PUMPS- Mechanical devices for transferring fluids from one place to another. When used for domestic or irrigation water supply, pumps are used to lift water from wells, rivers, lakes, and etc.

PUMP CLASSIFICATION POSITIVE DISPLACEMENT PUMPS – discharge the same volume of water

regardless of the head against which they operate. Commonly used in domestic water supply.

VARIABLE DISPLACEMENT PUMPS - has inverse relationship between the discharge rate and the pressure head.

POSITIVE DISPLACEMENT PUMPS1. RECIPROCATING – described as having a to-and-fro motion.

Lift Pump Force Pump

2. ROTARY- used primarily as source of fluid power in hydraulic systems.

VARIABLE DISPLACEMENT PUMPS (of impeller type)1. CENTRIFUGAL – centrifugal force acts on a body moving in a circular path,

tending to force it further away from the axis of rotation.2. MIXED FLOW 3. PROPELLER

- 2 & 3 are used for low head-high discharge operation.

CENTRIFUGAL PUMPS Most commonly used type of VDP for irrigation. centrifugal force acts on a body moving in a circular path, tending to force it

further away from the axis of rotation. The impeller provides rapid rotary motion on the water forcing the water out of

the casing through the discharge flange. classified on the following basis:a. Type of energy conversion; i) volute & ii) diffuserb. Number of stages; i) single-stage & ii) multi-stage.c. Impeller type; i) open, ii) semi-open, & iii) closedd. Type of suction inlet; i) single suction & ii) double suctione. Construction of casing; i) vertical split & ii) Horizontal splitf. Axis of rotation; i) horizontal & ii) verticalg. Method of drive i) close-coupled & ii) belt driven.

TYPES OF CENTRIFUGAL PUMPS VOLUTE CP - has casing made in the form of a spiral or volute curve.

Volute casing’s x-area was proportioned to change velocity head into pressure head.

DIFFUSER OR TURBINE CP – the impeller is surrounded by diffuser vanes.

Diffuser vanes have small openings near the impeller and enlarge gradually to the outer diameter. It is where the conversion of velocity to pressure takes place.

CHOICE….

VOLUTE type is preferred for large capacity – low head application. DIFFUSER types are usually used for high head conditions. They are most

popular in deep wells because of its design advantage where the diameter of the pump is limited.

Deep well Turbine Pumps & Submersible Pumps Deep well Turbine Pumps – uses an impeller which is suspended vertically on a

drive shaft within a long discharge pipe. Submersible Pump – type of pumps close-coupled with a smaller diameter electric

motor and operated under submerged conditions. Motor is filled with a special oil for water-proofing & is provided with

long waterproof cable.

Advantage of Submersible pump when used for deep well pumping Elimination of long drive shaft and bearing assemblies; Can be quickly and easily installed; Can be of smaller diameter; Cheaper than turbine pumps; and Do not need housing over the unit

As a disadvantage, this pump is generally lower in efficiency than the turbine pump.

PROPELLER & MIXED FLOW PUMPS are used for low head-high discharge operation. Can give high efficiency compare to Cp at heads less than a meter. For slightly higher heads but still below those usually produced efficiently by CP,

MFP are suitable. Both pumps are extensively used for irrigation & drainage pumping.

JET PUMPS As used in irrigation consist of a combination of CP a a jet mechanism or ejector. CP is placed at the ground surface & furnishes the driving head & capacity fro the

jet placed below the water surface. Jet consist of nozzle and venturi in the suction pipe. May be used for medium depth wells (lifts greater than 25 ft). Efficiency is only about 35% (inefficient!)

PRIMING Is the process of removing air in the suction line of the water pump.

Done by filling the suction line with liquid which replaces the air in the suction line.

Foot valve can be employed to hold water in the pump and in the suction line. Air in the suction line may also be removed by a vacuum pump or an auxiliary

piston pump.

PUMP SELECTION Requires not only the specified head & discharge but also its operation. It must

be near the rated conditions (optimum) which is the best efficiency point (max efficiency) and should function free of cavitations, vibrations, and any other undesirable characteristics.

FACTORS TO BE CONSIDERED Type of Pump – the quantity of water produced and operating conditions of

pumps govern the selection. The PDP are used to draw small quantity of water from a source.

Likewise, for large quantity of water such as for irrigation, the VDP are used.

Power – the source of available energy for use influences the selection (e.g. electricity, ICE, etc.)

Water Quality – determines the types of impeller (e.g. open, semi-open, or close-type if the liquid contain solids). The chemical composition of water affects the selection of material for the pump.

The System – characteristic curve and Pump performance characteristic curves. Curves are expressed in Q – H relationship. Heads vary because of a) seasonal variation static water level & b) temporary lowering of the dynamic water level due to prolong pumping & interference from other wells.

CAVITATION Is a phenomenon in which the water boils due to the reduction in water pressure.

But once the vapor is in contact with high pressure, it collapses causing damage to the impeller and producing impinging noise.

Could be addressed if the required NPSH specified by the manufacturer is considered.

Ha = absolute pressure on the liquid surface of the water in ft (m) of liquid Hs = elev. Of the liquid above or below the impeller eye while pumping in ft (m).

If the level is above the eye,Hs is +, if below then -. Hf = friction head losses in the suction piping in ft (m). Hvp = absolute vapor pressure of the liquid at the pumping temp. in ft (m)

FACTORS TO BE CONSIDERED ECONOMIC CONSIDERATION

The head-discharge characteristic of the system may be satisfied by different pumps that are available in the market.

Initial cost – one of the primary fixed cost. Operation & Maintenance – pumps driven by diesel engines have higher

fixed cost but lower operation & maintenance cost. Ease of repair and availability of parts in the locality should also be

considered.