Method for operating a reduced-pressure multi-fryer system

A method for operating a plural number of batch type reduced-pressure fryer units, the method including: connecting the fryer units, through a switch means, with vacuum pump lines including an initial vacuum pump line serving to reduce the frying bath pressure of a selected one of the fryer units in the stage of an initial frying treatment and a finish vacuum pump line serving to maintaining the frying baths of a plural number of the frying units simultaneously in reduced pressure condition in the stage of a finish frying treatment; while holding the respective vacuum pump lines in operation, switching the vacuum pump lines to connect the initial vacuum pump line with a selected fryer unit to reduce the pressure of the frying bath thereof for the initial frying treatment; switching the vacuum pump line to connect the selected fryer unit with the finish vacuum pump line for the finish frying treatment upon completion of the initial frying treatment; switching the vacuum pump lines to disconnect the selected fryer unit from the vacuum pump lines upon completion of the finish frying treatment; and repeating the switching operation sequentially and cyclically for each one of the fryer units in a predetermined timing.

BACKGROUND OF THE INVENTION 
1. Field of the Art 
This invention relates to a reduced-pressure fryer system for producing 
fried food products from various kinds of vegetables, fruits, sea products 
and live-stock products or molded or shaped products of such food stuff 
and a method for operating the reduced-pressure multi-fryer system, and 
more particularly to a reduced-pressure fryer system which is arranged to 
operate a plural number of batch type reduced-pressure fryers efficiently 
by the use of a vacuum generating means with a smaller number of vacuum 
pump lines, and an operating method therefor. 
2. Description of the Prior Art 
Generally, when producing fried food products by the use of a batch type 
reduced-pressure fryer, it is the usual practice to connect the fryer to a 
vacuum generating means which is constituted by a vacuum pump, a condenser 
etc., placing a basket, which holds the food material to be fried, in a 
frying bath while adjusting the amount and temperature of oil in the 
frying bath and reducing the pressure of the frying bath through the 
vacuum generating means, immersing and frying the food material in heated 
oil for a predetermined time period, lifting up the fried product after 
relieving the reduced pressure, and feeding fresh food material to the 
frying bath to repeat the same frying operation. 
In a case where a plural number of reduced-pressure fryers are used for the 
production of fried food, the general practice has been to connect each 
fryer to one of vacuum generating means which are provided exclusively for 
the respective fryers for independent frying operations. It follows that 
there have to be provided frying equipments of extremely large scale due 
to the necessity for incorporating a large number of vacuum generating 
means exclusively for the respective fryers, requiring an objectionably 
large installation space in addition to increases in equipments and 
production costs. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a 
reduced-pressure multi-fryer system which can operate a plural number of 
fryers efficiently by the use of a smaller number of vacuum generating 
means, and an operating method for such a fryer system. 
In accordance with the present invention, there is provided, for achieving 
the above-stated objective, a reduced-pressure multi-fryer system which 
essentially includes: a plural number of fryers each having a frying bath 
of pressure-resistant construction for immersing and frying food material 
in heated oil under reduced pressure; and vacuum generating means for 
reducing the pressure of the fryers, the vacuum generating means having a 
number of vacuum pump lines including an initial vacuum pump line for 
reducing the pressure of one of the fryers in the stage of an initial 
frying treatment and a finish vacuum pump line for maintaining a plural 
number of the fryers concurrently in reduced pressure condition in the 
stage of a finish frying treatment subsequent to the initial frying 
treatment, the vacuum pump lines being smaller than the number of the 
fryers in total number and sequentially connectible to the respective 
fryers in a predetermined timing by operation of switch valves. 
Each fryer is provided with a heater for heating the oil in the frying bath 
and an oil circulating passage with an oil strainer and a stirring pump, 
constantly stirring the heated oil by circulation through the oil 
circulating passage. 
The initial vacuum pump line for the initial frying treatment and the 
finish vacuum pump line for the finish frying treatment are constituted by 
a vacuum pump, a separator located upstream of the vacuum pump to separate 
and collect oil mist in suction air, and a cooling means for condensing 
water vapors in the suction air. 
Preferably, the frying bath of each fryer is provided with a vacuum signal 
transmitter or vacuum sensor which is adapted to produce an output signal 
varying commensurate with the vacuum level in the frying bath to switch 
the connection of the vacuum pump line from the initial vacuum pump line 
to the finish vacuum pump line according to the variation in the vacuum 
pressure level detected by the vacuum sensor. 
Further, the finish and initial vacuum pump lines may be arranged to 
generate vacuum pressures of the same level. However, in a preferred 
embodiment, the finish vacuum pump line is arranged to generate a higher 
vacuum pressure. 
Furthermore, desirably the reduced-pressure multi-frying system is operated 
automatically according to programmed routines under control of a 
microcomputer. 
In accordance with the present invention, there is also provided a method 
of operating a plural number of reduced-pressure fryer units each having a 
frying bath for immersing and frying food material in heated oil, the 
method including: connecting the fryer units, through a switch means, with 
vacuum pump lines including an initial vacuum pump line serving to reduce 
the frying bath pressure of one of the fryer units in the stage of an 
initial frying treatment and a finish vacuum pump line serving to maintain 
the frying baths of a plural number of frying units simultaneously in 
reduced pressure condition in the stage of a finish frying treatment; 
while holding the respective vacuum pump lines in operation, switching the 
vacuum pump lines to connect the initial vacuum pump line with one fryer 
unit to reduce the pressure of the frying bath thereof for the initial 
frying treatment; switching the vacuum pump lines to connect the fryer 
unit with the finish vacuum pump line for the finish frying treatment upon 
completion of the initial frying treatment; switching the vacuum pump 
lines to disconnect the fryer unit from the vacuum pump lines upon 
completion of the finish frying treatment; and repeating the switching 
operation sequentially and cyclically for each one of the fryer units in a 
predetermined timing to operate a plural number of fryer units by the use 
of a smaller number of vacuum pump lines. 
In this instance, it is desirable to detect variations in vacuum level of 
each fryer unit and to switch the connection with the vacuum pump line 
from the initial vacuum pump line to the finish vacuum pump line according 
to a variation in vacuum level resulting from release of steam from the 
food material being fried. More specifically, it is desirable to switch 
the vacuum pump line at a time point when the vacuum pressure in the 
frying bath restores, after a drop due to the release of steam from the 
food material, a value slightly lower than the initial vacuum pressure at 
the start of the initial frying treatment. 
Normally, the vacuum pressure in the finish frying treatment is preset at a 
level same as or higher than that of the initial frying treatment. 
In a preferred embodiment, the reduced-pressure multi-fryer system is 
operated automatically according to programmed routines under control of a 
microcomputer.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown a first embodiment of the 
reduced-pressure multi-fryer system according to the present invention, in 
which the reference characters 1a to 1n denote a plural number of batch 
type reduced-pressure fryer units employed for the production of fried 
food products, and the reference 2 denotes a vacuum generating means for 
reducing the pressure of the respective fryer units. 
As shown particularly in FIG. 2, the fryer units 1a to 1n are each provided 
with a heater 11 within a frying bath 10 of pressure-resistant 
construction, the heater 11 using steam as a heat source for heating up 
oil 12 in the frying bath 10 to a predetermined temperature. The oil 12 in 
the frying bath is constantly maintained in stirred state by circulation 
through an oil circulating passage 15 with an oil strainer 13 and a 
stirring pump 14. Indicated at 16 is an oil level sensor which detects the 
amount of oil in the frying bath, and at 17 is a thermo-sensor which 
detects the oil temperature. 
The frying bath 10 is provided with an inlet opening 21 and an outlet 
opening 22 for admission and ejection of a basket 20 which contains food 
material. The inlet and outlet openings 21 and 22 are normally 
hermetically closed by sealing doors 25 and 26 which are connected to 
cylinders 23 and 24, respectively. Conveyers 27 and 28 are provided on the 
outer side of the inlet and outlet openings 21 and 22, respectively. The 
basket 20 which has been fed to the frying bath 10 by the conveyer 27 is 
supported on a lift member 30 which is supported on a lift drive means 
such as a cylinder 31 vertically movably within the housing of the frying 
bath 10. In a frying operation, the lift member 30 is lowered to immerse 
the basket 20 in the oil 12. Further provided in the frying bath 10 is a 
vacuum sensor 32 which is arranged to measure the vacuum level of the bath 
and transmit a signal of the detected vacuum level to a microcomputer 3 
which operates the reduced-pressure multi-fryer system according to a 
given program. The reference numeral 4 in FIG. 1 denotes an interface. 
On the other hand, as shown also in FIG. 1, the vacuum generating means 2 
includes an initial vacuum pump line 40 which serves to reduce the 
pressure of one fryer unit in the stage of an initial frying treatment, 
and a finish vacuum pump line 41 which serves to maintain a plural number 
of fryer units simultaneously in reduced pressure condition in the stage 
of a finish frying treatment. These vacuum pump lines 40 and 41 are 
connectible to the respective fryer units 1a to 1n through switch valves 
42a to 42n and 43a to 43n, respectively, and are sequentially and 
cyclically connected to the fryer units 1a to 1n in a predetermined timing 
by operations of the switch valves 42a to 42n and 43a to 43n under control 
of the microcomputer 3. The total number of the initial and finish vacuum 
pump lines 40 and 41 is smaller than the total number of the fryer units 
1a to 1n. 
The initial and finish vacuum pump lines 40 and 41 are provided with vacuum 
pumps 46 and 47, separators 48 and 49 located upstream of the vacuum pumps 
46 and 47 to separate and collect oil mist in suction air, and cooling 
means 50 and 51 for condensing steam in suction air, respectively. 
Vacuum relief valves 52a to 52n are provided in the conduits which 
communicate the switch valves 42a to 42n and 43a to 43n with the fryer 
units 1a to 1n, respectively, each one of the vacuum relief valves 52a to 
52n being selectively opened upon completion of a frying operation to 
restore atmospheric pressure in the frying bath 10. 
The reduced-pressure multi-fryer system of the above construction is 
operated automatically under control of the microcomputer 3, for example, 
in the manner as follows. 
In a preparatory stage of the operation, the oil 12 in the frying bath 10 
of each one of the fryer units 1a to 1n is heated by the heater 11 and 
adjusted to a predetermined temperature by controlling the steam regulator 
valve 18 according to the output signal of the thermo-sensor 17, while 
maintaining a predetermined amount of oil in the bath 10 according to the 
output signal of the oil 12 level sensor 16 and forcibly circulating the 
oil 13 by the stirring pump 14 through the oil circulating passage 15 via 
oil strainer 13 to hold the oil constantly in stirred state. As a result, 
the oil temperature becomes uniform throughout the frying bath 10. Namely, 
when heating the oil 12 by the heater 11 which is located within the 
frying bath 10, the oil temperature would be elevated only in the regions 
around the heater 11 unless the oil 12 is constantly stirred by the forced 
circulation as described above. 
On the other hand, the vacuum pumps 46 and 47 in the initial and finish 
vacuum pump lines 40 and 41 are put in continuous operation. 
In this state, a metal basket 20 which contains food material is fed to the 
frying bath 10 of the first fryer unit 1a, and, as soon as the frying bath 
10 is hermetically closed, the switch valve 42a is opened, connecting the 
fryer unit 1a with the initial vacuum pump line 40 to start the pressure 
reduction of the first fryer unit 1a. 
The pressure in the frying bath 10 is constantly measured by the vacuum 
sensor 32, and the output signal of the vacuum sensor 32 is fed to the 
microcomputer 3. Upon the amount and temperature of the oil reaching 
predetermined values for initiation of the frying operation and, as shown 
in FIG. 3, the vacuum pressure in the frying bath 10 reaching a 
predetermined value Pa at the point a, the rod of the cylinder 31 is 
lowered to immerse the basket 20 on the lift member 30 in the heated oil 
12 to effect an initial frying treatment for a certain time period. At 
this time, as soon as the food material is immersed in the oil 12, the 
moisture content in the food material is abruptly evaporated. As a result, 
the vacuum pressure in the frying bath 10 is lowered temporarily. However, 
as the amount of evaporation decreases, the vacuum pressure starts to 
increase again. 
At a time point when the vacuum pressure reaches a predetermined level, 
namely, at the point b where the vacuum pressure restores a value Pb 
slightly lower than the vacuum pressure Pa at the start of the initial 
frying operation, the switch valve 42a is closed and instead the switch 
valve 43a is opened, disconnecting the fryer unit 1a from the initial 
vacuum pump line 40 and connecting same with the finish vacuum pump line 
41 to carry out a finish frying treatment for a certain period of time. In 
this stage of finish frying treatment, the food material gradually dries 
up by release of steam, so that the vacuum pressure in this stage is set 
substantially at the same level as the vacuum pressure Pa at the start of 
the initial frying treatment. 
The time t.sub.1 for the initial frying treatment and the time t.sub.2 for 
the entire frying treatment are almost invariable as long as the frying 
conditions such as the kind and amount of the food material, oil 
temperature, vacuum pressure level etc. are constant. Accordingly, the 
switching from the initial vacuum pump line 40 to the finish vacuum pump 
line 41 may be effected by a time-base control irrespective of the vacuum 
pressure of the frying bath. 
The above-described frying treatments are carried out in the circulated 
oil, which stirs the food material in the basket 20 to a suitable degree, 
so that it is not necessarily required to vibrate the basket 20 in the 
oil. However, depending upon the frying conditions such as the nature or 
amount of the food material to be fried, arrangements may be made to 
vibrate the basket 20 in vertical or lateral directions in fully or half 
immersed state in the oil. 
On the other hand, the initial vacuum pump line 40 which has been 
disconnected from the first fryer unit 1a, is then connected with the 
second fryer unit 1b by opening the switch valve 42b as shown in FIG. 4 to 
repeat the initial frying treatment in the second fryer unit 1b in the 
same manner as in the first fryer unit 1a described above, thereafter 
sequentially repeating the same operation for the succeeding fryer units 
1c to 1n. 
In the next place, upon lapse of a predetermined time period after the 
connection of the first fryer unit 1a with the finish vacuum pump line 41 
or upon completion of the finish frying treatment in the first fryer unit 
1a, the basket 20 is lifted up out of the oil, followed by a predetermined 
time period of oil draining to complete one frying operation. 
Upon completion of a frying operation, the switch valve 43a is closed and 
simultaneously the vacuum relief valve 52a is opened to restore the 
atmospheric pressure in the frying bath 10. Succeedingly, the food outlet 
22 and inlet 21 are opened to receive a basket 20 of fresh food material 
through the inlet 21 while ejecting the basket 20 of the fried food 
material through the outlet 22, holding the first fryer unit 1a in a 
stand-by state. 
Then, at the time point b when the n-th fryer 1n is disconnected from the 
initial vacuum pump line 40, the first fryer 1a is connected with the 
initial vacuum pump line 40 again to start the initial frying treatment in 
the first fryer unit 1a. Thereafter, a predetermined initial frying 
treatment is sequentially and cyclically repeated for each one of the 
fryer units 1a to 1n. 
The above-described embodiment employs the initial and finish vacuum pump 
lines 40 and 41 of the same capacity, maintaining in the finish frying 
treatment a vacuum pressures which is substantially same as the vacuum 
pressure level at the start of the initial frying treatment. However, if 
desired, arrangements may be made to increase the vacuum pressure in the 
finish frying treatment to a level higher than the vacuum pressure Pa at 
the start of the initial frying treatment, by employing a finish vacuum 
pump line 41 of a higher capacity. 
Thus, according to the present invention, a plural number of batch type 
reduced-pressure fryers 1a to 1n are continuously and efficiently operated 
in an overlapped fashion by the use of a smaller number of vacuum pump 
lines 40 and 41. 
The system may employ a plural number of the initial vacuum pump lines 40 
or finish vacuum pump lines 41 as long as the total number of the vacuum 
pump lines is smaller than the total number of the fryer units. A second 
preferred embodiment of the invention, shown in FIG. 5, exemplifies a 
vacuum generating means 2 which is constituted by a plural number of 
initial vacuum pump lines 40 and 40a and a single finish vacuum pump line 
41. More specifically, in the second embodiment, another initial vacuum 
pump line 40a is added to the vacuum pump line arrangement of the first 
embodiment, such that the additional vacuum pump line 40a is connectible 
with the respective reduced-pressure fryer units 1a to 1n through switch 
valves 44a to 44n. Since, except for the additional vacuum pump line, the 
second embodiment is same as the foregoing first embodiment in 
construction, its component parts are designated by the same reference 
characters and their description is omitted to avoid repetitions. 
More specifically, in the second embodiment, a plural number of initial 
vacuum pump lines 40 and 40a are alternately connected to the respective 
fryer units 1a to 1n for a frying treatment. Namely, as shown in FIG. 6, 
after the first initial vacuum pump line 40 has been connected to the 
first fryer unit 1a to start an initial frying treatment, the second 
initial vacuum pump line 40a is connected to the second fryer unit 1b with 
a certain time interval to start an intial frying treatment in the fryer 
unit 1b. The first and second fryers 1a and 1b are successively 
disconnected from the initial vacuum pump line at the point b at the end 
of the initial frying treatment, and connected with the finish vacuum pump 
line 41 to carry out a finish frying treatment. On the other hand, the 
initial vacuum pump lines 40 and 40a which have been disconnected from the 
fryer units 1a and 1b are successively connected with the third and fourth 
fryer units 1c and 1d in a predetermined timing to repeat the same 
treatment. Upon completing the frying treatment in the n-th fryer unit 1n, 
the operation goes back to the first and second fryer units 1a and 1b to 
repeat the same frying treatment. In this manner, a predetermined frying 
treatment is sequentially and cyclically repeated for each of the fryer 
units 1a to 1n. 
The numbers of the initial and finish vacuum pump lines are determined in 
consideration of the vacuum pump capacity and the number of the fryer 
units etc. 
In the foregoing embodiments, the frying treatment is not necessarily 
repeated in the order of the fryer units 1a to 1n, which can be changed 
depending upon operating conditions. Namely, in a case where the start of 
the frying operation needs to be delayed with regard to certain fryer 
units which are in stand-by state for some reason, for example, for not 
having reached a preset value in oil amount, oil temperature or vacuum 
pressure level on starting the frying operation of the whole system, it is 
possible to select automatically a number of fryer units which are ready 
for the frying operation, and to start the operation by sequentially 
connecting the selected fryers with an initial vacuum pump line under 
control of the microcomputer. 
Although the whole system is operated automatically by means of the 
microcomputer in the foregoing embodiments, it should be understood that 
all of or part of the operation can be carried out manually if desired. 
Thus, according to the present invention, a plural number of batch type 
reduced-pressure fryers can be operated continuously and effectively in an 
overlapped fashion by the use of a smaller number of vacuum generating 
means.