JP2006503220A - Screw pump - Google Patents

Abstract

The pump has a stator and at least one rotor provided in the housing. The housing has a first fluid channel extending around the rotor, and the rotor has at least one second fluid channel. A first sensor configured to output a signal representative of the temperature of the stator is provided, and a second sensor configured to output a signal representative of the temperature of the rotor is provided. The temperature of the fluid in the channel is controlled according to the magnitude of the signal output from the sensor.

Description

  The present invention is in the field of vacuum pumps. In particular, the present invention relates to thermal control of a screw-type vacuum pump.

  Screw pumps typically have two spaced apart parallel shafts, each supporting a male threaded rotor, the shaft being provided in the pump body such that the rotor threads engage each other. Due to the tight tolerance between the rotor threads at the intermeshing points and the inner surface of the pump body acting as a stator, the amount of gas being pumped between the inlet and outlet can be reduced between the rotor threads and the inner surface. Ingestion, thereby pushing into the pump when the rotor is rotating.

  Prior art screw pumps use a water-cooled jacket around the part of the machine to remove the heat of compression. However, the machine inlet does not have any cooling system. The reason is that in the low pressure state, little heat of compression has to be removed from the inlet. As the pressure increases, additional heat is dissipated from the inlet by increasing the gas flow rate through the inlet. If the pump is installed in a cold environment, the surface temperature in the pump inlet can be significantly reduced to produce a cold spot, so gaseous waste from the exhaust chamber can condense in these cold regions. It becomes a liquid pool (pool) state. These puddles can arise from corrosive acidic or basic fluids, which can cause damage to pump components, which can shorten the life of the device.

A double-headed screw pump in which a single inlet covers two outlets is known, and the rotors are arranged in a straight line. In such pumps, temperature variations between the inlet and outlet portions of the pump are significant and the concentricity of the bores in the housing components is important. As the housing components move and move out of alignment, the rotor is already more likely to collide with the stator because slight tolerances are already reduced or eliminated.
Screw pumps are increasingly used in a wide range of applications. For example, in the pharmaceutical process field, the same pump may need to perform a wide variety of applications. Pump configurations are often tailored for specific applications, but once the application is changed, the ideal conditions no longer exist and the pump will not operate at peak / optimal efficiency.
The object of the present invention is to solve some of the above-mentioned problems associated with screw pump technology.

According to one aspect of the invention, a pump includes a stator and at least one rotor disposed within the housing, the housing having a first fluid channel extending around the rotor, the rotor Has at least one second fluid channel and the pump is configured to output a first sensor configured to output a signal representative of the temperature of the stator and a signal representative of the temperature of the rotor. And a temperature control means for controlling the temperature of the fluid when present in the channel in accordance with the magnitude of the signal output from the sensor. .
The first temperature sensor may be located at the stator, whereas the second temperature sensor is in fluid contact with the process gas in the exhaust portion of the rotor in the exhaust plenum, or It may be provided in any of the housings, or the second temperature sensor may be arranged in a gear box of the pump.

  The thermal control means may include first control means and second control means for controlling the temperature of the fluid in the first channel and the second channel, respectively. At least one of the first control means and the second control means constituting the heat control means includes a transmission flow pump, a thermostat control valve, and a heat exchanger. These control means may be arranged to control the temperature of the fluid in each channel in accordance with one or more of the sensor outputs. The thermal control means may have a microprocessor, or the thermal control means may be controlled by the microprocessor.

  One of the thermostat control valves may be a mechanical differential temperature valve. The valve may have a third fluid channel in thermal communication with the second fluid channel. In order to control the flow rate of fluid through the third fluid channel, a flow restrictor (flow restrictor) may be provided in the third fluid channel. The position of the flow restrictor can be determined by signals received from the first sensor and the second sensor by a signal receptor, which signal receptor may form part of the valve. Each signal receptor may have a sealed part and its volume should expand during use. The degree of expansion is determined by the magnitude of the received signal and defines the relative position of the restrictor in the third fluid channel. The sealing part of the signal receptor may be composed of an expandable bellows. The flow restrictor may have a spindle and a seat. The spindle opens and closes the hole to control the flow rate of fluid passing through it in cooperation with the seat. The pump may be of any known form, such as, but not limited to, a screw pump, a claw pump, or a Roots pump.

  According to another feature of the invention, a double-headed pump comprising at least one rotor with one inlet portion and two discharge portions, a stator and a housing, the housing comprising an inner shell and Having an outer shell, a first cavity is formed by the inner shell, a rotor is provided in the inner shell, and a second cavity is formed between the inner shell and the outer shell of the housing; A double-headed pump is provided, wherein fluid circulates through the second cavity, the second cavity extending over and surrounding the length of the rotor.

According to another feature of the invention, the valve is a fluid channel, a flow restrictor that can be moved in the fluid channel to control the flow rate of fluid, and the magnitude of the received signal. There is provided a valve characterized in that it has two signal receptors for controlling the position of the flow restrictor in the fluid channel accordingly.
According to another aspect of the invention, there is provided a method for releasing a seized pump rotor due to the presence of deposits of material formed on the inner working surface of the pump during cooling, provided in the pump housing. The thermal fluid is introduced into the cavity surrounding the rotor components, the thermal fluid in the cavity is heated to a predetermined temperature high enough for the deposit to soften, and torque In addition to the rotor of the pump and overcoming the remaining disturbing forces caused by deposits that are attached to the inner working surface of the pump.

  According to another aspect of the present invention, there is provided a method for controlling a clearance between a rotor and a stator in a pump according to the present invention, wherein (a) the temperature of each of the stator and the rotor is determined using a signal output from a sensor. Recording, (b) calculating a temperature difference between the stator and the rotor, (c) comparing the temperature difference with a predetermined value, and (d) in the first fluid channel and in the second fluid channel. Determining a flow rate and a temperature of an appropriate value for the fluid in order to achieve a predetermined temperature difference; and (e) controlling the thermal control means to achieve the value determined in step (d). Is provided.

  The method steps may be repeated automatically at predetermined time intervals to manage perturbations in the form of the pump over time. The predetermined temperature difference may be corrected at predetermined time intervals to change the gap between the parts so that accumulated deposits can fall off the surface of the pump parts.

  The thermal control device may include a microprocessor embodied in the state of the computer, which is optionally programmed with computer software, and when the software is installed on the computer, the computer is Perform step (e) from a).

  With the present invention, the pump can receive an improved level of thermal control. This results in an optimized dynamic gap that increases the pump tolerance for excessive exhaust back pressure, reduces the occurrence of cold spots at the pump inlet, reduces heating delays in the system, and cools the deposits An advantage can be achieved during operation of the device in that it increases the possibility of restarting in the environment caused by.

Next, an example of the present invention will be described with reference to the accompanying drawings.
A screw pump is shown in FIGS. Two rotors 1 are provided in the outer housing 2. The two rotors 1 meshing with each other rotating in opposite directions are positioned so that their central axes are positioned in parallel to each other. The rotor 1 is provided in the housing 2 via a bearing 3. The single-head pump 1 in FIG. 1 has an inlet stator 4 and an exhaust stator 5, whereas the double-head pump in the example of FIG. 2 has an inlet disposed between two exhaust stators 5. A stator 4 is provided.

  The housing 2 is provided as a double shell structure. The inner shell serves as a pump stator. A cavity 6 is provided between the inner and outer shells of the housing 2 so that cooling fluid, e.g. water, can be circulated around the stator in order to carry away heat from the working part of the pump. It is like that. This cavity 6 surrounds the entire length of the stator, ie not only the inlet stator 4 but also the exhaust stator 5. The cooling fluid circulates through this cavity to remove heat from the hot surface. By providing a water jacket over the entire length of the stator, the heat generated towards the exhaust end of the rotor can be redistributed to the previous stage if necessary. This can reduce the temperature gradient and maintain a more uniform temperature across the surface of the pump. As a result, the “cold spot” found in the prior art can be avoided and condensation of potentially corrosive material at the rotor inlet is substantially reduced. Further, for example, a set of water jackets are provided that effectively prevent rapid temperature changes on the stator and rotor surfaces due to wind cooling effects, thus introducing a heating delay into the system. By maintaining a uniform temperature, all of the stator components expand from the central reference (shaft) at the same speed, thus maintaining concentricity, so that the rotor can maintain the relative position of the rotor within the stator. It can be held and collision between parts can be avoided.

  Conventional pumps with thermal jackets typically use convection to circulate thermal liquid through the stator. This may result in a non-uniform distribution of temperature throughout the pump, especially in the lower region of the pump and the higher region in the upper region. Such localized cold spots can cause the process gas to condense and become increasingly corrosive. By embodying a circulation pump in the thermal fluid, consistent thermal control can be achieved to minimize local temperature variations.

  In some cases, the waste that has passed through the pump contains waxy or viscous material, and deposits are formed on the surface of the pump during operation. These deposits may cool and solidify when the pump is shut down. If such deposits are present in the gap area between the components, the deposits may be baked by these deposits. In this case, the torque provided by the motor may be insufficient to overcome this additional friction, thereby causing the rotor to rotate. Additional torque can be applied by inserting the lever bar into a receptacle provided on the shaft and then manually rotating it. However, such techniques can apply significant loads to the rotor and cause damage. However, it may not be possible to disengage the mechanism and apply sufficient load to rotate the shaft, and under these circumstances, the device will be shut down and used for replacement or repair. It may be necessary to cancel. Another use of the water jacket of the present invention can be realized in these situations where the pump is seized due to the cooling of the rotor. When the fluid in the cavity 6 of the housing 2 is heated, the temperatures of the stators 4 and 5 and the rotor 1 can be raised. This can increase the flexibility of the residue and help release the machine.

  FIG. 3 shows how the fluid circuits 11, 12, 12a, 15 can be used to control the thermal conditions within the pump. A coolant, typically a mixture of water and antifreeze, is provided in the first closed circuit 11 by a circulation pump 17. The second fluid circuit 12 includes a pressurized water circuit and a thermostat control valve 13. Typically, mains water is sent to this circuit at the inlet 25 and removed at the outlet 26. A heat exchange component 14 is provided between the two fluid circuits 11 and 12. The valve 13 receives an input signal from a temperature sensor 21 provided at the stator and uses it to maintain an appropriate flow rate in the second circuit 12 to determine the temperature gradient across the heat exchange component 14. . This temperature gradient maintains the temperature of the first circuit 11.

  As shown in FIG. 2, the rotor 1 has a threaded portion 9 and a separate shaft component 8. The threaded portion 9 is provided with an internal cooling cavity 7 into which the body of a separate shaft 8 is inserted. The body of the shaft 8 is partially smaller in diameter than the diameter of the cooling cavity 7 in the rotor body. Thus, a cooling channel is obtained through which coolant, typically oil, can be dropped. This channel is kept small to maximize the coolant flow rate. Its purpose is to maintain the temperature difference between the rotor and the coolant and to promote the cooling function by sending heat back to the coolant reservoir. The inlet and outlet of the cooling system are provided through the shaft part 8.

  Referring to FIG. 3, it can be seen that the oil is held in another closed circuit 15. The circuit 15 includes a circulation pump 19, a filter 20, and a heat exchange component 14a. This heat exchange component is in contact with the second cooling circuit 12 a and has another thermostat control valve 16. The thermostat control valve 16 receives an input signal from the second temperature sensor 22, which indicates the rotor temperature via oil from the circuit 15 or process gas in the subsequent stage of the rotor. . The temperature may be monitored in the exhaust plenum (ie, the cavity between the end of the rotor and the stator wall), but here the temperature will drop more quickly than the temperature of the rotor.

By introducing the two thermostat control valves as described above, the temperature of the pump rotor relative to the temperature of the stator can be controlled. The clearance d (shown in FIG. 4) between the rotor and stator of the screw pump is a function of this difference in temperature between the rotor and stator. By controlling the temperature of these components, the size of the gap d can be controlled. Furthermore, it is this gap d that determines the level of process gas leakage between the rotor and stator, and therefore the amount of leakage is described by Nigel Harris, “Modern Vacuum Practice (Modern Vacuum Practice). practice ”, as shown on page 231 of McGraw Hill, which is proportional to d ³ for intermediate transition flows. Since leakage adversely affects pump performance, it is assumed that pump performance can be optimized by controlling the temperature of these components. Furthermore, it is advantageous if the gap d is maintained so that the particles as the contents of the process gas do not form obstructions in these gaps and thus do not prevent free rotation of the rotor 1. . Such disturbances can seriously affect pump performance by requiring additional torque to be applied by the motor to maintain the proper rotational speed of the rotor, as well as throttling the process gas flow rate. There is.

  By providing the temperature control circuit in the rotor, it is possible to optimize the gap d between the rotor and the stator by controlling the rotor temperature with respect to the stator temperature by the action of a thermostat. The present invention, in its simplest embodiment, can be readily utilized to avoid cold spots and thus eliminate corrosion due to condensate deposition as described above. In a more complex and elaborate embodiment, when input signals are received from sensors attached to each of the stators 4, 5 and the rotor 1 and these signals are analyzed / processed by a closed loop control system, the set temperature is less than 135 ° C. Can be maintained. Thereby, the pump using the present invention can safely process a substance having a known self-ignition temperature.

  However, as discussed above, the present invention can be utilized at a very high level of complexity so as to select a particular temperature that results in a particular gap d being achieved and maintained. FIG. 5 shows how a processor or central processing unit (CPU) 27 can be incorporated into the system to receive signals representative of the respective rotor and stator temperatures from sensors 22a, 21a. These signals are inputs that allow the processor 27 to determine the required temperature for each of the components. In this case, the processor 27 controls the electronically activated valves 13a, 16a to provide the appropriate level of coolant fluid to the heat exchange components 14, 14a to achieve the required thermal balance and then the gap d. To achieve.

  Under normal steady state operation, the dry pump will achieve a specific pumping speed determined by the gap between the rotor and the stator. If the pump inlet pressure is increased, more gas will flow into the pump. This additional gas cools the rotor relative to the stator, thus increasing the gap d between these two components. It is assumed that a considerable amount of leakage around the rotor occurs in the high pressure state. This typically results in low pump speeds and is particularly problematic when pumping gaseous species such as helium, for example, to achieve gas throughput as exhaust pressure is approached. Become. According to the control feature of the present invention, the gap d between the rotor and the stator can be artificially reduced. As a result, leakage around the rotor can be reduced and the efficiency of the pump can be significantly improved. In the above example, when pumping helium, it is desirable to maintain a slight gap to prevent leakage. In other applications where argon is pumped where a large gap is required, the same pump may be used. A multi-purpose pump is achieved by providing a pump that can be essentially optimized during operation to function efficiently under a variety of conditions. This functionality can be effectively utilized in fields where it is necessary to use a single pump for different applications, for example the pharmaceutical industry or the chemical process industry, using the same mechanical equipment.

The temperature control should be dynamic within a specific process range. At start-up, the temperature difference is generally large. The reason is that the rotor temperature increases at a faster rate than the stator due to the large difference in the thermal mass of the relative components. However, once the pump reaches a steady state, this temperature difference becomes smaller. By performing the temperature control dynamically, the initial temperature difference is minimized and the gap d can be maintained at a substantially steady value. This provides a more consistent level of pump efficiency.
The dynamic control of the gap can be realized in a periodic manner when the pump is operating under normal conditions. If the thermal condition is changed at a predetermined interval, the gap between the rotor and the stator can be reduced in a short period of time. This has the effect of removing / dropping process deposits that have become attached to these components. If this is repeated at intervals, the cumulative build-up of solids on the inner surface of the pump can be substantially reduced, thus preventing pump sticking or seizure.

  Pump sticking can be further avoided by providing additional sensors that monitor the pressure in the pump or the power consumption of the pump. If any of these values increase significantly, this may be an indication that the gap is closed and seizure is imminent. By monitoring these values, it is possible to initiate a maximum cooling state of the rotor parts to maximize the gap between the rotor 1 and the stators 4 and 5, thus preventing pump seizure.

  As a variant, as shown in FIGS. 6 and 7, the thermal control means can be provided by purely mechanical means, in which case a certain temperature difference between the stator and the rotor can be automatically maintained. . In this way, a simple but robust device can be put into practical use for a pump that is exposed to certain harsh conditions. The mechanical thermal controller 24 is directly connected to the sensor 22 arranged as described above to indicate the rotor motion by the process gas in the sweep volume or by the oil temperature in the gearbox, A sensor 23 provided in the stator of the pump is also directly connected. The latter sensor 23 may be arranged at the same position as the sensor 21 that provides the input to the thermal control valve 13 in FIG. Each end of the operating temperature valve receives a temperature difference from each sensor and the sealed sensor / bellows structure is heated, thus causing the bellows to expand. These two expandable bellows structures cooperate to position the internal valve. This valve position defines the amount of cooling fluid that can pass through the thermal circuit, thus changing the amount of heat removed by the heat exchange unit 14a. This controls the clearance in the pump by changing the temperature of the pump components. This simple example maintains the temperature difference between the rotor 1 and the stators 4 and 5 rather than actively controlling each component individually. However, by maintaining these relative temperatures, a consistent gap can be maintained. The valve 24 can be physically changed, for example, by limiting the degree of expansion of one of the bellows components, thereby adjusting the magnitude of the temperature difference between the rotor 1 and the stators 4, 5, and thus various Can handle the process.

  The invention is not limited to use with screw pumps, but can be readily applied to other types of pumps, such as claw pumps or roots pumps. In practice, some roots blowers may experience fairly high exhaust pressures (in some cases up to 2-3 bar). Such high pressures can cause a significant increase in the temperature of the components within the pump, which can cause problems in maintaining proper clearance. By implementing the dynamic thermal control of the present invention, these gaps can be maintained at a consistent level, thus increasing the tolerance of the pump to various operating conditions.

  A roots blower rotor 35 is shown in FIG. 8, and cooling channels 34 may be introduced into the rotor 35 in a manner similar to that seen in the screw rotor 1 of FIG. is necessary. Again, the channel is kept small so that the coolant flow rate is as high as possible. The purpose is to maintain the temperature difference between the rotor 35 and the coolant and enhance the cooling function by sending heat back to the coolant reservoir, typically a gear box (not shown). The cooling channel inlet 32 and outlet 33 are provided through the rotor shaft part 31. The cooling channel extends into each of the lobes 30 provided in the roots rotor 35 and may be provided with two lobes as shown, or it may be easily provided with three, four or more lobes in the rotor. it can.

  The foregoing shows only a few embodiments of the present invention, and other embodiments can certainly be conceived by those skilled in the art without departing from the true spirit of the invention as set forth in the claims. is there.

It is a schematic sectional plan view of the screw pump of the present invention. It is a cross-sectional top view of the double-headed screw pump of this invention. 1 is a schematic diagram of a temperature control circuit of the present invention. It is a figure which shows the detail of the interface between the rotor and stator of the pump shown in FIG. It is a figure which shows the more complicated elaborate modification of this invention. It is a figure which shows another example of this invention used in a severe environment. It is a figure which shows the detail of the operating temperature valve used for the pump of FIG. It is a figure which shows the Roots blower which implements the thermal control of this invention.

Claims (31)

A pump,
Having a stator,
Having at least one rotor provided in the housing, the housing having a first fluid channel extending around the rotor, the rotor having at least one second fluid channel;
A first sensor configured to output a signal representative of the temperature of the stator;
A second sensor configured to output a signal representative of the temperature of the rotor;
A pump comprising temperature control means for controlling the temperature of a fluid when present in the channel according to the magnitude of a signal output from a sensor.   The pump according to claim 1, wherein the first temperature sensor is disposed at the stator.   The pump according to claim 1, wherein the second temperature sensor is disposed in the gear box.   3. A pump according to claim 1, wherein the second temperature sensor is disposed in the housing in use and in fluid contact with the process gas in the exhaust portion of the rotor.   The temperature control means includes first control means for controlling the temperature of the fluid in the first fluid channel, and second control means for controlling the temperature of the fluid in the at least one second fluid channel. The pump as described in any one of Claims 1-4 characterized by the above-mentioned.   6. The pump according to claim 5, wherein the first control means includes at least one flow pump, at least one control valve, and at least one heat exchanger.   The first control means is configured to control the temperature of the fluid in the first fluid channel in accordance with the magnitude of the signal output from the first sensor. The pump described.   The pump according to any one of claims 5 to 7, wherein the second control means includes at least one flow pump, at least one control valve, and at least one heat exchanger. .   The second control means is configured to control the temperature of the fluid in the at least one second fluid channel according to the magnitude of the signal output from the second sensor. Item 9. The pump according to any one of Items 5 to 8.   The second control means has at least one second output depending on the magnitude of the signal output from the second sensor and the signal output from the additional sensor configured to output a signal indicating the temperature of the stator. The pump according to claim 5, wherein the pump is configured to control the temperature of the fluid in the fluid channel.   The second control means is configured to control the temperature of the fluid in the at least one second fluid channel according to the magnitude of the signal output from the first sensor and the second sensor. The pump according to any one of claims 5 to 9, wherein   The pump according to any one of claims 5 to 11, further comprising a microprocessor that controls at least one of the first control means and the second control means.   The pump according to any one of claims 5 to 12, further comprising a microprocessor that controls both the first control means and the second control means.   A third sensor configured to output to the microprocessor a signal representative of one of the group consisting of pump pressure and power consumption, the microprocessor at least a second depending on the magnitude of the signal; 14. The pump according to claim 12, wherein the control means is controlled.   The pump according to any one of claims 9 to 12, as a dependent claim, wherein the at least one control valve of the second control means comprises a mechanical differential temperature valve. .   The mechanical valve is in a third fluid channel in thermal communication with at least one second fluid channel, a flow restrictor capable of moving in the third fluid channel to control the flow rate of fluid through, and 2 receives signals from the first sensor and the second sensor, respectively, and controls the position of the flow restrictor in the third fluid channel according to the magnitudes of the signals received from the first signal and the second signal. 16. The pump according to claim 15, comprising one signal receptor.   Each temperature receptor has a sealing part, and the volume of each sealing part is expanded according to the magnitude of the received signal during use to control the relative position of the restrictor in the third fluid channel. The pump according to claim 15.   18. A pump according to claim 17, wherein each signal receptor includes an expandable bellows.   The flow restrictor has a spindle and a receiving seat, and the spindle opens and closes a hole so as to control a flow rate of fluid during use in cooperation with the receiving seat. The pump according to any one of 18.   The pump according to any one of claims 1 to 19, wherein the pump is one selected from the group consisting of a screw pump, a claw pump, and a roots pump.   The housing has an inner shell and an outer shell, a first cavity is formed by the inner shell, a rotor is provided in the inner shell, and a first fluid channel is formed between the inner shell and the outer shell of the housing. 21. The pump according to any one of claims 1 to 20, wherein the pump is formed between the rotors and extends around the length of the rotor.   The pump according to claim 21, wherein the inner shell of the housing becomes a stator during use. A double-headed pump,
At least one rotor with one inlet part and two discharge parts;
A stator,
A housing having an inner shell and an outer shell, wherein the first cavity is formed by the inner shell, the rotor is provided in the inner shell, and the second cavity is the inner shell of the housing. And in use, fluid circulates through the second cavity, which extends around the length of the rotor, surrounding it.
This is a double-headed pump. A valve,
A fluid channel;
A flow restrictor capable of moving within the fluid channel to control the flow rate of the fluid;
Two signal receptors for receiving the respective signals and controlling the position of the flow restrictor in the fluid channel according to the magnitude of the received signals;
The valve characterized by having. A method of releasing a seized pump rotor due to the presence of deposits of material produced on the inner working surface of the pump during cooling,
Introducing thermal fluid into a cavity provided in a pump housing and surrounding a rotor component;
Heating the thermal fluid in the cavity to a predetermined temperature high enough for the deposit to soften;
Applying torque to the rotor of the pump to overcome the remaining disturbing force caused by deposits present on the inner working surface of the pump;
A method comprising the steps of: A method for controlling a gap between a rotor and a stator in a pump according to any one of claims 1 to 22,
(A) recording the temperature of each of the stator and the rotor using a signal output from the sensor;
(B) calculating a temperature difference between the stator and the rotor;
(C) comparing the temperature difference with a predetermined value;
(D) determining an appropriate value of flow rate and temperature for the fluid in the first and second fluid channels to achieve a predetermined temperature difference;
(E) controlling the thermal control means to achieve the value determined in step (d);
A method comprising the steps of:   27. The method of claim 26, wherein the steps of the method are automatically repeated at predetermined time intervals to manage perturbations in the form of pumps over time.   28. A predetermined temperature difference is corrected at a predetermined time interval to change a gap between parts so that accumulated deposits can fall off the surface of the parts of the pump. The method described.   29. A computer program that, when installed on a computer, causes the computer to perform the method of claim 26, 27 or 28.   A carrier medium readable by a computer, wherein the computer program according to claim 29 is installed.   32. The computer readable carrier medium of claim 30, wherein the carrier medium is selected from a floppy disk, CD-ROM, mini disk or digital tape.

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