Pumps – Plural pumps with individual or relative control
Patent
1987-04-14
1989-04-18
Freeh, William L.
Pumps
Plural pumps with individual or relative control
1841031, F01M 1106, F04B 3902
Patent
active
048222593
DESCRIPTION:
BRIEF SUMMARY
This invention relates to levelling the oil of compressors and/or compression machines for fluids (vapor or gas) which are connected in parallel in the same circuit.
It relates to a device which may be used in the Industrial Engineering area, for levelling the crankcase oil, when two or more compression machines for gas or vapor are connected in parallel, in the same circuit.
The system provided by the present invention may be specifically used for air conditioning and refrigeration, or more generally to compressed air and simple processes for mechanical compression of vapor and gas.
The compressors used in the present invention may be, for example, piston (reciprocal), centrifugal, blade, or screw type machines of volumetric displacement, which function to reduce the specific volume of a fluid in the physical state of vapor or gas.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of a conventional compressor.
FIG. 2 is a schematic of two conventional compressors connected in parallel.
FIG. 3 is a schematic of the preferred embodiment of a system of compressors connected in parallel in accordance with the present invention.
FIG. 4 is a schematic of another embodiment of a system in accordance with the present invention.
FIG. 5 is a schematic of yet another embodiment of a system in accordance with the present invention.
FIG. 1 shows a conventional compressor having two pressure chambers: a high pressure or discharge (1) and a low pressure or suction (2).
The crankcase of the conventitonal compressor of FIG. 1 is generally operated at suction pressure.
Present techniques of levelling the crankcase oil in compression units, when connected in parallel in the same circuit include use of two pressure equalization connections.
Referring to FIG. 2, the connection whose axis passes by the oil level (19) line is called OIL EQUALIZATION (3). The connection over the oil level line (19) is called GAS EQUALIZATION (4).
This technique recommends the use of identical compression units, i.e., with the same volumetric displacement, and the same rotation with suction and discharge intakes, with equal pressure losses.
Reaching such recommendation is based on obtaining identical volumetric efficiency, which is difficult in practice due to:
1--having unequal mechanical wear in different machines, propitiated by different operating times;
2--the difficulty in obtaining the same rotation for all the compressors, caused by little differences of velocity at the electrical motors or by different friction forces of the movement transmission belts.
In view of these differences, one of the machines connected in parallel will have a pressure lower than the other, thus causing vapor or gas flow through the equalization pipes from the machine or higher pressure to the one of lower pressure.
In the compression units, oil can be returned by means of an OIL SEPARATOR (5) placed in the collective or individual discharge of the compressors and also by means of a SUCTION MANIFOLD (6) in systems having fluids in which the lubricating oil is miscible.
Considering these assumptions, the oil flow will prefer the return to the compressor of lower suction pressure, following the internal flow of the gas by the oil equalization pipe (3).
When this tendency has been maintained during a relatively long operating time, the ol level considerably increases in the compressor of lowest pressure and, therefore, there is a drawdown of the oil level of the other compressors. This subjects the machine of lowest pressure to the risk of overflowing of "liquid hammers", while subjecting the others to the risk of the lack of lubrication, due to the absence of oil.
In the case of machines with individual control of capacity i.e., which operate at partial charge, the above situation is even more critical, considering the big pressure difference created by the unequal volumetric displacements.
The same occurs with parallel compression units of different models.
In the last two cases, present techniques include use of individual oil level controls for each cr
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