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Патент USA US2403818

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My 9, 1946'
Filed Aug‘. 26,. 1943
'2 Sheets-Sheet 1
Patentecl July 9, 1946
William L. McGrath, Syracuse, N. Y., assignor to
Minneapolis-Honeywell Regulator Company,.
Minneapolis, Minn., a ‘corporation ofDelaware
Application August 26, 1943, Serial No. 500,043
(C1. 6233)
The present invention relatesin generalitocon
trol means for a refrigeration system.
of ?the refrigerant 2passed through said thermo
static expansion valve,
The old by-pass system of control, as applied
.-A vconventional refrigeration vsystem may
achieve a measure of control by operating or
stopping a compressor in response ‘to a condition
of the medium being :cooled .and by using a
to a refrigeration system, Jfrequently results in
overéheatedgases being supplied the compressor,
blltihis ldili?élility is ObViatGd inilthe presentin- '
stance by passing the Icy-passed refrigerant
thermostatic expansion valve to controllthei?ow
of refrigerant to the'ev'aporator. Limit devices
comprising :a cut-out opened by'exce'ssive ‘head
through the evaporator where said gases are
cooled by ‘the-"expanding liquid refrigerant. asso
pressures and a cut-out opened by abnormallylow 10 ciated therewith. It is, therefore, "an ‘object of
this. invention to providea system of vby-passicon
suction pressures are sometimes connected ‘in
trol‘for a refrigeration system inwhich'thegases
series with the compressor'control means to pre
in "the suction means are maintained at a safe
vent injury to .the mechanism. The control sys-"
tem thus outlined is sui?cient for some installa
tions, but is not'adequate for ‘other applications, 15 'I't'is a Tfur'ttherdbje'ct of the present invention
to supplement ' the :control of .a ‘thermostatic ‘ex
especially under conditions of ‘light load, With
pansion valve‘ bypassing both ‘liquid and gaseous
refrigerantthroug‘ha ?xed ori?ce preceding" said
expansion valve. Other objects of this invention
will become apparent from the following descrip
tion and from the appended claims.
light .‘loads and a throttled flow of refrigerant,
the evaporator isipumped down quite‘r'apidly and
“short cycling” takes place, ' Attempts have been
made to ‘prevent “short. cycling”'byfthrottling' the
suction, but fthi's'may cause abnormallylow suc
tion pressure at the compressor and result ‘in
For a full'disclosure of myinvention, reference
is ‘made to the following speci?cation and accom
mechanical dif?culties.
panying drawings, in which:
Other attempts-ateontrol h‘av'eiincluded the use
o‘i'a by-pass:from the hot gas line to the suction r25 Figure l'illustrates diagrammatically a multiple
?xture ‘refrigeration system embodying the pres
line, but this has resulted ingases of excessively
ent control system;
high-temperature damaging the compressor. The
‘Figure 2 ‘shows a modi?ed system similar to
present system supplements the control exercised
thatof Figure l,‘but using onlyiasingle evapora
by ‘a thermostatic expansion valve over an evapo
rator by by-passing hot gaseous refrigerant 30 tor "an'd’a differently located 'by-pass; and
{Figure ‘3-sh'ows asystem somewhat similar to '
around the condenser and ‘through said-evapora
that 'of Figure ‘2 in ‘which the by-pass incorpo
rates a constant ‘pressure reducing valve.
It is, therefore, an object of the present inven
tion to improve the control of a refrigeration‘sys
Referring‘to ‘Figure LcOmpressor ‘Ill, driven’by
tem by by-passing gaseous refrigerant-around the 135 motor‘! l,'di'scharges’through pipe 12 to condenser
'l3‘and toby-p‘ass ‘branch M. A liquid line 15
condenser and passing same through ‘the evapo
conveys liqui?ed refrigerant from condenser 13
to conduits l9, '2?,~and 2| which-connect liquid
line l5 to evaporators l6, I1, and I8, respectively.
It is a further object to control the conditions
under which cooling .may‘take place by prevent~
ing the evaporator pressure and’ temperature
from dropping below a predetermined point-said
pressure being maintained by 'by-passed gaseous
Each evaporator is controlled by a thermostatic
_ expansion‘valve-iandlan associated ‘by-p‘assevap
The by-pass system of control as "previously
known is not :well adapted to multiple ?xture
operation, for the building up of suction pres
sureby any one of a plurality of by-passes'a'?ects'
the suction pressure of each ‘of theevaporators.
It is thus .a further object of this invention toip'ro
vide .a system of control utilizing by-p‘assed re to
frigerant .whichmay be used with multiplei?xture
It is aifurther object of ‘this invention ‘to-sup
plement the control of 1a thermostatic ‘expansion
valve over an evaporator lby ‘varyingiithequality i5
orator it being provided witha thermostatic ex
pansion valve 722 *andiby-ipass ~23 ; evaporator 13-‘! is
provided with expansion valve 24 and by-pass
while evaporator 17% is equipped with'expan
siOn valve 126 and fa 3by-pass 21. Evaporators i6,
11, and 1:8 arec'onnected to main suction mean-s
2783163’ suction ~‘means '29, 30, and ‘GI, ‘respectively,
vMain-'si'ietion means 128 may be provided with,
‘if desired, ‘a throttling'valve 732 controlled ‘by
pressure ‘controller 33. ~Compre'ssor motor vH
‘may be controlled by means "including ‘switch
means‘ 34v connected lt'orsuction means "28 -by ‘tube
35. switch-means 34'is~als01connected to the
high‘pressure refrigerant line I2 by tube“. De
vice 54 may comprise a conventional low suction
pressure cut-out and a high head pressure cut
suction means 29 to main suction means 28. Bel~
lows 45, as shown, is in a fully retracted position
due to the satis?ed condition of the medium
out in series therewith to prevent operation of
compressor motor II in the event of an excessive
cooled by evaporator l6; bulb 44, connected to
head pressure or extremely low suction pressure. CH bellows 45, being responsive to the temperature
Further, said device 34 may comprise a device
such as described in the patent application of Carl
of said medium. Arm 46 is therefore at the ex
treme left of potentiometer coil 41 and has driven
G. Kronmiller, Serial No. 371,001, ?led Decem
ber 20, 1940, now Patent No. 2,377,503, issued
position. With valve 43 open, a ?ow of gaseous
June 5, 1945.
Hot gas by-pass means 23, 25, and 21 are ?tted
with modulating valve means 40, 4| and 42, re
spectively. Valve means 40 is controlled by ther
mostatic means 43. Thermostatic means 43 com
prises a volatile ?uid ?lled bulb 44 and a con
nected bellows means 45, said bellows operating
an arm 45 over potentiometer coil 41.
Valve 4|
is controlled by thermostatic device 48, similar to
43; and valve 42 is controlled by thermostatic de
vice 49, also similar to 43. The valve means 48,
4| and 42 are each powered by a modulating mo
tor of the sort described in the patent of D. G.
Taylor, No. 2,028,110.
If desired, conduits I9, 20, and 2| may be
?tted with check valves 50, 5| and 52, respec
tively, said check valves being located up stream
in said conduits above the con?uence of the by
motor valve 45, normally closed, to a Wide open
10 refrigerant enters conduit I9, mixes with. liquid
refrigerant from branch l5; and the mixture
passes on to feed expansion valve 22, evapora
tor i5, pipe 29 and main suction means 28. With
small flows of hot gas and with sub-cooled liquid
refrigerant, the gas will tend to liquify and the
amount of sub-cooling will be lessened. At large
flows of gaseous refrigerant, where the amount
of sub-cooling is insu?icient to liquify said gas,
a mixture of gaseous and liquid refrigerant re
Under some conditions, the by-passed
gaseous refrigerant may enter conduit | 9 at a
pressure exceeding that of the refrigerant in
pipe I5, thus preventing flow from | 5 into l9.
However, check valve 5|! prevents the by-pass
gases from ?owing into l5, thus preventing said
by-pass from interfering with the control of
other evaporators. The ?ow of gaseous refrig
erant through evaporator l6 prevents that evap
check valves permitting flow only toward their re
orator from being pumped down to a low pressure
spective evaporators.
30 and temperature. Expansion valve 22 tends to
Downstream of the con?uence of the by-pass
maintain an open position as the by-pass gases
25 and liquid line 20, a ?xed ori?ce 54 may be
are added to the liquid refrigerant, for the high
provided ahead of expansion valve 24. The ?xed
er the percentage of gas entering the evaporator,
ori?ce is proportioned to permit only su?icient
the less the heat needed to give the required num
liquid refrigerant to pass therethrough to operate
ber of degrees of superheat to open said expan
the associated evaporator at full capacity. This
slon valve. Under extreme conditions in which
ori?ce supplements the control, in association
hot, gaseous refrigerant only is flowing through
with a by-pass, of thermostatic expansion valve
the expansionvalve, the valve may remain wide
24. The introduction of by-passed gaseous re
open, the rate of ?ow being limited by friction
frigerant into the liquid line ahead of said ori 40 and by the restrictions offered by valve 22 and
?ce, tends to decrease the density of the refrig
other means. By raising the temperature of the
erant passing through said ori?ce and the ex
evaporator its cooling effect is lessened, thereby
pansion valve, and thereby results in a lesser flow,
providing temperature control of the medium be
by weight, of refrigerant to the associated evap
ing cooled. The capacity of each hot gas by-pass
orator, thereby resulting in less refrigeration be
may be limited in such manner that the maxi
ing possible at said evaporator. Further, the
mum amount of gas passing through same Will be
heat of the refrigerant is increased by the ad
only that necessary to control the associated evap
mixed hot gases, hence less heat must be added
orator. Such limiting means may comprise an
to same to give a predetermined number of de
ori?ce or other such restriction in the'gas line
grees of superheat. The ori?ce also helps to 50 or may comprise an adjustment of the electrical
uniformly mix the gaseous and liquid refrigerant.
means controlling the modulating valve in such
As the thermostatic expansion valve also forms,
manner that the valve can only be opened a de
in effect, an ori?ce, supplementary ori?ce means
sired amount.
may be used or not as a matter of choice.
Thermostatic bulb ‘H and its associated bellows
The relation and action of the various parts 55 72, responsive to the conditions of the medium
will be further illustrated in the following opera
cooled by evaporator [1, have driven arm 73 to
tion schedule.
about the mid point of coil 14, thereby driving
Operation of Figure 1
valve 4| partiallylopen. With valve 4| partially
passed refrigerant and the liquid refrigerant, said
open, hot gas flows through pipe |4,.by-pass line
With the switches in device 34 in closed posi 60 25 and into conduit 25 where it mixes with liquid
tion, motor || may be started in any convenient
refrigerant ?owing from branch |5 into ‘said con
manner such‘ as by closing switch 60, the circuit
duit 26. The mixture of gas and liquid refriger
being: line 6i, wire 62, switch 60, wire 63, switch
ant ?ows through ori?ce 54 where it is further
device 34, wire 64, motor H, wire 65, and line 66.
mixed, and then through expansion valve 24,
With motor II and compressor l0 operating, 65 evaporator I‘! and pipe 30 into main suction
gaseous refrigerant is discharged through pipe
means 28'. Because the density of the refriger
l2 into condenser I3 and to by-pass line I4.
ant passing through ori?ce 54 has been lowered
Heat is extracted from the refrigerant in con
by the introduction of gaseous refrigerant the
denser l3 in any convenient manner and the
total quantity of refrigerant ?owing through ex
refrigerant is thereby liqui?ed. Liquid refrig
70 pansion valve 24 and evaporator IT, is reduced
erant from condenser I3 is led to the evaporators
and the'heat of same is increased, hence com
by branch |5, evaporator l6 obtaining its refrig
paratively little heat is required to be added
erant from branch I 5 through conduit [9, includ
through the evaporator to give sufficient super
ing check valve 50 and thermostatic expansion
heat to open the expansion valve 24 and raise
valve 22, said refrigerant being exhausted through 75 the pressure and ‘temperature‘within the evapo
place;v thesystem‘ is» operating atlf-ulr capacity-.
rator; The?capacity of! evaporator: is is thereby;
controllably reducedi~
With light load and normal control this; would
result in frequent stopping’: andstarting of the
Bulb "I ?andbellows ‘I1 lof- the thermostatic ‘de
compressing equipment due to the suction switch
vice tit-indicate a condition offmaximum demand.
and arm 7831s latvthe: extreme right- of' coil ‘I19,
. means'ofs'devicev III], and thus-'cause-‘un'due‘wear.
andi'tear on mechanism. In-the present'example"
as‘ the1 demand becomes partially satis?ed; arm
I‘I8 is:drawn-acrosswcoili I I9 and operates valve‘
whereby valve 42 remains in closedv positi‘onland
no; gas" is by-passed;
Refrigerant, therefore‘,
passes‘ through pipe I5, conduit 21I, thermostatic‘
expan'siongvalve 2t, evaporator I13! and pipe'3-i4
to imainisuction means-2'3‘ in v a» conventional man
I~'I~3*'from' closed- to open'position‘thereby permits
ting by-passing-of refrigerant through pipe‘ I05
to evaporator I08. In the position shown; arm"
I‘I8i is’ about halfway‘ across coil H3, hence,
valve" I I3~is partially'open; hot gas‘ is’ being‘ by.
pass‘edtintov evaporator I68" whererit adds heat
ner and evaporator I8; operates at full capacity.
If used, the throttling valve ill-introduced in
mainisuction. means» I 28% is~control1ed by pressure»
controller‘ 33! in- such manner that the suction
pressure imposed on'compressor Iii may bellm 15 and" raises thepressuretherein. As'the pressure
within the evaporator is increased, its temper
itedi to a. predetermined>high=limit, thereby pro
ature is likewiseincreased and its cooling effect
tecting“ said (compressor- against unduly, ‘ high-suc
of; gaseous. refrigerant. ' Under someconditions,
is "lessened, thereby‘making"possible the balanc
ing of the‘refrigeration‘supplied’and 13116102111416;
demand of a compressor rises- with increased _'
mechanism‘. When the demand ‘for, refrigeration,
however, this control is- not‘ needed for the'power 20 mand" and permitting continuous running of the
suction-pressure only-to apredetermined amount
as determined by thermostatic device I'M, be
and with further rise in suction pressure, power
comes satis?ed, arm-"- II 8" is- advanced ‘ across coil
consumption falls off;
“9 and" moves~va1ve~ H3 toward open position
~ thereby‘byepassing’more gas to said-evaporator.
Figure 2
An‘increasein demand causes an, expansion of
Inv Figure 2;.compressor IDI, driven by motor
I62; discharges through pipe I53 to condenser
thereby driving valve II 3 toward closed » position
bellows-1H6 and drives;I*I8 towardthe left of* I It‘
and-permitting’full ‘capacity-ofthe system as pre
IM'and'by-pass line H35‘. Condenser I04‘ sup
7 pliesliquidrefrigerant through pipe I05‘ tolther
viously described;
mostatic expansion valve I01 and evaporator Hill,
said evaporator being connected‘ by main suc
tion'means' I59 to compressor I'Il’I’. Compressor
IGI= is'protected‘by. a‘ devicetlw'similar to 34 in
the.‘ above example, said‘. device IIB being con
nected to‘ suction means IBB'b'y tube II I,‘ and to
high'pressure pipe I03 by tube H2. By-pa-ss W5
is ?tted'with a normally closed'modul'ating valve
II3 under. the control of thermostatic device H4, 40
said'by-pass I95 being, connected'to evaporator
lil?immediately‘down stream of expansion valve
I01. Thermostatic expansion valve Ill'i‘may be
of the conventional sort, but preferably has its
pressure chamber connected I_ to suction means
In summary,‘ afc'onventional system, as shown
in- Figure 21,‘ may be controlled by varying the
pressure)" Within-7 the evaporator by lay-passing
gaseous refrigerant thereinto; By increasing the
pressure within‘ an" evaporator, the temperature
of" same-will? automatically be raised, thereby
lessening its cooling effects. Further, by action
of‘v the thermostatic expansion valve means~,the
gas; passing from the evaporator has av tempera
ture-* only a ‘predetermined; number of degrees
above; that‘ corresponding to the pressure of the
refrigerant within the’ evaporator and therefore
within a safe'limit ‘for induction‘into-compres
Figure 3
I09 by equalizer line I15, there being less pres
sure ?uctuation at the exhaust end‘of evaporator
I68 than at the head‘end‘when the by-passmeans
are usedifor control.’
' Thermostatic device I14‘ comprises bellows H6’
Figure 3‘,i-a's noted, also shows by-pass- control
However, the system
shown-in thi‘s?gure may beused for plural evapo
of_-' a1 single evaporator.
‘rator ihs-ta'llatibns wherein the‘ lower limit of
and an associatedvolatile ?uid ?lled, bulb II'I;
temperaturedesired for each of the evaporators
said bellows .I I6' actuating an arm H8 and mov
isfthe same:
ingsa'me over potentiometer coi1‘I‘I9'.
Operation, 0 1 Figure 2 -
,. condenser I541'and‘byJ-pa'ss1pipe I552
AS in the previous example, compressor I?I
and its'motor I92 may be controlled in any. con
venient manner such as by manual switch‘ E29‘,
the circuit controlling motor I021 being: current
supplyiwire I2'I, wire I22, switch.l20,.wire. I23,
switch device : Isl 0, wire. I 24; . motor:
v ‘
In: this ?gure;v compressor I5! is- driven by
motor- I5'2and' discharges through pipe: I531to‘
II'IZ, wire. I25,
andv current supply :wire. I 26.
With the switches of-"device IIO‘in closed -po-'
sition andv manual. switch. l2il- closed, motor.v I92
I5'41- supplies'l‘iquid refrigerant through pipe I56
to thermostatic expansion valve I51 and its asso
'ciatedievaporator I58; saidievaporator I58being
connected?- by suction means I59 to compressor
I5II .' Hotf-gasjby-pass I55 includes a pressure re-~
ducingl valve-of'the constantpressure type, I66;
saidi by-pass=connecting to evaporator‘ I53>just
down-‘stream of expansion valve I51. Motor I52
isprotected‘ against overload" by high pressure
andi compressor IOI are in operation, said‘ com
cut-out I6I. connected to. line I53’ by, tube I62.
pressor IOI ‘discharging through pipe I03 into
condenser I04 and by-pass line I05.‘ With valve
The operation of.’ the. motorv is, controlled‘ by‘
' thermostatic. device I65 operating in series with
I13 closed,refrigerant:fromcondenser I04 passes
through“ line I06, expansion. valve: I01, evaporator
device I619. Thermostatic device IE3 comprises
bellows’ I64, and an associated bulb I65, said bel-.
I08; suction means I09 and into'compressor. Isl
in a conventional manner.. Expansionlvalve' IBTI
is'wco‘nstructed to maintain 1a; predetermined num
ber; of degreesof superheat atT-the exit of‘7 evap
lows ractuating mercury switch means. I68 in such
manner‘ that‘ when" a_ refrigeration demand is
satis?ed; contact is broken in said switch". When
there is: an demand: for refrigeration‘,‘ contact- is:
orator I58; Asbeforelindicated} with,va1ve.-I.I3@ '75 made;.by;said; switch: The;operatiomofthasysa
closed and nol:by-passin'g :oiirefrigerant taking;
tem thus outlined will be brought out in the fol
lowing schedule.
Operation of Figure 3‘
The system of Figure 3, as above outlined, has
if each, of the evaporators has the same lower
limit of pressure and temperature.
In the examples of the invention above de
scribed, the systems have been controlled by
means, responsive to temperature, but this is to
less flexibility of control than does the previous
be considered as illustrative only and not lim
example. However, under some conditions, ?exi
iting the scope of the invention.
bility of control may be properly sacri?ced by
the protection characteristics inherent with the
system of this ?gure in a manner that will be
come apparent.
midity sensitive devices may be used instead of
10 the thermostats shown and the present systems
, ‘
Upon a demand for refrigeration, as deter
mined by thermostatic device I63, mercury switch
I63 closes a circuit and the compressor is started '
as follows: current supply wire I10, wire I‘II,
mercury switch I66, Wire I12, high pressure cut
out IBI, wire Il3, motor I52, wire I14, and cur
rent supply wire I15. Assuming that valve ISO
in by-pass I55 is closed, refrigeration takes place
in a conventional manner.
other condition responsive means such as hu
may be regulated to govern humidity rather than
temperature. In the, present case, psychrometric
is considered descriptive of both temperature and
humidity conditions. The protection means il
lustrated for the compressor motors is to be
considered as illustrative only as these controls
may be dispensed with, or any other conventional
controls may be substituted therefor.
Many other modifications and adaptations of
Gaseous refrigerant 20 the present invention are readily apparent to
is compressed in compressor I5I, discharged
one skilled in the art, hence the scope of the
through pipe I53 into condenser I54, and heat is
invention is to be determined by the following
removed from said refrigerant in said condenser
in the usual manner, thus liquifying said re
I claim as my invention:
frigerant. Liquid refrigerant from condenser I54 25
1. In a refrigeration system, means controlling
goes through pipe I56 to thermostatic expansion
valve I5‘! which feeds refrigerant into evaporator
I58 wherein it is evaporated by heat extracted
from the medium being cooled, and the resulting
gaseous refrigerant goes through pipe I59 back
to compressor I5! to be further compressed and
to complete the cycle. Thermostatic expansion
valve I5’! adjusts the flow of refrigerant to evapo
rator I58 in such manner that the refrigerant
?owing out of evaporator I58 will have a pre
determined number of degrees of superheat.
Under light loads, with a system functioning in
a conventional manner as above outlined, com
pressor I 5i will be frequently stopped and started
in response to thermostatic device I63. Further,
with light loads, the flow of refrigerant through
thermostatic expansion valve I51 is considerably
reduced and compressor
I5I tends to pump
the capacity of an evaporator comprising a ther
mostatic expansion valve for controlling the flow
of fluid to said evaporator, means for varying the
density of refrigerant supplied to said‘ thermo
static expansion valve means, and ori?ce means
limiting the volume of said variable density re
frigerant supplied to said expansion valve.
2. In a refrigerating system, in combination, a
source of gaseous refrigerant underpressure, a
supply of liquid refrigerant under. less pressure,
an expansion valve of the superheat responsive
type, an evaporator, conduit means connecting
said supply of liquid refrigerant to said expansion
valve and evaporator, b-y-pass means compris
ing a valve connecting said source of ‘gaseous
refrigerant to said conduit at a point up-stream
of the expansion valve, and means responsive to
a psychrometric condition in control of said by
evaporator I58 down to very low pressures. Under
pass valve.
some conditions of cooling, this is not objection 45
3. In a refrigerating system, a source of gase
able; but in other cases the very low suction
ous refrigerant under pressure, a supply of liquid
pressures obtained result in bad running of the
refrigerant under less pressure, a thermostatic
compressor and also result in excessive dehumidi
expansion valve, an evaporator, conduit means
?cation of ' the medium being treated by said
connecting said supply of liquid refrigerant to
evaporator. It is the function of by-pass I55 and 50 said expansion valve and evaporator, by-pass
its associated valve I68 to provide a lower limit
means comprising a valve connecting said source
of pressure and temperature for said evaporator
of gaseous refrigerant to said conduit at a point
I58 to thereby limit the dehumidifying effect of
up-stream of said expansion valve, means re
said evaporator and to protect said compressor
sponsive to a psychrometric condition in control
from unduly low operating pressure.
of said by-pass valve, and ?xed ori?ce means in
In practice, the lowest pressure and tempera
said conduit between the junction of said by
ture desired at said evaporator I58 is determined,
pass means and conduit means and said expan
both from the standpoint of dehumidi?cation
sion valve.
and from the effect on the compressing equip
4. In a refrigerating system, a source of gaseous
ment. With a pressure for I58 determined, valve 60 refrigerant under pressure, a supply of liquid re
IE8 is set to open at that pressure. In operation,
frigerant under less pressure, a plurality of evap
the- system as thus outlined will operate in a
orators, expansion valve means for each of said
strictly conventional manner until the evaporator
evaporators for controlling refrigerant ?ow there
pressure reaches the predetermined low limit, at
to, conduit means connecting said supply of liquid
which point valve It!) opens and permits hot 65 refrigerant to said expansion valve means and
gaseous refrigerant to ?ow through by-pass I55
said evaporators; and ori?ce means proportioned
into said evaporator in sufficient quantities to
to pass su?icient liquid refrigerant to give the
maintain said predetermined pressure.
desired maximum refrigerating capacity to an
minimum pressure of the evaporator being
associated evaporator, said ori?ce means being
limited, the minimum temperature is also limited 70 located up-stream from the expansion valve as
and its ability to dehumidify air being treated,
sociated with said evaporator.
or product being cooled, is limited. Obviously,
5. In a refrigerating system, a source of gaseous
valve I Bil may be set to open at any desired pres
refrigerant under pressure, a supply of liquid re
sure. As before stated, a system of this sort may
frigerant under less pressure, a plurality of evap
be used with a multiple evaporator installation 75 orator means, conduitmeans including a Dlll~
9/ v
rality of expansion valve means connecting said
supply of liquid refrigerant to said plurality of
evaporator means, ?ow limiting restriction means
tors, conduit means connecting said liquid re
' fri-gerant supply means to said expansion valve
in said conduit means up-stream of at least one
of said expansion valve means, and lay-pass
means including valve means connecting said
means and said evaporators, a plurality of by
lpass means for mixing said gaseous refrigerant
with said liquid refrigerant upstream of said ex
pansion valve means to vary the density of the re
source of gaseous refrigerant to said conduit
frigerant passed through the same, and means
plying liquid refrigerant under less pressure, a
supply‘of liquid refrigerant under less pressure,
plurality of evaporators, thermostatic expansion
evaporator means, an expansion valve means for
valve means for controlling each of said evapo
rators, conduit means connecting said liquid re
frigerant supply means to said expansion valve
means and said evaporators, and means mixing
controlling refrigerant ?ow through said evapora
supplying liquid refrigerant to said expansion
including condition responsive means for control
means up-stream of said expansion valve means
ling each of said by-pass means.
and nip-stream of said restriction means.
8. In a, refrigerating system, in combination, a
6. In a refrigerating system, means supplying 10
source of gaseous refrigerant under pressure, a
gaseous refrigerant under pressure, means sup
said ‘compressed gaseous refrigerant with said
liquid refrigerant yup-stream of said expansion
valve means to vary the density of the refrigerant 20
passed through the same.
'7. In a refrigerating system, means supplying
gaseous refrigerant under pressure, means sup
plying liquid refrigerant under less pressure, a
tor means, conduit means connecting said means
valve means and said evaporator means, and by
pass means including valve means vfor mixing said
compressed gaseous refrigerant with said liquid
refrigerant nip-stream of said expansion valve
means for varying the density of the refrigerant
passed through said expansion valve means, said
by-epass valve means being of the two way sort
and controlling the ?ow of the gaseous refriger
plurality of evaporators, thermostatic expansion 26 ant.
valve means for controlling each of said evapora
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