Valve arrangement for a compressor

Details Valve arrangement for a compressor Valve arrangement for a compressor

2001-08-15

2002-10-22

Esquivel, Denise L. (Department: 3744)

Refrigeration

Automatic control

Refrigeration producer

C062S470000

Reexamination Certificate

active

06467287

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to compressors, and more particularly to valve arrangements for controlling the flow of fluid through compressors.
BACKGROUND OF THE INVENTION
It is known to use positive displacement compressors, and more specifically screw compressors, to compress fluids. The rotors or screws of a screw compressor are susceptible to backward rotation when the compressor is stopped because the pressure differential between the discharge side of the compressor and the suction side of the compressor naturally tends to equalize over the rotors. While the compressors can be designed to handle such backward rotation of the rotors, the noise generated by the backward-turning rotors is undesirable.
SUMMARY OF THE INVENTION
To prevent pressure equalization over the compressor, and the resultant backward rotation of the rotors, it is known to use check valves. For the purposes of this description, the compressor is described as being part of a temperature control system, however, it is to be understood that the compressor need not be used in conjunction with a temperature control system.
FIG. 1
schematically illustrates a prior art refrigeration system
10
. The system
10
includes a compressor (represented by the dashed box
14
) having two screws or rotors
16
and a discharge line
18
through which high-pressure refrigerant and lubricating oil exit the rotors
16
at the discharge end of the compressor
14
. The discharge line
18
communicates with an oil separator
22
that separates the oil from the high-pressure refrigerant. The oil returns to an oil sump
26
where it can be reintroduced into the rotors
16
via an oil supply line
30
. The high-pressure refrigerant exits the compressor
14
through the oil separator
22
and travels to a condenser
34
. After exiting the condenser
34
, the condensed refrigerant passes through an expansion valve
38
before reaching an evaporator
42
. From the evaporator
42
, the low-pressure refrigerant returns to the compressor
14
and the refrigeration cycle repeats.
As seen in
FIG. 1
, a check valve
46
is located at the suction end of the compressor
14
. The check valve
46
prevents high-pressure refrigerant from flowing back through the rotors
16
toward the lower pressure at the suction end of the compressor
14
, and thereby prevents backward rotation of the rotors
16
. An advantage of locating the check valve
46
at the suction end of the compressor
14
is that when the compressor
14
is shut down there is no pressure equalization over the oil system so oil will not be displaced from the oil sump
26
into the rotors
16
. Rather, the pressure is equalized downstream of the discharge end of the compressor
14
.
The disadvantage of locating the check valve
46
as shown in
FIG. 1
is that the check valve
46
must be relatively large to prevent the high-pressure gas from taking its natural equalization path over the compressor to the lower-pressure suction end. Additionally, any pressure drop caused by the check valve
46
while the system is operating will substantially reduce the system's capacity.
FIG. 2
shows another prior art refrigeration system
10
′, with like parts having like reference numerals. In the system
10
′, a check valve
50
is located downstream of the oil separator
22
. The check valve
50
prevents high-pressure refrigerant from flowing back into the oil separator
22
and the rotors
16
. Locating the check valve
50
downstream of the oil separator
22
also provides advantages. First, the check valve
50
can be relatively small because the high-pressure refrigerant will naturally flow toward the lower-pressure environment of the condenser
34
. In other words, because the high-pressure refrigerant downstream of the oil separator
22
does not tend to flow back into the oil separator
22
, the check valve
50
can be relatively small. Additionally, any pressure drop caused by the check valve
50
while the system is operating will only affect power consumption and not system capacity.
The disadvantage with the location shown in
FIG. 2
is that, in most situations, the volume of high-pressure refrigerant in the oil separator
22
is still large enough to cause noticeable backward rotation of the compressor rotors
16
as the pressure equalizes over the compressor
14
. To alleviate this problem, it is known to add a second check valve
54
at the suction end of the compressor
14
. This second check valve
54
operates in the manner described above with respect to the check valve
46
, so that the volume of high-pressure refrigerant in the oil separator
22
does not flow back through the rotors
16
. While this configuration creates maximum isolation of the compressor
14
from the remaining components of the refrigeration system
10
′, it necessitates the use of two check valves
50
and
54
, and adds to the cost of the refrigeration system
10
′.
FIG. 3
shows yet another prior art refrigeration system
10
″, with like parts having like reference numerals. A check valve
58
is located at the discharge end of the compressor
14
, between the rotors
16
and the oil separator
22
. When the compressor
14
stops running, the pressure between the discharge end and the suction end of the compressor
14
equalizes over the oil system via the oil supply line
30
. The disadvantage with this check valve location is that when the pressure is equalized over the oil system, oil from the oil sump
26
is displaced into the rotors
16
, the bearings (not shown), the gears (not shown), and the seal cavities (not shown). Too much oil in the rotors
16
makes the compressor
14
difficult to start and reduces the overall life of the compressor
14
. For example, since oil is not a compressible medium, too much oil in the rotors
16
could create a hydraulic lock situation. To overcome these problems, it has been known to place a solenoid valve
62
in the oil supply line
30
. The solenoid valve
62
is opened when the compressor
14
is running and closed when the compressor
14
is stopped.
One disadvantage with using the solenoid valve
62
is the additional cost. Furthermore, failure of the solenoid valve
62
could cause problems. For example, if the solenoid valve
62
is stuck closed when the compressor
14
is running, the compressor
14
will not get lubrication and will eventually seize. If the solenoid valve
62
is stuck open when the compressor
14
is stopped, oil will be displaced to the rotors
16
, creating the difficult starting conditions that the solenoid valve
62
was intended to prevent.
The present invention provides a valve arrangement that offers many of the advantages discussed above, without most of the disadvantages. More particularly, the invention provides a valve arrangement having a single, relatively small valve located in the discharge line of the compressor. When the compressor is running, the valve provides the necessary fluid communication between the compressor and the oil separator. When the compressor is shut down, the valve blocks fluid communication between the rotors and the oil separator to prevent the high-pressure fluid from flowing back over the rotors.
In addition, the valve arrangement also prevents displacement of oil to the rotors when the compressor shuts down, and does so without the use of a solenoid valve in the oil supply line. To accomplish this, the valve arrangement includes a bleed line communicating between the oil supply line and the discharge line. When the compressor is not operating, the valve and the bleed line provide a pathway for the high and low pressure fluid to equalize over the oil cavities in the compressor while short-circuiting the oil separator and the oil sump. Because the pressure equalization does not occur over the oil sump, substantially no oil is displaced to the rotors.
The valve provides selective communication between the discharge end of the compressor, the oil separator, and the bleed line. A movable member in the valve responds to system pressure so

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