Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
2001-11-15
2003-06-10
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
C092S086000
Reexamination Certificate
active
06574960
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
Applicant hereby claims foreign priority benefits under 35 U.S.C. §119 of German Application No. 100 56 568.9, filed Nov. 15, 2000, the disclosure of which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
The invention concerns a method and an apparatus for maintaining the correct oil overflow quantity in diaphragm compressors.
Diaphragm compressors work similarly to normal piston compressors, but with a separating diaphragm between the gas side and the oil side. The oil side is made as the usual piston-cylinder unit, whose working and dead volumes are entirely filled with oil. On the gas side are gas suction and pressure outlet valves. By the oscillating movement of the piston a displaced volume is transmitted to the diaphragm, which then on its other side takes on the suction, the compression and the expelling of the gas. Since the oil pressure during all of the strokes of the suction and compression process corresponds to the course of the pressure on the gas side, one can talk here about the operation of a piston compressor.
A small difference in comparison to piston compressors however exists in that in diaphragm compressors a secondary oil circuit has to be installed in order to compensate for the leakage oil of the piston. For this purpose a compensation pump, driven by an eccentric cam on the crankshaft, is used. This pump sprays a small amount of oil into the oil space of the compressor synchronously with each piston stroke. This amount of oil must theoretically be exactly of the same size as the leakage at the compressor piston. Since this is not technically realizable, a sprayed in amount of oil is always used which is larger than the leakage. This has in turn the result that with each stroke of the compressor piston somewhat too much oil is contained in the oil space which then in the forward dead point of the diaphragm (=engaging the cover) leads to an uncontrollable oil pressure increase. To avoid this there must also be provided an oil overflow valve which limits the oil pressure at the forward dead point of the piston to a value which is slightly more than the maximum pressure of the gas.
The spring loaded oil overflow valve, which works as a safety valve, dare however let out only an amount of oil which is actually the excess amount entering the oil space from the compensation pump. This amount, which is let out with each stroke, is on one hand dependent on the opening characteristic of the oil overflow valve, for which the construction of the seat part and the spring characteristics are contributing elements, and on the other hand the energy content of the oil space (pressure×volume) has a strong influence on the responsiveness of the oil overflow valve.
The latter leads to undesirably long open times of the oil overflow valve during which more oil is let out than supplied by the compensation pump. This has then the result that in many strokes the diaphragm is no longer moved to its dead point. Accordingly not all of the compressed gas is exhausted, which is connected with a rapid decline of the suction efficiency.
The diaphragm pump described in DE 44 20 863 A1 has the described oil space with inlet and outlet conductors to an oil reservoir, wherein oil overflow valves are arranged in the inlet and outlet conductors which compensate for the oil loss in the oil space.
SUMMARY OF THE INVENTION
The object of this invention is to provide a method and apparatus whereby the too long open times of the oil overflow valve at different operating conditions of the oil space are avoided.
This object is solved in that in the outlet conductor in front of the oil overflow valve, with respect to the flow direction, is arranged a control valve with a throttle restriction, and in that the control valve in dependence on the differential pressure at the throttle restriction is so controlled that upon an increasing differential pressure an opening of the control valve is made free, through which opening an additional amount of oil then flows to the oil reservoir.
An advantageous elaboration of the invention is given in the claims.
REFERENCES:
patent: 4430048 (1984-02-01), Fritsch
patent: 4865528 (1989-09-01), Fritsch et al.
patent: 5246351 (1993-09-01), Horn et al.
patent: 5655894 (1997-08-01), Fritsch
patent: 37 08 868 (1988-10-01), None
patent: 44 20 863 (1995-12-01), None
Lazo Thomas E.
Look Edward K.
McCormick Paulding & Huber LLP
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