Patent GB-905519-A (GB)
Title: Fluid pressure control system for gas compressors
IPC: F25B49/02
Filed: 1958-10-06
Abstract: 905,519. Refrigerating. SVENSKA TURBIN A.B. LJUNGSTROM. Oct. 6, 1958 [Nov. 16, 1957], No. 31819/58. Class 29. [Also in Groups XXVIII and XXIX] Three multi-cylinder compressors 1-3, Fig. 1, in a refrigerating system each have one or more of their cylinders provided with unloading means, whilst a manual or automatic interrupter 4 and an automatic starter 5 is associated with each compressor; the cylinders may be connected in groups. Each compressor is provided with a control valve 6 connected to a suction conduit 7 common to all the compressors, and an oil pump 8 connected by a capillary tube II to both the valve 6 via a conduit 12, and a distribution device 9 via conduit 13, 14, the conduit 13 incorporating a cut-off valve 15. The distribution devices 9 each comprise a spring-loaded piston 20, Fig. 2, in a cylinder 19 into which open conduits 13, 14, 22, 25, 34, 37 and 47; conduit 22 leads to the unloading means 23 in the compressor cylinder head B, whilst conduit 24 leads to the unloading means of another cylinder in the same compressor. Conduit 25 joins conduit 22 via non-return valves 26, 27, Fig. 1, and another conduit 28 connects conduits 25 with conduit 13 of the next compressor; conduit 28 also leads by another conduit 29 to the starter 5. Associated with the piston 20, Fig. 2, is a locking-piston 32 in a cylinder 30 supplied with oil via the conduit 34 connected to the distribution device 9 of an adjacent compressor; a valve-controlled conduit 36 bridges the locking-piston 32 to enable the latter to be manually put out of action. The conduit 37 leads from the cylinder 30 to the related cylinder 19, the conduit 47 of which is connected to an oil sump. Cut-off valves 39, 41, 44, Fig. 1, are disposed in conduits 28, 34 and 36, respectively. In operation, compressor 1 and the oil pump 8 are started and if the evaporation pressure in conduit 7 is too high the control valve 6 is closed, so increasing the pressure in conduits 13, 14, whereby the piston 20 is urged rightwardly interconnecting conduits 14, 22 and admitting pressure to the unloading means 23; further closing movement of the valve 6 causes additional movement of the piston 20 and interconnects conduits 14, 24 so bringing into operation another cylinder of the compressor 1. Any further movement of the piston 20 will cause conduit 25 to be connected to conduit 14, whereupon the second compressor 2 is started and if the compressor capacity is now too large compressor 2 continues to operate but the capacity of both compressors is reduced. When the required compressor capacity is large enough to require operation of the unloading means 23 of the first cylinder of the second compressor 2 then the piston 32 of compressor 1 is supplied with pressure and moves rightwardly to lock the piston 20 in its right-hand position. The need for further compressor capacity is met by sequentially bringing into operation the other cylinders of the second compressor 12 and then the third compressor 3 and its cylinders as previously described. Upon a fall of evaporation pressure in the conduit 7 the control valve 7 opens so decreasing the oil pressure in conduit 15 and if the first compressor 1 is at full load with its device 9 locked then the capacity of the other compressors is sequentially reduced and the compressors stopped, the locking pistons 32 of each device 9 being retracted just prior to the adjacent compressor being shut down. In a modification, the refrigerating plant is used as a heat pump and another control valve 61 is provided which is connected by a conduit 60 to a pneumatic control acted upon by the condensate in the conduit 7. In another modification, the control valves are temperature responsive. Specification 764,821 is referred to.