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Hydraulic pump type - What are they?

 Hydraulic pump type - What are they?
Contrary to what many people think, hydraulic pumps are not capable of generating a pressure, they only provide a flow, as constant as possible, to the circuit. The pressure appears when the flow supplied by the pump has to overcome some resistance.

What is true is that the hydraulic pump has to be able to work at high or optimal pressures. The pump sucks the fluid that reaches it (return) from the circuit at a pressure and has to work with that pressure, but does not generate that pressure.

Definition of Hydraulic Pump

A Hydraulic pump is a generating machine that transforms the energy (usually mechanical energy) with which it is driven into hydraulic energy of the incompressible fluid that moves. The incompressible fluid can be liquid or a mixture of liquids and solids such as concrete before setting or paper pulp. By increasing the energy of the fluid, its pressure, its speed or its height are increased, all of them related according to Bernoulli's principle. In general, a pump is used to increase the pressure of a liquid by adding energy to the hydraulic system, to move the fluid from an area of lower pressure or altitude to another of higher pressure or altitude. There is an ambiguity in the use of the term pump, since it is generally used to refer to fluid machines that transfer energy, or pump incompressible fluids, and therefore do not alter the density of your working fluid, unlike other machines, as are the compressors, whose field of application is pneumatic and not hydraulic. However, it is also common to find the term pump to refer to machines that pump other types of fluids, as are vacuum pumps or air pumps.

Classification

The main classification of the pumps according to the operation on which it is based:
  • Positive or volumetric displacement pumps, in which the principle of operation is based on hydrostatics, so that the pressure increase is made by pushing the walls of the chambers that vary in volume. In this type of pumps, in each cycle the propellant organ generates a given or displacement volume positively, which is why they are also called volumetric pumps.
In case of being able to vary the maximum volume of the displacement, it is spoken of pumps of variable volume. If that volume cannot be varied, then it is said that the pump is of fixed volume. In turn, these types of pumps can be subdivided into:

  • Alternative piston pumps, in which there is one or several fixed compartments, but of variable volume, by the action of a piston or a membrane. In these machines, the movement of the fluid is discontinuous and valves that open and close alternately carry out the loading and unloading processes. Some examples of this type of pump are the alternative piston pump, the rotary piston pump or the axially driven piston pump.
  • Rotary or rotattatic volumetric pumps, in which a fluid mass is confined in one or more compartments that move from the inlet zone (low pressure) to the outlet zone (high pressure) of the machine. Some examples of this type of machines are the vane pump, the lobe pump, the gear pump, the screw pump or the peristaltic pump.
  • Rotodynamic pumps, in which the principle of operation is based on the exchange of amount of movement between the machine and the fluid, applying hydrodynamics. In this type of pumps, there are one or several impellers with blades that rotate generating a pressure field in the fluid. In this type of machines, the fluid flow is continuous.

These generating hydraulic turbomachines can be subdivided into:
  • Radial or centrifugal, when the movement of the fluid follows a path perpendicular to the axis of the impeller impeller.
  • Axial, when the fluid passes through the channels of the blades following a path contained in a cylinder.
  • Diagonal or helicocentrifuges when the fluid path is made in another direction between the previous ones, that is, in a coaxial cone with the impeller axis.

Depending on the type of drive

Electric pumps. Generically, they are those powered by an electric motor, to distinguish them from motor pumps, usually driven by internal combustion engines. Pneumatic pumps that are positive displacement pumps in which the input energy is pneumatic, usually from compressed air. Hydraulic drive pumps, such as ram pump or Ferris wheel. Hand pumps. One type of manual pump is the rocker pump.

Types of Pumps

  1. Plunger pump
  2. Piston pump
  3. Vane pump
  4. Lobe pump
  5. Gear pump
  6. Screw pump
  7. Peristaltic pump
  8. Centrifugal pump
  9. Ram pump
  10. Hydraulic Pumps Enerpac, Manual, Battery Driven, Electric, Pneumatic, and Gasoline Engines

Hydraulic pump type

Hydraulics creates a flexible and efficient way of transferring energy. With the amount of modern machinery that exists today, there was a need to nurture them by inducing new creations of hydraulic pumps; The new hydraulic pump technology is often chosen for its efficiency and simple designs. In the industrial world there are various types of hydraulic pumps and each of them has its own mechanism.

The hydraulic pump refers to a device that transforms a linear or rotary movement into hydraulic energy. The fluid inside the pump will assume a higher pressure and speed than at the beginning of the process. It should be noted that the pump does not cause pressure, it only causes flow, assuming the ability to perform this process at high pressures.

What are the types of hydraulic pumps?

Hydraulic pumps are used in a wide range of engineering fields and this comes in a wide variety of designs. But each type has a different internal mechanism established in the same fundamental beginnings. So, here are some of the most common types of hydraulic pumps.

Plunger pump

The plunger pump is a positive displacement pump, designed to pump high solids contents (18-20% solids), which are commonly found in untreated influencers. Wastecorp is one of the largest manufacturers of this style of pump in the world. This technology is specified for pumping effluent (spills), as well as for industrial discharges. Together with the progressive cavity pumps that have existed since the 1930s, the plunger pump first began pumping municipal sludge in the 1920s. Until 2008, there are more than 18,000 plunger pumps in operation worldwide.

Generalities

Rotary piston pumps, also called “Roots pumps”, have been applied for many years in the empty version and are well known in industries that need to produce vacuum due to their high volumetric displacement. The maintenance is reduced practically to the monitoring and control of the oil of greasing of the boxes that lodge the mechanical parts, this greasing is carried out by barbate and the consumption of oil is practically null. The sealing of the passage of the drive shaft carries an oil sight glass to control the oil level and consequently its good sealing.

Features

They are preferably applied in the high, medium and low vacuum domain, that is, from pressures of 100 mbar. Up to 10-4 mbar as empty limit. Its application is excellent when large quantities of gas, steam have to be pumped or large containers must be quickly evacuated without disturbances during operation. Depending on the vacuum zone selected or the application needs, many parameters must be taken into account for the type of pump selected and its safety. They operate at low pressures and their limit is due to molecular regime conditions and therefore they can reach high compression ratios, consequently it is not possible to work against atmospheric pressure.

In most cases these are applied as the final stage of a group of pumps connected in series with a "pre-pump" that is able to discharge at atmospheric pressure, with suction pressures of some millibar. The previous vacuum pressure produced by the previous pumps and their suction capacity decisively condition the characteristics of the rotary piston pump.

The pre-pumps can be, for example, vane pumps, oscillating pistons , trochoids, liquid ring, with or without gas ejector, etc., and also pre-admission rotary piston blowers that work dry. The mission of the previous pumps is to compress the aspirated gas quantities at atmospheric pressure. The effective suction capacity and the differential pressure through the rotary piston pump is directly proportional to the capacity of the previous pump and the term "compression ratio" is used to describe this relationship.

In practice, the compression ratio can vary from 1: 1 to 20: 1 and greater. The most commonly used are between 5: 1 and 10: 1. The determination of the compression ratio is a function of many parameters, including the capacity we need and the operating pressure. The latter is important since high compression ratios and relative high suction pressures can cause excessive temperature generation. The consumption of absorbed power of the rotary piston pumps is directly proportional to the differential pressure (mean differential between the suction and discharge flanges of the pump). If the differential pressure is too high, both the motor and the rotary piston pump can be thermally overloaded.

The pumped gas itself, by the radiation of the pump body, evacuates the heat produced by the compression and by the lubricating oil that radiates its heat through the crankcases. As the pressure inside the pump is very small (empty), the mass flow rate is very small and there is practically no effective cooling. When the permissible differential pressure is overloaded, the pistons dilate more than the body and consequently the rotary pistons can become seized. In continuous mode, the preset value cannot be exceeded; this value (mbar.) is different for each size of rotary piston pump.

Piston pump

The piston pumps are generally used in industry for high performance and ease to work at a pressure above 2000 lb. / in2 and have a volumetric efficiency of about 95 to 98%.

Classification

Due to the wide variety of piston pumps, these can be classified as:
  • Radial piston pumps: The pistons slide radially inside the pump body that rotates around an arrow.
  • Axial piston pumps: The pistons move in and out on a plane parallel to the axis of the driving arrow.
  • Piston pumps angular barrel (Vickers): Fillers for pump drive and thrust loads by the pumping action will supported by three ball bearings single row and a ball bearing double - row. This pump design has given excellent service to the aviation industry.
  • Angular thrust plate piston pumps (Denison): This type of pump incorporates piston shoes that slide on the angular thrust plate or cam. Lack of lubrication will cause wear.

Features

In the wide variety of piston pumps, we find the following characteristics:
  • Pumping of particulate products and products sensitive to shear stress.
  • Handling whole fruits and vegetables, leaves, slices, pieces and fruit dice.
  • Hygienic design.
  • Working temperature: 120ยบ C or more depending on the design.
  • Work in a vacuum.

Pneumatic piston pumps

Pneumatic piston pumps are composed of an air motor and a defined “pumping group” structure. The fundamental parts of the pneumatic motor are the piston and the valve device. This allows automatic reversal of the piston movement. The flow rate of a piston pump depends on the amount of material it supplies in each cycle.

Operating principle

These piston pumps work coupled to an alternative air-powered pneumatic motor. The alternative movement is repeated indefinitely while the air supply is connected, regardless of whether the pump is supplied with liquid or not.

Oscillating piston pumps

These small units are suitable for applications in the most different sectors. The structure of the pump requires installation in protected places.

Oscillating piston pumps

These small units are suitable for applications in the most different sectors. The structure of the pump requires installation in protected places.

Axial piston pumps with inclined turntable this type of pump can work in both directions. The inclined plate is moved by the axis and the angle of the plate determines the stroke of the piston. The valves are necessary to direct the flow in the correct direction.

Vane pump

Vane pumps have a set of fins with radial kinematics. The fins slide or oscillate in a hollow cylinder with radial grooves in the rotor. With respect to the axis of the pump body, the rotor is positioned eccentrically, with respect to which during the rotation the fins perform reciprocating or reciprocating movements.

Function

At the ends of the vane pump, the stator is pressed inside and the vanes slide along it. The working chamber is filled between two adjacent vanes, the stator and the rotor. During the rotor rotation, the volume of product increases until reaching a maximum value that, after reaching this, closes to transfer the product to the pump's cavity. At the same time, the evacuation of the liquid from the working chamber begins in an equal amount. At its useful volume. They do not have the same degree of tightness as other rotary pumps and to improve the degree of tightness can be done by raising the number of vanes.

The drive is carried out by means of a splined shaft that meshes with the inner groove of the rotor. There are different designs to get contact between the palette and the ring; in some the centrifugal force that prints the rotation of the rotor is used, in these models a minimum speed of rotation is required to guarantee the correct support of the vane on the ring; in other models this centrifugal force is reinforced with springs placed between the vane and its housing in the rotor, this decreases the minimum speed necessary for the support; Other models use reduced hydraulic pressure to push the paddle.

Vane pumps are relatively small depending on the powers they develop and their tolerance to the contaminant is quite acceptable.

The oil enters from the left side, where it is collected by the vanes that open by centrifugal force and is propelled to the pressure side by them until they are incorporated into the pressure outlet. Special grooves in the rotor connect the pressure side with the bottom of the vanes to help the centrifugal force propel them outward.

The aspiration is produced by increasing the volume of the chamber during rotation.

The lower the tolerances between the end of the vane and the ring and between these and the pressure plates, the better the pump performance.

In any case, a certain tolerance has to be maintained in the friction zones, so it is important that the force exerted by the vane on the ring is not excessive since then the lubricant film would break and there would be contact between the end of the paddle and the ring.

The oil inlet and outlet ports are located on the sides of the rotor and next to it; we can see the grooves that give pressure to the bottom of the vanes.

Multiple pumps

Multiple pumps are combinations of two or more pumping elements placed in a single housing and driven by the same drive shaft.

Multiple pumps can be composed of several bodies (pumping groups) equal in operation (gears + gears, vanes + vanes, pistons + pistons) which in turn can be of the same or different displacement. Another option is the combination of different bodies (pistons + vanes, vanes + gears, etc.).

Multiple pumps constructed from independent bodies usually have a suction hole and an outlet for each pump body; in other models, the housing has been specially designed for this application and has a single suction for several pumping units. In any case, the body that supplies more flow or the one that absorbs more power will always be the closest to the engine.

An example of the application of a multiple pump with different bodies would be the operation of a forklift, with a body for the displacement system (wheel drive), another body for the forklift and positioning circuit and another for the steering circuit.

Another possibility is to join in series two pumps of equal displacement in which the output of one is directly to the input of the other. These pumps thus connected offer a double pressure to that normally reached by only one of the pumping units.

Main characteristics of vane pumps

In the wide variety of vane pumps, we find the following characteristics:

Vane pumps are used in installations with a maximum pressure of 200 bar. A uniform flow (pulse free) and a low noise level.

The stator ring is circular and eccentric with respect to the rotor. This eccentricity determines the displacement (flow).

When the eccentricity is zero, there is no flow rate; therefore, no liquid will be delivered to the system. This allows regulating the flow of the vane pumps.

The vanes are the delicate part in this type of pumps.
Vane pumps consist of several parts
  • Eccentric ring.
  • Rotor.
  • Pallets
  • End caps or plates.
Vane pumps are relatively small depending on the powers they develop and their tolerance to the contaminant is quite acceptable.
  • Entry opening
  • Download opening.
  • Suction port.
  • Drive port.
  • Distance between rotor and stator axes.

Life of vane pumps

The life of this type of pumps is very long, as long as a review is done periodically and this for the following reason:

The vanes are the delicate part in this type of bombs. When they remain stopped for a long time, the paddles can stick inside their housing slots. These adhesions are due to the residues of the transported products and consequently the pump will not work. To ensure proper operation again, the moving parts must be cleaned and the vanes slide freely in their guides.

How to regulate the working volume of vane pumps

Vane pumps admit the possibility of regulating their working volume, modifying the eccentricity of the rotor with respect to the stator. If the eccentricity decreases, the supply of the pump is reduced, keeping the number of revolutions invariable, and vice versa, but for this it is required that in the construction of the pump, this possibility is foreseen, by means of the appropriate device.

Applications and advantages of vane pumps, main advantages of vane pumps

Some of its main advantages are:
Direction of fluid flow independent of the direction of rotation of the shaft (for special execution pumps).

  • Simple and fast maintenance.
  • There is no compression, push, drag.
  • Ability to transport high viscosity products.
  • Volumetric pump regardless of rotation speed or viscosity.
  • Great suction power.
  • Technical simplicity
  • Great lifespan
  • Variable work volume
  • Integrated safety valve allowing circuit protection.
  • Vane pump applications
Vane pumps are applied in various industries and processes, which include:
  • Product transfer in the oil sector.
  • Transfer of chemical products.
  • Transfer of products for the textile industry.
  • Oil cleaning in closed circuits.
  • Water transfer in refrigeration facilities.
  • Emptying industrial fryers.
  • Lubrication of machine tools.
  • Lubrication of railway equipment.
  • Transfer of food products for beehive farming.
  • Water transfer in refrigeration facilities.
  • Lubrication of public works machines.

Lobe pump

The lobe pump is a mechanical, volumetric and positive displacement pump. They are work chambers that move the liquid. There are external and internal lobes gear pumps. Both types of pumps are presented below and their characteristics as well as the advantages of each are specified.

External lobes

They are external gear rotary pumps that differ from these in the way of driving the gears. Both gears have only three teeth that are much wider and more rounded than those of an external gear pump are. Its drive is independent by means of a gear system external to the pumping chamber.

Advantage
Within the wide variety of external lobe pumps, we find the following advantages:
  • The lobes are operated independently by means of a gear system external to the pumping chamber.
  • They offer greater displacement, but their cost is greater than pumps of another type.
  • This pump is suitable for use with fluids that are more sensitive to the effect of tangential stress (or shear).
  • It is excellent for handling fluids with trapped gases or particles.

Internal lobes

They are internal gear rotary pumps that differ in the way the gears are driven. This pump combines an internal gear into an external gear. The internal gear is mounted on the shaft and carries a tooth less than the outer gear.

Advantage

In the wide variety of internal lobe pumps, we find the following advantages:
  • This pump has greater volumetric efficiency than the semi-moon working at low speeds.
  • The volumetric and total performance of this type of pumps is generally similar to that offered by external gear pumps.

Gear pump

The gear pumps are used to pump oil lubrication, and usually have a strong vibration component in the frequency of the gear, which is the number of teeth on the gear by RPM. This component will depend heavily on the pump outlet pressure. If the gear frequency is changed significantly, and there is an occurrence of harmonics or sidebands, in the vibration spectrum, this could be an indication of a cracked or otherwise damaged tooth.

Gear pumps are robust fixed flow pumps, with operating pressures up to 250 bar (3600psi) and speeds up to 6000 rpm. With flow rates of up to 250 cc / rev, they combine high reliability and special sealing technology with high efficiency.

Features

  • Reversible and unidirectional, versions with SAE flange, DIN and European flange.
  • Rotary flow dividers.
  • Bodies in reinforced aluminum and steel.
  • High performance and high temperatures.
  • Low noise level Long duration in extreme conditions.
  • Excellent versatility Wide range of applications.
  • Compact design. High reliability

Types of gear pumps

  • Aluminum pumps with bearings
  • Aluminum pumps with bearings
  • Casting pumps with bearings
  • Cast iron pumps with bearings
  • Truck pumps

External gear pumps

They produce flow by transporting the fluid between the teeth of two coupled gears. One of them is driven by the pump shaft (drive), and it spins the other (free).

  • External low-pressure gear pumps: What happens is the origin of a vacuum in the aspiration when the teeth are separated, due to the increase in the volume in the aspiration chamber. At the same time, the teeth go away, taking the fluid in the aspiration chamber. The drive originates at the opposite end of the pump due to the decrease in volume that occurs when the separate teeth are engaged.
  • External high-pressure gear pumps: The most commonly used type of pumps are those of straight gears, in addition to helical and behelicoidal. In optimal conditions, these pumps can reach 93% volumetric efficiency.

Internal gear pumps:

They are composed of two gears, external and internal. They have one or two teeth less than the outer gear. Its wear is lower due to the reduced speed ratio. They are used in small flows and can be of two types: crescent and gerotor. This type of pump produces flow by transporting the fluid between the teeth of two coupled gears. The pump shaft (drive) drives one of them, and it spins the other (free).

Functioning

The gear pump operates by the principle of displacement; a pinion is driven and rotates the other in the opposite direction. In the pump, the intake chamber, by the separation of the teeth, in the relationship the tooth gaps are released.

This depression causes the aspiration of the liquid from the reservoir.

The filled teeth transport the liquid along the wall of the housing to the discharge chamber.

In the chamber, the gears that gear the liquid out of the teeth and prevent the return of the liquid.

Therefore, the liquid in the chamber has to exit towards the receiver; the volume of the liquid supplied per revolution is designated as the volume supplied (cm3 / rev).

Gear pump performance

The operation and efficiency of the hydraulic pump, in its basic function of obtaining a certain pressure, at a certain number of revolutions per minute is also defined by three performances:

Volumetric performance of the gear pump

The volumetric efficiency of the pump is the ratio obtained by dividing the flow of liquid that compresses the pump and which theoretically should compress. In other words, the volumetric efficiency expresses the leakage of liquid in the pump during the compression process. The volumetric performance is a very important pump factor, since from it you can analyze the design capacity and the state of wear in which a pump is located. The pressure of the hydraulic fluid being transported and the temperature thereof also affects the volumetric efficiency.

Mechanical performance of the gear pump

Mechanical performance measures the losses of mechanical energy that occur in the pump, caused by friction and friction of the internal mechanisms.

In general terms, it can be said that a low mechanical performance pump is an accelerated wear pump. Total or overall performance of the gear pump Total or overall performance is the product of the volumetric and mechanical performances. It is called total because it measures the overall efficiency of the pump in its function of pumping liquid under pressure, with the minimum supply of energy to the pump shaft.

Thus, the total efficiency is expressed as the energy consumption necessary to produce the nominal hydraulic pressure of the system.

Screw pump

Screw pump. It is a type of hydraulic pump considered positive displacement, which differs from the usual, better known as centrifugal pump. This pump uses an eccentric helical screw that moves inside a jacket and makes the liquid flow between the screw and the jacket.

Activity you do

It is specifically indicated for pumping viscous fluids, with high solids contents, that do not need to be removed or that form foams if they are stirred. As the screw pump displaces the liquid, it does not suffer sudden movements, even being able to pump whole grapes. One of the uses it has is to pump sludge from the different stages of the treatment plants, and can even pump dehydrated sludge from press filters with 22-25% dryness. These types of pumps are widely used in the oil industry worldwide, for the pumping of highly viscous crude oils and with appreciable solids contents. New developments of these pumps allow multi-phase pumping.

In this type of pumps, they can operate with fixed flows to their discharge, even when they pump against a variable pressure network. Turning them into excellent pumping equipment to be used in oil collection networks. In the case of centrifugal pumps. The flow delivered depends on the pressure at its discharge. The liquid is transported by means of an eccentric helical screw that moves inside a jacket (stator). The pump insert core is easy to replace. The driven screws are driven hydraulically.

Single screw pumps (progressive cavity)

The primary components are the rotor and the stator. The rotor is of a simple external propeller and the stator is of an internal propeller.

Double screw pumps

These pumps transport their contents axially, uniformly and continuously. Turbulence is not generated during the rotation of the drive screws.

Triple screw pumps

The triple screw pump generates sealed chambers in the pump core, due to the special profiling of its flanks. Details of running pumps screw pumps a screw with fixed volume capacity:
  1. Connection for accessories.
  2. Stator.
  3. Solid construction bolts.
  4. Two cleaning ports
  5. Flange of the suction shell.
  6. Axis solid impeller.
  7. Ball bearings.
  8. Flange discharge.
  9. Rotor.
  10. Suction shell.
  11. Drain plugs.
  12. Connection bar
  13. Drive shaft
  14. Shaft seal.

Single screw pumps (variable capacity)

A capacity-regulating piston (1) with horizontal movement drives the sliding valve (2). This modifies the size of the exhaust port (3), thus regulating the transport volume capacity.
  • Piston regulating capacity.
  • Sliding valve.
  • Exhaust hole.
  • Screw pump outlet.
  • Screw.
  • Screw pump inlet.

Double screw pumps

The profile of the screws is such that the conduit is completely discharged, driven by the driver who is the one who performs the displacement work, acting at the same time, as a rotor and as a displacer. The screw driven performs the mission of separating the intake and discharge cavities, but without dislodging the liquid.

Triple screw pumps

These pumps need the screws to have a cycloidal profile. In a three-screw helical pump, the central one is the conductor and the two lateral ones are driven.

Peristaltic pump

A peristaltic pump is a type of positive displacement hydraulic pump used to pump a variety of fluids. The fluid is contained within a flexible tube embedded inside a circular pump casing (although linear peristaltic pumps have been made). A rotor with a number of rollers, shoes or cleaners attached to the outer circumference compresses the flexible tube. As the rotor turns, the part of the tube under compression is closed (or occluded) forcing, in this way, the fluid to be pumped to move through the tube. Additionally, while the tube is reopened to its natural state after the passage of the cam ('restitution'), fluid flow is induced to the pump. This process is called peristalsis and is used in many biological systems such as the digestive system.

Definition

The peristaltic pump is a type of positive displacement pump, that is, it has a suction part and an ejection part, so it is used to pump a wide variety of fluids. The fluid is transported by means of a flexible tube placed inside a circular cover of the pump.

Operating principle

The peristaltic pumps they operate in a similar way to the strategy that the bodies of living beings use to displace liquids inside. A flexible conduit is compressed progressively by displacing the content as the compression progresses through the conduit. It is similar to what happens when we press a tube of toothpaste or paint. To emulate progressive muscle movement, the most commonly used mechanism is composed of 2 or 3 rollers that rotate in a circular compartment, progressively compressing a special flexible hose. The rollers are integral through some mechanism with the axis of an engine, so that when the motor is rotated, the rollers press the hose progressively and advance the contents within it. It is interesting that in this system the content that is being pumped is never in contact with the mechanism, only with the inside of the duct. Pumping can also be as slow as one wishes. In the following figure, we can see an example with a 3-roller system.

Note that at no time do the rollers stop pressing the hose at least one point. This is important because if at any time the cylinders stopped pressing the conduit, the liquid could recede. The direction of rotation of the motor determines the direction of the flow of the content.

The volume of content displaced by the pump at each turn will depend on the inside diameter of the duct used and the crushing suffered by it in the rollers. This implies that as the hose wears out and loses its flexibility, the volume displaced by the pump must be recalculated. The time in which this wear occurs will depend on the material used for the duct and the thickness of the walls of the duct.

Safety device for peristaltic pumps

Because the peristaltic pump is positively displaced, when it is pumped against a closed valve or when it is closed with the pump running, or, when there are losses of excessive loads in the discharge, the internal hose of the pump can be broken due to the overpressure.

To avoid this, it is important that all installations with peristaltic pumps have a stop or bypass device that alerts when the pump exceeds the limit pressure. This security device can be:
  • Pressure switch (pressure regulator).
  • Security valve.
  • Torque Limiter (torque limiter).
  • Among others.

Peristaltic dosing pumps

The peristaltic pumps are ideal for dispensing liquids or pastes controlled manner, which are applied at one time or continuously in certain processes.

Classification of peristaltic pumps

Peristaltic pumps are manufactured, according to the specific needs of their application, in different combinations of flexible tubes, rollers and other elements.

  • High-pressure peristaltic pumps: They can operate with up to 16 bar, usually using shoes. They have covers with lubricant to prevent abrasion of the outside of the pump tube and help heat dissipation. These types of pumps use reinforced tubes, often called "hoses," so they are often called "hose pumps."
  • Low-pressure peristaltic pumps: Generally, they have dry covers and use rollers, in addition to non-reinforced pipes. This type of pump is sometimes called a "tube pump" or "pipe pump."

Centrifugal pump

Centrifugal pump. It is a type of hydraulic pump that transforms the mechanical energy of a rotary impeller called impeller into required kinetic and potential energy. The fluid enters through the center of the impeller, which has blades for conducting the fluid, and due to the effect of centrifugal force it is propelled outwards, where it is collected by the casing or body of the pump, which by its contour forms it leads to the outlet pipes or to the next impeller (next stage).

Main elements

  • A static element consisting of chimaeras, stopper and cover.
  • A dynamic-rotating element formed by an impeller and an arrow.

In recent years, thanks to the facilities that have been taking place in the supply of electric power, the use of pumps has been greatly extended. Since most of the pumps are driven with electric motors, this improvement in the flow of electricity allowed designers and manufacturers of electric motors to provide powerful and reliable motors.

Functioning

Energy from an outside source is applied to the axis A that rotates the impeller, B, within the fixed envelope, C. The blades or blades of the impeller, when rotating, produce a partial vacuum at the entrance or mouth of the impeller. This causes the liquid to enter the impeller from the suction pipe, D. This liquid is driven outward, along the vanes, with increasing speed.

The speed load that you have acquired when you leave the ends of the fins becomes a pressure load when the liquid passes inside the chamber in volute and leaves it through the discharge, E. The main advantages of the centrifugal pump are its simplicity, its low initial cost, its uniform expense (without pulsations), the small space it occupies, its low conservation cost, its quiet operation and the adaptability for its coupling to an electric motor or a turbine.

Types

Centrifugal pumps of a single jump or stage: The term pumps for chemical compounds is usually applied to those of a jump and simple design. These pumps are constructed so that it is easy to disassemble them, which are accessible and with special pressure glands to handle corrosive liquids.
They are used for general water supply and circulation services and for handling chemical compounds that do not corrode iron or bronze.

  • Directly coupled pumps: These units, in which the electric motor, or sometimes a steam turbine, is mounted directly on the same axis as the impeller, are extremely compact and suitable for a wide variety of services when it is possible to use them in their construction iron and bronze
  • Multi-hop or stage pumps: These pumps are generally used for services that require loads (pressures) greater than those achieved with single-jump pumps do. These services include high-pressure pumps for water supplies, fire-fighting pumps, boiler feed and refinery pumps. Multi-jump pumps, or several impellers, can be volute or diffuser.

Rotary pumps

The rotary pumps differ from centrifugal and piston that render a positive amount of fluid with varying load conditions or pressure, When constructed from suitable materials, can manipulate any liquid of sand or abrasive material. This type of pump consists of a fixed envelope in which one or several rotating members are located. When it has only one rotating member, or impeller, it is mounted eccentrically on the shaft. The impeller of this type of pump is usually of circular section and has one or several fins of alternative movement or a horizontal projection.

Performance

The performance of a centrifugal machine is the ratio between the power absorbed by the fluid and the power to the brake (supplied to the pump shaft). The performance is expressed as a dimensionless relationship, varies with speed and flow.

Power (to the brake) consumed by the pumps: The power required for the movement of a pump is that required to overcome all losses and provide the desired energy to the fluid. Absorbed Power: By the fluid will be determined by the energy of the fluid when leaving the pump. The power to the brake, in the axis of the pump is the energy required by the apparatus in the unit of time. The performance of a centrifugal pump is generally described because of its characteristics:
  • Flow rate or capacity "Q" (volume units / time unit, L3 / T).
  • Increase of energy contained in the pumped fluid, load or head "H" (energy unit / mass unit or unit of length L).
  • Input or consumption power "P" (work unit / time unit ML / T).
  • Efficiency "e" or ratio between the useful work developed and the power of energy.
  • Rotation speed "V" (rpm).

The hydraulic performance of a pump can vary greatly compared to published specifications. When it occurs, the cause of the discrepancy must be found. It is usually about external aspects of the bomb, which will be visible. There may not be enough NPSH, there may be vapors trapped in the suction tubes because a high point has no breath into the vapors space in the supply vessel; the motor may be connected for reverse rotation, the discharge or suction tubes may be clogged, the pump may not be well primed, etc.

Load, Head or Energy Increase of a Centrifugal Pump: It is the pressure exerted by a column of liquid in a vertical tube, on the horizontal surface at the bottom of it. Head or Static Load of a Pump: It is the vertical distance in units of length, from the level of supply of the fluid, to the central axis of the pump. When the pump is above the supply level, it is called Static Lifting Head, and when the pump is below that level, it is called Static Suction Head.

Static Discharge Head: It is the vertical distance, in units of length, from the central axis of the pump, to the free point of delivery of the fluid. Total Static Head: It is the sum of the previous Heads. To define the Head or Total Load of a Pump, use is made of the mechanical energy balance equation or Bernoulli equation between point "1" or suction and point "2" or discharge:

Where:

V1, V2 = Speed or kinetic energy of the fluid (L / T). Z1, Z2 = Height of the points with respect to the central axis of the pump (L). P1, P2 = Pressure at the points (F / L2). Ewp = Power supplied to the fluid (FL / M). Hf = Friction losses (FL / M). g = Acceleration of gravity (L / T2). GC = Conversion factor (ML / FT2). @ = Density of the fluid (M / L3).

Positive Net Suction Head (NSPH): It is the absolute pressure at the pump inlet, in units of length, plus the kinetic energy or velocity load, minus the vapor pressure of the fluid at the pumping temperature; represents the maximum allowable suction lift from the tank at atmospheric conditions.

NSPH = (V12) / 2g + [(P1-Pv) / @] (GC / g)

Where: NSPH = Head or Net Positive Suction Load (L). V1 = Average Speed in Suction (L / T). P1 = Absolute pressure in suction (F / L2). PV = Vapor pressure of the fluid (F / L2).

Positive Net Suction Head Available (NSPHD): Represents the energy level of the fluid above the vapor pressure at the pump inlet, it is a function of the system, and that is, it depends on:
  • The static load of suction or elevation.
  • Friction losses.
  • The vapor pressure of the fluid.
To express the NSPHD, an energy balance is made between the level of liquid in the power supply (1 ') and the suction point of the pump:

(V12) / 2g + Z1 '+ (P1' / @) (GC / g) - (V12) / 2g + Z1 + (P1 / @) (GC / g) + hf

Taking point 1 as the reference level, knowing that V1 '= 0 and based on the NSPH equation you have

NSPHD = [(P1'-PV) / @] (GC / g) -hf + Z1)]

Where: NSHPD = Net Positive Suction Head available (L) P1 '= Absolute pressure at the supply level (F / L2) hf = Friction losses between section 1'-1 (L) Z' = Height of the level of suction (L)

Suction conditions

When liquids are pumped, the pressure at any point inside the pump should never be allowed to fall below the vapor pressure of the liquid at the pumping temperature. You should always have enough energy available in the pump suction to make the liquid reach the impeller and counteract the losses between the suction nozzle and the pump impeller inlet. In this place, the impeller blades apply more energy to the liquid.

An additional feature of the pump is the (NPSH) R. It is the energy, in ft, of liquid charge that is needed in the pump suction above the vapor pressure of the liquid so that the pump delivers a given capacity at a given speed. Changes in (NPSH) A do not alter pump performance as long as (NPSH) A is greater than (NPSH) B.

Cavitation

Cavitation causes the rapid destruction of the constituent metal of the impeller of the pumps and turbines, of the blades, of the venturimeters and sometimes of the pipes. This happens when the pressure of the liquid becomes less than its vapor tension.

Pumps in series and pumps in parallel

One or more pumps in series can be damaged by the loss of NPSH due to the failure of an upstream pump. In series pumps, you can follow a reduced flow even if one of them does not work. This flow through the idle pump will cause the impeller to rotate in the opposite direction and loosen the nuts that hold the impeller and the sleeves on the shaft. When the idle pump is restarted, loose parts will damage it in a short time.

The suction manifold for several pumps must receive special attention for its design and size, because the cavitation produced at the entrance to a suction tube can be propagated along the manifold to other suction tubes or, a pump, can deprive to all others of your suction pressure, which reduces your (NPSH).

Priming a pump

When a pump is first put into service, the waterways are full of air. If the suction supply is above the atmospheric pressure, the priming is carried out by removing the trapped air content from the pump by means of a valve provided for this purpose. If the pump carries out the suction of a supply located under it, the air in the pump must be evacuated with some vacuum producing device, thereby placing a foot valve in the suction line, that the pump and the pipe of Suction can be filled with liquid or, providing the suction line with a priming chamber.

Characteristics of Hydraulic Pumps

In hydraulic pumps, we have to take into account certain technical values and other considerations for the correct choice of the pump:

Engine. Its expression is in cm3 / r, where r are the revolutions. The displacement is the volume of fluid displaced according to the complete rotation of the pump shaft. Volumetric efficiency. It is never 100%, for two reasons, total performance and pressure. The volumetric yield is the relationship between the effective and the theoretical flow.

Cavitation. It is a physical phenomenon that occurs when the fluid has difficulty being aspirated by the pump; therefore, pressure is lost, resulting in bubbles in the fluid itself. The bubbles are constituted by the vapors of the fluid itself. This phenomenon has pernicious consequences for the pump itself, since when the bubbles pass from the suction zone to the impulse zone, the bubbles themselves explode and micro particles can be removed from the pump. It must be taken into account that the bubbles entering the discharge zone are under high pressures and with temperature. A bubble with a temperature of 100 ° C can reach 500 ° C if a pressure is added and compressed. There are several causes for the phenomenon of cavitation to occur. These include dirt in the pump suction filter.