The pump A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action. 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. 1
Types Specifications Pumps are commonly rated by horsepower, flow rate, outlet pressure in metres (or feet) of head, inlet suction in suction feet (or metres) of head. The head can be simplified as the number of feet or metres the pump can raise or lower a column of water at atmospheric pressure. From an initial design point of view, engineers often use a quantity termed the specific speed to identify the most suitable pump type for a particular combination of flow rate and head. Pump material The pump material can be Stainless steel (SS 316 or SS 304), cast iron etc. It depends on the application of the pump. In the water industry and for pharma applications SS 316 is normally used, as stainless steel gives better results at high temperatures. Positive displacement pump 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. 2
Positive displacement types : A positive displacement pump can be further classified according to the mechanism used to move the fluid: 1-Rotary-type positive displacement : gear, screw,rotary vane, shuttle block, flexible vane or sliding vane, circumferential piston, flexible impeller, helical twisted roots (e.g. the Wendelkolben pump) or liquid ring vacuum pump. 2-Reciprocating-type positive displacement: piston,plunger and diaphragm pumps. Rotary positive displacement pumps : Positive displacement rotary pumps move fluid using a rotating mechanism that creates a vacuum that captures and draws in the liquid. 1-Rotary positive displacement pumps fall into three main types: 1-1Gear pumps - a simple type of rotary pump where the liquid is pushed between two gears. 3
Advantages Only two moving parts Only one stuffing box Excellent for high-viscosity liquids Constant and even discharge regardless of pressure conditions Operates well in either direction Can be made to operate with one direction of flow with either rotation Low NPSH required Flexible design offers application customization Disadvantages Usually requires moderate speeds Medium pressure limitations Overhung load on shaft bearing Applications Common internal gear pump applications include, but are not limited to: All varieties of fuel oil and lube oil Resins and Polymers Alcohols and solvents Asphalt, Bitumen, and Tar Polyurethane foam (Isocyanate and polyol) Food products such as corn syrup, chocolate, and peanut butter Paint, inks, and pigments 1-2Screw pumps - the shape of the internals of this pump usually two screws turning against each other pump the liquid. 4
Advantages Pumps raw water with heavy solids and floating debris Slow Speed, Simple and Rugged design 'Gentle handling' of biological floc Long lifetime ( > 20-40 years) Pump capacity is self-regulating with incoming level Constant high efficiency with variable capacity Disadvantages Possible blockages at reduced capacities Heavy solids cannot be pumped High friction losses in pipes Highly skilled maintenance staff required 1-3 Rotary vane pumps - similar to scroll compressors, these have a cylindrical rotor encased in a similarly shaped housing. As the rotor orbits, the vanes trap. 5
Advantages Handles thin liquids at relatively higher pressures Sometimes preferred for solvents, LPG Can run dry for short periods Develops good vacuum Disadvantages Complex housing and many parts Not suitable for high pressures Not suitable for high viscosity Not good with abrasives Applications Aviation Service - Fuel Transfer, Deicing Auto Industry - Fuels, Lubes, Refrigeration Coolants Bulk Transfer of LPG and NH3 Alcohols Refrigeration - Freons, Ammonia Solvents Aqueous solutions 6
2-Reciprocating positive displacement pumps Reciprocating pumps move the fluid using one or more oscillating pistons, plungers, or membranes (diaphragms), while valves restrict fluid motion to the desired direction. Typical reciprocating pumps are: 2-1Plunger pumps - a reciprocating plunger pushes the fluid through one or two open valves, closed by suction on the way back. are capable of generating high levels of pressure, they re useful for moving highly viscous or heavy substances such oil. Smaller, lighter 2-2Diaphragm pumps - similar to plunger pumps, where the plunger pressurizes hydraulic oil which is used to flex a diaphragm in the pumping cylinder. Diaphragm valves are used to pump hazardous and toxic fluids. Advantages Air diaphragm pumps are a very efficient type of transfer pump. These pumps can handle liquids with high, medium or low viscosities. They are also designed to pump liquids that feature a considerable amount of solids. 7
This type of pump can be constructed out of materials that can handle pumping even the most acidic chemicals. Disadvantages Most air diaphragm pumps require around 20 standard cubic-feet per minute and 100 psi of air intake to operate efficiently. these types of pumps tend not to pump very accurately at their bottom end. 2-3Piston displacement pumps - usually simple devices for pumping small amounts of liquid or gel manually. The common hand soap dispenser is such a pump. Advantages Reciprocating pumps will deliver fluid at high pressure (High Delivery Head). They are 'Self-priming' - No need to fill the cylinders before starting Pressure can be controlled without affecting flow rate. 8
Disadvantages Reciprocating pumps give a pulsating flow. The suction stroke is difficult when pumping viscous liquids. The cost of producing piston pumps is high. This is due to the very accurate sizes of the cylinders and pistons. Also, the gearing needed to convert the rotation of the drive motor into a reciprocating action involves extra equipment and cost. The close fitting moving parts cause maintenance problems, especially when the pump is handling fluids containing suspended solids, as the particles can get into the small clearances and cause severe wear. The piston pump therefore, should not be used for slurries. They give low volume rates of flow compared to other types of pump Centrifugal pump A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure and flow rate of a fluid. Centrifugal pumps are the most common type of pump used to move liquids through a piping system. 9
Centrifugal pumps are typically used for large discharge through smaller heads. Advantages Small in size, space saving & less capital costs Easy for maintenance No danger creates if discharge v/v is closed while starting Deal with large volume Able to work medium to low head Able to work medium to low viscous fluid Disadvantages Cannot be able to work high head. Cannot deal with high viscous fluid. P&ID symbols pumps : 10
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