Rotary expansible chamber devices – Multistage – Interengaging rotary members
Patent
1997-05-28
1999-01-19
Vrablik, John J.
Rotary expansible chamber devices
Multistage
Interengaging rotary members
4182012, 417310, F04C 1816, F04C 2300, F04C 2910
Patent
active
058608010
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a rotary screw compressor having at least one stage and each stage being provided with at least one relief lift valve.
It is common to provide rotary screw air compressors with devices for unloading the compressor at starting up and at periods with low demand on compressed air. Therethrough the power consumption can be reduced. A frequently used method is to throttle the compressor inlet channel down to about 10% of the normal inlet pressure. Although a certain amount of drive energy can be saved this way there still remains a considerable work to compress the air. Another solution is to provide the wall of the working space with valve controlled openings for reducing the capacity and the internal volume ratio (V.sub.i) of the compressor during the starting up periods as disclosed in GB-1 576 230. This disclosure, however, does not mention anything about the valve arrangement for the openings. Normally such openings are provided with so called lift valves as disclosed in U.S. Pat. No. 4,453,900. The lift valves in U.S. Pat. No. 4,453,900 are, as is the common way, actuated by oil pressure, which is relatively complicated, requiring circumstantial measures for manufacturing and maintenance.
OBJECT AND SUMMARY OF THE INVENTION
The object of the present invention is to provide a rotary screw compressor with an unloading system through which a high degree of power saving is attained and which is simple and reliable.
By unloading through lift valves a higher degree of power savings can be reached than through inlet throttling, since only a small amount of air is compressed and with a low pressure increase. By actuating the lift valves pneumatically with the air in the discharge channel as the air source a very simple regulation of the valves is attained and the valves will close and open automatically in response to the air pressure in the discharge channel.
The advantages of the invention will be of particular importance when applied to a multi-stage compressor.
According to the invention a branch conduit ending in ambient air is connected to the discharge channel and is provided with a valve. By controlling this valve in dependence of the pressure in the delivery conduit, unloading of the compressor at reduced or interrupted demand of compressed air can be established automatically.
The invention will be explained through the following detailed description of a preferred embodiment thereof with reference to the accompanying drawing which schematically illustrates a two-stage compressor according to the invention.
BRIEF DESCRIPTION OF THE DRAWING
The illustrated compressor has a first stage 10 and a second or end stage 20. The first stage 10 has an inlet channel 12 for air and an outlet channel 13 connected to the inlet channel 22 of the end stage 20. The air leaves the end stage 20 through the discharge channel 23 connected to the delivery conduit 37 via a check valve 35.
DETAILED DESCRIPTION
In each stage the air is compressed by a pair of meshing screw rotors of which only one 11, 21 can be seen in each stage. The rotors 11, 21 have helically extending lobes and intermediate grooves through which they mesh with the related rotor forming chevron-shaped working chambers. A working chamber is limited by a forerunning and afterrunning sealing line, each sealing line consisting of portions formed between the rotors and between each rotor and the walls of the working space. In the figure the forerunning sealing line 19a, 29a and the afterrunning sealing line 19b, 29b are indicated for a working chamber in a position immediately before being brought into communication with the outlet. Each chamber initially during a filling phase communicates with the inlet, thereafter during a compression phase defines a closed space with decreasing volume as the chamber travels towards the outlet and finally during a discharge phase communicates with the outlet. The ratio between the volume of a working chamber immediately after communication with the inlet h
REFERENCES:
patent: 2358815 (1944-09-01), Lysholm
patent: 4453900 (1984-06-01), Schibbye et al.
patent: 4498849 (1985-02-01), Schibbye et al.
patent: 4946362 (1990-08-01), Soderlund et al.
Patent Abstracts of Japan, vol. 10, No. 6, M-445, abstract of JP A 60-169694 (Nippon Denso K.K.), 3 Aug. 1985.
Svenska Rotor Maskiner AB
Vrablik John J.
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