mud pump cavitation in stock

Cavitation is an undesirable condition that reduces pump efficiency and leads to excessive wear and damage to pump components. Factors that can contribute to cavitation, such as fluid velocity and pressure, can sometimes be attributed to an inadequate mud system design and/or the diminishing performance of the mud pump’s feed system.

Although cavitation is avoidable, without proper inspection of the feed system, it can accelerate the wear of fluid end parts. Over time, cavitation can also lead to expensive maintenance issues and a potentially catastrophic failure.

When a mud pump has entered full cavitation, rig crews and field service technicians will see the equipment shaking and hear the pump “knocking,” which typically sounds like marbles and stones being thrown around inside the equipment. However, the process of cavitation starts long before audible signs reveal themselves – hence the name “the silent killer.”

Mild cavitation begins to occur when the mud pump is starved for fluid. While the pump itself may not be making noise, damage is still being done to the internal components of the fluid end. In the early stages, cavitation can damage a pump’s module, piston and valve assembly.

The imperceptible but intense shock waves generated by cavitation travel directly from the fluid end to the pump’s power end, causing premature vibrational damage to the crosshead slides. The vibrations are then passed onto the shaft, bull gear and into the main bearings.

If not corrected, the vibrations caused by cavitation will work their way directly to critical power end components, which will result in the premature failure of the mud pump. A busted mud pump means expensive downtime and repair costs.

As illustrated in Figures 1 and 2, cavitation causes numerous pits to form on the module’s internal surface. Typically, cavitation pits create a stress concentration, which can reduce the module’s fatigue life.

To stop cavitation before it starts, install and tune high-speed pressure sensors on the mud suction line set to sound an alarm if the pressure falls below 30 psi.

Accelerometers can also be used to detect slight changes in module performance and can be an effective early warning system for cavitation prevention.

Although the pump may not be knocking loudly when cavitation first presents, regular inspections by a properly trained field technician may be able to detect moderate vibrations and slight knocking sounds.

Gardner Denver offers Pump University, a mobile classroom that travels to facilities and/or drilling rigs and trains rig crews on best practices for pumping equipment maintenance.

Severe cavitation will drastically decrease module life and will eventually lead to catastrophic pump failure. Along with downtime and repair costs, the failure of the drilling pump can also cause damage to the suction and discharge piping.

When a mud pump has entered full cavitation, rig crews and field service technicians will see the equipment shaking and hear the pump ‘knocking’… However, the process of cavitation starts long before audible signs reveal themselves – hence the name ‘the silent killer.’In 2017, a leading North American drilling contractor was encountering chronic mud system issues on multiple rigs. The contractor engaged in more than 25 premature module washes in one year and suffered a major power-end failure.

Gardner Denver’s engineering team spent time on the contractor’s rigs, observing the pumps during operation and surveying the mud system’s design and configuration.

The engineering team discovered that the suction systems were undersized, feed lines were too small and there was no dampening on the suction side of the pump.

Following the implementation of these recommendations, the contractor saw significant performance improvements from the drilling pumps. Consumables life was extended significantly, and module washes were reduced by nearly 85%.

Although pump age does not affect its susceptibility to cavitation, the age of the rig can. An older rig’s mud systems may not be equipped for the way pumps are run today – at maximum horsepower.

I’ve run into several instances of insufficient suction stabilization on rigs where a “standpipe” is installed off the suction manifold. The thought behind this design was to create a gas-over-fluid column for the reciprocating pump and eliminate cavitation.

When the standpipe is installed on the suction manifold’s deadhead side, there’s little opportunity to get fluid into all the cylinders to prevent cavitation. Also, the reciprocating pump and charge pump are not isolated.

Installing a suction stabilizer from the suction manifold port supports the manifold’s capacity to pull adequate fluid and eliminates the chance of manifold fluid deficiency, which ultimately prevents cavitation.

The suction stabilizer’s compressible feature is designed to absorb the negative energies and promote smooth fluid flow. As a result, pump isolation is achieved between the charge pump and the reciprocating pump.

The isolation eliminates pump chatter, and because the reciprocating pump’s negative energies never reach the charge pump, the pump’s expendable life is extended.

Investing in suction stabilizers will ensure your pumps operate consistently and efficiently. They can also prevent most challenges related to pressure surges or pulsations in the most difficult piping environments.

Have a pump that makes popping sounds, or sounds like it"s pumping marbles? If so, you may have a cavitation problem. Pump cavitation can cause a number of issues for your pumping system, including excess noise and energy usage, not to mention serious damage to the pump itself.

Simply defined, cavitation is the formation of bubbles or cavities in liquid, developed in areas of relatively low pressure around an impeller. The imploding or collapsing of these bubbles trigger intense shockwaves inside the pump, causing significant damage to the impeller and/or the pump housing.

When a pump is under low pressure or high vacuum conditions, suction cavitation occurs. If the pump is "starved" or is not receiving enough flow, bubbles or cavities will form at the eye of the impeller. As the bubbles carry over to the discharge side of the pump, the fluid conditions change, compressing the bubble into liquid and causing it to implode against the face of the impeller.

An impeller that has fallen victim to suction cavitation will have large chunks or very small bits of material missing, causing it to look like a sponge. Damage to the impeller appears around the eye of the impeller when suction cavitation is present.

When a pump"s discharge pressure is extremely high or runs at less than 10% of its best efficiency point (BEP), discharge cavitation occurs. The high discharge pressure makes it difficult for the fluid to flow out of the pump, so it circulates inside the pump. Liquid flows between the impeller and the housing at very high velocity, causing a vacuum at the housing wall and the formation of bubbles.

As with suction cavitation, the implosion of those bubbles triggers intense shockwaves, causing premature wear of the impeller tips and pump housing. In extreme cases, discharge cavitation can cause the impeller shaft to break.

Reference the pump"s curve - Use a pressure gauge and/or a flowmeter to understand where your pump is operating on the curve. Make sure it is running at its best efficiency point. Running the pump off its best efficiency point not only causes excess recirculation, expect excessive heat, radial loads, vibration, high seal temperatures, and lowered efficiency.

Re-evaluate pipe design - Ensure the path the liquid takes to get to and from your pump is ideal for the pump"s operating conditions. Designs with inverted “U”s on the suction side can trap air, while designs with a 90° immediately before the pump can cause turbulence inside the pump. Both result in suction problems and pump cavitation.

For more information about how to detect and prevent pump cavitation, be sure to check out our post: Technologies To Detect and Prevent Pump Cavitation.

Cavitation is a common problem in pumping systems, but with proper pump sizing, pipe design, and care of filters and strainers, damage to pumps and their impellers can be largely avoided.

Pump cavitation is the formation of bubbles or cavities in the liquid, developed in areas of relatively low pressure around the eye of an impeller. As the bubbles/cavities travel to the discharge side of the pump, moving to a high pressure area, the cavities implode. The imploding or collapsing of these bubbles triggers intense shockwaves inside the pump, causing damage to the impeller, vibration, and excess noise.

So what’s the cause of cavitation? What causes those cavities to develop? Generally, it’s the lack of NPSHA (Net Positive Suction Head Available). Essentially, the pump is being starved of fluid. (Read more about how this can happen: 9 System Changes That Screw With NPSH)

In a perfect world, your pump should be sized properly for the application and your piping design should match. However, that"s not always possible. If you’re dealing with pump cavitation, be aware that there is technology and techniques available to detect, monitor, and prevent pump cavitation. Here"s a list of options available.

With cavitation comes vibration. One of the newest technologies on the market is able to detect higher than normal vibration levels and alert operators to the pump"s upset conditions. The i-ALERT®2 is very cost-effective and can be installed on any pump (or rotating equipment).

One of the best things about this technology is that it has datalogging capability. So if your pump is cavitating or experiencing upset conditions when no one is around, or on another shift, you"ll know about it.

There are a number of things you can try to prevent cavitation. You can re-evaluate the piping design leading to the pump, ensure the pump is running at its best efficiency point, among others. But there is also technology available for cavitation prevention.

ITT"s PumpSmart automatically right-sizes your pump to your system. The video below illustrates how cavitation is prevented when tank level is low, and NPSHA is too low.

Installing gauges within your pump system is always a good monitoring option. You can reference the gauges to understand where the pump is on the curve. If it is starting to fall off track, your pump might be having a cavitation problem that requires investigation.

Clogged filters are a common cause of cavitation issues. As debris and particulates gather in the filter, NPSHA is reduced if the pump is not sized correctly.

Automatic self-cleaning filters like Eaton’s DCF and MCFseries are popular choices for processes where production can’t be stopped. Self-cleaning filters are great because, as the name suggests, they clean themselves. Once installed, they automatically filter any solids or debris from whatever liquid you are pumping. They are known to improve pump efficiency while requiring minimal operator intervention. Click to see a video on how self cleaning filters work.

A duplex strainer, also known as a twin-basket strainer, filters and removes large particles of dirt or debris from liquid pumping systems. They never require downtime for cleaning because a valve is placed between the two baskets, changing the flow of liquid to one strainer while the other is being cleaned.

An ounce of prevention is worth a pound of cure, as they say, so it’s best to properly size your pump from the beginning and ensure the piping design fits the application.

But we know that flows and processes change over time, creating an unintentional chain of events that can sometimes cause a cavitation problem where there wasn’t one before. Take advantage of the technology now available to properly manage and monitor the pumps in your facility.

Still not sure how to resolve a potential cavitation problem? Contact us! We’re happy to provide technical assistance to businesses in Wisconsin and Upper Michigan.

Many things go into getting the most life out of your mud pump and its components — all important to extend the usage of this vital piece of equipment on an HDD jobsite. Some of the most important key points are covered below.

The most important thing you can do is service your pump, per the manufacturer’s requirements. We get plenty of pumps in the shop for service work that look like they have been abused for years without having basic maintenance,  such as regular oil changes. You wouldn’t dream of treating your personal vehicle like that, so why would you treat your pump like that.

Check the oil daily and change the oil regularly. If you find water or drilling mud contamination in the oil, change the oil as soon as possible. Failure to do so will most likely leave you a substantial bill to rebuild the gear end, which could have been avoided if proper maintenance procedures would have been followed. Water in the oil does not allow the oil to perform correctly, which will burn up your gear end. Drilling mud in your gear end will act as a lapping compound and will wear out all of the bearing surfaces in your pump. Either way it will be costly. The main reasons for having water or drilling mud in the gear end of your pump is because your pony rod packing is failing and/or you have let your liners and pistons get severely worn. Indication of this is fluid that should be contained inside the fluid end of your pump is now moving past your piston and spraying into the cradle of the pump, which forces its way past the pony rod packing. Pony rod packing is meant to keep the oil in the gear end and the liner wash fluid out of the gear end. Even with brand new packing, you can have water or drilling fluid enter the gear end if it is sprayed with sufficient force, because a piston or liner is worn out.

There is also usually a valve on the inlet of the spray bar. This valve should be closed enough so that liner wash fluid does not spray all over the top of the pump and other components.

Liner wash fluid can be comprised of different fluids, but we recommend just using clean water. In extremely cold conditions, you can use RV antifreeze. The liner wash or rod wash system is usually a closed loop type of system, consisting of a tank, a small pump and a spray bar. The pump will move fluid from the tank through the spray bar, and onto the inside of the liner to cool the liner, preventing scorching. The fluid will then collect in the bottom of the cradle of the pump and drain back down into the collection tank below the cradle and repeat the cycle. It is important to have clean fluid no matter what fluid you use. If your liners are leaking and the tank is full of drilling fluid, you will not cool the liners properly — which will just make the situation worse. There is also usually a valve on the inlet of the spray bar. This valve should be closed enough so that liner wash fluid does not spray all over the top of the pump and other components. Ensure that the water is spraying inside the liner and that any overspray is not traveling out of the pump onto the ground or onto the pony rod packing where it could be pulled into the gear end. If the fluid is spraying out of the cradle area and falling onto the ground, it won’t be long before your liner wash tank is empty. It only takes a minute without the cooling fluid being sprayed before the liners become scorched. You will then need to replace the pistons and liners, which is an avoidable costly repair. Make a point to check the liner wash fluid level several times a day.

Drilling fluid — whether pumping drilling mud, straight water or some combination of fluid — needs to be clean. Clean meaning free of solids. If you are recycling your fluid, make sure you are using a quality mud recycling system and check the solids content often throughout the day to make sure the system is doing its job. A quality mud system being run correctly should be able to keep your solids content down to one quarter of 1 percent or lower. When filling your mud recycling system, be sure to screen the fluid coming into the tanks. If it is a mud recycling system, simply make sure the fluid is going over the scalping shaker with screens in the shaker. If using some other type of tank, use an inline filter or some other method of filtering. Pumping out of creeks, rivers, lakes and ponds can introduce plenty of solids into your tanks if you are not filtering this fluid. When obtaining water out of a fire hydrant, there can be a lot of sand in the line, so don’t assume it’s clean and ensure it’s filtered before use.

Cavitation is a whole other detailed discussion, but all triplex pumps have a minimum amount of suction pressure that is required to run properly. Make sure this suction pressure is maintained at all times or your pump may cavitate. If you run a pump that is cavitating, it will shorten the life of all fluid end expendables and, in severe cases, can lead to gear end and fluid end destruction. If the pump is experiencing cavitation issues, the problem must be identified and corrected immediately.

The long and the short of it is to use clean drilling fluid and you will extend the life of your pumps expendables and downhole tooling, and keep up with your maintenance on the gear end of your pump. Avoid pump cavitation at all times. Taking a few minutes a day to inspect and maintain your pump can save you downtime and costly repair bills.

Mud pump cavitation: Routineinspections, maintenance canprevent ‘silent killer’ from reducingrig efficiency, equipment reliabilityWith pumps being run at max horsepower at today’s well sites, best practicescan help contractors to avoid premature damage, extend consumables life

CAVITATION IS AN UNDESIR ABLE will see the equipment shaking and hear the a sealing surface. These unexpected failurescondition that causes a reduction in pump pump “knocking,” which typically sounds are expensive and lead to a minimum ofefficiency and excessive wear/damage to like marbles and stones being thrown around eight hours of rig downtime for modulepump components. Factors that can contrib- inside the equipment. However, the process replacement.ute to cavitation, such as fluid velocity and of cavitation starts long before audible signspressure, can sometimes be attributed to an reveal themselves – hence the name, “the PREVENTING CAVITATIONinadequate mud system design and/or the silent killer.” Stopping cavitation before it starts is adiminishing performance of the mud pump’s Mild cavitation begins to occur when matter of routine inspection and mainte-feed system. the mud pump is “starved” for fluid. While nance. For starters, install and tune high- Other factors contributing to cavitation the pump itself may not be making noise, speed pressure sensors on the mud suctioninclude: damage is still being done to the internal line to alarm if the pressure falls below • Improper sizing of charge pump; components of the fluid end. Mild cavita- 30 psi. Accelerometers can also be used to • Improper maintenance of charge pump tion damages the module, piston and valve detect slight changes in module performanceimpellers – worn impellers cause a reduction assembly. These hidden and intense shock and can be a good early warning systemof fluid pressure; waves generated by cavitation travel directly for cavitation prevention. Routinely conduct • Dirty or clogged charge pump feed and from the fluid end to the pump’s power end, visual inspections on the pump. While thedischarge lines; causing premature damage (vibration) to knocking may not be loud, if inspections are • Improper size of plumbing from charge the crosshead slides, thus passing onto the conducted on a regular basis, a field techni-pump to mud pump; shaft, bull gear and into the main bearings. cian will be able to detect moderate vibra- • Elevation changes and excessive elbows If not corrected, the vibrations caused by tions or knocking sounds. Finally, maintainin plumbing from mud tank to mud pump; cavitation will work their way directly to the gear end of the pump and check oil on aand these critical power end components, caus- regular basis. • Lack of/or inadequate suction and dis- ing premature failure, expensive downtime Gardner Denver offers Pump Universitycharge dampening. and repair costs. (PumpU), a mobile classroom that travels to Cavitation is an avoidable issue, but with- As referenced in Figures 1 and 2, the customers’ facilities and/or drilling rigs andout proper inspection of the feed system it process of cavitation causes numerous pits trains rig crews on how to properly maintaincan accelerate the wear of fluid end parts. Tis to form on the module’s internal surface. pumping equipment. Participants in thecan lead to expensive maintenance issues and Typically, cavitation pits result in a stress program have found that their improveda potentially catastrophic failure. concentration that results in a reduced maintenance skills have extended the life fatigue life of the module. Washouts are one of fluid end expendables on their sites, inMILD VS SEVERE CAVITATION of the leading causes of module failure and addition to lowering repair costs, decreasing When a mud pump has entered full cavita- take place when the high-pressure fluid cuts production costs and reducing workplacetion, rig crews and field service technicians through the module’s surface and damages hazards.

FIGURES 1 (LEFT) AND 2: Long-term, severe cavitation can cause surface pitting on a module crossbore and reduce the module’s fatigue life. Overtime, cavitation can lead to expensive maintenance issues and a potentially catastrophic failure.

RESULTS OF CAVITATION formance. Consumables life has been extend- The best way to prevent pump cavitation At the onset of cavitation, there will be ed significantly, and module washes have is to check the system’s feed lines and equip-reduced life in expendables and gradual wear been reduced by nearly 85%. This improved ment daily for any signs of abnormal noise oron the modules and power end. Severe cavi- performance has drastically reduced rig vibrations. Although it’s impractical to flushtation will drastically decrease module life downtime and has increased the operational system piping during drilling operations,and will eventually lead to catastrophic pump efficiency and customer satisfaction for the strainer screens should be checked daily tofailure, causing unwanted and costly down- drilling contractor. remove any debris or other flow restrictions.time. In addition, failure of the drilling pump Additionally pre-charge (centrifugal) pumpscan also cause damage to the suction and THE IMPACT OF TODAY’S DRILLING should be inspected regularly to ensure out-discharge piping. RIGS put flow and pressure is adequate. Following While pump age does not affect its sus- these simple steps will allow you to achieveCAVITATION IN THE FIELD ceptibility to cavitation, the rig’s age can. maximum performance from your pumping A leading North American drilling con- Oftentimes, a rig’s mud systems aren’t equipment and reduce unplanned equipmenttractor encountered chronic mud system equipped for the way pumps are run today – outages. DCissues on multiple rigs. The company expe- at maximum horsepower.rienced more than 25 premature modulewashes in one year and a major power-endfailure. Gardner Denver’s engineering teamwas called and spent time on the contractor’s When a mud pump has entered fullrigs observing the pumps during operation

technicians will see the equipment shakingtems were undersized, feed lines were toosmall and there was no dampening on thesuction side of the pump. There were also

and hear the pump ‘knocking’... However,issues with the feed line maintenance – linesweren’t cleaned out on a regular basis andsolids from the fluid had formed a thick cake

the process of cavitation starts long beforeon the bottom of the pipe, further reducingits diameter. The engineering team recom-mended increasing the diameter of the feed

audible signs reveal themselves – hence thelines and routine cleanings to improve flowand reduce the risk of cavitation. Following the implementation of these

Water hammer is a surge of pressure that can arise in pumping systems. The pressure is created when the pumping system undergoes an abrupt change in flow. The main causes of water hammering include opening and closing of valves, pump starts and stops, and separation and closure of the water columns. Due to these factors, the water column undergoes a change in momentum and this abrupt change can produce shock waves that travel back and forth within the system. Depending on the magnitude of the shock wave, physical damage in the system can be severe.

The phenomenon can be understood by an example in which water is pumped in a pipe that has valves on its both ends. The inlet valve is opened and the water column starts traveling towards the discharge valve. At this point, the discharge valve is closed instantly and the leading edge of the water column strikes the closed valve and begins to compress. A pressure wave (shock wave) begins to travel along the backstream (towards the inlet valve). The shock wave travels back and forth between the two valves until it finally diminishes due to friction losses. This water hammer shock wave is so fast that it can make a round trip between the two valves in less than half a second in the case of a 1000 feet pipe. The pressure created by this shock wave depends on the wave velocity (a), the velocity of water in the pipe (V), and the universal gravitational constant (g). Mathematically,

Cavitation is a common problem for centrifugal pumps. If you hear strange noises coming from your pump there’s a good chance cavitation is the issue. But what exactly is cavitation? And how can you go about preventing it? Read on to find out.

To understand how to prevent pump cavitation, it’s important to have a good understanding of what the problem is and how it arises. There are several types of cavitation which we’ll discuss below, but the process is similar.

Cavitation Defined: Cavitation is the formation and accumulation of bubbles around a pump impeller. This tends to form in liquids of any viscosity as they are being transported through and around a pump system. When each of these tiny bubbles collapses or bursts, it creates a high energy shock wave inside the liquid. Imagine throwing a stone into a pond. The circular ripples which are created in this process are similar to cavitation bubbles exploding. The difference here is that due to the sheer number of bubbles creating these shock waves, the impeller and other pump components can be eroded over time.

1. Vaporisation: Also known as inadequate NPSHa cavitation or ‘classic cavitation’, this is the most common form. It occurs when a centrifugal pump imparts velocity on a liquid as it passes through the eye of the impeller. If the impeller isn’t functioning correctly, some of the liquid may be boiled quickly (vaporised), creating those tiny shock waves we discussed above.

2. Turbulence: If parts of the system - pipes, valves, filters, elbows etc. - are inadequate for the amount or type of liquid you are pumping, this can create vortexes in said liquid. In essence, this leads to the liquid becoming turbulent and experiencing pressure differences throughout. These differences can erode solid materials over time, in the same way that a river erodes the ground.

3. Vane Syndrome: Also known as ‘vane passing syndrome’, this type of cavitation occurs when either the impeller used has too large a diameter, or the housing has too thick a coating. Either or both of these creates less space within the housing itself. When this happens, the small amount of free space creates increased velocity in the liquid, which in turn leads to lower pressure. This lower pressure heats the liquid, creating cavitation bubbles.

4. Internal Re-circulation: In this instance, the pump cannot discharge at the proper rate and so the liquid is re-circulated around the impeller. The liquid travels through low and high pressure zones resulting in heat and high velocity. The end result? Vaporised bubbles. Common cause for this, is when a discharge valve has been close while the pump is running.

5. Air Aspiration Cavitation: Another common form. Air can sometimes be sucked into a pump through failing valves or other weak points such as joint rings. Once inside, the air has nowhere to go but along for the ride. As the liquid is swished around, the air forms bubbles which then gets popped under pressure by the impeller.

As with any structural or mechanical issue, it’s important to have a reliable maintenance process. Checking on components and the performance of your pump is a great way to identify early warning signs of cavitation.

Decreased Flow or Pressure: If your pump is not producing the amount of flow as stated by the manufacturer, this could mean that cavitation is occurring.

Erratic Power Consumption: If bubbles are forming around the impeller, or the impeller itself has already started to fail, you may notice that your pump requires more power than usual to transport its media. You may also notice fluctuations of power use as suction rises and falls depending on how the impeller is performing.

Noise: If there’s one sign of cavitation, it’s noise. When the bubbles implode they can make a series of bubbling, cracking, sounds. Alternatively, it might sound like tiny marbles or ball bearings rattling around inside the impeller housing.

In addition to the above, operating a centrifugal pump to the far right of the BEP (or off the end of curve) can cause cavitation. When the flow increases, Net Positive Suction Head required (NPSHr) also increases and when the NPSHr exceeds the Net Positive Suction Head available (NPSHa), cavitation occurs.

Now that you know what to look for, and understand the different types of cavitation you might encounter, you can formulate a plan to prevent cavitation, saving large amounts in maintenance and replacement parts.

Ensure you are not exceeding your pump’s manufacturer performance guidelines. A pump system which is pushed too hard will inevitably fail. Such as running the pump off the end of the performance curve. It is best to increase

Preventing vane passing or vane syndrome cavitation is relatively easy. Ensure that the free space between your impeller and its housing is 4% of your impeller’s diameter or more. Any less and cavitation will begin.

This can be a tricky one to prevent. Even the smallest amount of air being sucked into the system could over time cause cavitation. Going over your installation with a fine tooth comb to make sure all joints and connections are sealed properly, is the best approach.

By preventing cavitation, you will significantly increase the efficiency and lifespan of your pump. Remember, prevention is worth a thousand cures, so take the time to carry out a thorough maintenance program and it will save you in the long run.

If you need any help identifying which components you need for your system, don’t hesitate to contact one of our pump experts, be assured with the best advice from Global Pumps, Australia"s Most Trusted Industrial Pump Provider.

Detect a failing pump before it becomes a major problem: Learn about Condition Monitoring for Pumps and other Rotating Equipment. Global Pumps provide the latest remote condition monitoring technology available in Australia.

From a technical standpoint, cavitation occurs when the absolute pressure at the eye of the impeller reaches the vapor pressure. At this pressure, bubbles or “cavities” form in the liquid. As the bubbles move from the low-pressure area near the impeller toward the high-pressure area surrounding the pump discharge, they implode.

These little implosions of collapsing bubbles cause loud popping noises, which operators can hear externally while their pumps are operating. Internally, this repeated popping creates shockwaves that can result in considerable physical damage. Over time, cavitation can destroy impellers and pump housing, result in seal and bearing failure, impact flow and pressure rates, and consume significantly more power.

Depending on your application and setup, you could be experiencing suction cavitation or discharge cavitation. In either case, the end result can be very damaging — and very costly — to repair or replace.

Did you know pump vibration levels are an excellent diagnostic tool?Click here to view the GIW® Minerals chart of Pump Vibration Levels to see how your pump is holding up.

As far as general maintenance is concerned, it’s important to ensure your pipe and filters are free of blockages and that your pump is operating at its most efficient point on its pump curve. However, the most effective form of prevention is to select the right pump from the start. Find a centrifugal pump that operates far below the required critical suction pressure or net positive suction head (NPSH). It’s also important that your system’s flow in and out of the pump doesn’t exceed the pump’s capabilities.

By selecting a pump that’s an ideal fit for your pressure, flow, and overall application, cavitation should never be a concern. If you fear that cavitation is affecting your operations, it’s a good idea to get in touch with an expert who can help you diagnose precisely why. With the right pump — and the right partner — you can avoid this costly and catastrophic problem!

The GIW Tech Services slurry pump experts can ensure you have the right pump for the job so cavitation doesn’t harm your system — or your bottom line. Contact us today to see what our highly experienced crew can do for you.

Cavitation is not a new phenomenon that impacts a pump system, but it is an issue that occurs far too often. It occurs when air bubbles are generated inside a pump because of the partial pressure drop of the flowing liquid, resulting in a tiny air bubble. The air bubbles move, pressure is increased and the air bubbles instantaneously implode. The collapse of the vapor bubbles erode the impeller surface and pump casing. If strong cavitation occurs at the pump inlet, pump performance decreases, which can lead to premature pumping failure.

Pump cavitation is most commonly found with centrifugal pumps due to NPSH requirements but can also be found within positive displacement pumps.  This can occur when the temperature and pressure of the liquid at the suction of the impeller equals the vapor pressure. It can happen at low pressures and normal operating temperatures. It is extremely important to understand the different types of pump cavitation and steps that should be taken to prevent it at all costs.

Air is unpredictable and can sometimes be sucked into a pump through failing valves or other weak components. The air will eventually start to form bubbles that then gets popped under pressure by the pump impeller. Some tips to prevent this type of cavitation include:

This type of cavitation prevents the pump from discharging at your desired rate, meaning that the liquid will now re-circulate around the impeller. The liquid travels through low- and high-pressure zones resulting in heat and high velocity, which in turn creates vaporized bubbles. Some tips to prevent this type of cavitation include:

Any kind of turbulence within a pump is never a good sign. If the system has been designed with parts that are inadequate for the amount of liquid you’re trying to pump, it will in turn create vortexes in said liquid. These vortexes will become turbulent and experience major pressure differences throughout the system. This all leads to erosion of solid materials over time. Some tips to eliminate turbulence in your system include:

This cavitation occurs if the pumps impeller uses too large of a diameter or the housing coat is too thick. Both problems here create less space throughout the pump housing. The pump will then have an increased velocity in the liquid from the small amount of free space available, which in turn leads to lower overall pressure. This is where you will see cavitation bubbles because the lower pressure is now heating the liquid. Some tips to prevent this cavitation include:

Also called inadequate NPSHa (Net Positive Suction Head Available) cavitation – this is the most common form. This type of cavitation occurs when a centrifugal pump imparts velocity on a liquid as it passes through the eye of the impeller. Liquid gets vaporized quickly if the impeller is not functioning correctly, which then creates tiny shock waves. Some tips to prevent cavitation due to vaporization include:

Regularly checking on the performance of your pump and maintaining a reliable maintenance process is the best way to identify early warning signs of cavitation. Some common symptoms of cavitation include: Decreased flow or pressure, unexpected vibrations, seal/bearing failure, noise, erratic power consumption and impeller erosion.

You will significantly increase the efficiency and lifespan of your pump by taking the necessary steps to prevent pump cavitation. Detect a failing pump before it becomes a major problem. If you need any help identifying which components you need for your system, don’t hesitate to contact one of our pump experts here.

The only way to avoid cavitation is to properly design the system with cavitation prevention in mind – plain and simple. With decades of experience in the industrial pump market space, Anderson Process is uniquely positioned to deliver superior system designs for even the most complex liquid process equipment challenges. Pump cavitation isn’t going anywhere – Contact us today to start the process of designing the best suited system for your application.

Centrifugal pumps are one of the most common types used in industry. It’s a device that pumps mud for solids control equipment. Figure 1 shows a generic, single stage centrifugal pump and Figure 2 illustrates a multistage centrifugal pump.

These pumps can utilize either open or closed impellers and may have single or multiple stage designs. Centrifugal pumps utilize Bernoulli’s principle to develop pressure (see Bernoulli’s Principle Explained below) by first increasing the fluid velocity inside an impeller and then decreasing the fluid velocity in the discharge nozzle. These pumps consist of a shaft with bearings for support and an impeller as well as a pump casing. To prevent leakage from the pump casing to the atmosphere, most pumps employ packing, single or dual mechanical shaft seals.

Centrifugal pump performance is typically presented graphically with a series of curves similar to the group shown in Figure 3. The manufacturer usually provides curves that describe how flow, differential head, net positive head required, and efficiency change with pump flow.

B. If a centrifugal pump has more than one impeller inside of it is called a multistage pump. If it has, for example five impellers in it, then it is a five stage pump

Centrifugal pumps may be operated in a series or parallel (see Figure 1.4) configuration. When operating pumps in series, the pressure is increased across each pump, but the flow through each pump is identical (minus any minor flow losses due to leakage). When operating in parallel, the pressure rise on each pump is identical, but the total flow is increased. However, the overall flow is not doubled with two pumps operating in parallel because of “system head” or pressure.

The easiest way to understand system head is to remember that the discharge pipe size stays the same diameter and therefore tends to restrict the higher flow generated by two pumps operating in parallel. This bottleneck effect means that two pumps operating in parallel will always deliver less than twice the flow that one pump can deliver.

The last rule is the reason centrifugal pumps and centrifugal compressors are able to convert a high velocity flow from a rotating impeller into high pressure.

Cavitation is a serious operating condition that sounds like gravel is passing through a pump. This unique “gravelly” sound associated with cavitation is due to the fact that vapor cavities or bubbles are continually forming and then collapsing in the pump’s inlet. If cavitation is not addressed and corrected quickly, the internal components of a centrifugal or positive displacement pump may be seriously damaged.

Cavitation is caused by either 1) operating a pump too close to the boiling point of the liquid at its suction or 2) by trying to pump more than a pump is designed to handle. Pump designers use a term called net positive suction head (NPSH) to determine whether there is enough suction pressure to prevent cavitation. Typical net positive suction head requirements can be seen in Figure 1.3 (Centrifugal Pump Curves), where they are depicted as dotted vertical lines, labeled: 2′, 2.5′, 3′, 3.5′, 4′, 4.5′. 2′ means that at this particular flow, two feet of liquid suction head is required to prevent cavitation, 2.5′ means that at this particular flow, two and a half feet of liquid suction head is required to prevent cavitation, and so forth.

As an operator, you simply need to remember that the higher the flow rate out of a pump the greater the suction pressure must be to insure that cavitation does not take place. An operator is in the position to control some parameters that will affect NPSHA. For example, if the pump is taking suction from a tower or tank, either the liquid level or the pressure can be increased as a means of stopping or reducing pump cavitation. Reducing the pump flow can have a positive effect on the NPSHA as well and may stop cavitation.

When you detect a pump problem and decide to act, always list the symptom or symptoms that were noted on the work request, such as not enough pressure or flow, a seal is leaking, the drive motor is tripping off line, there is high vibration on the pump, etc. Do not list what should be done about the suspected problem on the work request. Comments such as: fix the pump, change the pump, replace the pump, etc. are not helpful to the maintenance planner. Comments such as: Seized, vibrating, low pressure, tripping offline, etc. are helpful. Always, allow the maintenance crew to investigate the situation and perform what they think are the necessary corrections, adjustments or repairs.

Pump cavitation is one of the most searched topics on fluid power, which is justified, because cavitation is unfortunately an all-too-common cause of pump failure on mobile equipment. Liquids are able to hold dissolved gasses in solution, and the gas saturation level within any liquid is dependent upon the pressure, the temperature and the type of liquid itself, among other things. Cavitation is literally the bubbles spontaneously formed during conditions that prevent the liquid from holding that gas in saturation, such as a drop in relative pressure.

The best example to explain the gas saturation concept and the cavitation principle can be found for a couple bucks at the convenience store—a trusty bottle of soda pop. To ensure the pop is fizzy when it hits your lips, carbon dioxide is super-saturated within the delicious beverage, and pressure maintains that artificial level of fizz until you open the bottle. Upon opening the bottle, you can see cavitation at work, as bubbles seem to form out of nowhere, and other than the fact hydraulic fluid simply has common air dissolved within itself, the principle is the same.

The problem with my example is in trying to translate some harmless bubbles that tickle your taste buds into the damage that can eat away at solid metal. Cavitation bubbles themselves do little damage just floating around in your hydraulic oil, but it’s when the bubbles reach the pressure side of your pump that they do their harm.

Cavitation bubbles would rather form within the imperfections on the surface of the metal parts of your pump, such as the lens plate of a piston pump, or the gear of a gear pump, rather than just popping into existence in the middle of the fluid. The damage from cavitation occurs when the bubbles make their way around to the pressure size of the pump, where they implode under pressure, creating super-hot jets of fluid that pierce the bubble. Because the bubbles are most often located on metal parts, these little implosion jets heat up the surface of the metal, and you end up with little pits that destroy the pump’s efficiency until it just can’t pump at all.

Cavitation is difficult to detect on mobile equipment because of the noise of the engine or the machine itself, but if it ever sounds like someone threw a bag of marbles into your pump, it’s probably a result of cavitation. However, a diesel engine knock sounds not-unlike cavitation, making it difficult to distinguish cavitation noise, especially from inside the cab. Also, cavitation can be unnoticeable even in quiet ambient conditions if it’s not severe, and damage may not be discovered until the pump fails.

Because cavitation is bad, and cannot be corrected or repaired by your dentist, I’m going to give you seven tips on how to avoid cavitation in your hydraulic system. If these tips are heeded, I promise you cavitation will be a thing of your past, like your plaid grunge look or that weekend in Bangkok.

1 – Don’t use a suction strainer. Suction strainers are installed in the reservoir on the suction line of the hydraulic pump. They are intended to protect the pump from ingesting dirt and filth, which should subsequently protect the pump. However, think about the method in which a suction strainer prevents dirt from entering the pump; it collects it across its flow path. Larger particles and other junk get trapped in the suction strainer, but over time it gets clogged.

Most often, maintenance personnel don’t know the power unit even has a suction strainer, so it can get overlooked during routine maintenance, especially because most mobile reservoirs have no clean-out panel. Don’t get me wrong, it could take an easy decade to clog a suction filter, but when it does clog, it will cause slowly increasing levels of cavitation. You might as well have a clamp over the suction hose that you tighten at regular intervals. The biggest problem I have with suction strainers is that they’re redundant anyway if your hydraulic system is designed and maintained well to begin with.

2 – Ensure pumps have flooded suction. A pump can create vacuum at the inlet port to pull up fluid a short distance, but excessive pump head height will cause cavitation. A flooded suction condition uses the force of gravity and atmospheric pressure to push fluid into the pump, rather than the pump having to draw it in. A flooded suction is easy for PTO-mounted pumps because the pumps sit so low in the chassis, but with pumps driven off the engine, you may want to consider mounting your tank high on the machine to compensate for the long run to the front of the truck. With a pump mounted below or to the side of the reservoir, cavitation is nearly impossible unless something catastrophic occurs, like a rag being thrown into the reservoir and blocking the suction line.

3 – Don’t leave rags in the reservoir. It may sound ridiculous for me to offer that as a suggestion, but every hydraulic technician worth their weight in oil counts the number of rags they show up to and leave a job with. The best tools for cleaning out reservoirs are rags, and you will have to trust me when I say that it’s more common than you’d think to leave them in the reservoir. And if you leave a rag in the reservoir, it will most definitely find its way to the suction tube of the pump(s), starving them and causing cavitation.

While we’re at it, be considerate of more than just rags when maintaining a hydraulic machine. I’ve heard of tools, cell phones and dead animals finding their way into reservoirs, not all of which can clog a suction strainer or pump inlet, but their existence there is cause for concern. For a possum to make its way into a tank for a nap, a cover must have been left off, and this lack of consideration for the hydraulic system is unacceptable. Reservoirs are buttoned up for a reason, so I recommend keeping it that way if you care about the health of your machine.

4 – Properly size inlet plumbing. The recommended maximum velocity for suction lines is only a few feet per second, and because the relative action of fluid being “pulled” into the pump already causes a drop in suction pressure, the condition of sucking too much fluid through a small straw will cause cavitation. By simply sizing suction plumbing large enough, especially if you’re running a pump far from the reservoir, you can reduce the chance of cavitation.

5 – Use high quality hydraulic fluid. The quality of hydraulic fluid is often overlooked, and unfortunately, the good stuff is very expensive. Synthetic hydraulic fluid has many properties making it superior to standard dino oil, which has limited capacity to work well outside a narrow window of operating conditions. Speaking on viscosity alone, thicker oil is harder to pump and is more prone to cavitation.

Problems occur during machine start-up, such as on a cold morning, when standard hydraulic fluid is rather thick, making it difficult to pump. If cold and thick oil is not given time to warm before the machine is run at full pressure, cavitation could result. Even if the period of cavitation is short, because oil can heat quickly, the damage can accumulate during every cold start. By switching to synthetic fluid with a high viscosity index, you help ensure cold starts provide little drama. Viscosity index is the quality of oil to maintain its tested viscosity over a wide temperature range, and the bigger the number, the better. So even with a 46 cSt oil which could be prone to cavitating a pump at 20° below if it were normal oil, a high quality oil will still be relatively thin and easy to pump.

6 – Heat your hydraulic oil. Odd as it may sound, because heating oil in mobile machinery is rare, heating the oil before machine start-up can also help prevent cavitation due to cold-related high-viscosity. You wouldn’t fire up your rig and drive off without letting the engine warm up, so the same consideration should be paid to the hydraulic system. Oil doesn’t need much time to come up to temperature in most cases, so just running the pump to circulate oil through the system and operating some low pressure functions could heat up the oil before the serious work begins.

7 – Keep your oil dry. This recommendation comes from a specific example of pump cavitation, which could have been prevented by considering a few of these tips. This brutal past winter broke down more than one hydraulic machine, and this particular example occurred on a half-dozen machines powered by a 12 VDC electric power unit. Excessive water saturation within these power units caused ice to form on the suction strainers, both cavitating the pumps and imploding the strainers.

By following these tips, your chances of experiencing pump cavitation are slim to none. Mobile hydraulic systems already have so much to worry about; creating conditions conducive to cavitation should not be one of them.