2.4 CONSTRUCTION OF TI-fE COMPRESSOR
(see
fig.
2.3)
- The very ng,d compressor casing. made of tow poros1ty
case iron. cons,sts of a doJble walt stater (4) shut off on
either side by an Inlet and discharge housing ( 1 and 8) in
wh1ch the rotor shafts run in sleeve bearings. and an out
tet housing (10) on drrving eno The staio.- as a whnle 1s
formed by a gas tight outer shell encompass ng a double
cylindrical inner housing (6) in which the rotors operate
wllh a very sllghl clearance The annuIar space {5) be·
tween outer shell and inner t1ous1ng ts connected wnh the
suctlon chamber (2) and serves
as
by-pass for
111e
return
gas when the compressor opera:es under part-foad.
- The dynarrncally balanced male and female romr (7 ano
19), including their 1ntegral shaft ends. are made of a spe
cial hot rolled malleabte S1eel and supponed in flange
mounied steel backed babb11 sleeve beanngs (3), w,1ch
take up the radial load. The axial load on bath rotors Is
largely compensated by one oil oressunzed balance pis
ton (15). rotating wlth the male
rotor
sh.ift and s1wa1ed on
suct1on
s1de 1n
line w1th th1s shaft.
The
remammg
ax,al
torce Is taken up by IWO angular cont.ict ball bear1ngs (9)
mounted on each of the rotor shatts on d1scharge sicle
These hall beanngs atso serve for accurate ax
1
a
,
pos 1100•
Ing of the rotors inside the1r double cyl,ndrrcal hous1ng
The journals and the seal urea of the rotor shafts are
chromeplated for longer life
- The rotor shaft passage to the outs1de ,s prov1ded w1th an
oll tlooded, carbon face rotary shatt seal (36) Refer al�o
to paragraph 2.5.
• A sl,de vatve capacIty control system provides �fficienl.
surge-fr
e
e, infinitely variable modulation from 100% down
to
10%. The system uses a mecharueally posi1ioneo pilot
valve (23) to control 011 flow to and fror11 the hydrauhc cy
Under (26) whtch moves the sl1de valve {28). Aefer also to
paragraph 2.6.
The suctIon connect,on (33) ,s locateo on top of the st.J•
tor. The d1scharge c0Mect1on (20) ls prov1ded In the front
of the outlel housing (
1
0) on the
driving
end ol the com
pressor
casing.
- Except in the rotor grooves at the end of compress1on and
In
the
discharge chamber (21) communrcating
w1th
the
oullet port in the inner hous1ng and 1he <:11schargf: connec
t1on, suct1on pressure prevails in the enlire compressor
cas1ng.
- All compressor !ypes, m stancacd verSton. a,e equ1pped
w1th lwo so-called ·economizer" connecllons. One of
them. the main connectîon (3'1), is located near the top on
the discharge housing (8}. The cthe• ado1tional oonnec•
t,on (35) 1s situated on the other s1<1e ot tne same hous1ng
on rotor
shaft
level.
For
NHs only lhe
main connection
1s
used;
tor
R22 both connec11ons are used simultaneously
and in p;:i.r,iilpl
When no economizer systerrt 1s applted. both connect,ons
are plugged off.
2,5 ROTARY SHAFT SEAL
(see figure
2.4)
GRBSSi:ï
IICUt lrilfte��.,.,_.,...,. .......Uffl.l,HC,
�U.�"141Q\.a,,n�
To pass lhe male rotor shaft gashght to ltie outs1de. the
compressor is provIóeo with a conventlonal type oi rotary
shaft s
eal
,
the design
of which, however, has been adapted
to the special cond111ons of high speed and high pressure
drfference The oar'.s 01 tll1s seal are retained in a shalt seal
housing (5) mounted inside the outlet housing (6).
The sealing between rotatmg and stationary parts is ef
tecied on
the
slice face between a carbon shp ring ( 1 0} rt>·
taling w1th tne rotor shalt and a stat1onary counter-shp
surface. be1ng an 1n1egral parl of the shaft seal cover (9)
and made of a spec•aJ iron alloy. The sliding surfaces ol
both shp rng and seal cover are pohshed to extreme ltnisn
and
lapped.
The shp rt'lg can slice axially over the rotor shaft and 1s
presseo on10 me coun1er•sl1p surface by means of coli
$Ormgs (15). [, Is camed by a spring helder as a part of the
shaft seal cage (4), wh1cn ,tself 1s secured on a drive disc
(
•
6)
by
a
onve
pu, (2).
The whole assembly rota1es together
w1th the rotor shafl due to a securing pin {17) that connects
the drive disc and the thrust ball bear1ng loek nut {1 ). To en
sure the
seall<lg
between slip ring and rotor shaft a second•
ary seal (12) Is prov.dod
The shart seal hous1ng
(5)
1s secured against ro1at1on
by
e
loek pin (13) f
t
tted 111to a reoess of the shaft seal cover
To
re"l'lov@
the
fricuonal
heat developed by the slip faces,
the entIre shaft sent Is mcorporated in the lubnca11ng 011 cir
cuit via the 011 supply port (7) and tha 011 overtlow hole
(3).
2,6 CAPACITV CONTROL SYSTEM
-
The
capacity
con trol
of
the
Grassoscrew
GSL.
1.e.
reduc-
1,on of lM suct,on volume at constant speed, ,s ach1eved
by causmg the 009,nning of compression to tal<e place
later As shown schematJcally in figure 2.5 th1s is reahseo
oy allow1ng each rotor groove pair, after 1t h3lio been
sealed off trom the lnlet port. to remain în communicalion
with the suction chamber ( 16) for some length of time via
a return Por1 (8) 1n the lower cyhndncaJ part of the rotor
housing. Consequently. the suction gas trapped in the
rotor grooves Is partially bypassed to the suctIon cham
oer. The
return port. of whIcn the sIze Is înf1rntely vanable
between zero ano a maximum value (correspond1ng to full
load operahon and mînimum capacity respect1vely) ,s cre
ated by a
s
oe
oa
ll
y shaped shde valve (17}, wh1ch forms
an mtegraJ part of the bottom of the rotor nousing and can
be moved in either direct,on parallel to the ax1s of the
ro
tors by mear>s of a tod (5) In thts way almost loss-free
anc s1eoless capac,ty comrol Is obtatned, havmg a practi
cal rango oi from approx. , O to 100
%.
The sllde 11a1Ve rad (5) 1s connected to a single actmg pls
to'l
(d,
1n a cyhnder
(6)
wh1cn uses hycJraJ.Jlic force
(011
pressure) to unload the compressor Because of the gas
pressure difference across the shde valve (suc11on press
ure on one side and d1scharge pressure on the other)
tnere
Is a large ,orce to 1he left tending to close the shde
valve or to load the compressor. By admltllng high press
ure 011 1nto the nuthoard chamber (2) behtnd the piston, or
92.01
Compressor Package GSLP
Page 2.3
