Tag Archives: Vertical Turbine Pumps

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.

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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.

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.