mercredi 13 octobre 2010

PUMPS

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PUMPS & ITS TYPES:

Pumps come in a variety of sizes for a wide range of applications. They can be classified according to their basic operating principle as dynamic or displacement pumps. Dynamic pumps can be sub-classified as centrifugal and special effect pumps. Displacement pumps can be sub-classified as rotary or reciprocating pumps. In principle, any liquid can be handled by any of the pump designs. Where different pump designs could be used, the centrifugal pump is generally the most economical followed by rotary and reciprocating pumps. Although, positive displacement pumps are generally more efficient than centrifugal pumps, the benefit of higher efficiency tends to be offset by increased maintenance costs.

PUMP SET:A Pump & a motor together constitute a Pump Set.

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SPECIFICATION OF THE PUMP:

In a pumping system, the objective, in most cases, is either to transfer a liquid from a source to a required destination, e.g. filling a high level reservoir, or to circulate liquid around a system, e.g. as a means of heat transfer in heat exchanger.

A pressure is needed to make the liquid flow at the required rate and this must overcome head ‘losses’ in the system. Losses are of two types: static and friction head.

Static head is simply the difference in height of the supply and destination reservoirs, as in Figure a. In this illustration, flow velocity in the pipe is assumed to be very small. Another example of a system with only static head is pumping into a pressurised vessel with short pipe runs. Static head is independent of flow and graphically would be shown as in Figure a

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FIGURE a STATIC HEAD

FIGURE b STATIC HEAD vs FLOW

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Friction head (sometimes called dynamic head loss) is the friction loss, on the liquid being moved,in pipes, valves and equipment in the system. Friction tables are universally available for various pipe fittings and valves. These tables show friction loss per 100 feet (or metres) of a specific pipe size at various flow rates. In case of fittings, friction is stated as an equivalent length of pipe of the same size.

FIGURE c FRICTION HEAD vs FLOW

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Pump Specification:

Q in Cubic meter per

sec

Head in

meters

A pump has to be specified as to its Total head (H) in meters and its Discharge (Q)

in Cubic meter per second.

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Energy Conservation Opportunities in Pumping Systems:

*) Ensure adequate NPSH at site of installation

*) Ensure availability of basic instruments at pumps like pressure gauges, flow meters.

*) Operate pumps near best efficiency point.

*) Modify pumping system and pumps losses to minimize throttling.

*) Adapt to wide load variation with variable speed drives or sequenced control of multiple units.

*) Stop running multiple pumps - add an auto-start for an on-line spare or add a booster pump in the problem area.

*) Use booster pumps for small loads requiring higher pressures.

*) Increase fluid temperature differentials to reduce pumping rates in case of heat exchangers.

*) Repair seals and packing to minimize water loss by dripping.

*) Balance the system to minimize flows and reduce pump power requirements.

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THANK YOU