Pumps – Condition responsive control of pump drive motor – With condition responsive control of pump fluid valve
Patent
1996-04-24
1997-12-16
Gluck, Richard E.
Pumps
Condition responsive control of pump drive motor
With condition responsive control of pump fluid valve
418 84, 417 53, F04C 2900, F04C 2902
Patent
active
056977638
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to improvements in rotary compressor systems. Rotary compressor systems include screw compressors utilising intermeshing rotors, vane and scroll type compressors.
Conveniently, rotary compressor systems comprise a compressor unit, a drive motor drivingly coupled to the compressor unit to drive same, a separator vessel defining a volume containing a supply of lubricating liquid (hereinafter called "oil") and arranged to receive a mixture of compressed gas and liquid from the compressor unit, a filter element through which compressed gas flows to a clean compressed gas storage tank, an oil filter and oil cooling device through which oil passes in a return line from the separator vessel to an inlet region of the compressor unit, and appropriate piping and valving linking the system together. Various improvements have been proposed to such systems to improve performance, limit componentry to decrease manufacturing costs and to decrease package sizes, however, such systems still remain relatively complex with package sizes larger than equivalent reciprocating compressor systems, particularly in smaller capacity machines.
Such systems have also always had competing design interests. For example, to reduce package sizes, it is desirable to, reduce the physical size of the larger volume components such as the separator vessel and the gas storage tank. However, to improve capability of the machine to work longer between service periods to replace the oil, it is desirable for the separator vessel to be as large as possible so that the volume of oil used in the system can also be as large as possible. Moreover, with systems using minimum pressure valves (mpv) to maintain a minimum pressure in the separator so as to allow oil circulation back to the compressor unit by pressure differential, it is generally desirable to keep the separator volume below a certain level so as to prevent too much of a delay at start up before the minimum pressure is achieved so that lubricating oil can be returned to the compressor unit. The problem is exacerbated by the oil desirably entering the compressor unit at a pressure greater than atmospheric pressure (say 2.5 atmospheres) so as not to obstruct suction volumes of air through the compressor unit. Thus, the minimum pressure level needs to be above this level (say 3.5 atmospheres) to create the necessary pressure differential. Thus, if the separator volume is too large the screw rotors may seize before lubricating oil starts to flow. Opposed to this, it is also desirable to have a separator vessel volume as large as possible so that it can cope with oil foaming (which occurs during certain stages of system operation) without having the foaming oil flowing into bulk contact with the final filter element. The tendency has, however, been to design compressor systems with ever decreasing sized separator vessel volumes sometimes with attempts to solve the aforementioned oil volume and foaming problems by other techniques. It still remains, however, a desirable attribute that the separator vessel be as large as possible to allow use of increased oil volumes.
There is a still further problem with many rotary compressor systems in that they commonly employ a pressure lowering valve to lower the pressure in the separator vessel down to the minimum pressure level so as to reduce the compression ratio of the compressor during unloaded operation or when it is stopped. Some systems also operate under loaded and unloaded conditions cyclically and if, each time, it is operated unloaded, the pressure lowering valve dumps pressure from the separator vessel, then this amounts to a significant efficiency loss from the system. The operational mode of some systems is on a stop/start cycle basis and again when the system is stopped, pressure is each time dumped from the separator vessel resulting in a significant lack of efficiency. This of course also emphasises the problems discussed above with systems using pressure lowering valves.
The objective of the present invention i
REFERENCES:
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patent: 3813850 (1974-06-01), Uratani
patent: 4171188 (1979-10-01), Anderson et al.
patent: 4180986 (1980-01-01), Shaw
patent: 4475876 (1984-10-01), Olen
Patent Abstracts of Japan, M1560, p. 80, JP,A, 5-296172 (Hitachi Ltd.) 9 Nov. 1993.
patent Abstracts of Japan, M1389, p. 137, JP,A, 4-325796 (Hitachi Ltd.) 16 Nov. 1992.
Cash Engineering Research Pty Ltd
Gluck Richard E.
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