Refrigeration system

Claim 2

A multistage refrigeration system for product-display cases, comprising: (a) a housing defining a temperature controlled refrigerating zone; (b) expansion and evaporating means disposed in said housing for utilizing pressurized liquid refrigerant to refrigerate said refrigerating zone; (c) high-stage compressor means and condenser means connected in series and disposed in an equipment location remote from said housing for supplying pressurized liquid refrigerant; (d) first conduit means for communicating pressurized liquid refrigerant from said condenser means to said expansion and evaporating means; (e) a low-stage refrigeration compressor disposed in said housing for compressing gaseous refrigerant received from said evaporating means, said low-stage compressor operating in response to the cooling load in said refrigerating zone to maintain the desired temperature in said refrigerating zone; (f) second conduit means for communicating compressed refrigerant from said low-stage compressor to said high-stage compressor means in said equipment location; and (g) said low-stage compressor has a lubricant sump and oil control means for introducing exess lubricant in said low-stage compressor sump into said compressed refrigerant discharged from said low-stage compressor.

Claim 3

A multistage refrigeration system as claimed in claim 1, wherein said control means comprises a vent tube extending from a zone of minimum pressure in said low-stage compressor to a point slightly above the normal lubricant level in said low-stage compressor sump.

Claim 4

A multistage refrigeration system as claimed in claim 2, wherein said high-stage compressor means and said low-stage compressor are full hermetic compressors.

Claim 5

A multistage refrigeration system as claimed in claim 3, wherein said high-stage compressor means has the same lubricant control means as said low-stage compressor.

Claim 6

A multistage refrigeration system for product-display cases, comprising: (a) a housing defining a temperature controlled refrigerating zone; (b) expansion and evaporating means disposed in said housing for utilizing pressurized liquid refrigerant to refrigerate said refrigerating zone; (c) high-stage compressor means and condenser means connected in series and disposed in an equipment location remote from said housing for supplying pressurized liquid refrigerant; (d) first conduit means for communicating pressurized liquid refrigerant from said condenser means to said expansion and evaporating means; (e) a low-stage refrigeration compressor disposed in said housing for compressing gaseous refrigerant received from said evaporating means, said low-stage compressor operating in response to the cooling load in said refrigerating zone to maintain the desired temperature in said refrigerating zone; (f) second conduit means for communicating compressed refrigerant from said low-stage compressor to said high-stage compressor means in said equipment location; and (g) a liquid/suction heat exchanger disposed in said housing for utilizing cold refrigerant vapor for said evaporating means to cool liquid refrigerant supplied to said expansion and evaporating means.

Claim 7

A multistage refrigeration system for product-display cases, comprising: (a) a housing defining a temperature controlled refrigerating zone; (b) expansion and evaporating means disposed in said housing for utilizing pressurized liquid refrigerant to refrigerate said refrigerating zone; (c) high-stage compressor means and condenser means connected in series and disposed in an equipment location remote from said housing for supplying pressurized liquid refrigerant; (d) first conduit means for communicating pressurized liquid refrigerant from said condenser means to said expansion and evaporating means; (e) a low-stage refrigeration compressor disposed in said housing for compressing gaseous refrigerant received from said evaporating means, said low-stage compressor operating in response to the cooling load in said refrigerating zone to maintain the desired temperature in said refrigerating zone; (f) second conduit means for communicating compressed refrigerant from said low-stage compressor to said high-stage compressor means in said equipment location; and (g) a liquid/suction heat exchanger disposed in said housing for utilizing cold refrigerant vapor for said evaporating means to cool liquid refrigerant supplied to said expansion and evaporating means.

Claim 8

A multistage refrigeration system as claimed in claim 5, wherein said low-stage compressor cycles on and off in response to cooling demand.

Claim 9

A multistage refrigeration system as claimed in claim 5, wherein said low-stage compressor operates at different speeds in response to cooling demand.

Claim 10

A multistage refrigeration system as claimed in claim 5, wherein said low-stage compressor operates solely in response to the cooling load in said refrigerating zone.

Claim 11

A multistage refrigeration system as claimed in claim 8, wherein said low-stage compressor is controlled by a refrigerator-type thermostat disposed in said refrigerating zone.

Claim 12

A multistage refrigeration system as claimed in claim 5, further comprising a subcooler for subcooling refrigerant flowing from said condenser means to said expansion and evaporating means.

Claim 13

A multistage refrigeration system as claimed in claim 10, wherein said subcooler normally expands a portion of the condensed refrigerant downstream of said condenser means for subcooling refrigerant flowing to said expansion and evaporator means, and further comprising means for feeding said expanded portion of refrigerant to the inlet of said high-stage compressor means.

Claim 14

A multistage refrigeration system as claimed in claim 5, wherein said high-stage compressor means comprises a plurality of high-stage compressors connected in parallel.

Claim 15

A multistage refrigeration system as claimed in claim 12, wherein one of said high-stage compressors is a variable speed compressor.

Claim 16

A multistage refrigeration system as claimed in claim 12, further comprising a trimmer compressor connected in parallel with said plurality of high-stage compressors, said trimmer compressor being of smaller capacity than each of the other high-stage compressors.

Claim 17

A multistage refrigeration system as claimed in claim 14, wherein said trimmer compressor is a variable speed compressor.

Claim 18

A multistage refrigeration system as claimed in claim 5, further comprising a conduit bypassing said high-stage compressor means, and a check valve in said conduit to prevent reverse refrigerant flow in said system.

Claim 19

A multistage refrigeration system as claimed in claim 5, further comprising lubricant control means for controlling the distribution of lubricant between said high-stage compressor means and said low-stage compressor.

Claim 20

A multistage refrigeration system as claimed in claim 5, further comprising a second low-stage refrigerating compressor disposed in said housing and connected to parallel to said first-mentioned low-stage compressor.

Claim 21

A multistage refrigeration system as claimed in claim 18, wherein at least one of said low-stage compressors is a variable speed compressor.

Claim 22

A multistage refrigeration system as claimed in claim 18, wherein each of said low-stage compressors is a fixed speed compressor.

Claim 23

A multistage refrigeration system for product-display cases, comprising: (a) a housing defining a temperature controlled refrigerating zone; (b) expansion and evaporating means disposed in said housing for utilizing pressurized liquid refrigerant to refregierate said refrigerating zone; (c) high-stage compressor means and condenser means connected in series and disposed in an equipment location remote from said housing for supplying pressurized liquid refrigerant; (d) first conduit means for communicating pressurized liquid refrigerant from said condenser means to said expansion and evaporating means; (e) a low-stage refrigeration compressor disposed in said housing for compressing gaseous refrigerant received from said evaporating means, said low-stage compressor operating in response to the cooling load in said refrigerating zone to maintain the desired temperature in said refrigerating zone; (f) second conduit means for communicating compressed refrigerant from said low-stage compressor to said high-stage compressor means in said equipment location; and (g) a lubricant sump associated with said high-stage compressor means, and means for metering a small flow of lubricant from said sump to said pressurized liquid refrigerant supplied to said expansion and evaporating means.

Claim 24

A multistage refrigeration system for product-display cases, comprising: (a) a housing defining a temperature controlled refrigerating zone; (b) expansion and evaporating means disposed in said housing for utilizing pressurized liquid refrigerant to refregierate said refrigerating zone; (c) high-stage compressor means and condenser means connected in series and disposed in an equipment location remote from said housing for supplying pressurized liquid refrigerant; (d) first conduit means for communicating pressurized liquid refrigerant from said condenser means to said expansion and evaporating means; (e) a low-stage refrigeration compressor disposed in said housing for compressing gaseous refrigerant received from said evaporating means, said low-stage compressor operating in response to the cooling load in said refrigerating zone to maintain the desired temperature in said refrigerating zone; (f) second conduit means for communicating compressed refrigerant from said low-stage compressor to said high-stage compressor means in said equipment location; and (g) a lubricant sump associated with said high-stage compressor means, and means for metering a small flow of lubricant from said sump to said pressurized liquid refrigerant supplied to said expansion and evaporating means.

Claim 25

A multistage refrigeration system as claimed in claim 21, wherein said low-stage compressor has a lubricant sump and oil control means for introducing excess lubricant in said low-stage compressor sump into said compressed refrigerant discharged from said low-stage compressor.

Claim 26

A multistage refrigeration system as claimed in claim 22, wherein said control means comprises a vent tube extending from a zone of minimum pressure in said low-stage compressor to a point slightly above the normal lubricant level in said low-stage compressor sump.

Claim 27

A refrigeration system comprising: (a) a low-stage compressor for discharging compressed refrigerant into a high-stage suction line; (b) a high-stage discharge line; (c) first and second high-stage compressors connected in parallel between said suction and discharge lines; (d) a condenser and evaporating means connected in series between said discharge line and the inlet of said low-stage compressor; and (e) a subcooler for expanding a portion of the condensed refrigerant downstream of said condenser for subcooling refrigerant flowing to said evaporating means, and including conduit means for feeding said expanded portion of refrigerant to said suction line, (f) said second compressor being upstream of said first compressor with respect to the output of said subcooler; (g) said first compressor being upstream of said second compressor with respect to the output of said low-stage compressor, and (h) a check valve in said suction line between said first and second compressors so that said second compressor can maintain subcooling when said first compressor is not operating.

Claim 28

A refrigeration system comprising: (a) a low-stage compressor for discharging compressed refrigerant into a high-stage suction line; (b) a high-stage discharge line; (c) first and second high-stage compressors connected in parallel between said suction and discharge lines; (d) a condenser and evaporating means connected in series between said discharge line and the inlet of said low-stage compressor; and (e) a subcooler for expanding a portion of the condensed refrigerant downstream of said condenser for subcooling refrigerant flowing to said evaporating means, and including conduit means for feeding said expanded portion of refrigerant to said suction line, (f) said second compressor being upstream of said first compressor with respect to the output of said subcooler; (g) said first compressor being upstream of said second compressor with respect to the output of said low-stage compressor, and (h) a check valve in said suction line between said first and second compressors so that said second compressor can maintain subcooling when said first compressor is not operating.

Claim 29

A refirgeration system as claimed in claim 24, wherein said second compressor is of less capacity than said first compressor.

Claim 30

A refrigeration system as claimed in claimed 25, wherein said second compressor operates continuously to trim the output of said first compressor.

Claim 31

A refrigeration system as claimed in claim 25, wherein said second compressor is a variable speed compressor.

Claim 32

A refrigeration system as claimed in claim 25, further comprising a bypass line between said suction and discharge lines, said bypass line having a check valve therein to prevent flow from said discharge line to said suction line, said bypass line being connected to said suction line downstream of said second compressor with regard to said subcooler.

Claim 33

A refrigeration system as claimed in claim 25, wherein said high-stage compressors are disposed in an equipment room and said low-stage compressor is disposed in a remotely located product-display case.

Claim 34

A refrigeration system comprising: (a) a low-stage compressor for discharging compressed refrigerant into a high-stage suction line; (b) a high-stage discharge line; (c) high-stage compressor means connected between said suction and discharge lines; (d) a lubricant separator, a condenser, a refrigerant receiver and evaporator means connected in that order in series between said discharge line and the inlet of said low-stage compressor; and (e) feed means for metering on a continuous basis a small quantity of lubricant from said lubricant separator to said receiver to provide a source of lubricant for said low-stage compressor.

Claim 35

A refrigeration system comprising: (a) a low-stage compressor for discharging compressed refrigerant into a high-stage suction line; (b) a high-stage discharge line; (c) high-stage compressor means connected between said suction and discharge lines; (d) a lubricant separator, a condenser, a refrigerant receiver and evaporator means connected in that order in series between said discharge line and the inlet of said low-stage compressor; and (e) feed means for metering on a continuous basis a small quantity of lubricant from said lubricant separator to said receiver to provide a source of lubricant for said low-stage compressor.

Claim 36

A refrigeration system as claimed in claim 30, wherein said feed means comprises a semi-capillary line.

Claim 37

A refrigeration system as claimed in claim 30, wherein said lubricant is introduced into said receiver near the top of the level of liquid refrigerant therein.

Claim 38

A refrigeration system as claimed in claim 30, comprising a plurality of said low-stage compressors connected in parallel.

Claim 39

A refrigeration system as claimed in claim 30, wherein said high-stage compressor means is disposed in an equipment room and said low-stage compressor is disposed in a remotely located product-display case.

Claim 40

A multistage refrigeration system comprising: a first housing defining a first refrigerating zone; first evaporating means disposed in said first housing for utilizing pressurized refrigerant to refrigerate said first refrigerating zone; a second housing defining a second refrigerating zone; second evaporating means disposed in said second housing for utilizing pressurized refrigerant to refrigerate said second refrigerating zone; high-stage compressor means and condenser means connected in series and disposed in a location remote from said first and second housings for supplying pressurized liquid refrigerant; first conduit means for communicating pressurized liquid refrigerant from said condenser means to said second evaporating means; second conduit means for communicating refrigerant from said second evaporating means to said first evaporating means; a low-stage refrigerating compressor disposed in said first housing for compressing gaseous refrigerant received from said first evaporating means; and third conduit means for communicating compressed refrigerant from said low-stage compressor to said high-stage compressor means.

Claim 41

A multistage refrigeration system comprising: a first housing defining a first refrigerating zone; first evaporating means disposed in said first housing for utilizing pressurized refrigerant to refrigerate said first refrigerating zone; a second housing defining a second refrigerating zone; second evaporating means disposed in said second housing for utilizing pressurized refrigerant to refrigerate said second refrigerating zone; high-stage compressor means and condenser means connected in series and disposed in a location remote from said first and second housings for supplying pressurized liquid refrigerant; first conduit means for communicating pressurized liquid refrigerant from said condenser means to said second evaporating means; second conduit means for communicating refrigerant from said second evaporating means to said first evaporating means; a low-stage refrigerating compressor disposed in said first housing for compressing gaseous refrigerant received from said first evaporating means; and third conduit means for communicating compressed refrigerant from said low-stage compressor to said high-stage compressor means.

Claim 42

A multistage refrigeration system as claimed in claim 35, further comprising refrigerant expansion means disposed in said second housing between said first conduit and said second evaporating means.

Claim 43

A multistage refrigeration system as claimed in claim 36, wherein said expansion means is controlled by the output temperature of said first evaporating means.

Claim 44

A multistage refrigeration system as claimed in claim 35, wherein said first conduit means passes through said first housing.

Claim 45

A multistage refrigeration system as claimed in claim 38, further comprising a liquid-suction heat exchanger disposed in said first housing for utilizing cool refrigerant from said second evaporating means to cool liquid refrigerant in said first conduit.

Claim 46

A multistage refrigeration system comprising: a first housing defining a first refrigerating zone having individual temperature control, including a first thermostat; first expansion and evaporating means disposed in said first housing for utilizing pressurized liquid refrigerant to refrigerate said first refrigerating zone; a second housing defining a second refrigerating zone having individual temperature control, including a second thermostat; second expansion and evaporating means disposed in said second housing for utilizing pressurized liquid refrigerant to refrigerate said second refrigerating zone; high-stage compressor means and condenser means connected in series and disposed in a location remote from said first and second housings for supplying pressurized liquid refrigerant; first conduit means for communicating pressurized liquid refrigerant from said condenser means to said first and second expansion and evaporating means; a first low-stage refrigerating compressor disposed in said first housing for compressing gaseous refrigerant received from said first evaporating means, said first low-stage compressor being controlled by said first thermostat to maintain the desired temperature in said first refrigerating zone; a second low-stage refrigerant compressor disposed in said second housing for compressing gaseous refrigerant received from said second evaporating means, said second low-stage compressor being controlled by said second thermostat to maintain the desired temperature in said second refrigerating zone; second conduit means for communicating compressed refrigerant from said first and second low-stage compressors to said high-stage compressor means; and means independent of said first and second thermostat for controlling operation of said high stage compressor means.

Claim 47

A multistage refrigeration system comprising: a first housing defining a first refrigerating zone having individual temperature control, including a first thermostat; first expansion and evaporating means disposed in said first housing for utilizing pressurized liquid refrigerant to refrigerate said first refrigerating zone; a second housing defining a second refrigerating zone having individual temperature control, including a second thermostat; second expansion and evaporating means disposed in said second housing for utilizing pressurized liquid refrigerant to refrigerate said second refrigerating zone; high-stage compressor means and condenser means connected in series and disposed in a location remote from said first and second housings for supplying pressurized liquid refrigerant; first conduit means for communicating pressurized liquid refrigerant from said condenser means to said first and second expansion and evaporating means; a first low-stage refrigerating compressor disposed in said first housing for compressing gaseous refrigerant received from said first evaporating means, said first low-stage compressor being controlled by said first thermostat to maintain the desired temperature in said first refrigerating zone; a second low-stage refrigerant compressor disposed in said second housing for compressing gaseous refrigerant received from said second evaporating means, said second low-stage compressor being controlled by said second thermostat to maintain the desired temperature in said second refrigerating zone; second conduit means for communicating compressed refrigerant from said first and second low-stage compressors to said high-stage compressor means; and means independent of said first and second thermostat for controlling operation of said high stage compressor means.

Claim 48

A multistage refrigeration system as claimed in claim 40, wherein said low-stage compressors cycle on and off in response to cooling demand.

Claim 49

A multistage refrigeration system as claimed in claim 40, wherein said low-stage compressors operate at different speeds in response to cooling demand.

Claim 50

A multistage refrigeration system as claimed in claim 40, further comprising a liquid/suction heat exchanger disposed in each said housing for utilizing cold refrigerant vapor from evaporating means disposed therein to cool liquid refrigerant supplied to said expansion and evaporating means disposed therein.

Claim 51

A multistage refrigerant system as claimed in claim 40, further comprising a subcooler for subcooling refrigerant flowing from said condenser means to each of said expansion and evaporating means.

Claim 52

A multistage refrigeration system as claimed in claim 44, wherein said subcooler normally expands a portion of the condensed refrigerant downstream of said condenser means for subcooling refrigerant flowing to each of said expansion and evaporator means, and further comprising means for feeding said expanded portion of refrigerant to the inlet of said high-stage compressor means.

Claim 53

A multistage refrigeration system as claimed in claim 40, wherein said high-stage compressor means comprises a plurality of high-stage compressors connected in parallel.

Claim 54

A multistage refrigeration system as claimed in claim 46, wherein one of said high-stage compressors is a variable speed compressor.

Claim 55

A multistage refrigeration system as claimed in claim 46, further comprising a trimmer compressor connected in parallel with said plurality of high-stage compressors, said trimmer compressor being of smaller capacity than each of the other high-stage compressors.

Claim 56

A multistage refrigeration system as claimed in claim 48, wherein said trimmer compressor is a variable speed compressor.

Claim 57

A multistage refrigeration system as claimed in claim 40, further comprising lubricant control means for controlling the distribution of lubricant between said high-stage compressor means and said low-stage compressors.

Claim 58

A multistage refrigeration system as claimed in claim 40, wherein said high-stage compressor means comprises a plurality of semi-hermetic type compressors connected in parallel, and each of said low-stage compressors is a full hermetic type compressor.

Claim 59

A multistage refrigeration system comprising: a first housing defining a first refrigerating zone having individual temperature control, including a first thermostat; first expansion and evaporating means disposed in said first housing for utilizing pressurized liquid refrigerant to refrigerate said first refrigerating zone; a second housing defining a second refrigerating zone having individual temperature control, including a second thermostat; second expansion and evaporating means disposed in said second housing for utilizing pressurized liquid refrigerant to refrigerate said second refrigerating zone; high-stage compressor means and condenser means connected in series and disposed in a location remote from said first and second housings for supplying pressurized liquid refrigerant; first conduit means for communicating pressurized liquid refrigerant from said condenser means to said first and second expansion and evaporating means; a first low-stage refrigerating compressor disposed in said first housing for compressing gaseous refrigerant received from said first evaporating means, said first low-stage compressor being controlled by said first thermostat to maintain the desired temperature in said first refrigerating zone; a second low-stage refrigerant compressor disposed in said second housing for compressing gaseous refrigerant received from said second evaporating means, said second low-stage compressor being controlled by said second thermostat to maintain the desired temperature in said second refrigerating zone; second conduit means for communicating compressed refrigerant from said first and second low-stage compressors to said high-stage compressor means; and a lubricant sump associated with said high-stage compressor means and means for metering a small flow of lubricant from said sump to said pressurized liquid refrigerant supplied to each of said expansion and evaporating means.

Claim 60

A multistage refrigeration system comprising: a first housing defining a first refrigerating zone having individual temperature control, including a first thermostat; first expansion and evaporating means disposed in said first housing for utilizing pressurized liquid refrigerant to refrigerate said first refrigerating zone; a second housing defining a second refrigerating zone having individual temperature control, including a second thermostat; second expansion and evaporating means disposed in said second housing for utilizing pressurized liquid refrigerant to refrigerate said second refrigerating zone; high-stage compressor means and condenser means connected in series and disposed in a location remote from said first and second housings for supplying pressurized liquid refrigerant; first conduit means for communicating pressurized liquid refrigerant from said condenser means to said first and second expansion and evaporating means; a first low-stage refrigerating compressor disposed in said first housing for compressing gaseous refrigerant received from said first evaporating means, said first low-stage compressor being controlled by said first thermostat to maintain the desired temperature in said first refrigerating zone; a second low-stage refrigerant compressor disposed in said second housing for compressing gaseous refrigerant received from said second evaporating means, said second low-stage compressor being controlled by said second thermostat to maintain the desired temperature in said second refrigerating zone; second conduit means for communicating compressed refrigerant from said first and second low-stage compressors to said high-stage compressor means; and a lubricant sump associated with said high-stage compressor means and means for metering a small flow of lubricant from said sump to said pressurized liquid refrigerant supplied to each of said expansion and evaporating means.

Claim 61

A multistage refrigeration system as claimed in claim 52, wherein each said low-stage compressor has a lubricant sump and oil control means for introducing excess lubricant in said low-stage compressor sump into the compressed refrigerant discharged from said low-stage compressor.

Claim 62

A multistage refrigeration system as claimed in claim 53, wherein said control means coprises a vent tube extending from a zone of minimum pressure in each said low-stage compressor to a point slightly above the normal lubricant level therein.

Claim 63

A multistage refrigeration system comprising: a first housing defining a first refrigerating zone having individual temperature control, including a first thermostat; first expansion and evaporating means disposed in said first housing for utilizing pressurized liquid refrigerant to refrigerate said first refrigerating zone; a second housing defining a second refrigerating zone having individual temperature control, including a second thermostat; second expansion and evaporating means disposed in said second housing for utilizing pressurized liquid refrigerant to refrigerate said second refrigerating zone; high-stage compressor means and condenser means connected in series and disposed in a location remote from said first and second housings for supplying pressurized liquid refrigerant; first conduit means for communicating pressurized liquid refrigerant from said condenser means to said first and second expansion and evaporating means; a first low-stage refrigerating compressor disposed in said first housing for compressing gaseous refrigerant received from said first evaporating means, said first low-stage compressor being controlled by said first thermostat to maintain the desired temperature in said first refrigerating zone; a second low-stage refrigerant compressor disposed in said second housing for compressing gaseous refrigerant received from said second evaporating means, said second low-stage compressor being controlled by said second thermostat to maintain the desired temperature in said second refrigerating zone; second conduit means for communicating compressed refrigerant from said first and second low-stage compressors to said high-stage compressor means; and each said low-stage compressor has a lubricant sump and oil control means for introducing excess lubricant therein into the compressed refrigerant discharge therefrom.

Claim 64

A multistage refrigeration system comprising: a first housing defining a first refrigerating zone having individual temperature control, including a first thermostat; first expansion and evaporating means disposed in said first housing for utilizing pressurized liquid refrigerant to refrigerate said first refrigerating zone; a second housing defining a second refrigerating zone having individual temperature control, including a second thermostat; second expansion and evaporating means disposed in said second housing for utilizing pressurized liquid refrigerant to refrigerate said second refrigerating zone; high-stage compressor means and condenser means connected in series and disposed in a location remote from said first and second housings for supplying pressurized liquid refrigerant; first conduit means for communicating pressurized liquid refrigerant from said condenser means to said first and second expansion and evaporating means; a first low-stage refrigerating compressor disposed in said first housing for compressing gaseous refrigerant received from said first evaporating means, said first low-stage compressor being controlled by said first thermostat to maintain the desired temperature in said first refrigerating zone; a second low-stage refrigerant compressor disposed in said second housing for compressing gaseous refrigerant received from said second evaporating means, said second low-stage compressor being controlled by said second thermostat to maintain the desired temperature in said second refrigerating zone; second conduit means for communicating compressed refrigerant from said first and second low-stage compressors to said high-stage compressor means; and each said low-stage compressor has a lubricant sump and oil control means for introducing excess lubricant therein into the compressed refrigerant discharge therefrom.

Claim 65

A multistage refrigeration system as claimed in claim 55, wherein said control means comprises a vent tube extending from a zone of minimum pressure in each said low-stage compressor to a point slightly above the normal lubricant level therein.

Claim 66

A multistage refrigeration system as claimed in claim 56, wherein said high-stage compressor means and each of said low-stage compressors are full hermetic compressors.

Claim 67

A multistage refrigeration system as claimed in claim 57, wherein said high-stage compressor means has the same lubricant control means as each said low-stage compressor.