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A pump is a device that moves fluids liquids or gases , or sometimes slurries , by mechanical action. Pumps can be classified into three major groups according to the method they use to move the fluid: Pumps operate by some mechanism typically reciprocating or rotary , and consume energy to perform mechanical work by moving the fluid.
Pumps operate via many energy sources, including manual operation, electricity , engines , or wind power , come in many sizes, from microscopic for use in medical applications to large industrial pumps. Mechanical pumps serve in a wide range of applications such as pumping water from wells , aquarium filtering , pond filtering and aeration , in the car industry for water-cooling and fuel injection , in the energy industry for pumping oil and natural gas or for operating cooling towers.
In the medical industry , pumps are used for biochemical processes in developing and manufacturing medicine, and as artificial replacements for body parts, in particular the artificial heart and penile prosthesis. When a casing contains only one revolving impeller , it is called a single stage pump. When a casing contains two or more revolving impellers, it is called a double or multi-stage pump. In biology, many different types of chemical and bio-mechanical pumps have evolved , and biomimicry is sometimes used in developing new types of mechanical pumps.
Mechanical pumps may be submerged in the fluid they are pumping or be placed external to the fluid. Pumps can be classified by their method of displacement into positive displacement pumps , impulse pumps , velocity pumps , gravity pumps , steam pumps and valveless pumps. There are two basic types of pumps: Although axial-flow pumps are frequently classified as a separate type, they have essentially the same operating principles as centrifugal pumps.
A positive displacement pump makes a fluid move by trapping a fixed amount and forcing displacing that trapped volume into the discharge pipe. Some positive displacement pumps use an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. The volume is constant through each cycle of operation.
Positive displacement pumps, unlike centrifugal or roto-dynamic pumps, theoretically can produce the same flow at a given speed RPM no matter what the discharge pressure.
Thus, positive displacement pumps are constant flow machines. However, a slight increase in internal leakage as the pressure increases prevents a truly constant flow rate. A positive displacement pump must not operate against a closed valve on the discharge side of the pump, because it has no shutoff head like centrifugal pumps.
A positive displacement pump operating against a closed discharge valve continues to produce flow and the pressure in the discharge line increases until the line bursts, the pump is severely damaged, or both.
A relief or safety valve on the discharge side of the positive displacement pump is therefore necessary. The relief valve can be internal or external. The pump manufacturer normally has the option to supply internal relief or safety valves. The internal valve is usually used only as a safety precaution. An external relief valve in the discharge line, with a return line back to the suction line or supply tank provides increased safety.
A positive displacement pump can be further classified according to the mechanism used to move the fluid:. These pumps move fluid using a rotating mechanism that creates a vacuum that captures and draws in the liquid. Rotary pumps are very efficient [ citation needed ] because they can handle highly viscous fluids with higher flow rates as viscosity increases.
The nature of the pump requires very close clearances between the rotating pump and the outer edge, making it rotate at a slow, steady speed. If rotary pumps are operated at high speeds, the fluids cause erosion, which eventually causes enlarged clearances that liquid can pass through, which reduces efficiency.
Reciprocating pumps move the fluid using one or more oscillating pistons, plungers, or membranes diaphragms , while valves restrict fluid motion to the desired direction. In order for suction to take place, the pump must first pull the plunger in an outward motion to decrease pressure in the chamber. Once the plunger pushes back, it will increase the pressure chamber and the inward pressure of the plunger will then open the discharge valve and release the fluid into the delivery pipe at a high velocity.
Pumps in this category range from simplex , with one cylinder, to in some cases quad four cylinders, or more. Many reciprocating-type pumps are duplex two or triplex three cylinder.
They can be either single-acting with suction during one direction of piston motion and discharge on the other, or double-acting with suction and discharge in both directions. The pumps can be powered manually, by air or steam, or by a belt driven by an engine. This type of pump was used extensively in the 19th century—in the early days of steam propulsion—as boiler feed water pumps. Now reciprocating pumps typically pump highly viscous fluids like concrete and heavy oils, and serve in special applications that demand low flow rates against high resistance.
Reciprocating hand pumps were widely used to pump water from wells. Common bicycle pumps and foot pumps for inflation use reciprocating action. These positive displacement pumps have an expanding cavity on the suction side and a decreasing cavity on the discharge side.
Liquid flows into the pumps as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. This is the simplest of rotary positive displacement pumps. It consists of two meshed gears that rotate in a closely fitted casing. The tooth spaces trap fluid and force it around the outer periphery. The fluid does not travel back on the meshed part, because the teeth mesh closely in the center.
Gear pumps see wide use in car engine oil pumps and in various hydraulic power packs. A screw pump is a more complicated type of rotary pump that uses two or three screws with opposing thread — e.
The screws are mounted on parallel shafts that have gears that mesh so the shafts turn together and everything stays in place. The screws turn on the shafts and drive fluid through the pump. As with other forms of rotary pumps, the clearance between moving parts and the pump's casing is minimal. Widely used for pumping difficult materials, such as sewage sludge contaminated with large particles, this pump consists of a helical rotor, about ten times as long as its width.
This can be visualized as a central core of diameter x with, typically, a curved spiral wound around of thickness half x , though in reality it is manufactured in single casting. This shaft fits inside a heavy duty rubber sleeve, of wall thickness also typically x. As the shaft rotates, the rotor gradually forces fluid up the rubber sleeve.
Such pumps can develop very high pressure at low volumes. This design produces a continuous flow with equal volume and no vortex. It can work at low pulsation rates, and offers gentle performance that some applications require. A peristaltic pump is a type of positive displacement pump.
It contains fluid within a flexible tube fitted inside a circular pump casing though linear peristaltic pumps have been made. A number of rollers , shoes , or wipers attached to a rotor compresses the flexible tube. As the rotor turns, the part of the tube under compression closes or occludes , forcing the fluid through the tube.
Additionally, when the tube opens to its natural state after the passing of the cam it draws restitution fluid into the pump. This process is called peristalsis and is used in many biological systems such as the gastrointestinal tract. These consist of a cylinder with a reciprocating plunger. The suction and discharge valves are mounted in the head of the cylinder. In the suction stroke the plunger retracts and the suction valves open causing suction of fluid into the cylinder.
In the forward stroke the plunger pushes the liquid out of the discharge valve. Efficiency and common problems: With only one cylinder in plunger pumps, the fluid flow varies between maximum flow when the plunger moves through the middle positions, and zero flow when the plunger is at the end positions.
A lot of energy is wasted when the fluid is accelerated in the piping system. Vibration and water hammer may be a serious problem. In general the problems are compensated for by using two or more cylinders not working in phase with each other.
Triplex plunger pumps use three plungers, which reduces the pulsation of single reciprocating plunger pumps. Adding a pulsation dampener on the pump outlet can further smooth the pump ripple , or ripple graph of a pump transducer. The dynamic relationship of the high-pressure fluid and plunger generally requires high-quality plunger seals.
Plunger pumps with a larger number of plungers have the benefit of increased flow, or smoother flow without a pulsation damper. The increase in moving parts and crankshaft load is one drawback. Car washes often use these triplex-style plunger pumps perhaps without pulsation dampers.
In , William Bruggeman reduced the size of the triplex pump and increased the lifespan so that car washes could use equipment with smaller footprints. Durable high-pressure seals, low-pressure seals and oil seals, hardened crankshafts, hardened connecting rods, thick ceramic plungers and heavier duty ball and roller bearings improve reliability in triplex pumps. Triplex pumps now are in a myriad of markets across the world.
Triplex pumps with shorter lifetimes are commonplace to the home user. A person who uses a home pressure washer for 10 hours a year may be satisfied with a pump that lasts hours between rebuilds. Industrial-grade or continuous duty triplex pumps on the other end of the quality spectrum may run for as much as 2, hours a year. The oil and gas drilling industry uses massive semi trailer-transported triplex pumps called mud pumps to pump drilling mud , which cools the drill bit and carries the cuttings back to the surface.
One modern application of positive displacement pumps is compressed-air-powered double- diaphragm pumps. Run on compressed air these pumps are intrinsically safe by design, although all manufacturers offer ATEX certified models to comply with industry regulation.
These double-diaphragm pumps can handle viscous fluids and abrasive materials with a gentle pumping process ideal for transporting shear sensitive media.
Devised in China as chain pumps over years ago, these pumps can be made from very simple materials: A rope, a wheel and a PVC pipe are sufficient to make a simple rope pump. Rope pump efficiency has been studied by grass roots organizations and the techniques for making and running them have been continuously improved.
Impulse pumps use pressure created by gas usually air. In some impulse pumps the gas trapped in the liquid usually water , is released and accumulated somewhere in the pump, creating a pressure that can push part of the liquid upwards. Instead of a gas accumulation and releasing cycle, the pressure can be created by burning of hydrocarbons. Such combustion driven pumps directly transmit the impulse form a combustion event through the actuation membrane to the pump fluid.