Internal Recirculation in CDLF Stainless Steel Multistage Pumps at Low Flow Conditions | Shanghai Shangcheng Pump Valve

 Internal Recirculation in CDLF Stainless Steel Multistage Pumps at Low Flow Conditions | Shanghai Shangcheng Pump Valve

In many industrial water supply and fluid transfer systems, CDLF stainless steel multistage centrifugal pumps are valued for their high efficiency, stable pressure, and compact structure. However, one operating condition that is often overlooked is prolonged operation in the low-flow region. While the pump may appear to run normally from the outside, internal recirculation can gradually develop, affecting performance and service life.

More information about CDLF stainless steel multistage pumps can be found here: https://www.scpv.cn/pumps/CDLF.html

What Is Internal Recirculation?

Internal recirculation occurs when the pump flow rate drops significantly below its designed operating range. Under these conditions, the liquid flow inside the impeller passages becomes unstable. Instead of moving smoothly from inlet to outlet, part of the fluid circulates repeatedly within the impeller and guide vane channels.

This phenomenon creates localized turbulence, eddies, and pressure fluctuations inside the pump.

Why Does Internal Recirculation Occur?

Several factors can push a CDLF pump into the low-flow operating zone:

Excessive throttling of the discharge valve

Actual system demand lower than design capacity

Oversized pump selection

Variable operating conditions with frequent load reduction

Long-term intermittent water consumption

When flow decreases below the recommended minimum continuous stable flow, hydraulic conditions inside the pump deteriorate and recirculation becomes more likely.

Common Effects of Internal Recirculation

Increased Vibration

Recirculating flow creates hydraulic imbalance inside the impeller, generating additional radial forces. Operators may notice increased vibration levels even when bearings and alignment remain normal.

Higher Noise Levels

A pump suffering from internal recirculation often produces unusual humming, rumbling, or hydraulic noise. The sound may become more noticeable as flow decreases further.

Temperature Rise

Because some fluid repeatedly circulates inside the pump rather than moving through the system, energy converts into heat. This can gradually increase liquid and component temperatures.

Reduced Hydraulic Efficiency

Internal turbulence wastes energy and lowers overall pump efficiency. The motor continues consuming power while useful output decreases.

Accelerated Wear

Long-term recirculation may increase wear on:

Impeller inlet edges

Guide vanes

Mechanical seals

Bearings

In severe cases, it may also contribute to cavitation-like damage.

How to Reduce Internal Recirculation Risk

To keep a CDLF multistage pump operating efficiently:

Operate as close as possible to the Best Efficiency Point (BEP).

Avoid running for extended periods with nearly closed discharge valves.

Select pump models based on actual system requirements rather than maximum theoretical demand.

Install minimum-flow bypass systems where necessary.

Regularly monitor vibration, temperature, pressure, and flow data.

Practical Advice

In many facilities, operators focus on whether the pump is running or stopped, but the operating point is equally important. A CDLF pump can appear stable while internal hydraulic issues are developing. Long-term low-flow operation may not cause immediate failure, but it often shortens component life and increases maintenance costs.

Shanghai Shangcheng Pump Valve recommends evaluating system flow conditions whenever abnormal noise, vibration, or efficiency loss appears. Proper pump selection and operation remain the most effective ways to prevent internal recirculation and maintain reliable performance.

Learn more about CDLF stainless steel multistage centrifugal pumps:

https://www.scpv.cn/pumps/CDLF.html