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Pumps,

pumping equipment

General classification of pumps (pumping equipment)

A pump is a hydraulic unit used for pumping, conveying, feeding and circulation of different fluids containing some steam, gas and solids in a closed circuit, as well as for transferring mechanical power via fluids to drive some mechanisms.

The key requirements to a pump are its high efficiency, reliability, low weight and small structural size, easy maintenance, easy installation and dismounting of its elements, cost-effectiveness and low price.

Depending on the the type of chamber pumps are divided into positive displacement or dynamic pumps.

A positive displacement pump handles the fluid by cyclic changing of pump chamber volume.

Positive displacement pumps include:

  • Reciprocating pumps (piston, plunger and diaphragm pumps);
  • Impeller pumps;
  • Rotary-type pumps (rotary, reciprocating, swinging, etc.).

Positive displacement pumps are classified by:

  • movement of operating elements;
  • movement of pump driving member;
  • fluid flow direction;
  • type of operating elements;
  • type of transmission of motion to the operating elements, etc.

Dynamic pumps move fluids by energy impact inside the pump chamber.

Dynamic pumps include:

  • Rotary vane pumps (centrifugal and axial);
  • Electromagnetic pumps;
  • Friction pumps (vortex, jet, screw, vibration pumps, etc.)

Dynamic pumps are classified by:

  • type of energy;
  • fluid flow direction;
  • discharge type;
  • impeller design, etc.

Positive displacement and dynamic pumps are classified based on their size, power, location, number of stages, number of flows, pump orientation, operational requirements, rotation axis direction or operating element movement direction, support structure, arrangement of operating elements, design and type of housing joint, inlet location, suction conditions, environmental impact and temperature conditions.

In our experience the most popular classifications important for selecting a pump are application, industrial use and type of fluids.

When choosing a pump for fluids of different types and aggressiveness, be sure to select a pump from proper materials, which are designated by special symbols in the pump marking.

Materials:

A Carbon steel J Silicon iron
B Bronze K Chromium-Nickel-Silicon steel
C Iron (including grey iron) L Nickel-based alloy
D Graphite M Plastic
E Chromium iron or chromium steel N Rubber coating
F Chromium-Nickel-Molybdenum Steel O Titanium and its alloys
H Chromium-Nickel-Molybdenum-Copper steel P Ceramics, porcelain
I Chromium-Nickel steel Q Aluminium alloys

Pump applications and key specifications

Today almost every industry is using pumps and pumping systems of different designs though until recently they had only been used for intake, pumping and delivery of water only. It is for this purpose that the first pumps were invented as early as in the BC Era, mostly for fire-fighting.

The 20th century with its accelerated hi-tech development set new goals for the designers of pumping equipment, since there was a dire need to convey not only water, but other fluids diverse in their physical, chemical properties and specifications, and, in particular, oil and its derivatives. Oil pipelines are being built everywhere extending for many thousands of kilometres instead of much shorter lines of the past.

Pumps are widely used in construction industry for various applications. These include temporary water supply, fire-fighting, pumping out of ground waters for laying of foundations and drainage. Pumps are used to move concrete and cement, to feed special chemically active substances into loose soil for strengthening, as hydraulic assistance tools for such auxiliary processes as road watering, spraying of freshly poured concrete, sand and gravel washing.

State-of-the-art pumps are capable of moving and feeding different media under pressure for the required distances and to the targeted heights, or supporting fluid circulation in closed circuits by converting drive power into fluid movement energy.

When selecting your pumping equipment you should take into account its design and key specifications, which include, primarily:

  • Pump efficiency determines feasibility of operation while changing drive power, head and flow, calculated with regard to all hydraulic, mechanical and volumetric losses in the process of pumping equipment operation.
  • Power (kW) is drive motor power required to generate the target operating head considering inevitable losses. 
  • Head (М) is the height of a column of the fluid above the set initial level corresponding to the increase in fluid energy from suction to discharge.
  • Flow rate (m³/h or l/s) is fluid volume fed into the discharge line per unit of time.

Pump efficiency

Efficiency of any unit is calculated as a function of useful generated power to consumed drive power in the process of operation. Since there is no such invention yet as a drive transferring energy without any loss, efficiency in no case may equal 100%.

Zero efficiency is possible if the pump is operating, but there is no movement of fluid at increasing pressure, because the pressure valve is closed; or if the valve is open, fluid is moving, but there is no pressure in the system.

In other words, efficiency of any pump may change depending on its operation mode. Efficiencies of pumps of different sizes and designs vary significantly.

For example, efficiency of a pump equipped with a rotor can be as high as 80%. The efficiency of contemporary large pumps at maximum load is 90-92%, that of small pumps is 60-80%.

When calculating pump efficiency one should take into account all the losses occurring in the process of drive power transfer to the fluid. They are rationally divided into mechanical, hydraulic and volumetric losses.

Hydraulic losses are composed of vortex losses and losses occurring during fluid friction against its guiding surfaces. Vortex losses happen when there is sudden expansion of pipe diameter, or a sharp turn of flow, or an abrupt deviation in pump operation from threshold limit values.

Friction losses are proportional to squared average fluid velocity and depend  to a large extent on the size and wall smoothness of a flow system. Mechanical losses are disc losses occurring during friction of rotating parts (impellers and shaft) against fluids and friction losses of stuffing box bearings.

Volumetric losses happen when part of the fluid (that has already taken up some of the energy for its movement) does not pass through to the outlet valve because of gaps between the impeller and stationary parts of the casing and is returned to the suction line.

Types of pump motors

For pump driving different mechanical motors are used harnessing  the energy of: wind, water, heat, gas, electricity, etc.

The following factors play a part in selecting a pump motor:

  • pump type;
  • type of motor-to-pump coupling;
  • kind of energy available;
  • required consumed power;
  • cost factors.

Electric power is always preferential. Electric motors are always given priority compared to other types of motors and are easier to integrate into automated control of pump units.

If no electricity is available, or if there are lower-cost sources of energy, fuel, gas or steam, steam engines or other propulsion units may be used.

To provide for reliable uninterrupted operation of a pump unit, a back-up drive is usually installed in parallel to the electric drive to accommodate for possible outages, steam type in most cases.

Stand-alone movable pump units are driven by internal combustion engines running on petrol, diesel fuel or LNG.

Low-capacity pump units used from time to time and designed for low fluid volume and low pressure are usually equipped with a manual drive.

Classification of pump motors

Pumping systems are divided into three groups as a function of their operating energy:

  1. Mechanical energy pumps (piston/ rotary/screw/ centrifugal/ propeller). All of them are combined by a reversibility factor, i.e. they may function as a hydraulic drive. As for the operating principle and internal design of these machines, they, on the contrary, are quite different.
  2. Pumps driven by pressurized fluid (water jet pumps and hydraulic rams).
  3. Pumps fuelled by the energy of compressed steam, gas and air generated by separate units (Humphrey pump/ airlift/ steam injector/ pulsometer/ montejus pump).

Cavitation phenomenon. Cavitation in pumps

As a result of pumping system operation at low atmospheric pressures, or when handling high-temperature fluids, or if the suction height exceeds the threshold limit, cavitation  phenomenon may occur inside the pipeline, accompanied by indicative vibration, crackling, hissing and other noises inside the pump, which result in fast wearing of its impeller.

In some areas of a pipeline the pressure of operating flow may drop to the critical level, which causes multiple bubbles of steam and gas to escape from the fluid and form in the solid stream expanding in size under the impact of underpressure. When they get to the areas of higher-than-critical pressure, the bubbles burst and disappear as a result of condensation. This collapsing of bubbles happens very fast and is accompanied by hydraulic impacts resulting in erosion, which causes mechanical destruction of operating elements of the pump and complicates its further operation.

In order to guarantee that there is no cavitation, for each pump cavitation characteristics are calculated.

It is possible to prevent cavitation on the flow section of a pumping system considering the causes of total and local pressure drop. But a more reliable method to reduce and completely prevent cavitation is to carry out an optimal geodesic survey of the pump location and select corresponding suction height and fluid temperature. By reducing the suction height or increasing the suction head as compared to the estimated values, it is possible to create a certain reserve to guarantee a reliable and uninterrupted operation of the pumping system without cavitation.

Comparison of pumps

Pump type Operating principle Advantages Drawbacks
Dynamic pumps Fluid is moved by forces. Durability, reliability and high quality Suitable for homogeneous fluids.
Positive displacement pumps Fluid is conveyed by displacement of volume or by mechanical movement of some portion of the fluid into the discharge line. No disruption of fluid structure;
High pressure;
Possibility to dose viscous fluids of different degree of contamination.
Special maintenance is required;
Sensitive to physical and chemical properties of pumped media.
Peristaltic pumps The main operating element is a flexible multilayer elastomeric tube. Pump motor rotates the shaft with rollers or shoes, which pinch closed the tube moving the fluid inside it. Simple design, no end sealings, easy in operation, no danger from a dry run, working chamber is filled with lubricant, no temperature increase in operation; 
Self-suction of fluid from up to 9 meters deep;
Pumping of fluids of different aggressive properties, with fibers and abrasive inclusions;
Proportional feeding, can be used as a metering pump;
Operates well in either direction.
Hydraulic impacts in operation, free vent is desirable;
Tube wear;
High cost.
Internal gear pumps This is a variation of a gear pump where "gear-within-a-gear" principle is used, i.e. idler (small interior gear) is inside a rotor (large exterior gear) and is supported by a steel crescent shape. This design provides for larger displacement volume during gear rotation, which imparts a suction effect to the filled-up internal gear pump. Simple to operate;
High suction head;
Excellent for high-viscosity and high-temperature liquids;
Suction with full chamber is possible;
Operates well in either direction;
Low cost.
Disrupts fluid structure and destroys slurries;
Dry run is ruinous.
External gear pumps The simplest type of pumps using forced displacement caused by changing volumes in the cavities of individually-driven gears rotating against each other. Liquid travels around the interior of the casing in the pockets between the teeth and the casing. Simple to operate;
High suction head;
Excellent for high-viscosity and high-temperature liquids;
Operates well in either direction;
Low cost.
No self-suction;
Dry run is ruinous;
Disrupts fluid structure and destroys slurries;
Only suitable for thick liquids without inclusions.
Rotary pumps Liquids are moved by rotation of rotors, cams, screws, wedges, blades or similar parts in a stationary casing. No need for inlet, suction and outlet valves. Wear of parts which need to be replaced.
Cam pumps Liquid travels around the interior of the pump casing through rotation of two independent rotors. No wear parts;
Perfectly delicate and absolutely contamination-free pumping of viscous fluids without disrupting their structure and destroying solids;
The travel path inside the pump is optimal, the chamber has no cavities where fluids could accumulate;
Smooth flow at the outlet;
Low cam rotation speed; no noise or vibration during operation;
Operates well in either direction;
Low operating cost.
High price.
Screw pumps A metallic screw rotates in a stationary cavity (stator) made of elastomer material changing the volumes inside the pumping chamber and moving the fluid along the pump axis thereby creating a suction effect in the cavities. Simple design and easy to operate;
Self-suction of fluid from up to 9 meters deep;
Movement of viscous abrasive material with fibers and other inclusions;
Proportional feeding; it may be used as a metering pump;
Smooth flow at the outlet;
Operates well in either direction.
Dry run is inadmissible;
Stator is subject to wear.
Impeller pumps An impeller (wheel) with wings made of an elastic material rotates inside an eccentric casing the wings to bend and displace liquid from the pump. Simple design;
Easy to operate;
Capable to lift fluid from up to 5 meters deep, including dry pumping;
Good for viscous fluids and solid-containing slurries;
Operates well in either direction;
Low cost.
Wear parts, which need to be replaced;
Long dry run is ruinous for impeller;
Limited range of aggressive fluids depending on the type of elastomer material used;
Limited fluid temperature range depending on the type of elastomer material used.

Centrifugal pumps

A centrifugal pump consists of a casing, impeller, suction and discharge lines, stuffing box and bearings. After the casing is filled with water, the centrifugal force from impeller rotation whirls the water from the centre outward until it leaves through the discharge line. The vacuum generated in the centre causes suction effect. Liquid is fed into the pump continuously.

Where high pressure is required, multi-stage pumps are used consisting of several single-stage pumps connected in series inside a common casing.

Turbine pumps are equipped with an additional diffuser directing the flow into a spiral chamber.

Centrifugal pumps differ in their application, size, sturdiness, corrosion resistance, materials of parts, manufacturing and assembly technologies depending on their operating requirements.

The core part of a centrifugal pump is its impeller transmitting energy from the rotating pump shaft to the fluid. Impellers are usually made of iron, bronze or steel. Lead, ebonite, ceramics, rubber and some plastics are used for the impellers inside the pumps for caustic and aggressive liquids. Such pumps are sometimes equipped with protective replaceable discs from durable abrasive materials.

Impeller casting should be as clean as possible since its internal channels are not readily accessible for manual cleaning, while the quality of impeller surface machining is an important factor in cavitation resistance and efficiency of a pump. In view of this bronze impellers are more preferable. They can achieve peripheral velocity of up to 80 m/s, while for cast iron impellers admissible circumferential velocity is 50 m/s maximum.

The size of the wet part is determined by hydrodynamic calculation.

There are different designs of impellers - open-blade, semi-open, axial, single or double water inlet. Blades may be space-type and cylindrical. Pumps for heavily contaminated fluids are equipped with impellers with two to four blades. Most often centrifugal pump impellers have 6 to 8 blades. Axial pump impellers are designed like a propeller in a pipe.

Centrifugal pump characteristics

There are theoretical and experimental characteristics of pumps. Theoretical characteristics are calculated using basic formulae making adjustments for expected pump operation conditions. It is quite challenging to take into account all the factors using this approach, that is why more accurate ratios of key specifications of centrifugal pumps are determined during stand testing of finished pumps or their pilot models. During stand testing of pumps at the manufacturer’s plant the flow rate Q is plotted on the X-axis as a function of full head H, efficiency η and consumed power N graphed on the Y-axis

Manufacturing plants are equipped with special test stations where pumps are installed on stands fitted with all the required instrumentation to test pump characteristics. For large pumps and those whose specifications may vary significantly depending on operational conditions, the tests may be carried out at the site of their operation.

Before recording pump head and power values certain head should be set using a valve. Efficiency is calculated. All the measured values are plotted on a grid direct-to scale. Specifications are demonstrated by smooth curves connecting all the dots obtained during the test.

Classification

According to the number of impellers:

  1. Single-stage (one impeller);
  2. Multi-stage (several impellers).

According to number of entries:

  1. Single-entry pumps;
  2. Double-entry pumps;

According to shaft arrangement:

  1. Horizontal-shaft pumps;
  2. Vertical-shaft pumps.

According to handled fluid:

  1. Water pumps;
  2. Sewage (sanitary) pumps;
  3. Soil (dredging) pumps;
  4. Sand pumps;
  5. Sludge pumps;
  6. Acid pumps,
  7. etc.

According to application:

  1. General application
  2. Mine pumps;
  3. Water well (bore) pumps

Industrial application of centrifugal pumps

Centrifugal pumps and respective centrifugal systems are used for handling a wide range of fluids of any viscosity. These include hypersensitive and chemically aggressive substances, corrosive, abrasive, volatile, flammable, explosive and solid-containing fluids.

Due to simple operation and cost-efficiency resulting from low operational expenses, chemical pumps and food machinery of this type are now widely popular and are used in various areas.

In food industry, owing to their sanitary features and resistance to aggressive media, centrifugal food pumps are used to handle different pastes, milk, cream and other food products. They assist hemihydrate circulation in the process of demineralization.

In chemical and paint industries centrifugal pump units are used to move spirits, acids, alkalis, latex, liquid reagents, sludge, flocculants and chemical wastes. They are unique in handling glues and varnishes for printing application.

In mechanical engineering centrifugal pumps are indispensable for pumping all kinds of technical fluids, such as alkalis, acid concentrates, galvanic solutions for metal degreasing and etching, oils and solvents.

In water cleaning technologies chemical centrifugal pumps are essential as dosing units for alkalis and acids during pH-control of water. They are also successfully used for slurries and test samples.

In pulp and paper industry centrifugal chemical pumps are no less popular for moving coloured oxidisers and glues, as well as waste water evacuation.

Metering pumps

Due to their maximum accuracy in feeding the required volume of process fluids of any degree of activity and aggressiveness with minimal losses within specific time, metering pumps are now in demand in various leading-edge industries.

According to the type of pressurization metering pumps are divided into:

  • Plunger pumps;
  • Peristaltic pumps;
  • Mechanically actuated diaphragm pumps;
  • Hydraulically actuated diaphragm pumps.

According to the type of drive metering pumps may be split into:

  • Motor driven pumps;
  • Pneumatically driven pumps;
  • Electromagnetically driven pumps.
  • Metering pumps are used in chemical, food, pharmaceutical industry, agriculture and other areas due to their high accuracy of control and dosing of fluids in any systems. These pumps  due to such materials as stainless steel, PVC and PP used for the flow path manufacture are quite resistant to most aggressive chemical media and may be used not only as pumps, but also as metering and dosing units. Depending on the operational conditions and customer requirements metering pumps may be equipped either by less expensive and less accurate manual regulator or by an electronic controller, which is used for most critical production processes.
  • High-pressure metering pumps are equipped with multilayer diaphragms, and for heavy duty operation such pumps may have a special buffer tank filled with liquid. This liquid is necessary to uniformly distribute the diaphragm load, which extends its operation period at maximum pressure. To generate system pressure up to 180 bars it is recommended to use plunger pumps with several working heads operating with several fluids simultaneously as well as double head metering pumps with the capacity up to 4,000 l/h.

Piston pumps

Piston (plunger) pump – a type of positive displacement pump consisting of a stationary part – a cylindrical chamber with two valves, through which a moving part – a plunger or a piston is making a reciprocating motion.

The basic data for selecting a piston pump type are:

  • Specific output or working volume [cm3/rev] is equal to the fluid volume displaced from the pump in one full revolution of a shaft.
  • Maximum pressure of working media [bar, MPa]
  • Maximum rotation rate [rpm]

Undeniable advantages of piston pumps are:

  • pressure adjustment in the discharge line by controlling piston movement rate;
  • easy interchangeability of parts;
  • high head in spite of small size.

Screw pumps

Screw pumps as a type of rotary positive displacement units were invented in early 20th century and immediately became popular in chemical, food, tobacco, textile and metal working industries as metering units for special reagents in water treatment. Starting from early 1980s screw pumps have been widely used in oil producing and refining industries. At the beginning of this century screw pumps gained world-wide popularity due to their features that made them preferential for mechanized oil production. These include primarily their small size and ability to handle high-viscosity fluids containing solids and free gas since screw pumps do not have any reciprocating-motion parts or valves. This design feature prevents any wear of parts, clogging and gas locks which guarantees minimum and simple maintenance, easy installation and operation. Considering comparatively low investments and electricity consumption, the efficiency of screw pumps is 50-70% .

They have two core parts. A screw form chrome-plated or stainless steel and an elastic rubber cavity. The screw is connected to the shaft with a universal drive or another flexible coupling admitting for some misalignment between the motor shaft and the screw. The space between the screw and the cavity remains constant at any cross-section along the pump which provides for continuous flow without pulsation. The screw axis is displaced from that of the cavity by a constant value called “eccentricity”. During the drive shaft rotation the screw rotates on its axis while the screw axis rotates with a radius equal to its eccentricity.  As a result closed cavities are created which open and close moving the material from the suction chamber to the discharge chamber.

Screw pump capacity depends directly on the screw rotation rate and chamber volumes. Other key characteristics of screw pumps are pitch, diameter and eccentricity of screw axis. These characteristics and tension between the cavity and the screw determine the volume of pump chambers and profile of its operating elements.

Today’s screw pumps of a vertical or horizontal configuration with different number of screws, if used properly, are the most optimum and cost-saving mechanized units of choice.

Screw or helical pumps are rotary positive displacement pumps. Screw pumps providing for the smoothest movement of fluids as compared to other types of pumps are also known for their low electricity consumption and reasonable operation costs.

This type of pumps consists of a conical or cylindrical casing, a stator with helical grooving and one or several screw-type rotors driven from an electric motor.

The handled fluid is guided through the stator via helical grooves along the screw axis towards the outlet. The intermeshing screws create closed cavity which traps the fluid during rotor movement inside the stator preventing it from leaking backwards. The pump head is a function of the number of stages (pitches of rotor/stator screw pair).

Screw pumps may have one, two or three screws. Single-screw pumps are less common.

Screw or helical pumps have several advantages as compared to other types of contemporary pumps. They are characterised by a compact design, low noise, small size and simple configuration, which preconditions their easy installation, operation and maintenance. They provide for smooth feeding of fluids, self-suction of high-viscosity materials containing solid and abrasive particles from up to 8 meters deep. At the same time the rate of wear and damaging of parts is reasonably low, while high discharge pressure is achieved within a single cycle at low energy consumption rate. Screw pumps used for dosing viscous mixtures and slurries provide for accurate and careful delivery without foaming and any other disruption of fluid structure.

Considering all those advantages screw (helical) pumps are widely used in oil and gas production, petrochemical industry, public utilities, ore mining, cosmetics and food industries, shipbuilding and evacuation of sludge ponds.

When selecting a pump of this family it is important to know, primarily, viscosity and density of handled media, targeted discharge pressure and pipeline diameter. As a function of these specifications other parameters like rotor rotation rate, internal dimensions and number of stages are chosen, which helps extend service life of operating units and elements and reduce electricity consumption.

Sliding vane pump

Sliding vane pump is a hydraulic positive displacement pump forming several pumping chambers simultaneously by sealing off the volume between the casing, rotor and two adjacent vanes (blades). The rotor is arranged inside the casing and has slots for the vanes to slide freely (or under spring pressure) in and out contacting and sliding across the wall with one of their ends. Rotor and casing axes are displaced with respect to one another, so when the rotor is moving the volume of an individual chamber is changed thus moving the fluid.

Gear pump

Gear pump is a pumping unit that uses the meshing of gears to move fluid by displacement. The gears are arranged inside the casing and cavities are formed between the casing walls and adjacent gear teeth. When the gears are meshing they reduce the volume of respective cavities thus displacing a portion of the liquid into the discharge line.

Peristaltic (hose) pump

Peristaltic (hose) pump has simple design but unusual positive displacement principle of operation. The operating element of a peristaltic pump is a flexible tube or a hose bent around the rotor with rolls. The tube may be compressed by the rolls with tension force or pinched in special surface areas. The roll completely seals off the tube displacing part of its volume. As the rotor turns, the fluid is forced to move through the tube and is then induced to the discharge line.