## Characteristics of Centrifugal Pumps

What are the Characteristics of a Centrifugal Pump? Head, performance curve and affinity laws all contribute to the efficiency of centrifugal pumps.

Excerpt from Pumps & Systems, Sept. 2012, by Sharon James, Rockwell Automation

Pumps are generally grouped into two broad categories—positive displacement pumps and dynamic (centrifugal) pumps. Positive displacement pumps use a mechanical means to vary the size of (or move) the fluid chamber to cause the fluid to flow. On the other hand, centrifugal pumps impart momentum to the fluid by rotating impellers that are immersed in the fluid. The momentum produces an increase in pressure or flow at the pump outlet.

Positive displacement pumps have a constant torque characteristic, whereas centrifugal pumps demonstrate variable torque characteristics. This article will discuss only centrifugal pumps.

A centrifugal pump converts driver energy to kinetic energy in a liquid by accelerating the fluid to the outer rim of an impeller. The amount of energy given to the liquid corresponds to the velocity at the edge or vane tip of the impeller. The faster the impeller revolves or the bigger the impeller, then the higher the velocity of the liquid at the vane tip and the greater the energy imparted to the liquid.

Characteristics

Creating a resistance to the flow controls the kinetic energy of a liquid coming out of an impeller. The first resistance is created by the pump volute (casing), which catches the liquid and slows it down. When the liquid slows down in the pump casing, some of the kinetic energy is converted to pressure energy. It is the resistance to the pump’s flow that is read on a pressure gauge attached to the discharge line. A pump does not create pressure, it only creates flow. Pressure is a measurement of the resistance to flow.

Figure 2. Representation of static discharge head, static suction lift and total static head

In Newtonian (true) fluids (non-viscous liquids, such as water or gasoline), the term head is the measurement of the kinetic energy that a centrifugal pump creates. Imagine a pipe shooting a jet of water straight into the air. The height that the water reaches is the head. Head measures the height of a liquid column, which the pump could create resulting from the kinetic energy the centrifugal pump gives to the liquid. The main reason for using head instead of pressure to measure a centrifugal pump’s energy is that the pressure from a pump will change if the specific gravity (weight) of the liquid changes, but the head will not change. End users can always describe a pump’s performance on any Newtonian fluid, whether it is heavy (sulfuric acid) or light (gasoline), by using head. Head is related to the velocity that the liquid gains when going through the pump.

All the forms of energy involved in a liquid flow system can be expressed in terms of feet of liquid. The total of these heads determines the total system head or the work that a pump must perform in the system. The different types of head—friction, velocity and pressure—are defined in this section.

Friction head is the head required to overcome the resistance to flow in the pipe and fittings. It depends on the size, condition and type of pipe; the number and type of pipe fittings; flow rate; and nature of the liquid.

Velocity head is the energy of a liquid as a result of its motion at some velocity (V). It is the equivalent head in feet through which the water would have to fall to acquire the same velocity or, in other words, the head necessary to accelerate the water. Velocity head can be calculated using the following formula:

hv = V2/2g

Where:
g = 32.2 ft./sec.2
V = liquid velocity in ft./sec.

The velocity head is usually insignificant and can be ignored in most high-head systems. However, it can be a large factor and must be considered in low-head systems.

Pressure head must be considered when a pumping system either begins from or empties into a tank that is under some pressure other than atmospheric. The pressure in such a tank must first be converted to feet of liquid. A vacuum in the suction tank or a positive pressure in the discharge tank must be added to the system head, whereas a positive pressure in the suction tank or vacuum in the discharge tank would be subtracted. The following is a formula for converting inches of mercury vacuum into feet of liquid:

Vacuum, feet of liquid = (Vacuum, in. of hg x 1.13)/Specific Gravity

The different types of head are combined to make up the total system head at any particular flow rate. The descriptions in this section are of these combined or dynamic heads, as they apply to the centrifugal pump.

Read more at Pumps & Systems.

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.

## Pumping Solids In Chemical Processing Applications

Centrifugal Pumps for Pumping Solids In Chemical Processing Applications

Excerpt from Process Industry Informer, Oct. 15, 2015, by Malcolm Walker

Pumps designed to handle solids are often not the cheapest option. However, when you consider the costs of maintenance, production downtime, or even cleaning up escaped corrosive liquids, they often represent the cost-effective option for many applications.

Consider the centrifugal pump when selecting pumps for handling solids. There is a misconception that there aren’t any chemically-resistant centrifugal pumps capable of handling solids. It is a situation that needs correcting.

Centrifugal pumps featuring a stainless steel vortex impeller provide an excellent and well-proven solution. In operation, a whirlpool effect is formed in the volute by the rotating recessed cup-shaped impeller extending into the suction line, drawing the liquid/solids into the pump and then quickly through the discharge.

This motion minimizes the fluid/solids contact with the impeller and volute. It is a simple design that allows solids to pass through the pump without choking the impeller, so considerably reducing pump wear and the potential for blockages.

The fully recessed cup-shaped impeller and free passageways within the pump casing offer almost total freedom from blockages where solids and fibrous materials can be encountered in process waste water treatment plants.

Read more at Process Industry Informer.

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.

## Article Review: 4 Factors to Consider for Irrigation Pumps

### Determine how booster and suction lift applications are used.

Originally published in the February 2019 issue of Pumps & Systems by Justin McDaniel

Irrigation pump requirements are influenced by the type and scope of the system to be installed. Gathering some basic information from the irrigation plan is essential when selecting the correct pump for the application.

Specific site requirements may also influence pump selection. If the site has a limited window when watering can occur, the pumping system must be sized to deliver all of the water required during that window. An undersized pump prevents the system from meeting the total irrigation requirements during the hottest periods.

Additionally, the type of sprinkler selected and the location for the pump can have a material impact on the cost of the pumping equipment and long-term system operating costs. In general, pump selection is governed by four factors:

1 Required operating pressure. Gather the operating pressure requirements from the irrigation plan, noting the required maximum pressure.

2 System flow. It is important to understand the scope of the system.

3 Friction losses. Calculate the total head loss and elevation change from the outlet of the pump to the highest sprinkler head, as well as the suction lift head requirements.

4 Budget. The design of an irrigation system, as well as the site characteristics, can have dramatic ramifications for the cost of the pump. The available power supply is always an important factor to consider and may also impact the cost of the pump.

Common Irrigation Pumps
There are two main actions that a pump performs in an irrigation application: pressure boost or suction lift. The four styles of pumps that are typically used for these applications:

1. horizontal centrifugal
2. submersible
3. vertical turbines
4. vertical multistage pumps

Boost Applications
Booster pumps are used to increase (boost) the water pressure in the system. Primarily, booster pumps are used on domestic or municipal water systems when the existing pressure is not adequate for the irrigation system.

The two most widely used are horizontal centrifugal and vertical multistage. The selection of the pump depends on three factors:

1. pressure is required to run the system
2. what type of efficiency must be reached
3. the type of water: municipal, reclaimed water or gravity supply tanks

Vertical multistage pumps are designed to handle clean water that is free from large solids and debris. Vertical multistage pumps lend themselves to higher pressures, whereas horizontal centrifugal pumps lend themselves to a lower maximum pressure range but are generally more forgiving when handling dirty water.

Horizontal centrifugal pumps and vertical turbines can handle dirty water as long as a screen is present. The screen is important because, without it, the irrigation system can get plugged up. Submersibles and vertical multistage pumps are recommended for boosting clean water. Solids or debris can damage these without the use of components such as filters.

Suction Lift Applications
In a suction lift application, the system does not have incoming pressure but is instead pulling from a water source, such as a lake, river, sump, etc. Suction lift applications commonly require the use of horizontal centrifugal pumps and vertical turbines. An advantage of horizontal centrifugal pumps is that they are easier to install and maintain because the internal parts are easily accessible. Vertical turbines and submersibles are suited to suction lift applications since they are located in the water and do not need to create the vacuum to lift water to the pump intake.

Variable Frequency Drives & Irrigation Systems
VFDs are not required for smaller irrigation systems with nonvarying flows. They are recommended for larger systems to enable soft starts and energy reduction.

Industry News from the Pumps & Systems

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.

## What You Need to Know About NPSH

Most pump problems are related to net positive suction head (NPSH).
By Terry Henshaw, Pumps & Systems February 2018

Definition of NPSH
The margin of pressure over vapor pressure, at the pump suction nozzle, is net positive suction head (NPSH). NPSH is the difference between suction pressure (stagnation) and vapor pressure. In equation form:

NPSH = Ps – Pvap

Where:
NPSH = NPSH available from the system, at the pump inlet, with the pump running
Ps = stagnation suction pressure, at the pump inlet, with the pump running
Pvap = vapor pressure of the pumpage at inlet temperature

Since vapor pressure is always expressed on the absolute scale, suction pressure must also be in absolute terms. In U.S. customary units, both pressures must be in pounds per square inch absolute (psia). Gauge pressure is converted to absolute pressure by adding atmospheric pressure. The above equation provides an answer in units of pressure (psi). This can be converted to units of head (feet) by the following equation:

h = 2.31p/SG

Where:
p = pressure in psi
SG = specific gravity of the liquid

Importance of NPSH
NPSH is a subject of extreme importance in all pumping systems. It has been estimated that 80 percent of all pump problems are due to inadequate suction conditions, and most suction problems are related to NPSH. (Either the system does not provide as much as anticipated, or the pump requires more than anticipated.) It is therefore probable that most pump problems are NPSH problems.

Units of NPSH
For centrifugal pumps, NPSH values are expressed in units of specific energy (equivalent column height) such as feet or meters. For displacement pumps (rotary and reciprocating), NPSH values are normally expressed in pressure units such as pounds per square inch (psi), kilopascals pr bars.

NPSH values are neither gauge pressures nor absolute pressures. The “g” in psig means that the pressure is measured above atmospheric pressure. The “a” in psia means that the pressure is measured above absolute zero, a perfect vacuum. NPSH is a measurement of pressure above vapor pressure, so the units of NPSH (in the U.S.) are just psi or feet.

NPSH Available: A System Characteristic
NPSHa stands for NPSH available from the system. It can be calculated by measuring suction pressure at the pump suction nozzle, correcting to datum, adding atmospheric pressure, adding velocity head and subtracting vapor pressure. In equation form:

NPSH = Psg + Pz + Patm + Pvel – Pvap

Where:
NPSHa = NPSH available to the pump, psi
Psg = gauge pressure measured at suction nozzle, psig
Pz = elevation of gauge above pump centerline, converted to pressure unites, psi
Patm = atmospheric pressure, psia
Pvel = velocity head, converted to pressure united, psi
Pvap = vapor pressure of the pumpage, at the pump suction nozzle, psia

If desired, all units can be converted to head (feet) prior to plugging into the equation. If the system has not been built, it is necessary to calculate the NPSHa by starting with the pressure in the suction tank. Add atmospheric pressure, add (or subtract) the liquid level above (below) datum, subtract all losses from the tank to the pump and subtract vapor pressure.

NPSH Required: A Pump Characteristic
The letters NPSHr stand for the NPSH required by the pump. This characteristic must be determined by test.
For proper operation of the pump, it is necessary that NPSHa > NPSHr. The system must provide more NPSH than the pump requires.

What Happens When NPSHr Exceeds NPSHa?
One potential complication when NPSHr exceeds NPSHa is cavitation. If at any time the static pressure on a liquid drops below vapor pressure, a portion of the liquid will boil-it will flash to a gas. This formation of gas bubbles is called cavitation. (Cavities form in the liquid.) Such gas formation in a suction pipe or inside a pump may cause a reduction in pump capacity and/or head. It may also cause damage to the pump. As liquid flows into any pump, there is a reduction in pressure. In a centrifugal pump, the liquid accelerates into the eye of the impeller, causing a reduction in pressure. The impeller vanes then slice into the liquid, creating zones of lower pressure.

If a sufficient pressure margin, over vapor pressure, is not provided at the pump inlet, some of the liquid will flash at the leading edge of each vane.

With displacement pumps, the situation is similar. Because the pressure drops as the pumpage moves into the pumping chamber, suction pressure must exceed vapor pressure by some margin to prevent cavitation.

Even though the liquid is cavitating, we usually say that the pump is cavitation. Possible effects of pump cavitation include noise, head and/or capacity loss, and equipment damage. It is not the formation of the bubbles that causes damage. Damage is caused to pump parts when the bubbles collapse or “implode.” When the bubbles collapse on a hard surface, they create a high pressure.

To Quieten a Cavitating CentrifugaI Pump
If a centrifugal pump sounds as if it is pumping gravel, if the system can tolerate it and if no other solution is readily available, inject about ½ percent (by volume) air (or other gas) just upstream (into the inlet) of the pump. Experiment to see how little air is necessary to obtain quiet operation. (Do not try this with a reciprocating pump!)

NPSHr & Suction Specific Speed
Suction specific speed, like specific speed, is not a speed at all. It is an index number, or “yardstick.” It is based on the NPSHr of a centrifugal pump, normally the 3 percent head drop NPSHr and normally at its best efficiency point (BEP). The equation for suction specific speed is the same as specific speed, except that NPSHr is substituted or head, as follows:

S = N√Q/NPSHr0.75

Where (in U.S. units):
S = suction specific speed
N = RPM of pump
Q = pump capacity*†, GPM
NPSHr = NPSH required by pump†, feet

*If the impeller is double suction, Q in the above equation is one-half the BEP capacity of the pump. This is a major difference from calculating specific speed, in which w use total pump capacity, whether the impeller is single suction or double suction.
†Normally calculated at the BEP

The symbol Nss is often used in place of S for suction specific speed. The value of S for most pumps is typically between 7,000 and 15,000. The higher values are more common in higher speed, higher capacity units.

Suction Specific Speed
For a number of years, the push from users and competitors required pump manufacturers to continually strive for lower values of NPSHr. The philosophy was that “The lower the NPSHr, the better the pump.” NPSHr in centrifugal pumps is normally reduced by increasing the diameter of the impeller eye. That philosophy has now changed.

Due to problems that have been attributed to oversized impeller eyes, pump users have established maximum values for S, which establishes minimum values for NPSHr. (See Pumps & Systems, December 2011, pumpsandsystems.com/ analyzing-impeller-eye).

Every centrifugal pump would like to run at its BEP. Pump components would experience maximum life at that capacity. Seldom does a pump run at its BEP, but component life will be significantly extended if it operates within its “stable” window of capacities. Suction specific speed can indicate the size of that window. Pumps with lower values of S have larger windows.

WAYS TO INCREASE & REDUCE NPSHa
If it is necessary to increase a system’s NPSHa, one or more of the following steps may be employed:

1. Raise the level of the liquid in the suction vessel.
2. Cool the liquid (after it leaves the vessel).
3. Reduce the losses in the suction line by reducing its length, increasing its diameter, reducing number of fittings, etc.
4. Install a booster pump.
5. With a reciprocating pump or pulsating rotary pump, install a bottle or suction stabilizer in the suction line adjacent to the pump.

Ways to Reduce NPSHr
If the pump is in the selection stage, one or more of the following options may be employed to reduce the NPSHr:

1. Use a double-suction impeller.
2. Use a larger pump.
3. Use a lower speed pump.
4. Use an inducer (a small axial-flow impeller built into the eye of the main impeller).
5. Install the pump at a lower elevation.
6. With a vertical turbine pump, lower the first-stage impeller (make the pump longer).

All of the above will normally increase the initial cost of the pump and/or installation. Options two and three will also likely result in higher operating cost due to lower efficiency. Option two may result in a pump operating in the hydraulically unstable range. If the pump is already installed, one or more of the following options may be employed to reduce the NPSHr:

1. If operating near or beyond the SEP, reduce pump capacity.
2. If operating near shut-off, increase pump capacity (with a bypass if necessary).
3. Reduce wear ring clearances.
4. Reduce seal flush flow.
5. Vent the seal chamber (stuffing box) back to the suction vessel.
6. On a horizontal multistage pump with a balancing drum, pipe balancing line back to the suction vessel. The valves in this line must be locked open.
7. On a vertical multistage pump, pipe the bleed-off line from the throat bushing back to the suction vessel. The valves in this line should be locked open.

This article was originally printed in Pumps & Systems magazine February 2018.

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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.

## Agricultural Mixing Pumps

End Suction Vortex Pumps Designed for a Wide Range of Agricultural Fertilizer Mixing Industry Applications

Vertiflo Pump Company’s Series 1500-1600 Series horizontal end suction vortex pumps have a wide range of agricultural mixing pump applications for fertilizers. Fully recessed design which accommodates passage of solids. All impellers have wiping vanes which reduce axial loading and prevent dirt from entering the sealing area. Impeller is keyed to shaft, and an impeller locking screw assures positive attachment. Vortex Design provides an unrestricted flow since the impeller is not normally in contact with the solids being pumped.

Capacities to 1600 GPM, heads to 170 feet TDH, temperature to 250 degrees Fahrenheit, fully recessed vortex impeller, with packing or mechanical seal.  Pumps are designed with back pull-out construction that permits easy inspection and access for service or maintenance — if it is ever needed — without disturbing the piping to the pump.  Standard construction is Cast Iron, 316 Stainless Steel fitted, all 316 Stainless Steel, Alloy 20 or CD4MCu.

The base-mounted Series 1500 pumps are designed for use with any T frame motor or with virtually any type of drive. Rugged heavy duty cast iron design incorporating integrally cast support and ribbed mounting feet which assure a solid, dependable pump installation and operation. One frame fits all pump sizes. External impeller adjustment is standard. Grease lubrication of bearings is standard; oil lubrication available. Packing or various mechanical seal arrangements are available as standard options of this pump. Shaft is 416 stainless steel, precision machined with preferred taper at impeller location. Positive attachment is provided with castellated impeller nut and cotter pin, which assures that the impeller will not back off the shaft if the pump is accidentally operated in reverse rotation. 316 stainless steel shaft is optional. Every power frame contains an external impeller adjustment utilizing jackscrews which provides for clearance adjustment of the impeller. This adjustment feature compensates for internal wear. Expensive casing and impeller wearing rings are eliminated.

Series 1600 horizontal close-coupled end suction pumps are designed for use with any NEMA Standard JP Shaft Motor. VERTIFLO’s close-coupled pumps are designed with back pull-out feature. NEMA standard JP shaft extension allows for easy interchangeability to packing, standard mechanical seal or optional single or double mechanical seals of various designs and materials of construction. Shaft construction of 316 stainless steel is standard. It is positively driven and gasketed, protecting motor shaft from liquid being pumped.

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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.

## How will pump efficiency be affected with variable speed drives?

By Hydraulic Institute

Q How much will pump efficiency be affected with the addition of a variable speed drive?

A It is a misconception that adding a variable speed drive (VSD) to a pump will increase its efficiency. When considering the wire-to-water efficiency of the pump, motor and VSD, each component that is added lowers the wire-to-water efficiency at a respective flow rate because each component has losses associated with it. Image 1 illustrates this concept showing the pump efficiency being the greatest, then the wire-to-water efficiency decreasing at the respective flow rate when the motor and VSD are added to the extended pump product.

The advantage that the VSD brings to the picture is that it can control the speed of the pump to meet the requirements of the system, which can reduce power consumed by less efficient controls that is not an essential requirement of the process. Additionally, the VSD can be used with on-off controls so the pump operates at a minimum speed where the specific energy consumption is optimized. Based on this, the VSD potentially increases the entire pump system efficiency by eliminating wasted head across control valves and wanted flow through bypass vales, and in some instances allows the pump to operate closer to its best efficiency point (BEP).

Image 2 illustrates two examples where the gray box represents power that is essential to the system and the orange box represents power that is not essential to the system. The orange box shows how much energy is wasted by throttling control in the first image or bypass control in the second image. In each case, the reduced speed pump curve can satisfy the operating flow without the orange wasted control power. The wasted control power typically outweighs the slight decrease in wire-to-water efficiency of the extended product. The two examples in Image 2 show systems with all friction head, and it is understood that the potential variable speed energy savings will decrease when static head is introduced to the system curve.

For more information on variable speed pumping and the application and efficiency considerations, refer to Hi’s Application Guideline for Variable Speed Pumping at pumps.org. ■

Link to original article in PUMPS & SYSTEMS Magazine Dec 2018.

HI Pump FAQs® is produced by the Hydraulic Institute as a service to pump users, contractors, distributors, reps and OEMs. For more information, visit pumps.org.

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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.

## Standards for Fossil Power Plant Pumps

By Hydraulic Institute

Q What standards are applied to fossil power plant pumps?

A Specifications for power plant pumps will invoke many standards and requirements that will vary based on the specifier. A specific design standard is not applied.

Pump manufacturers that supply to this industry have developed product lines designed to internal standards to meet the reliability and pricing requirements that the market demands. Sometimes American Petroleum Institute (API) design standards are applied or pumps complying with API standards are specified in the power gen industry.

Regarding the performance, testing and application of the pumps, Hydraulic Institute (HI) standards and , Hydraulic Institute (HI) standards and guidebooks can also be applied as follows:

• Important application considerations, pump types and typical materials of construction that are used in typical fossil power plant pump applications can be found in HI’s Pump Application Guidebook for Power Plant Pumps.

• Guidelines for the measurement of airborne sound can be found in ANSI/ HI 9.1-9.5 Pumps – General Guidelines.

• Guidelines on the application of net positive suction head (NPSH) margin and the preferred and allowable operating region can be found in ANSI/HI 9.6.1 Rotodynamic Pumps – Guideline for NPSH Margin and ANSI/HI 9.6.3 Rotodyanmic Pumps – Guideline for Operating Regions.

• Vibration acceptance testing of the pumps should be per ANSI/HI 9.6.4 Rotodynamic Pumps – Vibration Measurements and Allowable Values.

• Recommendations on the condition monitoring of the installed pump can be found in ANSI/HI 9.6.5 Rotodynamic Pumps – Guideline for Condition Monitoring.

• Important system components like piping connecting to the pump and free surface intakes should be designed to ANSI/HI 9.6.6 Rotodynamic Pumps for Pump Piping and ANSI/HI 9.8 Rotodynamic Pumps for Intake Design, respectively.

• Guidelines for dynamic analysis that should be conducted can be found in ANSI/HI 9.6.8 Rotodynamic Pumps – Guidelines for Condition Monitoring.

• Hydraulic performance, NPSH3, and hydrostatic acceptance testing of the pump should be per ANSI/HI 14.6 Rotodynamic Pumps for Hydraulic Performance Acceptance Tests.

View the original article publication at PUMPS & SYSTEMS Dec 2018 issue.

HI Pump FAQs® is produced by the Hydraulic Institute as a service to pump users, contractors, distributors, reps and OEMs. For more information, visit pumps.org.

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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.

## Flexible Couplings Alignment & Pumps in Explosive Atmospheres

Q: Is there a simple way to check the alignment of flexible couplings on a pump?

A: Laser alignment systems are used to determine the extent of shaft misalignment by measuring the movement of a laser beam across the surface of a detector plate as the shafts are rotated.

Many laser alignment systems are available, and the procedure for alignment is provided by the laser system’s producer. They are capable of aligning couplings with and without spacers and are most commonly used for precision alignments. Image 1 shows an example of a laser alignment system setup on a pump and motor shaft.  By following the instructions of the laser system, the computer will output adjustment requirements to align the shafts.

In the absence of a laser alignment system, users can check the alignment with some simple tools. The necessary tools used for checking the alignment of a flexible coupling are a straightedge and a taper gauge or a set of feeler gauges, or by use of dial indicators.

A rough check for angular alignment is made by inserting the taper gauge or feelers between the coupling faces at 90 degree intervals (see Image 2). Checks for angular and parallel alignment by this method can only be done if the face and outside diameters of the coupling halves are square and concentric with the coupling bores. A rough check for parallel alignment is made by placing a straightedge across both coupling rims at the top, bottom and at both sides (see Image 3). After rough alignment, fasten the indicator to the pump half of the coupling, with the indicator button resting on the other half coupling periphery (see Image 4). Set the dial to zero, and mark the coupling half beside where the button rests. Rotate both shafts by the same amount, i.e., all readings on the dial must be made with the button beside the mark. The dial readings will indicate whether the driver has to be raised, lowered or moved to either side.

After each adjustment, recheck both parallel and angular alignments. Accurate alignment of shaft centers can be obtained with the dial indicator method — even where faces or outside diameters of the coupling halves are not square or concentric with the bores—provided all measurements for angular alignment are made between the same two points on the outside diameters. For angular alignment, change the indicator so it bears against the face of the same coupling half and proceed as described for parallel alignment.

There are additional techniques not described in this answer that are required for proper pump alignment, such as correcting for indicator sag or compensating for cold aligning a hot pump system. Please reference industry standards and the pump and coupling manufacturer’s instructions as well.

For more information about coupling alignment for rotodynamic pumps, including additional considerations, see the American National Standard ANSI/HI 14.4 Rotodynamic Pumps for Manuals Describing Installation, Operation, and Maintenance at pumps.org.

Q: What is meant by the temperature class for my pumps that are rated for explosive atmospheres?

A: Pumps installed in potentially explosive atmospheres must be designed and operated in a way to limit their surface temperature based on the type of potentially explosive atmosphere.

A reference for the requirements of electrical and nonelectrical equipment is the European Union (EU) ATEX Directive 2014/34/EU (Ex). Within this directive, one requirement is that pumps have a temperature class as stated in the explosion (Ex) rating on the nameplate. These are based on a maximum ambient temperature of 40 C (104 F). Refer to the manufacturer for higher ambient temperatures.

The surface temperature on the pump is influenced by the liquid handled. The maximum permissible liquid temperature depends on the temperature class and must not exceed the values in Image 5. The temperature rise at the seals and bearings due to the minimum permitted fl ow rate is taken into account in the temperatures stated. Note that the plant operator is responsible for compliance with the specified maximum liquid temperature. Surface temperatures above 54 C (130 F) can cause irreversible skin damage and, therefore, require insulation to ensure personnel protection. For more information about the manuals describing the installation, operation and maintenance of rotodynamic pumps, refer to ANSI/HI 14.4 Rotodynamic Pumps for Manuals Describing Installation, Operation, and Maintenance at pumps.org.

HI Pump FAQs® is produced by the Hydraulic Institute as a service to pump users, contractors, distributors, reps and OEMs. For more information, visit pumps.org.

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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.

## What is a centrifugal pump?

What is the Difference Between Centrifugal & Rotodynamic Pumps

Rotodynamic pumps include centrifugal, mixed and axial flow pumps.
by Hydraulic Institute, February 27, 2019

Q: I am used to hearing the term “centrifugal” pump, but sometimes hear them referred to as “rotodynamic” pumps. Can these terms be used synonymously?

A: Rotodynamic pumps are kinetic machines in which energy is continuously imparted to the pumped fluid by means of a rotating impeller, propeller or rotor. These pumps transfer mechanical energy to the fluid primarily by increasing the fluid kinetic energy. Kinetic energy is then converted into potential energy (pressure) in the discharge collector. The most common types of rotodynamic pumps are radial (centrifugal), mixed flow and axial flow (propeller) pumps, including pumps historically referred to as vertical turbine pumps. Radial, mixed and axial flow impellers are shown in Image 1.

Image 1. Radial (centrifugal), mixed and axial flow impellers (Images courtesy of the Hydraulic Institute)

As seen from the definition of a rotodynamic pump and Image 1, it is a term used to describe a larger group of pumps that includes centrifugal (radial flow) pumps, but also includes mixed and axial flow pumps and some other unique constructions. Centrifugal pumps are the most common type and the term is synonymous with radial flow impellers where the flow enters the impeller in line with the pump shaft, but discharges the impeller perpendicular to the pump shaft.

Image 2. Rotodynamic pump types by classification

Rotodynamic pump types are also commonly described by their general mechanical configuration. To answer the question directly, a centrifugal pump is a type rotodynamic pump, and not all rotodynamic pumps are centrifugal pumps.

For more information, refer to ANSI/HI 14.1-14.2 rotodynamic pumps for nomenclature and definitions, and ANSI/HI 14.3 rotodynamic pumps for design and application at www.pumps.org.

## Pump Bearings & Housing Seal Lubrication – By Hydraulic Institute

What types of lubrication can be used for pump bearings?

March 2019 Pumps & Systems Magazine

There are many bearing types, which require different lubrication methods. This response focuses on the most common methods for lubricating rolling element bearings in horizontal process pumps and their application considerations include:

• Grease lubrication:
An advantage of grease lubrication is simplified maintenance, and some disadvantages are over-pressurization and limited heat dissipation. The use of grease is primarily limited to lower speed and horsepower pumps.
• Oil splash:
Some advantages of oil bath/splash lubrication are a wider range of speeds than grease and visual verification of oil level is possible, and some disadvantages are sensitivity to oil level and contaminants remaining in the oil bath. Oil splash lubrication can be achieved by the bearing being in direct contact with the oil, oil rings contacting the lubricant and splashing it throughout the bearing housing, or slinger disks that splash the lubricant throughout the bearing housing.
• Pure oil mist:
Some advantages of pure oil mist lubrication are lower operation temperature compared to oil bath, wear particles are not recirculated and lower oil consumption. Some disadvantages are that it requires higher level of application knowledge and higher initial costs compared to oil bath. The basic concept of oil mist lubrication system is dispersion of an oil aerosol into the bearing housing. There is no reservoir of oil in the housing, and oil rings are not used. The oil is atomized and airflow transports the small oil particles through a piping system into the pump bearing housing.
What methods can be used to maintain lubrication oil quantity and quality?
For oil bath lubrication, quantity of oil can always be adjusted by adding oil to maintain the manufacturer’s recommended level. However, another approach to maintain the proper quantity of oil is with bearing housing seals. When properly applied, bearing seals can eliminate lubrication leaks from the housing and help maintain recommended oil levels.
Examples are lip seals, labyrinth isolators and magnetic face seals shown in Image 1. These mentioned seals  are also useful in the reduction of oil contamination to maintain the quality of the oil.
Particle contamination can be avoided with consideration of materials, design and maintenance of lubricant containers, seals and bearing isolators. When selecting gaskets and seals, materials should be compatible with the lubricant.
When filling the bearing housing, the fill port should be cleaned prior to opening, the lubricant container should be closed until filling, and care should be taken to prevent atmospheric contaminants from entering the fill port during the fill process.
In addition to preventing lubricant leakage, bearing housing seals also serve to prevent contaminant ingress.
Focusing on isolator technology, labyrinth and magnetic face-type bearing isolators are widely used on pumps. Bearing isolators allow increased pressure created in the bearing housing by normal pump operation to vent through the isolator and have proven to be effective at reducing, and sometimes eliminating, contaminant ingress. The face design and the labyrinth design allow for the venting to occur while in operation.
The face design of the magnetic isolator protects the bearings against contaminants while the pump is shut off or in standby using the contacting faces.
Labyrinth isolators may use shut-off features to provide ingress protection when the equipment stops rotating, as shown in Image 2.
These shut-off devices are designed to prevent moisture from penetrating the bearing chamber when the equipment shuts down and air is drawn into the housing.
When properly specified, bearing housing lubrication quality­enhancing components-including oilers, bearing protection devices and vents-can be effective in maintaining the quality of bearing lubricants.
For more information about proper bearing lubrication and maintaining the quality of the lubrication, download HI’s new free white paper “Proper Lubrication Methods for Bearings” at pumps.org/lubrication. ■
HI Pump FAQs” is produced by the Hydraulic Institute as a service to pump users, contractors, distributors, reps and OEMs. For more information, visit pumps.org.

Vertiflo Pump Company – A Complete Line of Pumps for Industry

Vertiflo Pump Company’s vertical, horizontal 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 Pump Company, Inc. was established in 1979 to design, sell and build packaged lift stations. Since 1981, Vertiflo has concentrated on manufacturing vertical process pumps, sump pumps, end suction pumps and self-priming pumps in cast iron, stainless steel and special alloys.

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.

Vertiflo Pump Company, Dept. I, 7807 Redsky Drive, Cincinnati, OH 45249 • 513-530-0888 • www.vertiflopump.com[email protected]