Centrifugal Pumps Including ANSI
Centrifugal pumps are the most commonly used pump type and are available from D.L.Thurrott, Inc in a very wide variety of types, specifications, materials of construction, sizes, performance etc.
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The centrifugal pump has several characteristics, the most important of which are:
- Stages: The number of stages is dependent on the number of impellers in the pump; a centrifugal pump can be either a single-stage pump or a multistage pump.
- Position of pump shaft: Single-stage and multistage pumps come with horizontal or vertical pump shafts and are normally designated as horizontal or vertical pumps.
- Single-suction or double-suction impellers: Depending on the construction of the impeller, a pump can be fitted with either a single-suction impeller or a double-suction impeller.
- Pump casings: There are two types of pump casings – Volute Casing and Return Channels.
- Horizontal pump is a pump with a horizontal pump shaft
- Vertical pump is a pump with a vertical pump shaft
- Long-coupled pump connects to the motor by means of flexible coupling (basic or spacer). The motor and the pump have separate bearing constructions. If the pump is connected to the motor by a basic coupling, the motor must be disconnected when the pump is serviced. The pump must, therefore, be aligned upon mounting. If the pump is fitted with a spacer coupling, the pump can be serviced without removing the motor and alignment is less of an issue.
- Closed-coupled pump connects to the motor by means of a rigid coupling
Types of Centrifugal Pumps
Single stage pumps have a single impeller. Generally, single-stage pumps are used in applications that do not require a total head of more than 450 ft. Normally, single-stage pumps operate in the range of 6-300 ft. Single-stage pumps are characterized by a low head relative to the flow. Single-stage pumps come in both a vertical and horizontal design.
Multistage pumps have several series-coupled stages and are used in installations where a high head is needed. Several stages are connected in series and the flow is guided from the outlet of one stage to the inlet of the next. The final head that a multistage pump delivers is equal to the sum of the pressure that each of the stages provide. Multistage pumps provide high head relative to the flow and have a steeper curve that is more advantageous for variable speed drive, also known as variable frequency drive (VFD) applications. Like the single-stage pump, the multistage pump is available in both vertical and horizontal versions.
In end-suction pumps the liquid runs directly into the impeller. Inlet and outlet have a 90° angle between them.
The liquid runs directly through the pump in-line. The suction pipe and the discharge pipe are placed opposite one another and can be mounted directly in the piping system.
Vertical turbine pumps are used in a variety of commercial, industrial, mining and municipal applications. Vertical turbine pumps are available in short set, deep set, submersible, mixed flow and propeller designs. These vertical turbines feature vitreous enamel coated bowl assemblies, extra heavy duty casings, high efficiency enclosed or semi-open impellers, enclosed lineshaft assemblies and optional metallurgies.
Submersible / Immersible
Submersible / Immersible pumps. Submersible pumps can be installed entirely below the surface of the liquid being pumped. This enables them to be lowered into pits or sumps, where they always remain primed. Usually, submersible pumps are capable of handling solids up to specified maximum sizes.
An immersible pump is a pump-type where the pump part is immersed in the pumped liquid and the motor is kept dry. Normally, immersible pumps are mounted on top of or in the wall of tanks or containers. Immersible pumps are used in the machine tool industry, chip conveyor systems, grinding machines, machining centers, cooling units or in other industrial applications involving tanks or containers, such as industrial washing and filtering systems. Pumps for machine tools can be divided into two groups: Pumps for the clean side of the filter and pumps for the dirty side of the filter. Pumps with closed impellers are normally used for the clean side of the filter because they provide a high efficiency and a high pressure if necessary. Pumps with open or semi-open impellers are normally used for the dirty side of the filter because they can handle metal chips and particles.
Few international standards deal with centrifugal pumps. In fact, many countries have their own standards, which more or less overlap one another. A standard pump is a pump that complies with official regulations pertaining to the pump’s duty point. A couple of examples of international standards for pumps are:
- ANSI B73.1 standard: covers centrifugal pumps of horizontal end-suction single-stage, centerline design. This standard includes dimensional interchangeability requirements and certain design features to facilitate installation and maintenance.
- DIN 24255: applies to end-suction centrifugal pumps, also known as standard water pumps, with a rated pressure (PN) of 145 psi.
The standards mentioned above cover the installation dimensions and the duty points of the different pump types. The hydraulic parts of these pump types vary according to the manufacturer – so, no international standards are set for these parts. Pumps designed according to standards provide end users with advantages in installation, service, spare parts and maintenance.
Split-case pumps are designed with the pump housing divided axially into two parts. Usually, split-case pumps have a relatively high efficiency, are easy to service and have a wide performance range.
Self priming pumps are used in commercial, industrial and municipal applications and often feature back pull out impellers, quick self priming, full access to the impeller from the front of the casing, heavy duty check valves ensuring the casing remains full of liquid, heavy duty casings, semi-open solids handling impellers, oil lubricated mechanical seal, oil lubricated power frame and rubber coated wear plate.
Sanitary pumps are mainly used in food, beverage, pharmaceutical and bio-technological industries where liquid is pumped gently and pumps are easy to clean using clean-in-place (CIP) techniques. In order to meet process requirements in these industries, the pumps are required to have a surface roughness of 32 µ-in (0.8 µ-m) or better. This is best achieved by using forged or deep-drawn rolled stainless steel as the material of construction. These materials have a compact, pore-free surface finish that can be easily worked up to meet the various surface finish requirements. The U.S. recommended interior surface finishes range from 32 µ-in for food and beverage applications down to 10 µ-in for bio-processing applications. The main features of a sanitary pump are ease of cleaning and ease of maintenance. The leading manufacturers of sanitary pumps have designed their products to meet the material specifications of the U.S. Food and Drug Administration (FDA) and the voluntary standards developed by 3-A Sanitary Standards Inc., as well as other well known globally-recognized standards such as EHEDG - European Hygienic Engineering Design Group
Sump & Sewage
Sump & sewage pumps are immersible, solids handling units, typically with recessed open impellers to avoid clogging.
In recent years, magnetic-driven pumps have become increasingly popular for transferring aggressive and toxic liquids. The magnetic-driven pump is made of two groups of magnets: an inner magnet and an outer magnet. A non-magnetic can separates these two magnets. The can serves as a hermetically sealed barrier between the liquid and the atmosphere. The outer magnet is connected to the pump drive and the inner magnet is connected to the pump shaft. The torque from the pump drive is transmitted to the pump shaft by means of attraction between the inner and outer magnets. The pumped liquid serves as lubricant for the bearings in the pump, making sufficient venting crucial for the bearings.
Grinder pumps shred sewage discharge into a finely ground slurry that can be sent through a small-diameter pressure pipe. Grinder pumps are connected to septic pipes and transport waste from households and businesses to sewage treatment systems. Unlike a well pump, grinder pumps are fitted with special cutting ring systems that are mounted to the pump's motor shaft.
Drum emptying pumps are used to transfer materials from a container into a process or other container. They may be electrically, hydraulically, or pneumatically powered depending on the working environment or application.