parameters, the pump's load can be lightened, and the generation of negative pressure can be reduced.

3. Check sealing performance: The sealing performance of multistage pumps is crucial for preventing negative pressure. Check if the pump's sealing rings, shaft seals, and other sealing components are intact. If wear or damage is found, they should be replaced promptly.

4. Install pressure regulating devices: Installing pressure regulating devices (such as pressure reducing valves or pressure sensors) at the pump's outlet or inlet can help maintain stable pressure and prevent negative pressure generation. These devices can automatically adjust flow or pressure, keeping the pump in its optimal operating state.

5. Optimize the piping system: Check for issues in the piping system, such as whether the pipe diameter is appropriate or if there are air leaks. Optimizing the piping system can reduce fluid resistance and improve system stability, thereby reducing the generation of negative pressure.

6. Regular maintenance and inspection: Regular maintenance and inspection of the pump are key to preventing negative pressure. Regularly check if all pump components are intact, clean the pump's interior, and inspect the piping system for damage or blockages. This ensures the pump remains in good operating condition.

7. Seek professional help: If the above measures cannot solve the problem, it is recommended to seek professional assistance. They can provide more specialized advice and solutions based on the specific situation.

When dealing with negative pressure in high-flow, high-head multistage pumps, ensuring the pump's safe operation and extending its lifespan are crucial. By following the suggestions above, you can try to resolve this issue, ensuring stable pump operation and improving work efficiency.