what is hydraulic pump cavitation supplier

The second leading cause of hydraulic pump failure, behind contamination, is cavitation. Cavitation is a condition that can also potentially damage or compromise your hydraulic system. For this reason, understanding cavitation, its symptoms, and methods of prevention are critical to the efficiency and overall health of not just your hydraulic pump, but your hydraulic system as a whole.

The product of excessive vacuum conditions created at the hydraulic pump’s inlet (supply side), cavitation is the formation, and collapse of vapors within a hydraulic pump. High vacuum creates vapor bubbles within the oil, which are carried to the discharge (pressure) side. These bubbles then collapse, thus cavitation.

This type of hydraulic pump failure is caused by poor plumbing, flow restrictions, or high oil viscosity; however, the leading cause of cavitation is poor plumbing. Poor plumbing is the result of incorrectly sized hose or fittings and or an indirect (not straight or vertical) path from the pump to the reservoir. Flow restrictions, for example, include buildup in the strainer or the use of an incorrect length of hose or a valve that is not fully open. Lastly, high oil viscosity—or oil that is too viscous—will not flow easily to the pump. Oil viscosity must be appropriate for the climate and application in which the hydraulic pump is being used.

The greatest damage caused by cavitation results from the excessive heat generated as the vapor bubbles collapse under the pressure at the pump outlet or discharge side. On the discharge side, these vapor bubbles collapse as the pressure causes the gases to return to a liquid state. The collapses of these bubbles result in violent implosions, drawing surrounding material, or debris, into the collapse. The temperature at the point of implosion can exceed 5,000° F. Keep in mind that in order for these implosions to happen, there must be high vacuum at the inlet and high pressure at the outlet.

Without a pressure condition at the outlet, or discharge side, these vapors merely form voids in the oil that reduce lubrication effectiveness. This results in friction and wear, which while seemingly mild compared to the excessive heat and violent implosions, can become detrimental over time.

Cavitation is usually recognized by sound. The pump will either produce a “whining” sound (more mild conditions) or a “rattling” sound (from intense implosions) that can sound like marbles in a can. If you’re hearing either of these sounds, you first need to determine the source. Just because you hear one of these two sounds doesn’t guarantee that your hydraulic pump is the culprit.

To isolate the pump from the power take-off (PTO) to confirm the source, remove the bolts that connect the two components and detach the pump from the PTO. Next, run the PTO with no pump and see if the sound is still present. If not, it is safe to assume your hydraulic pump is the problem.

Another sign you may be experiencing cavitation is physical evidence. As part of your general maintenance, you should be inspecting and replacing the hydraulic oil filter"s elements at regular intervals based on the duty cycle of the application and how often it is used. If at any time during the inspection and replacement of these elements you find metallic debris, it could be a sign that you’re experiencing cavitation in the pump.

The easiest way to determine the health of your complete hydraulic circuit is to check the filter. Every system should have a hydraulic oil filter somewhere in-line. Return line filters should be plumbed in the, you guessed it, return line from the actuator back to tank—as close to the tank as possible. As mentioned earlier, this filter will have elements that should be replaced at regular intervals. If you find metallic debris, your pump could be experiencing cavitation. You’ll then need to flush the entire system and remove the pump for inspection.

Conversely, if you’ve already determined the pump to be damaged, you should remove the filter element, cut it open, and inspect it. If you find a lot of metal, you’ll need to flush the entire system and keep an eye on the other components that may be compromised as a result.

Once cavitation has been detected within the hydraulic pump, you’ll need to determine the exact cause of cavitation. If you don’t, cavitation can result in pump failure and compromise additional components—potentially costing you your system.

Since the pump is fed via gravity and atmospheric pressure, the path between the reservoir and the pump should be as vertical and straight as possible. This means that the pump should be located as close to the reservoir as is practical with no 90-degree fittings or unnecessary bends in the supply hose. Whenever possible, be sure to locate the reservoir above the pump and have the largest supply ports in the reservoir as well. And don"t forget, ensure the reservoir has a proper breather cap or is pressurized (3–5 PSI), either with an air system or pressure breather cap.

Be sure the supply line shut-off valve (if equipped) is fully open with no restrictions. This should be a “full-flow” ball valve with the same inside diameter (i.d.) as the supply hose. If feasible, locate a vacuum gauge that can be T’d into the supply line and plumb it at the pump inlet port. Activate the PTO and operate a hydraulic function while monitoring the gauge. If it reads >5 in. Hg, shut it off, and resume your inspection.

If a strainer is present in the reservoir, inspect it, and remove any gunk or buildup that may be restricting supply flow. Next, check the inlet (suction) hose for any visible layline (descriptive markings on the hose). The industry standard “suction” hose nomenclature will read 100R4, or possibly SAER4. This will indicate the hose has an inner bladder that’s been vulcanized to a heavy spiral wire.

A hose with an inner bladder vulcanized to a heavy spiral is designed to withstand vacuum conditions as opposed to outward pressure. The layline will also denote the size of the hose (i.d.). You can use Muncie Power’s PPC-1 hydraulic hose calculator to determine the optimal diameter for your particular application based on operating flows.

Another consideration, in regards to the inlet plumbing, is laminar flow. To reduce noise and turbulence at the pump inlet, the length of the supply hose should be at least 10 times its diameter. This means that any type of shut-off valve or strainer at the reservoir should be at least 10 diameters from the pump inlet. A flared, flange-style fitting at the pump inlet can also reduce pump noise by at least 50 percent compared to a SAE, JIC, or NPT fitting.

Selecting the proper viscosity of hydraulic fluid for your climate and application is also critical. Oil that is too viscous will not flow as easily to the pump. Consult your local hydraulic oil supplier for help selecting the optimal fluid viscosity.

By maintaining a regular maintenance schedule, remaining vigilant for any signs or symptoms, and taking preventative measures, the good news is that you should be able to prevent cavitation and experience efficient operation for the duration of your pump’s lifespan.

Poor plumbing is the leading cause of cavitation and can be prevented by selecting a properly sized hose, choosing the appropriate fittings, ensuring the most direct, straight routing from the pump to the reservoir, etc.

Since joining the company in 2007, Ben Gillum has served in various capacities including shipping and receiving clerk, CS assembly, customer service manager, product application specialist, training and education assistant manager, and warranty and returns manager.

Hydraulic pumps are used in various industries to pump liquid, fluid, and gas. Although this equipment features robust construction, it may fail at times due to various issues. Cavitation is one of the serious issues faced by this equipment. Like all other technical issues, right planning as well as troubleshooting will help avoid this issue to a large extent. What is pump cavitation and how to troubleshoot these it?

It is seen that many times, Strong cavitation that occurs at the impeller inlet may lead to pump failure. Pump cavitation usually affects centrifugal pumps, which may experience several working troubles. At times, submersible pumps may also be affected by pump cavitation.

Non-inertial Cavitation: This type of cavitation is initiated when a bubble in a fluid undergoes shape alterations due to an acoustic field or some other type of energy input.

Suction Cavitation: This cavitation is brought by high vacuum or low-pressure conditions that may affect the flow. These conditions will reduce the flow, and bubbles will be formed near the impeller eye. As these bubbles move towards the pump’s discharge end, they are compressed into liquid, and they will implode against the edge of the impeller.

Discharge Cavitation: Here, cavitation occurs when the pump’s discharge pressure becomes abnormally high, which in turn affects its efficiency. High discharge pressure will alter the flow of fluid, which leads to its recirculation inside the pump. The liquid will get stuck in a pattern between the housing, as well as the impeller, thereby creating a vacuum. This vacuum creates air bubbles, which will collapse and damage the impeller.

Sound: The pump affected by cavitation will produce a marble, rock, or gravel type of sound when in motion. The sound will begin as a small disturbance and its intensity will increase as the material slowly chips away from the surface of the pump.

Metallic Debris: If during the maintenance, you find metallic debris on the filter of the hydraulic pump then it may be a symptom of cavitation. One of the easiest ways to confirm it is to check the filter. If any debris is found, you should clean the entire system, and thoroughly inspect the pump.

Damage: This is one of the most obvious symptoms of cavitation. If you already know that the pump is damaged, you need to remove its filter, open, and inspect it thoroughly. If you find a lot of metal inside the filter, then flush the entire system, and check for damages in other parts, too.

If you notice any of the above-discussed symptoms, the next step would be to identify the causes, and rectify the changes in industrial pumps, otherwise, it may affect other components, too.

Avoid using suction strainers: These are designed to inhibit the ingestion of grime and dirt. However, these strainers do not succeed in their purpose, because they are not designed to entrap large particles. These large particles may get deposited in the flow path, thereby affecting the flow of fluid. The deposition also creates pressure, and produces bubbles, which may lead to cavitation.

Clean the reservoir: A dirty reservoir is one of the most common causes of cavitation. Various types of small and large objects may block the suction tube, and create pressure, thereby causing cavitation.

Use properly sized components: This is one of the important factors of cavitation prevention. If the inlet plumbing is too large, there will be too much liquid flow, which may trigger cavitation. Hence, check with the pump manufacturer to ensure that properly sized components are being used in the pump.

In addition to these preventive steps, you must source hydraulic pumps from a trusted manufacturer or supplier. JM Industrial is one of the industry-leading provider of unused and used industrial process equipment from industry-leading brands. These pumps can be availed at cost-effective prices.

Two leading causes why hydraulic pumps usually fail are: (1) contamination and (2) cavitation. In order to prevent any potential damage to your entire hydraulic system, it’s imperative to understand cavitation, the indications or symptoms from your system it is occurring, as well as the preventive measures.

How does cavitation happen exactly? It starts when vapor bubbles in the oil are created due to high vacuum. When these vapor bubbles are carried and collapsed on the pump outlet (discharge side), cavitation happens.

Make Sure Oil flow Paths are Straight – Hydraulic pumps are being supplied via atmospheric pressure and gravity, so it’s ideal to place the reservoir above it. Make sure that the path is as straight and vertical as possible. Keep an eye on bent or twisted supply hose.

Make Sure the Valve is Fully Open – If the supply line shut-off valve is equipped, make sure that it’s fully open without restrictions. This must be a “full flow” ball valve with the same inside diameter as your supply hose.

Check Laminar Flow – If you’re hearing turbulence or noise in pump inlet, make sure that the supply hose length is the correct ratio to its diameter. A flange-style, flared fitting in the pump inlet can also help in eliminating pump noise.

Check Proper Viscosity – It"s important to choose the hydraulic fluid with appropriate viscosity for your application and climate. Consult with your supplier for professional help in choosing the optimal fluid viscosity.

With regular maintenance, keeping an eye on symptoms, and taking preventive measures, you’d be able to avoid cavitation and expect efficient operation from your hydraulic pumps.

Cavitation is the second leading hydraulic pump failure cause, behind contamination. As this can potentially cause damage and compromise your hydraulic system, it is important to understand what it is as well as its symptoms.

Cavitation is the product of excessive vacuum conditions created at the hydraulic pump’s inlet. This causes high vacuums to create vapour bubbles within the hydraulic oil, these are then carried to the discharge side before they then collapse - causing cavitation to occur.

These high vacuums and cavitation are often caused by poor plumbing, flow restrictions, or high oil viscosity. Poor plumbing is often the main cause of this and is due to an incorrectly sized hose or fittings and/or an indirect (not straight or vertical) path from the pump to the reservoir.

The easiest way to identify cavitation is through noise. The hydraulic pump will either emit a “whining” or a “rattling” sound. If you hear either or both of these sounds you will need to isolate the pump to make sure that this is where it is coming from.

As part of your general maintenance, you should be inspecting and replacing the hydraulic oil filter"s elements at regular intervals based on the duty cycle of the application and how often it is used. If when replacing the filter you come to find metallic debris this could be a sign that cavitation is occurring within the pump. In this case it is best to flush the entire system and detach the pump for closer inspection.

When replacing the filter you find that it is damaged, this could be due to cavitation. To find out if this is the case, remove the filter element of the hydraulic system and inspect for metallic debris. If there is some present then flush the system to prevent damage being caused elsewhere. Now that you have identified cavitation has been occurring within the hydraulic pump, you’ll need to determine the exact cause of cavitation.

As there are so many causes and damage results from cavitation, it is important to regularly check your hydraulic pump for signs of cavitation. By simply checking the pump and filter you can prevent your hydraulic system from failing when you most need it.

Hydraulic pumps come in a variety of sizes, styles and fuel types, so if you are having issues with your pump browse our great range for a replacement or get in contact with our expert team for advice on any hydraulic issue.

Although cavitation can occur anywhere in a hydraulic system, it commonly occurs within the suction line of a pump. This will cause excessive noise in the pump – generally a high pitched “whining” sound. However, this excessive noise is only the tip of the iceberg! The real result of this phenomenon is severe pump damage and a decrease in pump life. I have personally seen many instances where a customer was replacing pumps frequently, thinking they were receiving defective pumps from their vendor. In reality, the pump failures were not due to poor pump quality – the failures were occurring because of cavitation.

Simply put, cavitation is the formation of vapor cavities in the hydraulic oil. In hydraulic pumps, cavitation will occur any time the pump is attempting to deliver more oil than it receives into the suction (inlet) line. This is commonly referred to as “starvation” and results from a partial vacuum in the suction line. To fully illustrate what is happening when this occurs, we need to discuss vapor pressure. Vapor pressure is the pressure below which a liquid at a given temperature will become a gas, and this pressure varies significantly depending on the liquid. Generally, as the temperature of a liquid rises, the vapor pressure will proportionally increase. Likewise, as the temperature decreases, the vapor pressure will decrease. Most of us know that water will boil (turn to vapor) at 212°F (100°C) at 14.7 PSI (atmospheric pressure at sea level). In other words, the vapor pressure of water at 212°F is 14.7 PSI. If the pressure is reduced, the temperature at which the water boils will be reduced. If the temperature is lowered, the vapor pressure will decrease. In fact, water will boil at room temperature if the pressure is sufficiently reduced! The same principle applies to hydraulic oil, although the vapor pressure will be somewhat different than that of water. The vapor pressure of hydraulic oil is somewhere between 2 and 3 PSI at normal temperatures. In ideal conditions, the pressure in the suction line of the pump will be around 14.7 PSI at sea level. Of course, this pressure decreases with altitude, but sufficient pressure will normally be maintained in the suction line to prevent cavitation of the oil. However, if the pressure in the suction line of the pump is sufficiently reduced to the vapor pressure of the oil, vapor cavities will form. As the oil passes from the suction line to the outlet of the pump, the pressure will increase and the vapor cavities will implode violently. These extremely powerful implosions will cause erosion and premature failure of the pump components. In fact, a brand-new pump can be destroyed in a matter of minutes if the cavitation is severe enough. The picture below shows a rotor and cam ring from a vane pump that had failed due to severe cavitation.

In my 35-plus years of troubleshooting hydraulic components, this is the worst case of cavitation damage I have ever seen. In addition to the usual erosion of the parts, the vanes were actually fused to the rotor slots! Although this is an extreme example, it shows the potential damage to a pump due to cavitation. The good news is that cavitation is preventable and we will look at several conditions that can trigger this phenomenon.

Pump cavitation is always a serious concern in the fluid power industry that leads to pump failure/breakdown. Cavitation occurs when liquid/oil contains dissolved gas and collapse during machine operation. In short, cavitation is the formation and collapse of air cavities in the liquid. The factors that affect air bubble formation are system pressure, temperature, fluid type, and external/internal leakages. This article will highlight all important facts about pump cavitation that includes its symptoms, method of prevention, and more.

What is pump cavitation? As we mentioned earlier, cavitation is the process of forming an air bubble in the hydraulic fluid. The primary reason for this issue is the partial pressure drop at the suction side of the pump caused while pumping fluid from the reservoir to the hydraulic pump. This pressure various will lead to the creation of a cavity inside the hydraulic pump. The produced air bubble will explode inside the pump causing system failure. There are numerous other causes for pump cavitation that includes the following.

Also, it is common for every hydraulic oil to contain 9% of dissolved air. The air will be pulled out of the oil when the pump doesn’t get sufficient oil. When this air bubble reaches a high-pressure area, it will explode or collapse.

Cavitation can be categorized based on its effect and different conditions. Based on the effects, cavitation can be of two types called inertial cavitation and non-inertial cavitation. Inertial cavitation will produce a shock wave when a bubble or void present in a liquid collapses. Whereas, non-inertial cavitation occurs when the air bubble in fluid changes its shape due to an acoustic field or some other type of energy input. Similarly, suction cavitation and discharge cavitation are two cavitation categories based on different conditions. I.e; suction cavitation occurs under high vacuum or low-pressure conditions that effects flow and discharge cavitation occurs when the pump’s discharge pressure becomes abnormally high.

The results of cavitation are excessive heat, reduced lubrication, violent implosions, friction and wear. These issues can cause serious damages to the pump leading to hydraulic system breakdown. The symptoms of cavitation are unusual sound while pump operation, presence of metal debris, and damage. When these symptoms occur, proper inspection and troubleshooting are necessary.

If pump cavitation is avoided, the pump will deliver maximum performance to a longer time period. Some tips for avoiding cavitation are mentioned below.

The phenomenon of cavitation consists in the disruption of continuity in the liquid where there is considerable local reduction of pressure. The formation of bubbles within liquids (cavitation) begins even in the presence of positive pressures that are equal to or close to the pressure of saturated vapor of the fluid at the given temperature.

Various liquids have different degrees of resistance to cavitation because they depend, to a considerable degree, upon the concentration of gas and foreign particles in the liquid.

The mechanism of cavitation can be described as follows: Any liquid will contain either gaseous or vaporous bubbles, which serve as the cavitation nuclei. When the pressure is reduced to a certain level, bubbles become the repository of vapor or of dissolved gases.

The immediate result of this condition is that the bubbles increase rapidly in size. Subsequently, when the bubbles enter a zone of reduced pressure, they are reduced in size as a result of condensation of the vapors that they contain.

This process of condensation takes place fairly quickly, accompanied by local hydraulic shocks, the emission of sound, the destruction of material bonds and other undesirable phenomena. It is believed that reduction in volumetric stability in most liquids is associated with the contents of various admixtures, such as solid unwetted particles and gas-vapor bubbles, particularly those on a submicroscopic level, which serve as cavitation nuclei.

A critical aspect of the cavitation wear process is surface destruction and material displacement caused by high relative motions between a surface and the exposed fluid. As a result of such motions, the local pressure of the fluid is reduced, which allows the temperature of the fluid to reach the boiling point and small vapor cavities to form.

When the pressure returns to normal (which is higher than the vapor pressure of the fluid), implosions occur causing the cavity or vapor bubbles to collapse. This collapse of bubbles generates shock waves that produce high impact forces on adjacent metal surfaces and cause work hardening, fatigue and cavitation pits.

Thus, cavitation is the name given to a mechanism in which vapor bubbles (or cavities) in a fluid grow and collapse due to local pressure fluctuations. These fluctuations can produce a low pressure, in the form of vapor pressure of the fluid. This vaporous cavitation process occurs at approximately constant temperature conditions.

Vaporous cavitation is an ebullition process that takes place if the bubble grows explosively in an unbounded manner as liquid rapidly changes into vapor. This situation occurs when the pressure level goes below the vapor pressure of the liquid.

Gaseous cavitation is a diffusion process that occurs whenever the pressure falls below the saturation pressure of the noncondensable gas dissolved in the liquid. While vaporous cavitation is extremely rapid, occurring in microseconds, gaseous cavitation is much slower; the time it takes depends upon the degree of convection (fluid circulation) present.

Cavitation wear occurs only under vaporous cavitation conditions - where the shock waves and microjets can erode the surfaces. Gaseous cavitation does not cause surface material to erode.

It only creates noise, generates high (even molecular level cracking) temperatures and degrades the chemical composition of the fluid through oxidation. Cavitation wear is also known as cavitation erosion, vaporous cavitation, cavitation pitting, cavitation fatigue, liquid impact erosion and wire-drawing.

Cavitation wear is a fluid-to-surface type of wear that occurs when a portion of the fluid is first exposed to tensile stresses that cause the fluid to boil, then exposed to compressive stresses that cause the vapor bubbles to collapse (implode).

This collapse produces a mechanical shock and causes microjets to impinge against the surfaces, unifying the fluid. Any system that can repeat this tensile and compressive stress pattern is subject to cavitation wear and all the horrors accompanying such destructive activity.

Cavitation wear is similar to surface fatigue wear; materials that resist surface fatigue (hard but not brittle substances) also resist cavitation damage.

Liquid is the medium that causes cavitation wear. Cavitation wear does not require a second surface; it requires only that high relative motion exists between the surface and the fluid. Such motion reduces the local pressure in the fluid. When the liquid reaches its boiling point and ebullition occurs, vapor bubbles form, which produces cavitation.

Each vapor cavity lasts a short time because almost any increase in pressure causes the vapor in the bubble to condense instantaneously and the bubble to collapse and produce a shock wave. This shock wave then impinges on adjacent metal surfaces and destroys the material bonds.

The shock wave first produces a compressive stress on the solid surface, and then when it is reflected, produces a tensile stress that is normal to the surface.

Figure 1 depicts the collapse of a vapor bubble and the birth of a microjet. Cavitation is generally found where a hydrodynamic condition, characterized by a sudden and gross change in hydrostatic pressure, exists. Because ebullition can occur the instant pressure drops, vapor bubbles form and collapse frequently and quickly.

Entrained air and dust particles in the fluid serve as nucleation sites for the formation of vapor cavities. These nuclei can be small gas-filled pockets in the crevices of the container or simply gas pockets on contaminant particles moving freely in the flow stream. Therefore, all confined fluids may contain sufficient impurities to produce cavitation.

Small voids near the surface or flow field, where minimum pressure exists, indicate that cavitation has begun. Once initiated, bubbles continue to grow as long as they remain in low-pressure regions. As the bubbles travel into high-pressure regions, they collapse, producing intense pressures and eroding any solid surfaces in the vicinity.

Equipment users can detect cavitation audibly, visually, by acoustical instrumentation, by machine vibration sensors, through sonoluminescence measurement or by a decrease or change in performance from that produced under single-phase flow conditions (for example, loss of flow, rigidity and response).

Under cavitating flow conditions, the wear rate can be many times greater than that caused by erosion and corrosion alone. Cavitation wear can destroy the strongest of materials - tool steels, stellites, etc. Such damage can occur rapidly and extensively.

The amount of damage that cavitation causes depends on how much pressure and velocity the collapsed bubbles create. As a result of this pressure and velocity, the exposed surface undergoes a variety of widely varying intensities.

Each imposition lasts only a short time; the impulse magnitudes and collapse times are greater for larger bubbles at given collapsing pressure differentials. Thus, the greater the tensile stress on the fluid (the lower the static pressure), the larger the bubbles, the more intense the cavitation and the more serious the damage.

The impulses that result when vapor bubbles form and collapse cause individual symmetrical craters and permanent material deformations when the collapse occurs next to the surface. Consequently, cavitation damage, like fatigue failure, has several periods of activity:

So the region where damage occurs is often quite separate from the region in which cavities are created - often leading to an incorrect diagnosis of the problem. Cavitation wear is mechanical in nature and cannot occur without the application of the tensile and compressive stresses.

In leakage paths (across seals, valve seats and spool lands) where high velocities cause pressure levels to drop below the vapor pressure of the fluid (a cavitation condition often referred to as wire-drawing) and

In all devices where fluid flow is subjected to sharp turns, reduction in cross-sections with subsequent expansions (in cocks, flaps, valves, diaphragms) and other deformations.

Cavitation disturbs the normal operating conditions of fluid-type mechanical systems and destroys the surfaces of components. The process consists of cavities forming when pressures are low, the growth of subsequent bubbles as pressure stabilizes and finally the collapse of the bubbles when the cavities (gaseous or vaporous bubbles) are exposed to high-pressure.

Note that the pressure drop across the component is the driving force for cavitation wear. Figure 2 depicts the cavitation process that occurs in a gear pump and in a spool valve showing how cavities generate, grow and collapse in fluid-type components.

In cavitation wear, microcracks propagate to the point where the material can no longer withstand the impulse load that the imploding vapor bubbles impose. Therefore, particles finally break off and enter the system.

As with any fatigue failure, microcracks first form at stress risers (notches, tears, undercuts, welding defects, etc.) or at heterogeneous areas of the material (such as at the directionality of metal flow, inclusions, and decarburized sections).

Therefore, a rough surface is prone to cavitation wear and because pittings and a rough profile characterize the cavitation damage, the damage increases as the surface becomes rougher.

The most basic means of combating cavitation wear is to minimize the tensile stress on the fluid. In other words, the equipment users must lower the level of refraction or vacuum conditions in zones of possible cavitation. In particular, the following steps may be appropriate:

In many cases, design engineers can minimize cavitation damage by properly selecting fabrication materials. For example, stainless steel may be selected instead of aluminum (Figure 3) and use hard facing with a cavitation-resistant alloy on the exposed surface. Rubber and other elastomeric coatings have also helped minimize cavitation wear. Despite their low resistance to cavitation, these surfaces reflect the shock wave without causing intense damage.

The size of the particles generated by cavitation wear is a function of the Brinell hardness of the exposed material. The largest particles occur during the accumulation period. The slopes of the cumulative particle size distribution curves increase as the strain energy of the material increases. The average size of the particles produced by cavitation decreases as the cavitation intensity increases.

When investigating a cavitation problem in a fluid system, you must identify all possible sources of low pressure (vacuum), high temperature (heat), and locations where air might be ingressing. The following list should serve as a guideline for identifying low pressure areas in a fluid system:

Reservoirs - sites where mechanical (agitation) type air entrainment occurs, swirling fluid exists, fluid impingement on liquid or solid surfaces, pressurized reservoir conditions, cyclonic flow at pump suction port, critical altitude (angled reservoir) occurring during operation that exposes the pump suction port to the atmosphere, jostling of the fluid due to movement over rough terrain and/or low reservoir fluid level that expose the pump suction port to the atmosphere.

Pump - small diameter conduits and/or ports, restrictive flow passages, flow diversions, and/or long suction line conditions, poor pump filling characteristics (restrictive internal flow passages, high pumping speed, overly large flow displacement); altitude too high to provide sufficient reservoir pressure to supply the pump at rated flow conditions; inadequate suction head to lift fluid to pump inlet level (that is, elevation between fluid level and pump intake too great), insufficient suction head to accelerate reservoir fluid to the rated flow conditions of the pump (non-responsive to the pump displacement demands).

Valves - jets discharging from orifices into limited flow space, streamline flow through channels terminating in chambers where low pressure is at the downstream walls of the valve, and/or throttle valves discharging into a low pressure (return line) conduit.

Actuators (extended seals) - air passing rod seals, air desorption existing, and/or vaporous cavities forming when negative loading occurs due to external inertial loads.

www.powermotiontech.com is using a security service for protection against online attacks. An action has triggered the service and blocked your request.

Please try again in a few minutes. If the issue persist, please contact the site owner for further assistance. Reference ID IP Address Date and Time 8bf2006c85a66667641f5dd58dcb3d35 63.210.148.230 03/07/2023 05:19 AM UTC

Most modern hydraulic pumps are reliable, robust pieces of equipment that will withstand years of constant service. However, any hydraulic pump can suffer from mechanical issues. Aeration and cavitation are two serious problems that can affect a hydraulic pump, and either problem can cause serious damage if the issue is ignored.

However, it can be difficult to figure out if a malfunctioning pump is suffering from aeration or cavitation, as the two problems tend to produce similar symptoms. Despite these similarities, aeration and cavitation have different causes and require different solutions, so knowing the difference between the two problems is vitally important knowledge for any hydraulic pump user.

All hydraulic pumps contain a small amount of air, which provides space for the pump"s hydraulic fluid to expand into as it heats up. However, excessive amounts of air in a hydraulic system can cause serious problems.

Aeration in hydraulic pumps occurs when air is drawn into the pump"s hydraulic fluid supply. Air can infiltrate your system through perished pump seals, damaged pipe connectors, leaking suction lines, and other forms of damage. This unwanted air mixes with and dissolves into the hydraulic fluid supply.

Hydraulic fluid that has been contaminated by exposure to air loses many of its functional properties. For example, hydraulic fluid containing excess air cannot conduct heat as efficiently, so aeration can cause rapid overheating in affected pumps and other hydraulic systems. Serious aeration can also impede the pump"s stroke cycle, causing a significant drop in usable power.

For a hydraulic pump to function properly, the flow of fluid from the pump"s reservoir to the pump itself must remain constant and unimpeded. If this flow speeds up or slows down for any reason (such as improper pressure settings or a block in the suction line), this can lead to a potentially catastrophic problem known as cavitation.

When a running hydraulic pump does not receive hydraulic fluid at the proper rate, fluid pressure in the pump"s suction line can drop dramatically. This causes the formation of bubbles inside the hydraulic fluid, which contain air and vaporized hydraulic fluid. These bubbles subsequently collapse, creating an incredible amount of force and heat.

The shockwaves created by these imploding bubbles can do an incredible amount of damage to a hydraulic pump in a short space of time. The pump"s impellers and interior surfaces tend to be particularly badly affected by cavitation, and a pump that has suffered from extensive cavitation may need a complete rebuild before it can be used again.

While cavitation and aeration have different causes, they can produce similar problems, making proper diagnosis difficult. High hydraulic fluid temperatures, lowered pumping rates, and visibly damaged valve seals can all be caused by either cavitation or aeration.

Generally, the easiest way to tell the difference is by listening to the malfunctioning pump, as both types of problem usually produce distinct noises. A cavitating pump tends to produce a steady, rhythmic pattern of knocking or whining noises. Unusual noises produced by aeration are more erratic and random and tend to sound more like rattling than knocking.

However, it is important to note that cavitation and aeration are not mutually exclusive problems, and a poorly maintained hydraulic pump may suffer from both problems simultaneously. Combined aeration and cavitation can lead to a particularly damaging form of cavitation, known as gaseous cavitation.

If your hydraulic pump is suffering from any signs of cavitation or aeration, calling in a professional hydraulic repair service is usually the fastest way to get to the bottom of the problem. These services have access to specialized testing tools and equipment that can quickly detect cavitation and aeration and will be able to provide rapid and effective solutions.

If your hydraulic pumping system is not functioning as it should, and you think cavitation or aeration may be the cause, contact the hydraulic experts at Quad Fluid Dynamics, Inc., for professional advice.

Across any pumping system there is a complex pressure profile. This arises from many properties of the system: the throughput rate, head pressure, friction losses both inside the pump and across the system as a whole. In a centrifugal pump, for example, there is a large drop in pressure at the impeller’s eye and an increase within its vanes (see Figure 1). In a positive displacement pump, the fluid’s pressure drops when it is drawn, essentially from rest, into the pumping chamber. The fluid’s pressure increases again when it is expelled.

If the pressure of the fluid at any point in a pump is lower than its vapour pressure, it will literally boil, forming vapour bubbles within the pump. The formation of bubbles leads to a loss in throughput and increased vibration and noise. However, when the bubbles pass on into a section of the pump at higher pressure, the vapour condenses and the bubbles implode, releasing, locally, damaging amounts of energy. This can cause severe erosion of pump components.

To avoid cavitation, it is important to match your pump to the fluid, system and application. This is a complex area and you are advised to discuss your application with the pump supplier.

The obvious symptoms of cavitation are noise and vibration. When bubbles of vapour implode they can make a series of bubbling, crackling, sounds as if gravel is rattling around the pump housing or pipework. In addition to the noise, there may be unusual vibrations not normally experienced when operating the pump and its associated equipment.

With centrifugal pumps, the discharge pressure will be reduced from that normally observed or predicted by the pump manufacturer. In positive displacement pumps, cavitation causes a reduction in flow rather than head or pressure because vapour bubbles displace fluid from the pumping chamber reducing its capacity.

Power consumption may also be affected under the erratic conditions associated with cavitation. It may fluctuate and will be higher to achieve the same throughput. Also, in extreme cases, when cavitation is damaging pump components, you may observe debris in the discharged liquid from pump components including seals and bearings.

Under the conditions favouring cavitation, vapour bubbles are seeded by surface defects on metal components within the pump: for example, the impeller of a centrifugal pump or the piston or gear of a positive displacement pump. When the bubbles are subjected to higher pressures at discharge they implode energetically, directing intense and highly focussed shockwaves, as high as 10,000MPa, at the metal surface on which the bubbles had nucleated. Since the bubbles preferentially form on tiny imperfections, more erosion occurs at these points.

When a pump is new, it is more resistant to cavitation because the metal components have few surface imperfections to seed bubble formation. There may be a period of operation before any damage occurs but, eventually, as surface defects accumulate, cavitation damage will become increasingly apparent.

Classic (or classical) cavitation occurs when a pump is essentially starved of fluid (it is also called vaporization cavitation and inadequate NPSH-A cavitation). This can occur because of clogged filters, narrow upstream pipework or restricting (perhaps partially closed) valves. If the pump is fed from a tank, the level of liquid (or pressure above it) may have fallen below a critical level.

In a centrifugal pump, ‘classic’ cavitation occurs at the eye of the impeller as it imparts velocity on the liquid (see Figure 1). In a positive displacement pump, it can happen in an expanding piston, plunger or suction-side chamber in a gear pump. Reciprocating pumps, for example, should not be used in self-priming applications without careful evaluation of the operating conditions. During the suction phase, the pump chamber could fill completely with vapour, which then condenses in a shockwave during the compression phase.

Vane Passing Syndrome, also known as vane syndrome, is a type of cavitation that occurs when the spacing between the vanes of a centrifugal pump’s impeller and its housing is too small, leading to turbulent and restricted flow and frictional heating. The pumped liquid expands as it passes beyond the constriction and cavitation occurs.

Suction recirculation (also called internal recirculation) is a potential problem observed with centrifugal pumps when operated at reduced flow rate. This might occur, for example, when a discharge valve has been left partially closed or when the pump is being operated at a flow below the minimum recommended by the pump manufacturer. Under these conditions, liquid may be ejected from the vanes back towards the suction pipe rather than up the discharge port. This causes turbulence and pressure pulses throughout the pump which may lead to intense cavitation.

Air can be sucked into a pumping system through leaking valves or other fittings and carried along, dissolved in the liquid. Air bubbles may form within the pump on the suction side, collapsing again with the higher pressure on the discharge side. This can create shock waves through the pump.

To avoid cavitation, the pressure of the fluid must be maintained above its vapour pressure at all points as it passes through the pump. Manufacturers of centrifugal pumps specify a property referred to as the Net Positive Suction Head Required or NPSH-R – this is the minimum recommended fluid inlet pressure. The documentation supplied with your pump may contain charts showing how NPSH-R varies with flow.

In fact, NPSH-R is defined as the suction-side pressure at which cavitation reduces the discharge pressure by 3%: a pump is already experiencing cavitation at this pressure. Consequently, it is important to build in a safety margin (about 0.5 to 1m) to take account of this and other factors such as:

So, in designing the suction-side pipework for your system, you must ensure that it exceeds the manufacturer’s NPSH-R rating for the operating conditions. Your calculated value is termed the NPSH-Available (NPSH-A).

Positive displacement pumps require an inlet pressure to be a certain differential greater than the vapour pressure of the fluid to avoid cavitation during the suction phase. This is discussed in terms of Net Positive Inlet Pressure (NPIP) in a similar manner to NPSH for centrifugal pumps. NPSH is measured in feet or meters and NPIP is measured in pressure such as psi or bar. When converted to the same units, NPSH and NPIP are the same. Manufacturers may quote NPIP-R as the recommended inlet pressure and provide charts showing how it varies with pump speed. The available or actual inlet pressure on an operating system is termed NPIP-A.

Cavitation is a potentially damaging effect that occurs when the pressure of a liquid drops below its saturated vapour pressure. Under these conditions it forms bubbles of vapour within the fluid. If the pressure is increased again, the bubbles implode, releasing damaging shockwaves. This can cause severe erosion of components. A common example of cavitation is when a centrifugal pump is starved of feed: vapour bubbles form in the eye of the impeller as it imparts velocity on the liquid and collapse again on the discharge side of the vanes as the fluid pressure increases. This can lead to damage to an impeller’s vanes, seal or bearing. Cavitation can also occur in positive displacement pumps such as gear pumps and plunger pumps.

With a centrifugal pump, ensure that NPSH-A is at least 0.5m greater than NPSH-R during operation. For example, if the pump is fed from a tank, ensure that the level of liquid in the tank (or pressure above it) is sufficient. For a positive displacement pump, make sure that the inlet pressure complies with the manufacturer’s NPIP requirements.

Bubbles might not seem very powerful, but the types of bubbles in pumping systems are nothing like the ones you make by waving a wand around with little kids. Tiny bubbles created by changes in pressure inside pumps collapse and create shock waves that occur over and over and the repeated shocks erode the components.

Pumps are designed to work with a full flowing water supply, but in some cases a flooded inlet is not enough to maintain pressure required to prevent cavitation. The inlet, or suction side of a pump is the point of lowest pressure in a given pump.For positive displacement pumps, the lowest pressure occurs just prior to rotor meshing; for centrifugal pumps, lowest pressure is near the eye of the impeller.

Cavitation is possible in all pump types and since its principles are essentially the same, we will focus on centrifugal pumps. The eye is where fluid is drawn into the impeller and where the rotation of the impeller begins to act on the fluid. When pressure acting on the liquid (Net Positive Suction Head Available) is too low, bubbles form, and as the liquid accelerates because of impeller rotation, pressure increases and the bubbles collapse.

Under normal atmospheric pressure conditions, fluids have predictable vapor pressure. As the pressure inside the pump falls below the liquid"s vapor pressure, bubbles form. The bubbles collapse when they reach areas of the liquid where the pressure is above the vapor pressure. In the case of cavitation, this formation and collapse is both rapid and violent.Disrupted or poorly executed processing lines can cause suction or discharge pressure to fall, which leads to cavitation.

At extremely high discharge pressure, some fluid circulates inside the pump instead of discharging. Fluid trapped between impeller and housing at very high velocity cause a drop in pressure, creating the same conditions as for suction cavitation.

Cavitation sounds like marbles or gravel circulating through the pump, pipes, or hoses. The effects of prolonged cavitation are visible on the pump impeller and other components.

Start by identifying the cause of the pressure drop. In many cases moving the pump closer to the fluid source and removing as many bends and valves as possible corrects the problem because each component causes additional pressure drop. When suction lift is too high to maintain pressure, move the pump closer to the fluid source or move the fluid source closer to the pump.

Enlarging suction lines can also be effective. In some obvious cases, a blockage occurs in piping or hoses near the pump. Clear those blockages to resolve the issue.Clean suction lines by clearing debris. Avoid blowing the debris back toward the fluid source because it’s likely to create a blockage again.

Don’t exceed your pump manufacturer’s performance guidelines. Pump curves tell you how much net positive suction head the pump requires, so check your pump’s performance curve to ensure it has the right specifications for your application.

The best way to prevent cavitation is to select the right pump for the application. Cavitation increases as pump head falls or as capacity increases, so selecting the correct pump to maintain a positive margin of NPSHa above NPSHr is the best first move.

NPHS at the inlet depends on atmospheric pressure, friction losses in the suction piping, and flow velocity. A good rule of thumb is for pressure at the pump inlet to be 10% greater than the pump"s specified NPSHr. For example, if NPSHr is 10 feet, NPSHa should be at least 11 feet.

Discharge cavitation occurs when pressure at the discharge end of the pump is too high. High discharge pressure limits the volume of fluid flowing out of the pump, causing high-velocity fluid to recirculate between pump impeller and housing, causing cavitation.

Check filters and strainers. Dirty or blocked filters and strainers generate pressure buildup inside the pump. Setting a maintenance schedule ensures that systems are in place to keep the pump system flowing at capacity.

Evaluate the curve. Consider the job pressure demands and then consider the pump data to see if it fits the application. From there you determine if the pump fits the needed flow rate.

The best ounce of cavitation prevention is pump selection and system design for maintaining pressure and flow. The goal of installation is therefore to maintain net positive suction head available (NPSHa) at greater than net positive suction head required (NPSHr) by considering four key variables:

Physically install the pump so the water flows into the pump suction inlet smoothly.Make sure that the suction lines leading to the inlet of the pump are adequately sloped to ensure that the pump housing is flooded.

Placing the pump at a point that is lower than the water level in the tank from which it pumps, for example, uses the force of gravity to maintain flooded suction, which in many cases prevents cavitation.

Pumps, and especially centrifugal pumps, work most efficiently when the fluid travels in a smooth, laminar flow, and turbulence of any kind reduces pump efficiency, so positioning the pump as close as possible to the fluid source makes sense.

In general, you want 12 cm of straight pipe for every centimeter of pump suction diameter.To maintain laminar flow, connect 5-10 pipe diameters of straight piping to the pump inlet. Do not include elbows, reducers, valves, or strainerswithin the final length of pipework. Connecting an elbow directly to the pump flange, for example, draws fluid towards the outer curve of the elbow instead of directly into the eye of the impeller.

Also, the piping arrangement must not cause strain on the pump casing, so pumps can never support the piping for suction or discharge. Use hangers and supports instead.

Good piping layouts prevent cavitation by helping to maintain constant velocity. Obstructions in piping layouts affect flow velocity, which changes fluid pressure, which can cause cavitation.

While it’s true that some cavitation can have positive purposes, such as for surgical equipment sterilization or to break down pollutants in water systems, it’s not something you want in your processing system, so time spent preventing cavitation is time well spent.

When your pump, pipe, or hose sounds like marbles or gravel are circulating, you"re witnessing cavitation and need to take immediate action or risk severe damage to components. When cavitation does occur, you need a trusted partner that can diagnose the cause, provide a long-term solution, and repair or replace parts that are damaged.

CSI"s pump service and maintenance program is designed to take the irritation and guesswork out of dealing with pump cavitation. Each audit and repair that CSI completes include an evaluation by an OEM-trained pump technician, a report on the findings, and all the materials required to perform the service. Call us today to schedule your next system audit or pump repair!

Central States Industrial Equipment (CSI) is a leader in distribution of hygienic pipe, valves, fittings, pumps, heat exchangers, and MRO supplies for hygienic industrial processors, with four distribution facilities across the U.S. CSI also provides detail design and execution for hygienic process systems in the food, dairy, beverage, pharmaceutical, biotechnology, and personal care industries. Specializing in process piping, system start-ups, and cleaning systems, CSI leverages technology, intellectual property, and industry expertise to deliver solutions to processing problems. More information can be found at www.csidesigns.com.

This guide is intended for engineers, production managers, or anyone concerned with proper pump selection for pharmaceutical, biotechnology, and other ultra-clean applications.

When designing a hydraulic system, it is important to understand the difference between cavitation and aeration—and understand the damage they can create.

As previously discussed in our April issue, it is critical to maintain proper fluid levels in the reservoir to ensure the Net Positive Suction Head Available (NPSHA) is greater than the Net Positive Suction Head Required (NPSHR) by the pump.

Anytime the NPSHA is equal to the NPSHR, the flow instabilities in the fluid moving to and through the pump will be affected to the point cavitation can (and will be) generated.

Aeration is a process where air is circulated with, mixed with or dissolved in the hydraulic fluid. It is created when air leaks into the system through the pump seals, pipe fittings and unions, which are all areas where air leakage is common.

Although you can not see cavitation, a demonstration at Eaton’s training facility in Maumee, Ohio, shows an extreme example of the effects of excessive air in hydraulic fluid.

Cavitation, on the other hand, is the formation of gas bubbles that create vapor cavities in a liquid. It occurs when the gas bubbles in the liquid are subjected to rapid changes of pressure. This higher pressure causes the air bubbles to implode, which generates an intense miniature water hammer (shock wave). This shock wave creates significant wear as the gas bubbles implode on or near a metal surface, causing cyclic stresses through repeated implosions.

Cavitation occurs when the volume of fluid demanded by any part of a hydraulic circuit exceeds the volume of fluid being supplied. This causes the absolute pressure in that part of the circuit to fall below the vapor pressure of the hydraulic fluid. This will result in the formation of gas bubbles.

The difference between the two is in how the air is getting into the system. Cavitation is caused by NPSHA, and can be stopped by simply slowing the fluid flowing through the system. If the problem is aeration, on the other hand, you have to locate and isolate the air leaking into the system, so resolving the problem can be more time-consuming. The damage by both is equal, however.

Abnormal noise in hydraulic systems is often caused by aeration and/or cavitation. Air in the hydraulic fluid makes a banging or knocking noise when it experiences high and low system pressures as it circulates through the system.

High fluid temperatures above 180° F (82° C) are detrimental to system operation and will damage seals and accelerate degradation of the fluid. High temperatures can be caused by anything that reduces the system’s capacity to dissipate heat (low reservoir level) or increases its heat load (air generates heat when compressed).

In addition to damaging seals and reducing the service life of the hydraulic fluid, high fluid temperature can cause damage to system components through boundary lubrication as a result of excessive thinning of the oil film (lower viscosity index), which in turn causes full film lubrication loss.

Slow operation, or a reduction in system performance, is often the first indication that there is something wrong. In a hydraulic system, flow controls speed and response. Therefore, a loss of speed indicates a loss of flow.

Consequences of cavitation in a hydraulic system can be serious. Cavitation causes metal erosion, thus damaging the system components and contaminating the fluid. Cavitation can also cause mechanical failure of system components.

Cavitation can occur anywhere within the hydraulic circuit; however, hydrodynamic cavitation commonly occurs at the pump. The pump suction line between the reservoir and pump should be open and not restricted. If the pump has an inlet strainer or filter, it is important to prevent it from becoming clogged. A partially closed suction valve or restricted intake line will cause the velocity of the fluid in the intake line to increase, causing the boiling temperature of the fluid to decrease as the fluid pressure goes below vapor pressure. This will vaporize some of the fluid molecules.

The damage caused by unresolved cavitation to a hydraulic system can be extremely expensive and cause extensive downtime. Prevent this problem with proper system design and maintenance. And always, listen to your hydraulic system. A rattling or knocking noise is not the sound of a welcome visitor.

While it’s common for people to think of a pump’s inlet as sucking in oil, in reality, it is atmospheric pressure doing the work. In essence, the weight of the atmosphere pushes the oil out of the reservoir and into a region of lower pressure—the inlet. Once the oil is forced from the reservoir and through the inlet, it then moves the volume of liquid into a region of decreasing volume to create flow. For this process to begin, there must be minimum pressure at the inlet of a hydraulic pump, as shown in the diagram below.

As you can see, the inlet of a pump plays a large role in how well it operates. Unfortunately, those designing and maintaining pump systems can become so focused on downstream flow that they overlook proper inlet maintenance. This can result in degradation of inlet function and serious problems such as cavitation.

Cavitation occurs when the absolute pressure on the inlet side of the pump is too low and air is drawn out of the solution, creating bubbles in the oil. As these bubbles get pushed around to the high-pressure outlet side of the pump, they collapse. This creates localized shock waves that blow bits of material out of the pump. It can also result in excessive heat and reduced lubrication that leads to friction and wear over time.

Cavitation can cause pump failure and it can damage other components of your system, which is why it is critical to examine the condition of the pump"s inlet on a regular basis.

PSI versus PSIA. What’s the difference? PSI, or pounds per square inch, is a unit of measurement for pressure used in the United States. PSIA describes the absolute pressure in psi, including the pressure of the atmosphere. Absolute pressure is also referred to as total pressure.

The energy it takes to lift oil through the suction line (including pressure drop due to flow). We refer to this action as Phase 1 pressure, because it represents the amount of energy it takes to accelerate the fluid through the pumps internal pathways and keep the pump full.

In order for a pump to function, atmospheric pressure must be greater than Phase 1 pressure + NPSH. Every pump has its own specifications regarding acceptable minimum/maximum inlet pressure, but we can use the example below to illustrate how to calculate it.

To begin, assume that you are maintaining an 18 GPM hydraulic pump. The NPSH is equal to 12 PSIA with standard hydraulic oil and 1800 RPM per manufacturer’s specifications.

Each foot of oil lift requires approx. = 0.4 PSI. Fluid velocity is 3.8 feet per second. A typical lookup table shows there will be a 0.05 PSI drop due to the flow through the pipe.

Total loss of the inlet line during steady state is 0.4 PSI + 0.05 PSI, or 0.45 PSI. 14.7 – 0.45 = 14.25 PSI. Because this final number—14.25 PSI—is greater than the NPSH of 12 PSIA, you can rest assured the system is functioning well.

If we apply the same numbers to a variable-volume pump, the result will be less acceptable. Here’s why: Imagine the pump is not in demand and is therefore being held off stroke, meaning there is no flow. When the pump is suddenly needed, it will come on stroke, requiring the column of oil in the suction line to accelerate. This sudden change in demand requires the pump pressure to accelerate from static to a pressure that is strong enough to move the oil and prevent cavitation.

Assume the pump strokes on in 70 milliseconds (msec). The volume of liquid that has to accelerate is 1.5in^2 x 18.1” = 27.1 cubic inch (