Hydraulic pump

Old manual bomb.

A hydraulic pump or water pump is a generating machine that transforms the energy with which it is driven (generally mechanical energy) into energy from the incompressible fluid that it moves. The incompressible fluid can be a liquid or a mixture of liquids and solids such as pre-set concrete or 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 fluid by adding energy to the hydraulic system, to move the fluid from an area of lower pressure to one of higher pressure.

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 Therefore, they do not alter the density of their working fluid, unlike other machines such as compressors, whose field of application is pneumatics and not hydraulics. But it is also common to find the term pump to refer to machines that pump other types of fluids, such as vacuum pumps or air pumps.

History

The first known pump was described by Archimedes in the 3rd century BCE. C. and is known as the Archimedean screw, although a similar system had previously been used by Sennacherib, king of Assyria in the seventh century BC. C.

In the 12th century, Al Khazari described and illustrated different types of pumps, including reversible pumps, double-acting pumps, vacuum pumps, water pumps, and positive displacement pumps.

Types of pumps

Double lobes pump.	Gear pump.
Axial rotodynamic pump.	5-stage centrifugal pump.

According to the principle of operation

The main classification of the pumps is established according to the operating system on which they are based.

• Pumps volumetrics, in which its operating principle is based on hydrostatic, so that the pressure increase is made by the thrust of the walls of the chambers that vary its volume. In this type of pump, in each cycle the propellant organ positively generates a given or cylindrical volume. In case the maximum volume of the cylindride can be varied, it is spoken of variable volume pumps. If that volume cannot be changed, then it is said that the pump is fixed volume. In turn this type of pump can be subdivided into:
• Alternative piston pumps, in which there is one or more fixed compartments, but of variable volume, by the action of a piston or of a membrane. In these machines, the fluid movement is discontinuous and the load and discharge processes are performed by valves that open and close alternatively. Examples of this type of pump are the alternative piston pump, the rotating piston pump or the axial drive piston pump.
• Rotary volumetric pumps or Rotation, in which a fluid mass is confined in one or more compartments that move from the input zone (low pressure) to the output area (high pressure) of the machine. Examples of this type of machine are pallet pump, lobe pump, gear pump, screw pump or peristaltic pump.
• Pumps rotodynamicsin which the operating principle is based on the exchange of amount of movement between the machine and the fluid, applying the hydrodynamics. In this type of pumps there are one or more rounds with links that rotate generating a field of pressure in the fluid. In this type of machines the flow of the fluid is continuous. These are hydraulic generators can be subdivided into:
• Radial or centrifugal, when the fluid movement follows a perpendicular path to the axis of the impeller surround.
• Axialeswhen the fluid passes through the channels of the links following a trajectory contained in a cylinder.
• Diagonal or helicocentrifugas when the path of the fluid is performed in another direction between the previous ones, that is, in a coaxial cone with the axis of the rodete.

Depending on drive type

• Electrobombas. Genericly, they are those driven by an electric motor, to distinguish them from the motobombas, usually driven by internal combustion engines.
• Pneumatic pumps which are positive displacement pumps in which the input energy is pneumatic, usually from compressed air.
• Hydraulic drive pumpsLike the water pump or the noria.
• Manual pumps. A type of manual bomb like the slug bomb.
• Diesel motorcycles. A type of bomb moved by a diesel engine.

Types of plunger pumps

Suction pump

Alternative piston vacuum pump.

In a "suction pump," a cylinder containing a movable piston is connected to the water supply by a tube. A valve blocks the entrance of the tube to the cylinder. The valve is like a door with hinges, which only opens upwards, letting the water rise, but not fall. Inside the piston, there is a second valve that works in the same way. When the crank is operated, the piston rises. This increases the volume under the piston, and therefore the pressure decreases. The normal air pressure acting on the surface of the water, from the well, makes the liquid rise up the tube, clearing the valve —which opens— and makes it enter the cylinder. When the piston goes down, the first valve closes, and the second opens, allowing water to pass to the top of the piston and fill the cylinder above it. The next upward stroke forces the water up the spigot and, at the same time, forces more water into the cylinder, below the piston. The action continues as the piston moves up and down.

A suction pump is limited-acting, in certain ways. It cannot provide a continuous stream of liquid or cause water to rise over a distance greater than 10 m. between the surface of the well and the lower valve, since normal air pressure can only act with sufficient force to maintain a column of water of that height. A booster pump overcomes those obstacles.

Seville Bomb

A type of suction pump that can lift water more than ten meters is the Seville pump, accidentally discovered in 1798, which was cited and commented on in foreign works. This pump lifts a mixture of air and water. It would be the inverse case of the waterspout.

Force pump

The booster pump consists of a cylinder, a piston, and a pipe that runs down to the water tank. It also has a valve that lets water into the cylinder, but not back. There is no valve on the piston, which is completely solid. From the lower end of the cylinder comes a second tube that reaches an air chamber. The entrance to that chamber is blocked by a valve that lets the water in, but not out. From the bottom end of the air chamber, another pipe carries the water to a tank or hose.

Priming of rotodynamic pumps

For the correct functioning of the rotodynamic pumps, they need to be filled with incompressible fluid, that is, liquid, since in the case of being filled with compressible fluid (any gas such as air) they would not work correctly.

Pump priming consists of filling the suction pipe and the pump casing with liquid, to facilitate the suction of liquid, avoiding air pockets inside. As this operation is necessary in rotodynamic pumps, it is said that they do not have self-priming capacity. However, positive displacement pumps are self-priming, that is, even if they are filled with air, they are capable of filling the suction circuit with fluid.

Scheme of a pump installed above the water level.

In a circuit like the one shown in the attached diagram without any additional device, when the centrifugal pump stops, the fluid from the suction circuit falls towards the tank, emptying the pump due to the vacuum created by the primary circuit.

The height of elevation H{displaystyle H} which provides the pump is always the same and responds to the following formula:

H=PI− − PAρ ρ g{displaystyle H={P_{I}-P_{A} over rho g}}

where PI{displaystyle P_{I}} It's impulsion pressure, PA{displaystyle P_{A}} It's the suction pressure, ρ ρ {displaystyle rho } is fluid density and g{displaystyle g} the acceleration of gravity.

Solving for the pressure difference, we have:

(PI− − PA)=ρ ρ gH{displaystyle (P_{I}-P_{A})={rho g H}

From this formula it can be seen that the pressure difference achieved by the pump between delivery and intake is greater the higher the density of the fluid to be moved. In such a way that for the specific case of water we have:

(PI− − PA)aire=ρ ρ airegH=1,29⋅ ⋅ 9,81⋅ ⋅ H{displaystyle (P_{I}-P_{A})_{aire}={rho _{aire} g}=1,29cdot 9,81cdot H}

(PI− − PA)agua=ρ ρ aguagH=1000⋅ ⋅ 9,81⋅ ⋅ H{displaystyle (P_{I}-P_{A})_{agua}={rho _{agua} g}=1000cdot 9,81cdot H}

Whereby:

(PI− − PA)aire(PI− − PA)agua=ρ ρ aireρ ρ agua=1,291000=0,00129{displaystyle {(P_{I}-P_{A})_{aire} over (P_{I}-P_{A})_{agua}={rho _{aire} over rho _{agua}}={1,29 over 1000}=0,00129}

That is, if the pump is filled with air, the suction pressure is 0.00129 times what the pump would achieve if it were filled with water, that is, if it were primed. Therefore, if the pump is empty, the height that the water in the suction circuit rises above the level of the water in the tank is minimal and totally insufficient for the water to reach the pump.

On the other hand, the operation of a centrifugal pump in a vacuum can damage the sealing of the pump due to poor cooling since no fluid circulates inside it, which helps to improve the dissipation of the heat produced by the pump.

Therefore, in pumping installations whose scheme coincides with the one indicated in the attached scheme, an additional system is necessary to prevent the pump from unpriming. Some of these systems are listed below:

• You can build an orifice at the top of the bomb housing and throw water on it so that the pump is filled with water and can pump properly. It's not a very efficient system.
• A foot valve can be used (antiretorn valve). It allows the passage of the liquid to the pump but prevents its return to the tank once the pump has been turned off, thus preventing the decebe of the impulsion pipe. It can present problems when the fluid has dirt that is deposited in the valve seat by decreasing its seal, on the other hand it represents a loss of load more or less important in the impulsion pipe so it increases the risk of cavitation in the pump.
• Use of a vacuum pump. The vacuum pump is a positive displacement pump that extracts the air from the impulsion pipe and makes the fluid reach the centrifugal pump and thus becomes barley.
• Finally another possibility is to install the pump under load, i.e. below the liquid level, although this arrangement is not always possible, unless it is installed submerged, so the pump has to be special.

Sealing of bombs

Gear pump.

Gear pump.

Gear pump.

The pumps require hydraulic seals to prevent the fluids that are being pumped from leaving the outside of the machine through the transmission path of movement from the motor to the internal mobile parts of the pump.

In the field of petroleum refining and petrochemicals there are mechanical seals for pumps standardized by API (American Petroleum Institute) which, although it is an American association, are applicable throughout the world. world. Each type of seal receives the name of PLAN API. These seals can be single or double and, in addition, they may or may not have a refrigeration system.

There is also an ANSI classification of pump seals.

The following is the API - ANSI equivalence of the most used sealing systems or plans:

• PLAN API 11 (ANSI PLAN 7311)
• PLAN API 12 (ANSI PLAN 7312)
• PLAN API 21 (ANSI PLAN 7321)
• PLAN API 22 (ANSI PLAN 7322)
• PLAN API 31 (ANSI PLAN 7331)
• PLAN API 41 (ANSI PLAN 7341)
• PLAN API 13 (ANSI PLAN 7313)
• PLAN API 23 (ANSI PLAN 7323)
• PLAN API 32 (ANSI PLAN 7332)
• PLAN API 62 (ANSI PLAN 7362)
• PLAN API 52 (ANSI PLAN 7352)
• PLAN API 53 (ANSI PLAN 7353)
• PLAN API 54 (ANSI PLAN 7354)