Control method for a dual-cylinder moisture removal apparatus

A control method for a dual-cylinder moisture removal apparatus of a pneumatic system is taught. The control method places a limitation on the time for drying of moist air in a drying cylinder. The drying of moist air in one drying cylinder and the regeneration of the absorbent used to dry moist air in a second cylinder are alternated at each predetermined time. When the air compressor is stopped each drying cylinder is switched to a reverse position to the position it occupied just prior to the stopping of the air compressor. Furthermore, when the air compressor resumes operation, the position of each drying cylinder is maintained in the position it occupied just before resumption of operation of the air compressor.

FIELD OF THE INVENTION 
The present invention relates, in general, to moisture removal equipment 
for pneumatic systems and, more particularly, this invention relates to a 
method of operating a two-cylinder type moisture removal apparatus. 
BACKGROUND OF THE INVENTION 
Equipment of this type is used, for example, in the pneumatic brake system 
of a railroad car. The prior art includes moisture removal devices such as 
those described in Japanese Utility Model Applications Nos. 55-23621 and 
59-86231 in addition to Japanese Patent No. 53-34664, which will be 
explained in some detail hereinafter with respect to FIGS. 3, 4, and 5 of 
the drawings. In these Drawings, there is illustrated in FIG. 3 a general 
two-cylinder type of moisture removal apparatus. As shown therein, an air 
compressor designated CO and a cooler designated CL are provided. The 
inlet of the cooler CL is connected in fluid communication with an outlet 
of the air compressor CO. The outlet of the cooler CL is connected in f 
luid communication to an inlet of a drain valve designated DV. MV1 and MV2 
designate a pair of solenoid valves having their flow inlets connected for 
fluid communication with the outlet of the drain valve DV. In this system, 
the solenoid valves MV1 and MV2 are switchable type valves. A pair of 
drying cylinders designated DR1 and DR2 are provided and have their inlet 
connected for fluid communication with the flow outlets of the solenoid 
valves MV1 and MV2. Each of the drying cylinders DR1 and DR2 contains an 
absorbent therein. Check valves designated CV1 and CV2 are connected in 
fluid communication with the outlets of the drying cylinders DR1 and DR2 
in a manner such that the direction of this outlet of the drying cylinder 
is a reverse direction. Connected to the check valves CV1 and CV2 in 
parallel are throttle valves designated NV1 and NV2. SR designates a 
regenerated air reservoir connected to the throttle valves NV1 and NV2 and 
to the check valves CV1 and CV2. A second air reservoir designated MR is 
connected for fluid communication with the regenerated air reservoir SR 
through a check valve designated CV3. The check valve CV3 is connected 
such that the direction of the regenerated air reservoir SR is the reverse 
direction. Also provided is a governor designated GO for the air reservoir 
MR. The governor GO detects the pressure regulation upper limit value P2 
and the lower limit value P1 (FIG. 5). In addition, the governor GO 
controls the air compressor CO and the drain valve DV. In this equipment, 
the solenoid valves MV1 and MV2 include an exhaust position designated (b) 
in which the flow outlet is opened to the atmosphere and the flow inlet is 
closed. This arrangement occurs when the apparatus is not energized or is 
off. Further, the solenoid valves MV1 and MV2 include a feed position 
designated (a) in which the exhaust outlet is closed and the flow inlet is 
connected to the flow outlet when the apparatus is energized or on. 
When the solenoid valve MV1 is ON and the solenoid valve MV2 is OFF, the 
moist air from the air compressor CO is communicated to the drying 
cylinder DR1 through the cooler CL, the drain valve DV and the feed 
position (a) of the solenoid valve MV1. The moist air is dried by the 
absorbent in the drying cylinder DR1 and is then communicated to the 
regenerated air reservoir SR via the check valve CV1 and is thereafter 
communicated to the air reservoir MR via the check valve CV3. During this 
time, a portion of the dried air passing through the check valve CV1 is 
directed and flows in the reverse direction to the inlet from the outlet 
of the other drying cylinder DR2, through the throttle valve NV2, where it 
regenerates the absorbent in the drying cylinder DR2. During this 
regeneration of the absorbent in the drying cylinder DR2 the air becomes 
moist and is then exhausted from the system through the exhaust position 
(b) of the solenoid valve MV2. Now when the solenoid valve MV1 is switched 
to the OFF position and the solenoid valve MV2 is switched to the ON 
position, in reverse to the sequence described in detail above, the moist 
air is dried in the other drying cylinder DR2 and at the same time the 
absorbent is being regenerated in the other drying cylinder DR1. At the 
time the pressure in the air reservoir MR reaches the pressure regulation 
upper limit value P2 of the governor GO the air compressor CO is stopped 
and the drain valve DV opens to drain. Thereafter, when the pressure in 
the air reservoir MR reaches the pressure regulation lower limit value P1 
of the governor GO, the drain valve DV closes thereby stopping draining 
and the air compressor CO goes into operation. 
FIGS. 4 and 5 are graphs which illustrate over time the control process for 
switching the drying and regeneration of the above-described pair of prior 
art drying cylinders DR1 and DR2. 
In one method of operation, according to the prior art and illustrated in 
FIG. 4, the solenoid valves MV1 and MV2 are always switched ON and OFF at 
each predetermined time T as determined by a timer which has not been 
illustrated in the drawings. In other words, one pair of drying cylinders 
DR1 and DR2 repeat the drying and regeneration cycles in alternation. 
In a second method of operation according to the prior art and illustrated 
in FIG. 5, from which the table in FIG. 3 of the Japanese Patent No. 
53-34664 was prepared, the ON/OFF operation of the governor GO which 
detects the pressure P in the air reservoir MR is linked to the operation 
and stopping of the air compressor CO. In this method of operation, when 
the air compressor CO is stopped, both solenoid valves MVl and MV2 go off 
and both drying cylinders DR1 and DR2 are switched to the regeneration 
status. In this method, when the air compressor CO is operated, the 
solenoid valves MV1 and MV2 are switched into the reverse status from the 
previous operating time interval and the drying and regeneration of the 
absorbent in the drying cylinders DR1 and DR2 can be switched. 
One of the principal disadvantages associated with the above-described 
methods is that the switching mechanism which includes the solenoid valves 
MV1 and MV2 and their control portions become worn out rather quickly. 
This condition can cause increased damage to the overall pneumatic system. 
In particular, the first method repeats the drying and the regeneration of 
the absorbent in the drying cylinders DR1 and DR2 in alternation during 
each predetermined time T as controlled by the timer regardless of the 
operation or inoperation of the air compressor CO. Because it can be 
switched even though the air compressor CO is stopped, the frequency of 
switching is increased causing additional wear on the above-described 
components. 
SUMMARY OF THE INVENTION 
A method of controlling a two-cylinder type moisture removal apparatus in 
which moist air from the air compressor is supplied from the inlet to the 
outlet direction of one drying cylinder of one pair of drying cylinders 
which contain a moisture absorbent therein, to be dried by such absorbent 
in the drying cylinder, and a portion of this dried air is communicated 
back from the outlet to the inlet direction of the other drying cylinder 
to regenerate the absorbent of the drying cylinder and these drying and 
regeneration operations are repeated in alternation. According to the 
present invention, the method of controlling such a two-cylinder type 
moisture removal apparatus includes the step of establishing a 
predetermined maximum drying time required in a drying cylinder and the 
drying and regeneration of this drying cylinder are switched at each 
predetermined time only when the air compressor has been in continuous 
operation for longer than the predetermined time. When the air compressor 
stops the drying cylinder is switched just before the air compressor stops 
and when the air compressor is in operation the status of the drying 
cylinder just before the air compressor goes into operation is maintained. 
OBJECTS OF THE PRESENT INVENTION 
It is therefore one of the primary objects of the present invention to 
provide a method of controlling a two-cylinder type moisture removal 
apparatus which will minimize switching between the two cylinders. 
Another object of the present invention is to provide a method of 
controlling a two-cylinder type moisture removal apparatus which will 
reduce the wear on the components caused by excessive switching. 
Still another object of the present invention is to provide a method of 
controlling a two-cylinder type moisture removal apparatus which maintains 
the drying capacity of the apparatus even with reduced switching between 
the two drying cylinders. 
The above and various other objects and advantages of the present invention 
will become more readily apparent to those persons skilled in the 
pneumatic fluid art from the following more detailed description of the 
invention when such description is taken in conjunction with the attached 
drawings and with the appended claims.

BRIEF DESCRIPTION OF THE INVENTION 
Now refer more particularly to FIGS. 1 and 2 for an understanding of a 
presently-preferred embodiment of the control method of a two-cylinder 
type moisture removal apparatus. It should be noted that the two-cylinder 
type moisture removal apparatus which is illustrated schematically in FIG. 
2 is almost the same as that illustrated in FIG. 3. For this reason, the 
detailed explanation of FIG. 2 will be minimized and incorporated as 
necessary into the description of the presently preferred control method. 
Reference is now made to the time graph shown in FIG. 1 which illustrates 
one example of the operation of the moisture removal equipment shown in 
FIG. 2. When the electric power supply of an electrical control circuit 
(not shown in the drawings) is turned ON the solenoid valve MV1 switches 
to an ON position which means it moves to the feed position (a) and the 
solenoid valve MV2 remains in an OFF position or in the exhaust position 
(b). At this particular point in time, the air reservoir MR is usually at 
atmospheric pressure. 
At the time the electrical power supply to the governor GO is turned ON, 
the governor GO detects the pressure in the air reservoir MR and switches 
ON. At this point, the air compressor CO begins to operate. The initial 
drying of the air takes place in the drying cylinder DR1 while a 
simultaneous regeneration of the absorbent is taking place in drying 
cylinder DR2. In this condition, when a first predetermined time T has 
elapsed, the solenoid valve MV1 switches to OFF and assumes the exhaust 
position (b) and the solenoid valve MV2 substantially simultaneously 
switches to ON and assumes the feed position (a). Consequently, 
regeneration of the absorbent now takes place in the drying cylinder DR1 
and drying of the air takes place in the drying cylinder DR2. This 
alternate switching of the drying and regeneration continues at 
predetermined time intervals until the air compressor is stopped. 
When the time T1 has passed and the pressure P in the air reservoir MR 
reaches the pressure regulation upper limit value P2, the governor GO 
detects this condition and turns OFF. At this point, the air compressor CO 
is stopped. In addition, and at the same time, the solenoid valves MV1 and 
MV2 switch to the positions which are the reverse of their 
immediately-prior status. In other words, in the embodiment illustrated in 
FIG. 1, the solenoid valve MV1 switches OFF and moves to the exhaust 
position (b) and the solenoid valve MV2 switches ON and moves to the feed 
position (a). Thereafter, when the time T2 has elapsed and the pressure P 
in the air reservoir MR has been consumed to the point where it reaches 
the pressure regulation lower limit value P1 the governor GO turns ON and 
the air compressor CO goes into operation once again. However, at this 
time, the solenoid valves MV1 and MV2 maintain the positions they had 
assumed just before the operation of the air compressor, i.e., the drying 
of the air takes place in the drying cylinder DR1, while the regeneration 
of the absorbent is taking place in the drying cylinder DR2. 
In the embodiment being described, the time T3 is less than the 
predetermined time T and therefore the drying cylinders DR1 and DR2 both 
maintain their positions. When this time T3 has elapsed and the governor 
GO switches OFF and the air compressor CO is again stopped, the solenoid 
valve MV1 switches ON and moves to the feed position (a) while the 
solenoid valve MV2 switches OFF and moves to the exhaust position (b) all 
at the same time. 
Time T4, which occurs after the time T3, is longer than the predetermined 
time T but the solenoid valves MV1 and MV2 are not switched. When time T4 
has elapsed, the governor GO turns ON and the air compressor CO goes into 
operation. However, the solenoid valves MV1 and MV2 at this time maintain 
their current positions. The time T5 is longer than the predetermined time 
T so that the solenoid valves MV1 and MV2 are switched after each 
predetermined time T; in other words, the drying and regeneration of the 
drying cylinders DR1 and DR2 are switched in alternation. 
Furthermore, the operation during times T6, T7, and T8 can easily be 
understood from the above detailed explanation and from reference to FIG. 
1. For that reason, and for the sake of brevity, further detailed 
explanations will not be presented here. 
In the above description of the invention, it should be noted that the 
solenoid valves MV1 and MV2 are those which will assume an air feed 
position when energized. However, it should be understood by those skilled 
in the art that solenoid valves which assume an air feed position when 
de-energized could also be used. 
According to the presently-preferred embodiment of the method of the 
invention described above, the operation of the air compressor is linked 
and the timer control is used at the same time. In other words, when the 
air compressor begins operation after having been stopped, the drying 
cylinders remain in their respective positions they had just before 
resumption of air compressor operation and also when the continuous 
operating time of the air compressor is less than the predetermined time 
T. Consequently, the switching of the drying and regeneration does not 
take place thereby eliminating the unnecessary switching which causes 
excessive wear and damage to the switching mechanism. Moreover, when the 
air compressor shuts down, the drying and regeneration are switched into 
the reverse of the position they occupied just before the shutdown of the 
air compressor. In addition, the drying and regeneration is switched when 
the operating time is greater than the predetermined time. Such switching 
occurs each time the operating time exceeds the predetermined time so that 
a decrease of the drying capacity of the drying cylinder can be prevented 
and efficient drying becomes possible. It has been discovered that it is 
not necessary to add extra absorbent when using the method of the present 
invention. 
Therefore, in the presently-preferred embodiment of the invention, when the 
continuous operating time of the air compressor is less than the 
predetermined length of time, and when the air compressor initially goes 
into operation, the switching of the drying and regeneration does not 
occur thereby eliminating an unnecessary switching process on the 
equipment. On the other hand, when the compressor switches from operation 
to shutdown, the drying and regeneration are switched and when the 
continuous operating time of the air compressor is longer than the 
predetermined time, the drying and regeneration are switched at the elapse 
of each predetermined time, thereby preventing any significant decrease in 
drying capacity when compared to the methods of the prior art. 
It can be seen, from the above description, that this invention 
accomplishes its objectives by providing a method of controlling a 
two-cylinder type moisture removal apparatus in which the moist air from 
the air compressor is communicated into the inlet of one drying cylinder, 
on one pair of drying cylinders, each of which contains an absorbent, to 
the outlet direction and is dried by the absorbent in the drying cylinder. 
A portion of this dried air is communicated in the reverse direction from 
the outlet to the inlet direction of the other drying cylinder to 
regenerate the absorbent in that drying cylinder, this drying and 
regeneration step being repeated in alternation. The elimination of the 
problem associated with the prior art described above is achieved by the 
control method of the present invention because such control method places 
a limitation on the time for drying the moist air with an absorbent in a 
drying cylinder and the drying and regeneration of the absorbent in the 
drying cylinder are conducted at each predetermined time only when the air 
compressor has been in continuous operation for a preset length of time. 
When the air compressor is stopped, the drying cylinder is automatically 
switched at that time to a reverse position with respect to the position 
it occupied just prior to the shutdown of such air compressor. In 
addition, when the air compressor resumes operation once again, the 
position of the drying cylinders is maintained the same as the position it 
occupied before resumption of operation of the air compressor occurred. 
While a presently-preferred embodiment of a control method for a 
dual-cylinder moisture removal apparatus in a pneumatic system has been 
described in detail above, with reference to the drawings, it should be 
understood by those persons skilled in the pneumatic art, that other 
modifications and adaptations can be made to the present invention without 
departure from the spirit and scope of the appended claims.