Problems With A Low-Flow Pump?

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If your newly repaired or installed pump is giving you low-flow problems, there’s several trouble-shooting procedures you can apply to figure out what’s going wrong. Centrifugal pumps that produce an inadequate flow or low flow can cause problems that impact all other equipment being used in the process, so it’s important to get started on our problem-solving process right away, using the simple process of elimination:

1. Look for a reversed impeller rotation: The impeller in your centrifugal pump should always rotate in the right direction. This isn’t a problem for pumps operating from a single phase electrical source, but if they operate from a three-phase electrical source, the proper phasing sequence of the wires supplying power to the pump must be correct. If any two wires are reversed, the motor will rotate in the other direction. Most centrifugal pumps have an arrow on the pump body or the motor, which shows the rotation direction. If your pump motor rotates in the opposite direction to that on the pump, reverse any two wires in the supply to change the rotation direction – and get your pump working the way it’s meant to.

2. Check the suction hose: Make sure the suction hose is free and clear of debris, and that the rubber lining of the hose hasn’t pulled away, causing partial blockage of the line. A good indicator that the hose lining is blocking the suction flow is if is the pump develops high vacuum but low discharge pressure. Gauge readings that are higher than normal can also be an indication of a collapsed lining. Luckily there’s a simple fix – just replace the hose!

3. Inspect the suction strainer: Regular inspections and cleaning of suction strainers help prevent clogging, particularly when pumping abrasive liquids or liquids that contain solids. If a pump’s suction check valve is clogged with debris of any kind, this could mean that the strainer is the wrong size (too small or too wide) or that its face clearance could be too wide. Alternatively, the strainer could be stuck in mud or other debris, plugging the suction side. A good indicator that debris is causing disrupted flow through the strainer is higher than normal gauge readings.

4. Look for debris in the impeller: A clog at the eye of the impeller can prevent it from creating an area of low pressure. Check for any signs of debris and remove if necessary.

5. Hunt for signs of wear on the impeller, wear ring, and wear plate: If the vanes on the impeller are worn, or the wear ring or wear plate opens up due to wear and tear (thus allowing more recirculation inside the pump) – the hydraulic capacity of the pump becomes less. Some technicians suggest a removable cover plate, which lets you access the impeller and wear plate quickly and easily. These wear out faster when pumping abrasive liquids or slurries, so a check every few months is recommended.

6. Find excessive clearances: Your pump’s efficiency will be less if the clearance between the impeller and wear plate or wear rings is too wide for the liquid being pumped. Fluid will recirculate inside the pump, which means there will be lower flow out of the pump. Check your clearances against the specifications in your manual and adjust if necessary.

7. Check the Bypass Valve: Make sure the flow isn’t being directed elsewhere through a bypass valve.

8. Keep an eye out for Vortexing: Vortexing can affect all kinds of centrifugal pumps, often leading to a reduction in flow. It occurs when water being drawn into a suction line results in a depression in the surface of the water, giving the impression of a whirling vortex much like you’d see when draining a bathtub. A vortex leading into the pump can cause the pump to suck up air, which reduces performance due to air being easier to pump than water. Make sure you meet minimum submergence requirements to keep the volume of liquid high enough to prevent vortexing.

If you’ve eliminated all the steps above, you might have a bigger system issue. A savvy technician with an understanding of pump curves and proper performance can help figure out your low flow problem, hopefully without the need to replace the pump! If you’ like our help, please call our toll-free number 1-800-367-4180. We have experts on hand to help you choose, install, and maintain a variety of equipment.