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Kompresor Torak


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A wide variety of compressor designs can be used on the separable

unit including horizontal, vertical, semi-radial and V-type. However, the most common design is the horizontal, balanced-

opposed compressor because of its stability and reduced vibration. The piston is driven by a crank shaft via a connecting rod. At the top of the cylinder are a suction valve and a discharge valve. A reciprocating compressor usually has two, three, four, or si

cylinders in it.

Reciprocating Compressors


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Single-Stage Double Acting


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2

4

3

Clearance

Discharge volume

Suction intake volume

Total cylinder volume

Piston displacement

volume

pressure

1

P-V Diagram


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In order to prevent the piston rom striking thevalve plate! a clearance volume must be allo"edat the end o the piston compression stroke#

$anuacturing design tolerances re%uire this toallo" or reasonable bearing "ear! "hich "ould

e&ectivel' lengthen the stroke# The space bet"een the bottom and top o the

valve assembl' adds e(tra to the clearancevolume#

The clearance volume "ill cause the gas notbeing completel' discharged ater compression#

The remaining gas trapped in the clearancevolume "ill re-e(pend in the ne(t suction stroke#

Clearance Space and Clearance )raction *+,


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As a result! the volume o the gas sucked in b'

the compressor in each stroke is less than thevolume the piston s"ept through#

So the compressor volumetric displacementmust be greater than the volume o gas to bedra"n in#

ther actors that cause reduction to thecompressor capacit'are.

pressure drop through valves "hich reduces theamount o gas sucked or discharged/ gas leaks

around closed valves or bet"een the piston andc'linder/ gas evaporating out o oil in thec'linder space/ the gas heated b' the c'linder"alls! thus! increasing its speci0c volume#

Clearance Space and Clearance )raction *1,

t


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ressure se n ec procat ng ompressor(with valve losses)


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Volumetric 23cienc'

3

3

,

,va

volume flow rate entering compressor m s

displacement rate of compressor m s

=

The perormance o reciprocating compressors can bedescribed b' volumetric e3cienc' and the actualvolumetric e3cienc' is de0ned as


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4reat care should be taken to prevent e(cess

li%uid rerigerant rom entering reciprocatingcompressors#

5hen large %uantities o li%uid suddenl' enterthe compressor or a short period o time it is

called slugging# The orce at the end o the discharge stroke

could easil' break valves and even connectingrods i there is li%uid slugging in the c'linder#

A related problem caused b' slugging is e(cessdilution o the lubricating oil b' the rerigerant#

This ma' result in ine&ective lubrication andrapid "ear o bearing or the piston andc'linder#

)or Rerigerant CompressorSlugging o6i%uid *+,


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5hen a compressor is not operating! thepressure in the crankcase is relativel' highand the oil is cold#

Some kinds o rerigerants vapor readil'dissolves in the oil! this reduces thecrankcase vapor pressure and cause aurther pressure di&erence that enhancesthe migration o rerigerant vapor#

5hen the compressor starts! the pressure in

the crankcase suddenl' drops and thererigerant boils rapidl' out o the oil#

The vapor bubbles ormed cause a oamingor surge o oil and li%uid rerigerant out o

the crankcase#

)or Rerigerant Compressor Slugging o6i%uid *1,


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A compressor "hose crankshat e(tendsthrough the compressor housing so that amotor can be e(ternall' coupled to the shatis called an open-t'pe compressor#

A seal must be used "here the shat comesthrough the compressor housing to prevent

rerigerant vapor rom leaking out or airrom leaking in i the crankcase pressure islo"er than atmospheric#

The disadvantage o the hermetic

compressors is that it is not serviceable"ithout cutting open the shell#

)or some hermetic compressors! thec'linder heads are usuall' removable so that

the valves and pistons can be serviced

semi-hermetic com ressor #

pen! Semi-hermetic and 7ermetic ReciprocatingCompressors


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7ermetic Compressor

The motor stator is either pressed or bolted to thecompressor bod' and the rotor is mounted directl' onthe compressor crankshat#

The semi-hermetic compressor is made in larger si8esthan the hermetic ones#


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small two-cylinder reciprocating compressor

Reciprocating

compressor

compresses the gas y

moving piston in

cylinder to change the

volume o! the

compression chamer"

The main elements #

$ piston,

$ cylinder,

$ valves,

$ connecting rod,

$ cranksha!t,

$ casing"

T"o C'linder ReciprocatingCompressors


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Kompresi 9ertingkat *+,


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Kompresi 9ertingkat*1,


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+1:;+ kompresi + tingkat

+


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