Cavitation in water pumps is the rapid creation of bubbles in a fluid and their subsequent collapse. In most cases, the force of cavitation is so strong that it can pit the metal components of the water pump, like the impeller, causing severe damage to the pump seals.
With impending damage looming around the corner of the cavitation process, it is vital to prevent cavitation from occurring if you want to protect the lifespan of your water pump. In this article, we will explore four ways to prevent water pump cavitation.
Why Does Pump Cavitation Occur?
Water pumps are designed to work with a full flow of water supply. However, in some cases, a flooded inlet is not enough to maintain the pressure needed to prevent cavitation. The suction side or the inlet is the point of lowest pressure in a given pump. For centrifugal pumps, the lowest pressure is near the eye of the impeller.
Under normal atmospheric pressure conditions, fluids have a predictable vapor pressure. As the pressure within the pump falls below the liquid’s vapor pressure, bubbles start forming. When the bubbles reach areas of the liquid where the pressure is higher than the vapor pressure, they collapse. In the case of cavitation, this formation and collapse of the bubbles are both violent and rapid. Poorly executed or disrupted processing lines can cause suction or discharge pressure to fall, leading to cavitation.
How to Recognise Pump Cavitation
- Cavitation sounds like gravel or marbles circulating through the pump, pipes, or hoses. Prolonged cavitation is visible on the pump impeller and other components. Typical symptoms of pump cavitation include:
- Noise
- Vibration
- Seal/bearing failure
- Impeller erosion
- Higher than usual power consumption
How to Prevent Pump Cavitation
Now that you understand what pump cavitation is, why it occurs, and what signs to look for, let’s try to prevent it from happening. First, identify the cause of your pressure drop. In most cases, moving your pump closer to the fluid source and removing as many bends and valves in your pump system will correct the problem. This is because each component causes additional drops in pressure. When your suction lift is too high to maintain pressure, move your pump closer to the fluid source or vice versa.
Enlarging your suction lines will also prove effective. In obvious cases, a blockage will occur in piping or hoses near the pump. To resolve the issue, clear those pipe blockages and clean your suction lines by removing any debris. However, be careful not to blow the debris back toward the fluid source; otherwise, you may deal with another blockage.
Below are four ways to prevent pump cavitation:
1. Pump Selection:
The best way to prevent pump cavitation is to select the right water pump for the application. Cavitation increases as the pump head falls or as the capacity increases. For this reason, it is vital to select the right pump to maintain a positive margin of NPSHa above NPSHr; this is your best first move.
The rule of thumb: The pressure at the pump inlet should be 10% greater than the pump’s specified NPHr.
How to Increase Available Suction Head
- Raise and maintain tank liquid level
- Elevate supply tank
- Reduce piping losses from too many fittings or too small a diameter
- Replace collapsed or compromised components
- Clear solids from inside of pipes
- Clear suction strainer
- Replace corroded pipe
- Check for a gasket protruding into the piping
2.Address Discharge Cavitation
When the pressure at the discharge end of the water pump is too high, then discharge cavitation occurs. High discharge pressure limits the volume of fluid flowing from the pump. This results in high-velocity fluid recirculating between the pump impeller and housing, causing cavitation.
Common causes of discharge cavitation include:
- Clogged filters
- Pipe blockages
- Poor piping design
You can prevent discharge cavitation if you:
- Keep reducers as close to the pump as possible.
- Install a control valve (if needed) on the discharge side. Never install one on the suction side.
- Avoid pockets where air or vapors can accumulate.
3. Routine Pump Maintenance
Once you have chosen the right pump for your application, regular maintenance is the best preventative measure for cavitation. It will extend your water pump’s life and ensure consistent performance.
- Check filters and strainers. Blocked or dirty filters and strainers cause pressure buildup inside the pump. Regular maintenance ensures that systems are in place to keep the pump system flowing at capacity.
- Assess the entire pump system design: Ensure the optimum flow rate is available through pump elevation and downward flow when possible.
- Evaluate the curve. Consider the job pressure demands and then consider the pump data to see if it fits the application. Then you can determine if the pump fits the needed flow rate.
- Monitor pressure sensing equipment.
- Look for cracks or collapsed piping/hoses that will disrupt the system.
4. Proper Installation
If you want to avoid pump cavitation, ensure you have correctly installed the right water pump system to maintain pressure and flow. The goal of installing a pump is to keep a net positive suction head (NPSHa) at greater than the net positive suction head required (NPSHr). You should consider the following four variables:
- Pump location: Install your pump so the water flows into the pump suction inlet effortlessly. Place your pump at a lower point than the water level in the tank from which it pumps.
- Suction pipe length and diameter: The general recommendation is 12cm of straight pipe for every centimeter of pump suction diameter. If you want to maintain laminar flow, then connect 5-10 pipe diameters of straight piping to the pump inlet. Within the final length of pipework, do not include elbows, reducers, valves, or strainers.
- Suction lift, or the vertical distance from water source to pump inlet: Suction places higher than necessary energy demands on pumps, decrease NPSHa, and increase turbulence. The best solution is to rather install your pump below the water level of the supply tank. Always stay within the necessary standards for the piping design.
- Friction loss: As fluids pass through the water pump’s pipes, friction between the fluid and inside surface of the pipe creates turbulence. This slows down the fluid and results in a drop in pressure. Friction loss is affected by pipe length, diameter, and flow rate.
Troubleshoot Guide
Below is a handy troubleshoot checklist:
- Is the pump installed too high above the fluid source?
- Is suction pipe diameter too small?
- Is the suction pipe too long?
- Are there too many fittings on the suction pipe?
- Is the pump running too fast?
- Is the suction line to the pump sloped properly?
If you are concerned about finding the right water pump, installing it correctly, and the maintenance thereafter, then reduce your stress levels and turn to the professionals of the water pump industry; Jordan Pumps. They will help you with everything from selecting the right pump for your application needs, installation, and full maintenance of the system to help you prevent cavitation. Contact Jordan Pumps today!
