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8/12/2019 SemVI_unit1qA

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Amet University

Test Questions.

3 mark questions.

Unit No.1

1. What is priming, Name the type of pump which is to be primed.2. What are the conditions under which a centrifugal p/p can loose suction?3. Name the different air handling methods used on a centrifugal pump.4. Why cooling is provided in the liquid ring primer system.5. What is a dry ring primer?6. What are the advantages of using a central priming system?7. What are materials used for a centrifugal pump used for seawater system.8. What are materials used for a centrifugal pump used for freshwater system.

12 mark questions.

Unit No.1

1.Sketch and describe a liquid ring primerarrangement.Ans:Liquid ring primer

This type is most frequently used. Its air handling capacity is good,

the extracted air being vented to atmosphere, although it can be

used to pump against pressure. It is used as a gas compressor and

as an air exhausted.


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The liquid ring air pump consists of a bladed circular rotorshrouded on the underside, rotating in an oval casing. Sealing

wateris drawn into the whirlpool casing through a make up supply

pipe, The water follows the periphery of the casing due to the

centrifugal force Imparted to it by the rotorand the water-

ring, revolving eccentric to the blade recedes from and re-

approaches the rotor boss twice in one revolution, thus producing

in effect a series of reciprocating water pistons between the

blades. The inner edge of the water-ring forms the boundary of

two eccentric cores round the rotor boss, while the blades run full

of water


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*Due to the casing shape the water is made to flow from andtowards the rotor centre during each revolution. The water motion

is utilised to act as suction and discharge for the air through

appropriate sets of ports.

*As the impeller vanes pass the suction port air is drawn in and

trapped between the water ring and the pump shaft. This 'slug'of

air is carried around and delivered to the discharge-port hence this

pump is a positive displacement type.

2. Explain with a neat sketch the functionig of rotatry

air extraction pump.


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At the initial start of main pump, there is no dischargepressure - the spring keeps operating piston towards "A" -

thereby keeping friction clutch engaged

Endangerment of friction clutch runs air extraction pump,which sucks air from the suction side of the main pump and

also water from the vessel.

As the main pump fills up and discharge pressure builds up,water pressure acts at "A", pushing operating piston towards

"B", thereby disengaging friction clutch and thus cutting off

the air extraction pump.


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The rotor casing is continuously cooled by a closed watercircuit from the pump discharge round the air pump jacket

and returns to the pump suction

2.Explain with a line sketch the functionig of ejectortype priming arrangment.

Pump starts but no discharge. Pressure transmitter sends signal to pressure controller. Controller sends signal to selector/transmitter relay. Two output signals from selector/transmitter relay:

To open solenoid valve "B"

To open solenoid valve "A"

Solenoid valve "B" allows air to flow throughventuri.


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Venturi or ejector creates vacuum and sucks up theair in the pump casing through solenoid

valve A.

Pump fills up with water and discharges pressurebuilds up.

Pressure transmitter detects the increased dischargepressure and sends a signal, which in turn closes

solenoid valves A and B.

4. Sketch and describe a central priming system.


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This system is often used when more than four pumps requirepriming facilities.

Gives a large air exhausting reservoir as well as a capacitygreater than individual pumps

The air exhausting units can be of any type but are usually ofthe liquid ring type

Water ring exhausters maintain a vacuum condition betweenpre-set limits in the vacuum tank. Opening the priming cock,

or solenoid-driven non-return valve, for a pump causes

priming to take place To prevent water entering the vacuum tank after priming,

float-operated air release valves will automatically close

Two water ring type of exhausters mounted on top of a watersupply tank are shown, one would act as a stand by unit, but

both could operate together in the event of heavy demand

5. What are the materials used for the following:a. seawater pump

casing being gunmetal or cast and machined bronze impeller aluminium bronze shaft material either stainless steel (EN57) for soft packed

stuffing boxes

Sleeves and wear rings are of bronze or nickel copper alloys,depending on the severity of service conditions.

b. freshwater pump


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cast iron is sometimes used for casings, but bronze is the mostcommon casing material for condensate and other low-pressure

pumps.

Impellers for low-pressure services are of bronze or nickel-copperalloys

Sleeves and wearing rings are of bronze, nickel-copper alloys orstainless steel depending on the severity of the service

c. Boiler feed pumps.

cast steel casings (0.25% carbon steel) with stainless steel shaftsand impellers.

Highly rated turbo-driven pumps have 3% Ni-Cu-Mo forged alloysteel shafts.

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