3. kompr torakkkkkkkkkkkkkkkkk
TRANSCRIPT
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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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