Dealing with low pump flow? Low flow problems with centrifugal pumps are certainly frustrating. They can leave your pump performing a bit flat. The problem can obviously be annoying but there is good chance that the root is not the pump. In this blog post our engineers discuss some of the common reasons behind low flow in centrifugal pumps:
Clogged Or Broken Suction
Most of the times low flow is due to clogging and blockages in the suction pipe. Start off by checking the suction pipe for any sort of debris, freezing and blockages. Less flow to the pump will obviously yield less flow out of it. Pumps can also become air locked where the upper head will trap air causing a loss of prime. Some pumps have a bleed plug located near the top of the pump housing that can be used with a small ball valve to quickly bleed air allowing the pump to prime. Minerals can also cause a pump to stop flowing and cease the entire housing if not attended to. Ground water or un-softened water containing minerals at the right pH will build minerals on the impeller causing clogging or reduced performance.
Reverse Rotating Impeller
Even though it may seem like a no-brainer, reverse rotating impellers are a common problem. This is why most engineers bump start the motor to check the direction of the impeller. If the motor runs in the opposite direction, it could end up backing off the shaft, leading to further damage. Normally centrifugal pumps can run a while without burning seals but some pumps may use special seals that are intolerant to dry operation. This can lead to leakage from the shaft seal and external failure.
If the clearances are wider for the type of fluid you are pumping, this will promote excessive slipping. The fluid will eventually continue to re-circulate inside the pump, leading to lower flow. There are different types of centrifugal pumps that are better suited for higher pressure operation, closed impeller high pressure pumps may be needed if higher pressure is needed.
Worn Out Impeller
The hydraulic capacity of the pump may also be reduced when the vanes of the pump are worn out. The case is the same with worn wear rings. When clearances start opening up there is more re circulation inside the pump, which may lead to low flow. This normally occurs with high dirt systems or systems with abnormal pH that attacks the pumps impeller. Impellers made of steel, bronze and stainless steel are available to fix these types of chemical compatibility issues.
Debris Stuck In Impeller
Any sort of debris stuck in the pump may also lead to lower hydraulic pressure and consequently, low flow. This falls into the category of filtration problems such as calcium, iron, biology, or dirt in the water. Most of the time a simple 200 mesh suction strainer can be applied to remedy contamination suction issues from aggregate, bio fouling, or mineral buildup. line sizes being to small at suction can also affect the pumps performance starving the inlet and reducing potential output.
An Open Bypass Valve
Inspect the entire system and make sure that no pressure is being diverted elsewhere through a bypass valve. Closed suction valves will lead to the same problem.
This problem is more common among vertical turbines and self-priming pumps in suction lift conditions. Make sure that the system meets the min submergence requirements to prevent flow vortex.
Centrifugal pumps producing low pressure will not just affect the pump but also any other equipment in the chain. Before you begin to diagnose the pump, make sure that you fully understand the issues mentioned in this post. If everything is good to go, there might a more complex issue at hand.
Low quality centrifugal pumps tend to require more frequent maintenance checks and are more prone to breaking down. Make sure you browse around our collection of centrifugal pumps, all of which come from industry leading brands. Get in touch for more information.