What Care Should Be Taken While Operating Pumps in Series?

💧 What Care Should Be Taken While Operating Pumps in Series?

In industrial fluid handling systems, centrifugal pumps are sometimes connected in series operation. This means the discharge of one pump is connected directly to the suction side of another pump. Series operation is typically used when a single pump cannot generate the required head (pressure), and multiple pumps are needed to achieve the desired system performance.  

However, operating pumps in series requires careful attention to avoid problems such as cavitation, vibration, or no‑flow conditions. Below are the key precautions and best practices.

🔹 Precautions for Operating Pumps in Series

1. Sequential Start and Stop  

   - Pumps must be started and stopped one after another with minimal time lag.  

   - The next pump in sequence should only be started once the delivery valve of the previous pump is partly opened.  

2. Air Venting  

   - Always keep the air vent of the next pump open before starting it.  

   - This ensures trapped air is released, preventing air locking and cavitation.  

3. Same Operating Speed  

   - Both pumps must run at the same speed.  

   - Different speeds can cause imbalance in flow and head, leading to unstable operation.  

4. Impeller Compatibility  

   - Pumps should have the same impeller width or closely matched capacities.  

   - If the first pump cannot supply enough liquid to the second, cavitation may occur.  

5. Ensure Liquid Priming  

   - Both pumps must be completely filled with liquid during start‑up and operation.  

   - Running pumps dry or partially filled can cause no discharge condition and damage to pump internals.  

🔹 Why These Precautions Matter

- Prevents Cavitation: Ensures smooth liquid transfer between pumps.  

- Improves Reliability: Reduces mechanical stress and vibration.  

- Maintains Efficiency: Proper synchronization avoids energy losses.  

- Protects Equipment: Prevents damage to impellers, bearings, and seals.  

🔹 Key Takeaways

- Pumps in series are used to increase head (pressure), not flow.  

- Always start and stop sequentially with proper venting.  

- Ensure same speed and impeller compatibility to avoid cavitation.  

- Pumps must be fully primed with liquid before operation.  

- Following these precautions ensures safe, efficient, and reliable pump performance.