Tag Archives: Intro to Pumps

How Do Modifications to Seal Faces Improve Their Operation?


Excerpt from the April 2022 Pumps & Systems Article by the Hydraulic Institute

Face treatments increase the opening force by hydrostatic or hydrodynamic methods.

Pumps are at the heart of most industrial processes and the second most common machine in the world (after the electric motor). Because they are so common, pumps are often overlooked as a potential source of improved productivity or a cause of excess costs if not operated properly.

The most common seal face pattern is a plain flat surface designed to operate with minimal friction. However, various treatments can be done to seal faces to meet specific application needs. In general, seal face treatments are a means of modifying the pressure distribution between the seal faces. Images 1 and 2 show two more common face treatments that include spiral grooves and hydropads.

The most common objective of face treatments is to increase the opening force and thereby reduce the force of the mechanical contact. It can be useful when friction must be reduced to prevent vaporization of the fluid film or in applications involving a combination of high pressure and low viscosity of fluid.

Face treatments increase the opening force by hydrostatic or hydrodynamic methods. Hydrostatic forces do not depend on the rotational speed, whereas hydrodynamic forces vary with the rotational speed and viscosity of the fluid.

The simplest face treatment is a plain face that is angled. This design produces forces that are primarily hydrostatic. An example is a face subject to pressure at the outer diameter that is lapped so it touches the mating ring at the inside diameter. This means that the leakage path is converging. Care must be taken in determining the optimum angle, as too little taper will reduce the lubrication to the faces causing them to run hot. Too much taper will cause face separation with high leakage.

>>Read more.


A Complete Line of Pumps for Industry

Vertiflo Pump Company’s Vertical Sump Centrifugal Pumps, Horizontal End Suction Centrifugal Pumps and self-priming pumps are delivered fast, usually in half the typical lead time. Vertiflo’s vertical sump pump line offers up to 3000 GPM, 250′ Heads and 26′ depth. The horizontal end suction pump line offers up to 3000 GPM and 300’ Heads.

Vertiflo pumps are designed for nonresidential applications and currently over 20,000 are operating successfully worldwide. Vertiflo is recognized as a quality manufacturer of dependable pumps, and continues to grow and encompass new applications in the pump industry.

Cavitation on a centrifugal pump impeller

How to Detect Cavitation

Pump Cavitation on an Impeller
Excerpt from the September 2021 Pumps & Systems Article by Asma Motlani

Learn the symptoms of cavitation and solutions to correct it.

Pumps are at the heart of most industrial processes and the second most common machine in the world (after the electric motor). Because they are so common, pumps are often overlooked as a potential source of improved productivity or a cause of excess costs if not operated properly.

As with any machine, some problems can occur. A common problem in pumping systems is pump cavitation. Pump cavitation causes a number of issues including excess noise, vibration and energy usage, not to mention serious damage to the pump itself.

What causes cavitation?

Imagine pinching a water hose and the water moves faster coming out but it is aerated and spread out. That is what happens with pump cavitation. It is a physical phenomenon that occurs when the pressure of the liquid incoming becomes lower than the vapor pressure of the liquid. A reduction in pressure is typically caused by increased speed of the fluid. When fluid pressure on the trailing side of the impeller blade (opposite the pump intake) falls below the vaporization point of the fluid, vapor bubbles begin to form. 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 trigger intense shockwaves inside the pump, causing damage to the impeller, vibration and excess noise.

These shock waves can cause mechanical damage to the impeller and pump, only increasing in severity over time and leading to potential pump failure. Factors that impact the degree of compression for the vapor bubbles are the speed and shape of the impeller.

When dealing with liquids of higher temperatures, the risk of this occurrence is increased due to increased vapor pressure.

What’s the difference between deadhead & cavitation?

Pump cavitation and dead head are similar concepts but far from the same.

When a pump operates with no flow through the pump due to a closed discharge valve or line blockage, a dead head has occurred. The pump recirculates the same water, causing water temperature to continually rise. If the pump continues to run in a dead-headed condition for too long, excessive heating can damage expensive seals and reduce the life of the pump.

Dead heading in a centrifugal pump can lead to explosions due to the energy being put into the liquid in the pump. Hydraulic overpressure and possible chemical reactions in the pump can also be caused by the overexertion of pressure. The same results can be caused by running the pump dry for an extended period, which can lead to cavitation.

Dead head means the outflow valve is open so the pump continues to circulate the same liquid over and over, which can damage the pump motor because the liquid can get too hot. The low power protection will work to detect this condition and trip to protect the motor.

Cavitation is similar in that the low power protection will detect it and trip and protect the motor as well. But this condition means that the pump is running dry and no liquid is there to pump. That too will cause the motor to overheat.

>>Read more.


A Complete Line of Pumps for Industry

Vertiflo Pump Company’s Vertical Sump Centrifugal Pumps, Horizontal End Suction Centrifugal Pumps and self-priming pumps are delivered fast, usually in half the typical lead time. Vertiflo’s vertical sump pump line offers up to 3000 GPM, 250′ Heads and 26′ depth. The horizontal end suction pump line offers up to 3000 GPM and 300’ Heads.

Vertiflo pumps are designed for nonresidential applications and currently over 20,000 are operating successfully worldwide. Vertiflo is recognized as a quality manufacturer of dependable pumps, and continues to grow and encompass new applications in the pump industry.

Probable NPSH for Zero Cavitation Erosion

NPSH: Know the Consequences of Disregarding Facts

Probable NPSH for Zero Cavitation Erosion
Excerpt from the December 2021 Pumps & Systems Article by Heinz P. Bloch

Understand cavitation, suction energy, specific gravity and more.

Process pumps are machines that take liquid from a suction condition to a discharge condition. In its typical form, there usually is a shaft-mounted impeller (or impellers) that, together, make up a rotor. Impellers impart velocity to the fluid as it passes from pump suction to pump discharge. Whereas in the pump casing’s internal passageways, the fluid velocity decreases and is converted to an elevated discharge head.

However, the resulting pressure is a function of the specific gravity of the product being pumped and the expression “head” is a universal indicator of the pump’s output. The height to which a droplet of water can be lifted as it leaves the tip of an impeller is determined strictly by the circumferential velocity with which the droplet leaves the tip. That velocity is a function of impeller diameter and shaft rotations per minute (rpm). Translation: At a certain speed and for a certain impeller diameter, a droplet of water with a specific gravity (SG) of 1.0 will be propelled to a height of, say, 100 feet (ft) and so would a droplet of mercury, which has an SG of 13.6. Comparing the pressure exerted by a column of mercury Y feet high with that of an equal-height column of water, the former would be 13.6 times greater than the latter, as would the power demanded to produce equal heads.

A certain pressure is needed to force a quantity of liquid into the eye of an impeller. The force (or pressure) also must overcome casing and pipe friction while creating a head of a certain magnitude. To design and manufacture a pump defined by needed flow and pressure, the OEM will propose a pump with an impeller requiring a designed-in net positive suction head (NPSH). The plant design needs to provide an available head or driving force (NPSHa) in excess of NPSHr (required). If there is no reasonable increment of NPSHa over NPSHr, the pump will cavitate and, other parameters remaining unchanged, the possible operating hours of the impeller(s), bearings and seals will be reduced. If a plant designer insists that a low NPSHa must be accommodated, the manufacturer’s offer will likely contain compromises or constraints that are of consequence to the buyer.

For decades, it had been incorrectly assumed and taught that a 1 foot (ft) incremental head difference was all that was needed. With evidence mounting that, for ammonia and other aqueous liquids, even 20 ft was barely enough and a multifaceted problem had to be faced nearly 100 years ago. It may require an NPSHa from two to 20 times NPSHr to fully suppress cavitation within a pump. Much depends on pump design, flow ratio (percentage of best efficiency point [BEP] flow) and how close the liquid’s temperature is to its vaporization temperature. Whatever fraction of driver power is converted into heat rise must not elevate temperatures to cause portions of the liquid to vaporize.

Cavitation Explained3

Cavitation is the effect of vapor bubbles collapsing and giving way to the surrounding liquid impinging on portions of the pump impeller. Collapsing bubbles cause variations in pump discharge pressure, which prompted interested parties to agree that a 3% fluctuation of discharge pressure indicated the onset of cavitation. However, by the time it becomes clear from a discharge pressure gauge needle, which hovers or jitters nervously between 100% and 97% of normal discharge pressure achieved, it is best to pay attention. Although industry calls it the onset of cavitation, destructive vibratory forces and impingement by collapsing vapor bubbles may already be well underway.

The pressure gauge needle dance is caused by collapsing vapor bubbles, which are accompanied by tiny high-velocity fluid jets that strike at points where collapsing bubbles contact impeller vanes or other internal surfaces. The struck material will erode, leaving behind millions of cavitation pockets. The extent of cavitation-induced damage differs, thus materials are classified in accordance with life factors. Mild steel is ranked lowest with an assigned number of 1. Aluminum-bronze tops the list of cavitation-tolerant materials with an 8, while stainless steels (4) are near the middle.

NPSH Plots 

Next came the belated emphasis on where NPSH differential head plot lines should intersect the vertical (Y-axis) of such plots. Since about 1960, many researchers found this tends to vary greatly and none intersected the vertical axis (Image 1). Curve trends varied with pump suction specific speed (Nss), which is calculated by taking the quantity (rpm [gpm per impeller eye])^1/2 and dividing it by (NPSHr)^3/4. Still, many phantom plots created the impression that operation at almost zero flow would be allowed and would result in a low delta NPSH requirement. But low flows cause pump-internal recirculation, which also creates vapor bubbles and curtails pump life.

>>Read more.


A Complete Line of Pumps for Industry

Vertiflo Pump Company’s Vertical Sump Centrifugal Pumps, Horizontal End Suction Centrifugal Pumps and self-priming pumps are delivered fast, usually in half the typical lead time. Vertiflo’s vertical sump pump line offers up to 3000 GPM, 250′ Heads and 26′ depth. The horizontal end suction pump line offers up to 3000 GPM and 300’ Heads.

Vertiflo pumps are designed for nonresidential applications and currently over 20,000 are operating successfully worldwide. Vertiflo is recognized as a quality manufacturer of dependable pumps, and continues to grow and encompass new applications in the pump industry.

Flow Rate and Water Hammer Curves

Valves’ Effect on Flow Rate & Water Hammer

Flow Rate and Water Hammer Curves
Excerpt from the December 2021 Pumps & Systems Article by Pete Gaydon

Not all valves are well suited for controlling system flow rate.

Can any valve be used for controlling flow rate in a pump system, and what is the effect on water hammer?

Not all valves are well suited for controlling system flow rate. Image 1 (header image) compares the valve characteristics of various valves. You can see that the gate valve, based on its position, increases flow rate the fastest out of any of the other valves. Of the valves presented here, the plug valve provides the most consistent flow increase versus its valve position, which is ideal for throttling. In this case, a gate valve would not be good for flow control because of the lack of linear control over the flow.

Overall, the performance and characteristics of each valve will affect the magnitude of any transients developed by valve closures and openings. It is important to consider rate of flow change versus valve position and control the closure rate of the valve such that the effects of system transients (water hammer) are reduced.

Upstream Valve Closure Data

In Image 2, we have a comparison of some common valves where each valve closes over 60 seconds. The middle chart shows the pressure rising immediately upstream. The globe valve has the minimum pressure rise because the characteristics of the globe valve shown in the image above are more linear than either the butterfly or ball valve.

You can see in Image 1 that the characteristic curve of the ball valve is relatively flat coming from the bottom, with anything less than 40% open having very little effect on the flow rate. Without much change in flow until about 55 seconds, there is significant decrease in flow over the last five seconds of closure, which results in a rapid change in velocity and a high pressure change upstream. Using the ball valve would result in the greatest likeliness of a water hammer effect. This sudden rise in pressure can be damaging to equipment within the system.

>>Read more.


A Complete Line of Pumps for Industry

Vertiflo Pump Company’s Vertical Sump Centrifugal Pumps, Horizontal End Suction Centrifugal Pumps and self-priming pumps are delivered fast, usually in half the typical lead time. Vertiflo’s vertical sump pump line offers up to 3000 GPM, 250′ Heads and 26′ depth. The horizontal end suction pump line offers up to 3000 GPM and 300’ Heads.

Vertiflo pumps are designed for nonresidential applications and currently over 20,000 are operating successfully worldwide. Vertiflo is recognized as a quality manufacturer of dependable pumps, and continues to grow and encompass new applications in the pump industry.

Total Head for Pumps & Systems

Total Head for Pumps & Systems

Total Head for Pumps & Systems
Excerpt from the October 2021 Pumps & Systems Article by Pete Gaydon

This foundation is beneficial to understand while working with an entire system.

The term “total head” (H) is used to describe the energy in pumping systems and is how manufacturers represent the performance of their pumps as a function of flow rate. Total head is also commonly referred to as total dynamic head (TDH); however, the Hydraulic Institute (HI) uses the term total head and it will be used throughout this article.

It is important to understand the nuances of what makes up the total head of the system as a function of flow rate and varying system conditions so that if a user is designing or operating a pump system, the pump can be selected and operated properly. Additionally, if the goal is to measure the pump performance after installation, it is important to understand how to do that in the same way that the pump manufacturer will.

Total head (system) is made up of three components:

Elevation head, which is the difference in elevation that liquid will travel. For example, if a user was pumping from one tank to another and the level in the tanks were the same, there would be zero elevation head. But if pumping from a tank at ground level to the roof of a 100-foot building, there would be 100 feet of elevation head.

Pressure head is the difference in pressure between source and destination. For example, if taking liquid from a lake at atmospheric pressure and delivering it to a tank that had 10 pounds per square inch (psi) above atmospheric pressure, the pressure head would be 10 psi expressed as feet of the liquid being pumped. The conversion between pressure and head is described in the pump total head measurement section.

Friction head is the head loss in the system due to friction and is a function of the liquids velocity or flow rate squared. As mentioned, the friction loss will depend on the flow rate but also the size of the piping, fittings, valves and end use equipment in the system. If there are control valves in the system that are used to actively regulate the flow rate, the friction loss across the control valve is referred to as control head. It is important to understand control head because it is often a source of energy consumption that can be improved.

>>Read more.


A Complete Line of Pumps for Industry

Vertiflo Pump Company’s Vertical Sump Centrifugal Pumps, Horizontal End Suction Centrifugal Pumps and self-priming pumps are delivered fast, usually in half the typical lead time. Vertiflo’s vertical sump pump line offers up to 3000 GPM, 250′ Heads and 26′ depth. The horizontal end suction pump line offers up to 3000 GPM and 300’ Heads.

Vertiflo pumps are designed for nonresidential applications and currently over 20,000 are operating successfully worldwide. Vertiflo is recognized as a quality manufacturer of dependable pumps, and continues to grow and encompass new applications in the pump industry.

Cavitation on a centrifugal pump impeller

What is Cavitation?

Cavitation on a centrifugal pump impeller
Excerpt from the August 2021 Pumps & Systems Article by Peter Wolff

Understand how cavitation can damage your system.

Cavitation is a condition that can affect any fluid flow system. Despite it being an ever-present threat, it is not well understood. In the simplest possible terms, cavitation involves the formation of water vapor bubbles that damage metal components when they collapse back to the liquid phase. Here are some common questions and answers that relate to cavitation.

Does a pump sound differently when it cavitates?

Yes. Cavitation has been described as sounding like gravel or coffee beans in the system.

How does cavitation damage system components?

One aspect of cavitation that is not widely understood is why these apparently harmless bubbles are so destructive when they implode. The answer is in the release of latent heat energy of condensation when the water vapor returns to its liquid phase. The collapse of the bubble and the energy released creates a small pressure jet that can strike a nearby solid surface, potentially damaging it. Because of the large number of bubbles formed in a cavitating system, these bubbles of water vapor can cause extensive damage to system components over time. Because cavitation takes place on the entry to a pump, the first system component that the bubbles encounter is the pump impeller.

Where else can cavitation happen?

Virtually anywhere that water is moving fast. The most well-known locations, aside from pumps, are ships’ propellers, control valve seats and small-bore orifice plates in water pipework.

What causes cavitation in pumps?

Cavitation in pumps is caused by excessively low pressure at the pump inlet. A blockage or restriction such as a clogged filter or part-closed valve mounted on the inlet to the pump can cause it. It can also happen when the pump is having to source its water supply from a sump installed below the pump—called a “suction lift.” Finally, hot water, close to boiling point, is a likely contributor.

Why does hot water allow pumps to cavitate more easily?

When water temperatures are low, the vapor pressure of water is also low. For example, at 32 F, the vapor pressure is a fraction of 1 pound per square inch (psi). As water temperatures rise, the vapor pressure climbs. At 212 F, the vapor pressure is the same as standard atmospheric pressure. At this temperature, when the vapor pressure is the same as the atmospheric pressure, the water will begin to vaporize—turn to gas, in layman’s terms. The commonly known term for this is boiling.

>>Read more.


A Complete Line of Pumps for Industry

Vertiflo Pump Company’s Vertical Sump Centrifugal Pumps, Horizontal End Suction Centrifugal Pumps and self-priming pumps are delivered fast, usually in half the typical lead time. Vertiflo’s vertical sump pump line offers up to 3000 GPM, 250′ Heads and 26′ depth. The horizontal end suction pump line offers up to 3000 GPM and 300’ Heads.

Vertiflo pumps are designed for nonresidential applications and currently over 20,000 are operating successfully worldwide. Vertiflo is recognized as a quality manufacturer of dependable pumps, and continues to grow and encompass new applications in the pump industry.

Pump Impeller Tip Speed

Wear in Centrifugal Pumps

Excerpt from the Dec. 2019 Pumps & Systems Article by Gary Dyson

Tips to recognize and reduce erosion and abrasive wear

Centrifugal pumps are sometimes used in environments where the pumped product contains suspended solids. While some pumps are specifically designed for solid handling or slurry applications, normal centrifugal pumps do not contain features to prevent performance degradation from the impact of solids.

There are a few key signs that a conventional centrifugal pump is suffering from erosive and abrasive wear. Here are assessment and mitigation strategies to be considered and applied when this occurs.

Particles are a problem in a centrifugal pump due to the way the machine adds velocity to the liquid as it passes up the impeller channels. In general, the higher the speed at the tip of the impeller, the more energy that is imparted to any particle that is suspended within the liquid. This energy can then cause damage to anything it impacts.

Pump Impeller Tip Speed

It is important to draw the distinction between tip speed and rotational speed. A small diameter impeller running at high speed could have a lower tip speed than a large diameter impeller running slowly. Tip speed is the velocity of the impeller at its outside diameter.

In general terms, the material loss by erosion is determined by the velocity of the particle cubed (Equation 1).

Equation 1:
Erosion = XC3

C is the velocity of the particle
X is a coefficient based on the liquid
being pumped

The velocity of the particle is directly associated to the tip speed of the impeller (Image 1). Lowering the tip speed of a machine has a significant impact on particle velocity and, thus, the erosive energy.

Volute Tip Wear

>>Read more.


A Complete Line of Pumps for Industry

Vertiflo Pump Company’s Vertical Sump Centrifugal Pumps, Horizontal End Suction Centrifugal Pumps and self-priming pumps are delivered fast, usually in half the typical lead time. Vertiflo’s vertical sump pump line offers up to 3000 GPM, 250′ Heads and 26′ depth. The horizontal end suction pump line offers up to 3000 GPM and 300’ Heads.

Vertiflo pumps are designed for nonresidential applications and currently over 20,000 are operating successfully worldwide. Vertiflo is recognized as a quality manufacturer of dependable pumps, and continues to grow and encompass new applications in the pump industry.

Pump Curve

Determine Power When Looking at Typical OEM’s Pump Curve

Excerpt from the Feb. 2021 Pumps & Systems Article by the Hydraulic Institute

There are two ways to estimate the power for a specific operating point.

How do I determine the power required when looking at a typical manufacturer’s curve?

A typical pump curve (Image 1) includes the pump head for various impeller trims as a function flow rate. It also includes lines of constant efficiency, power and NPSH3. There are two ways to estimate the power for a specific operating point.

Pump Curve

For the flow and head, you can see where it lines up between the lines of constant power to get an estimate. In Image 1, the design flow or 1,000 gpm and 100 feet of head will require approximately 30 horsepower (hp). From this curve, we can also see that if a higher flow rate would be needed for the appropriate pump trim, it would exceed the 30-hp line, and the next size motor would be required for full curve coverage.

For any flow and head, you can find the closest efficiency and manually calculate the power required.

For the same design point in Image 1, we can see that the efficiency will be between 82% and 85% but closer to 85%, so let’s pick 84%. For water at ambient temperature (specific gravity = 1.0), the power can be calculated using Equation 1.

Equation 1

Pump input power (hp) = Flow (gpm) x Head (ft) x Specific gravity / 3960 x Pump efficiency= (1000 x 100 x 1.0)/(3960 x 0.84) = 30 hp

>>Read more.


A Complete Line of Pumps for Industry

Vertiflo Pump Company’s Vertical Sump Centrifugal Pumps, Horizontal End Suction Centrifugal Pumps and self-priming pumps are delivered fast, usually in half the typical lead time. Vertiflo’s vertical sump pump line offers up to 3000 GPM, 250′ Heads and 26′ depth. The horizontal end suction pump line offers up to 3000 GPM and 300’ Heads.

Vertiflo pumps are designed for nonresidential applications and currently over 20,000 are operating successfully worldwide. Vertiflo is recognized as a quality manufacturer of dependable pumps, and continues to grow and encompass new applications in the pump industry.

NPSHA vs rate of flow

Considerations for Wastewater Pumps

Excerpt from the Jan. 2021 Pumps & Systems Article by the Hydraulic Institute

Hydraulic Institute on examining altitude, temperature and more when selecting a wastewater pump.

Aside from handling solid waste and sludge, what else must be considered for wastewater pumps?

Typical pumping considerations for a wastewater pump include the ability to pump solids, grit, corrosive materials, sludge, scum and smaller particles that have agglomerated into larger particles. Aside from these requirements, additional considerations should be made when selecting a pump for wastewater applications. These include the altitude, temperature, flow rate and rotative-speed limitations.

When considering altitude, it is important to know that the site evaluation for the pump installation can affect pump operation. In general, the higher the elevation of the installation, the less suction lift there is available for the pump. For pumping systems with atmospheric suction pressure, the net positive suction head available (NPSHa) calculation should be checked to include the actual atmospheric pressure at the job site.

NPSHA vs rate of flow for wastewater pumps

Altitude will also affect the selection of the pump driver and, when applicable, the variable frequency drive (VFD) because higher altitudes will result in the air providing less cooling. The reduced cooling may require the driver and VFD to be derated.

The temperature of the liquid pumped affects the ability of the pump to operate. Specifically, high-temperature liquids will have higher vapor pressure, reducing the NPSHa. If not properly accounted for, the pump may cavitate, which can cause reduced performance, physical damage to the pump components and can increase vibration.

Current wastewater pump design technology allows reliable operation of pumps with values of suction specific speed (Nss) through approximately 250 for metric units (13,000 for U.S. customary units, Nss), depending on eye peripheral velocity, materials of construction, range of operation, pumped liquid properties, and other factors.

Higher Nss values result in pumps designed with lower NPSH requirements at the same or higher operating speeds. The maximum speed for a pump (n) due to NPSHa can be calculated from the Nss formula by expressing the rotative speed as a function of NPSHa, pump rate of flow (Q), and Nss (Equation 1).

Equation 1

n = (Nss × NPSHa0.75)/Q0.50

>>Read more.


A Complete Line of Pumps for Industry

Vertiflo Pump Company’s Vertical Sump Centrifugal Pumps, Horizontal End Suction Centrifugal Pumps and self-priming pumps are delivered fast, usually in half the typical lead time. Vertiflo’s vertical sump pump line offers up to 3000 GPM, 250′ Heads and 26′ depth. The horizontal end suction pump line offers up to 3000 GPM and 300’ Heads.

Vertiflo pumps are designed for nonresidential applications and currently over 20,000 are operating successfully worldwide. Vertiflo is recognized as a quality manufacturer of dependable pumps, and continues to grow and encompass new applications in the pump industry.

Visualization of Gas-Liquid Flow Pattern in a Centrifugal Pump

Excerpt from the Feb. 2021 Vol. 13 of Measurement: Sensors research paper by LinZhao, Zhuang Chang, Zhenduo Zhang, Rui Huang, and Denghui He

1. Introduction

The centrifugal pump is extensively used in the fields of petroleum, chemical industry, nuclear power, agriculture, etc. The bubble flow is an important flow pattern that exists in the working process of a centrifugal pump. When bubbles are evenly distributed in the impeller channel, the pump performance is less affected by them. As the inlet gas volume fraction (IGVF) increases, bubbles may accumulate in the impeller, and thus, affect the pump performance. When bubbles coalesce further, it may form an air mass around the impeller inlet. With the increased gas concentration, the pump is prone to surge, resulting in a sudden drop in head, which is also accompanied by strong vibration and noise. In serious cases, the impeller channel will be blocked, resulting in “gas lock” effect, which makes the pump idle. This not only greatly reduces its service life, but also affects the normal production. Therefore, it is significantly important to study the flow pattern in the pump under bubble inflow condition for the safe and stable operation of pump.

Centrifugal Pumps

Murakami and Minemura classified four typical flow patterns in the pump impeller, i.e., the Bubble Flow (BF), the Agglomerated Bubble Flow (ABF), the Gas Pocket Flow (GPF) and the Segregated Flow (SF). For the pump operating under the bubbles inflow, the bubble behavior will affect the gas-liquid flow pattern in the pump, and thus, affect the pump performance. However, limited literature on the bubble behaviors in the pump are publicly available. Minemura and Murakami investigated the effect of the pressure gradient force, the drag force, the buoyancy force and the inertia force on bubbles motion in a centrifugal impeller. They reported that the governing factors for the bubble motion are the pressure gradient force and the drag force, and the effect of the inertia force increases as the diameter of bubble increases. Sterrett developed an analytical model for the motion of a single bubble through a pump impeller. The results showed that the Coriolis and buoyancy forces are important in describing the kinematics of gas phase.

The bubble motion is also influenced by the pump suction pressure. Barrios and Prado measured the bubble size inside the impeller channel of an Electric Submersible Pump (ESP) by using a high-speed instrumentation. They found that the majority of the bubbles inside the pump are not spherical. With the increase of the IGVF, the tendency of bubble coalescence as well as the bubble size increases. Similar results on the variation of bubble size were also reported by Cubas et al. Finally, the stagnant bubble at the impeller inlet causes the pump surging. Shao et al observed that for the BF and ABF patterns, the bubbles in the impeller rotate with the impeller, and the bubbles in the volute move along the volute channel. Once the IGVF reaches a critical value, some bubbles will flow back to the impeller near the volute tongue. When the flow pattern transits from the GPF pattern to the SF pattern, some bubbles in the discharge pipe return to the impeller near the volute tongue. When the height of the gas in the inlet pipe reaches the critical value, sometimes the bubble will flow into the volute, sometimes it will flow back to the impeller at a small velocity.

Stel et al experimentally and numerically investigated the bubbles motion in a centrifugal pump impeller. The effects of the bubble diameter and the liquid flow rate on the bubble trajectories were evaluated. The results indicated that the bubble movement is hindered by the bubble diameter and impeller rotational speed but facilitated by the liquid flow rate increasing. They also demonstrated that the behavior of the bubble inside the impeller is mostly dominated by a balance between the pressure gradient and the drag forces. This balance determines whether the bubble leaves or stays in the impeller. The bubble behaviors and their effects of the gas-liquid distribution in the impeller are still need further exploration.

2. Experimental setup and method

2.1. Experimental setup

Fig. 1 shows the gas-liquid two-phase flow loop employed in this study. The tap water and compressed air were used as the fluids. The experiment method and the parameters of the measurement devices employed in the present experiment are available in Ref. [18]. The measurement locations of the inlet pressure (Pin) and the pressure increment (ΔP) of the pump was shown in Fig. 1.

Centrifugal Pump Gas Flow

2.2. Centrifugal pump

The primary parameters of the centrifugal pump are shown in Table 1. As shown in Fig. 2, the pump inlet and the motor were designed in the same side to record the gas-liquid distributions in the whole impeller. The water flows into the pump through an annular inlet. The flow in the pump can be filmed from the hub of the impeller. The inlet part of the pump, the impeller and volute were made of polymethyl methacrylate (PMMA) (Fig. 3). The volute was designed with rectangular external shape and circular internal section to reduce the reflection and refraction of the light during the experiment, and thus, improving the shooting quality of high-speed photography. The pictures of the impeller and part of the volute are displayed in Fig. 3.

Centrifugal Pump Table 1

>>Read more.


A Complete Line of Pumps for Industry

Vertiflo Pump Company’s Vertical Sump Centrifugal Pumps, Horizontal End Suction Centrifugal Pumps and self-priming pumps are delivered fast, usually in half the typical lead time. Vertiflo’s vertical sump pump line offers up to 3000 GPM, 250′ Heads and 26′ depth. The horizontal end suction pump line offers up to 3000 GPM and 300’ Heads.

Vertiflo pumps are designed for nonresidential applications and currently over 20,000 are operating successfully worldwide. Vertiflo is recognized as a quality manufacturer of dependable pumps, and continues to grow and encompass new applications in the pump industry.