Tag Archives: Intro to Pumps

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

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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.

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

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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.

Paradigm Shift Towards Solar Powered Centrifugal Pumps

Excerpt from the Sept. 2019 article from Modern Pumping Today by Dave Namrata

Rapidly changing agricultural technology combined with constant improvement in farm machinery is leading to wide adoption of energy-efficient centrifugal pumps, creating pressure and flow in the irrigation system. Solar-powered water pumping system in agriculture is gaining popularity as an alternative to grid electricity. The modern agricultural system has led to the growing demand for irrigation solutions that reduces energy cost, improves productivity and safeguards water resource. Moreover, a reduction in the price of solar panels and components in solar power systems is driving the adoption of solar-powered centrifugal pumps and emerging as an economically viable option for irrigation.

The growing concern towards wastewater treatment in the past few years has resulted in wide application of centrifugal pumps. Rising competitiveness in the market is resulting in the development of centrifugal pump technology leading to better performance and reduction in the overall cost. From a design perspective, manufacturers of centrifugal pumps are focusing on improving the quality of shaft steel in the pumps to withstand vibration, fatigue, and stress. According to some industry experts, water shortage is likely to impact more than half of the world population by 2025. This is accelerating the wastewater treatment process across the countries.

Increasing energy costs and growing environmental awareness are motivating pump manufacturers to focus on developing energy-efficient centrifugal pumps for the end-use industries. Moreover, centrifugal pumps operating at a high speed pumping a large amount of liquid consume more power. This is leading to the integration of economically feasible and reliable solar power in the centrifugal pumping system.

Long product life and low maintenance cost of solar-powered centrifugal pumps are emerging as the perfect alternative to other pumping systems. Industries consider various factors while selecting a pumping system, such as pump lifecycle cost, including initial cost, maintenance cost and energy cost. On average, centrifugal pumps can consume around 60 percent of motor energy in the facility resulting in higher energy and maintenance costs.

Centrifugal Pumps
Centrifugal pumps generated by solar power

 

Increasing Focus on Energy Efficiency

In recent years, with an increasing cost of energy worldwide, energy efficiency is gaining attention from governments and pump manufacturers across countries. Despite various challenges, pump manufacturers are adding sustainable design features, enhancing productivity, quality, and services.

Solar-powered centrifugal pumps have gained popularity and are available on a large scale in the developed countries. However, the high initial cost of solar-powered centrifugal pumps as compared to the cost of fuel-powered pumps is the main obstacle for solar pumps in developing countries. This is driving the pump manufacturers in the developing regions to design next generation, cost-effective solar powered centrifugal pumps, eliminating the need for grid connection or fossil fuel.

Use of solar photovoltaic technology for centrifugal pumping system has gained immense popularity. Continuous reduction in solar cells cost is likely to drive the application for centrifugal pumps powered by the solar photovoltaic system in agriculture and other industries.

solar panels for centrifugal pumps
Solar panels for centrifugal pumps

With an aim to save the energy cost, replacement and refurbishing of the pumping system in water and wastewater treatment industry is on the rise. There has been a rise in the adoption of centrifugal pumps powered by solar energy in this industry.

Driven by rapid industrialization and urbanization, municipal water and wastewater industry in emerging countries is creating growth opportunities for centrifugal pumps manufacturers. However, manufacturers are facing a flood of new competition due to the increasing demand for energy-efficient pumps and stringent regulations. According to the American Hydraulics Institute, around 30 percent of the total electrical energy consumed by pumping systems can be saved by developing a highly efficient system and using appropriate pumps.

First-generation PV pumping systems using centrifugal pumps have shown significant advancements in recent years. The current solar-powered pumping technology uses an electronic system by further increasing the output power, performance and efficiency. PV modules account for nearly 60 to 80 percent of the total cost of PV system. A significant decline in the cost of PV modules across various regions has also reduced the overall cost of the pumping system. Moreover, an increase in the cost of crude oil, diesel, and gasoline has made solar powered pumps financially attractive.

There exists immense growth opportunity for centrifugal pumps in wastewater, pharmaceuticals, food and beverage, and chemical industries, as the sectors are set to grow at a stable pace in the near future. However, centrifugal pump demand will continue to be hit by the nuclear power generation, mining, and oil and gas sectors, which are likely to experience slow growth.

>>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.

Minimum Continuous Stable Flow

Centrifugal Pump Flow Operating Regions and Impact on Reliability

Ideally, a centrifugal pump should be operated at or near its best efficiency point (BEP) flow rate in order to minimize the life cycle costs. However, all centrifugal pumps have sweet spots beyond the BEP that will yield acceptable efficiency and reliability.

Excerpt from the Sept. 2016 article from WaterWorld

There are limitations, though, on the minimum and maximum flow rates, beyond which the pumps should not be operated continuously (or for an extended period of time), in order to avoid premature failures.

A first step in avoiding these negative, low-efficiency and low-reliability conditions is to determine the pump BEP, preferred operating region (POR), and allowable operating region (AOR) flow rates. It is especially important to determine these flow regions because not all pump applications are static in nature or closely match the expected system demand. Because of this, pumps are often required to operate over a broad range of flow rates, which can adversely affect the pump efficiency and reliability.

Centrifuge Flow Reliability Factor

A pump will always operate at the flow rate where the pump head-capacity curve intersects the system head-capacity curve. This means that it is also critical to accurately determine the true system H-Q curve, in order to establish the true operating flow rates.

Once these flow regions and the true system conditions are known, actions can be taken to maximize pump operation in the POR and avoid or minimize operation outside the AOR, thus optimizing pump life cycle costs.

BEP Flow Region

Pump performance and service life are optimized around a rate of flow designated as the BEP. At the BEP, the hydraulic efficiency is maximum, and the liquid enters the impeller vanes, casing tongue (discharge nozzle), and diffuser vanes in a shockless manner. At the BEP, flow through the impeller and diffuser vanes (if so equipped) is uniform, free of separation, and well-controlled.

Minimum Continuous Stable Flow

Lower and higher flow rates cause mismatch between the flow and the impeller and casing vanes. This mismatch causes turbulence within the impeller and casing flow passages, which both block the flow passages and increases the local velocities. This increase in velocity increases vaporization (cavitation) within the liquid. The greater this resulting turbulence and cavitation, the lower the pump efficiency and reliability, and the more severe are the levels of vibration, noise and erosion.

>>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.

What is a Centrifugal Pump?

centrifugal pump is a machine that uses rotation to impart velocity to a liquid and then converts that velocity into flow.

Excerpt from introtopumps.com

Let’s break that definition down into its components so that we can consider each one in turn:

  1. A centrifugal pump is a machine.
  2. A centrifugal pump uses rotation to impart velocity to a liquid.
  3. A centrifugal pump converts velocity into flow.

Every centrifugal pump includes an assembly of mechanical components that make operation of the pump possible. This mechanical assembly includes the pump shaft mounted on bearings, the sealing mechanism that keeps the pump from leaking excessively, structural components designed to handle the stresses and loads imposed on the pump during operation, and wear surfaces that allow the pump to be repaired and returned to its original specifications.

Every centrifugal pump includes an impeller. The impeller is the hydraulic component that rotates to impart velocity to the pumped liquid.

Every centrifugal pump includes a casing. The casing is the hydraulic component that captures the velocity imparted by the impeller and directs the pumped liquid to the pump discharge point.

At the most fundamental level, a centrifugal pump consists of just these three components:

  1. An impeller that rotates and imparts velocity to a liquid.
  2. A casing that captures the velocity generated by the impeller and transforms that velocity into a stable flow.
  3. An assembly of mechanical components that makes it possible for the impeller to be rotated within the pump casing.

>>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.