JPH07133760A - Multistage vacuum pump - Google Patents

Abstract

PURPOSE: To provide an oil-free multistage vacuum pump continuously operating in different modes by providing a piston in the inside of a cylinder having a central part with a large diameter, and forming a plurality of stage exhaust chambers therebetween. CONSTITUTION: This pump is provided with a cylinder 52 having both end parts 60, 62 with a substantially equal diameter and a central part 70 with a diameter larger than the above. The pump is also provided with a piston 42 having both cylindrical end parts 72, 74 with a substantially equal diameter and an intermediate part 76 with a diameter larger than the above. A first stage exhaust chamber 61 is formed between a closing plate 100 for closing one end of a cylinder 52 and a forward end face 94 of a piston 42. The intermediate part 76 of the piston 42 is made shorter than the central part 70 of the cylinder 52, and both a second and a third stage chambers 63 are formed on both sides of the intermediate part 76. All stage chambers 61, 63 and an inlet/ outlet are communicated with one another to gradually lower the pressure, and the piston 42 is reciprocated by plural exhaust units 14 to which one driving unit 12 is connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-stage vacuum pump, and more particularly to a single piston and cylinder assembly having a thickened central portion, one end of the assembly having a larger diameter central portion. A multi-stage vacuum pump with three stage exhaust chambers on either side, interconnected by passages.

[0002]

[Prior Art and Problems] Australian Patent No. 4
Nos. 81072 and 516210 disclose various forms of reciprocating piston-cylinder machines having a unique working piston in two working spaces.

In the practical application of such a machine, it is usual to provide a plurality of cylinders as each stage of a multi-stage (multi-stage) pump. This machine is particularly suitable for use as a mechanical vacuum pump utilizing a solid sealing ring or sleeve instead of oil or other fluid lubricant.

A four cylinder pump having a pair of parallel connected high vacuum cylinders connected in series with a medium vacuum cylinder and a low vacuum cylinder has the advantage that it is particularly suitable and suitable for a well-balanced construction. Have.

In the conventional pump, the connection between these stages is made by the closed passage and the conduit exposed to the outside. In particular, each working cylinder has two cylinders.
Due to the individual operating spaces, it was not easy to move these connections to the internal port and duct system arrangements.

US Pat. No. 4,560,327 describes
A plurality of passages extend vertically in the cylinder wall and communicate with the inside of the cylinder through the respective ports.
An arrangement of port and duct systems for a pair of adjacent cylinders of a multi-stage vacuum pump is disclosed.

A plurality of recesses in the form of curved depressions may be located at the cylinder wall ends or the cylinder head bottom surface aligned with respect to the passage or passages, and also for the supply of liquid into the cylinder or from inside the cylinder. A suitable opening is provided in the cylinder head in communication with the recess for draining the liquid.

Further, US Pat. No. 4,790,726 describes a reciprocating piston / cylinder machine adapted to be used as an oil-free vacuum pump. The vacuum pump disclosed in this specification has a first closed end.
A cylinder having a cylinder portion and a second cylinder portion adjacent to the first cylinder portion but having a smaller diameter; and a piston head portion slidable within the first cylinder portion; A piston having a slidable second cylindrical piston portion within the cylinder portion, the piston head portion having a leading end surface facing the closed end surface of the cylinder and an annular trailing end surface.

A gas inlet is provided between the tip of the piston head portion and the closed end of the cylinder when the piston reciprocates in order to introduce gas into the first cylinder portion.

A first discharge port is provided for discharging gas from the inside of the first cylinder portion in front of the piston head portion by the pump (exhaust) action in front of the piston head portion, and this first discharge port is provided. The port is provided with a one-way valve. The one-way valve is operable to discharge gas from the interior of the first cylinder portion in front of the piston head portion, and also to the rear of the piston head portion by pumping the rear surface of the piston head portion. A second exhaust port is provided for exhausting gas from within a first cylinder portion.

The piston head portion is provided with an airtight means which includes a sleeve of low friction material located on the cylindrical surface of the piston and which is exposed to temperatures encountered during normal operation of the pump. Throughout the range, gas leaks through the sleeve remain at a level of acceptable vacuum that is maintained by the pump, even with the slightest gap.

The second piston portion is also provided with a sleeve, and elastic means is provided adjacent the sleeve end remote from the first piston portion for sliding the sleeve onto the inner peripheral surface of the cylinder wall. Is provided.

Furthermore, the one-way valve arranged in the discharge port is provided with a projection adapted to engage with the piston for opening the valve of the discharge port, and the pressure in the cylinder is too low, for example. Each stroke of the piston can be controlled even if the valve cannot be opened against the pressure of the spring that presses the valve into its normally closed position.

In US Pat. No. 4,854,825,
Disclosed is an oil-free multi-stage vacuum pump having a cylinder, a crankcase and a passage formed by one-time casting, in which two pairs of cylinders of a crankshaft supporting means extending in a longitudinal direction of a cylinder axis. They are located on opposite sides of the shaft, generally in the same plane, facing each other. Each cylinder is provided with a large diameter portion adjacent the cylinder head and a small diameter portion adjacent the crankshaft axis.
A step piston is mounted on each sleeve so as to reciprocate, and is connected to a crankshaft so as to rotate in a crankcase.

The pair of piston and cylinder assemblies are
While considered to be the high pressure exhaust assembly, the other pair of piston and cylinder assemblies is considered to be the low pressure exhaust assembly.

While such vacuum pumps can provide extremely low pressures, the four piston and cylinder assembly requires significantly greater pump size and weight, and the noise level is too high. Moreover, such multi-stage vacuum pumps are very complex in construction, require too many parts and are too expensive.

One special feature of the multi-stage vacuum pump with great difficulty is that it requires four atmospheric pressure seals. Since this pump requires four pistons for operation, each piston is provided with a flexible seal in its small diameter section to prevent atmospheric pressure air from leaking into the working part of the pump. It is important to prevent atmospheric pressure air from leaking into or out of the pump.

Not only can air leak into the pump, but exhaust gases may also leak out of the pump, especially during the fourth compression stage when the pressure inside the pump exceeds atmospheric pressure. The same can occur in all cylinders while operating at high pressure, i.e. when evacuating the vessel from atmospheric pressure.

[0019]

SUMMARY OF THE INVENTION According to the present invention, there is provided a new and improved oil-free multi-stage vacuum pump in which the various drawbacks of the prior art pumps are eliminated.

Also according to the invention, there is only a single assembly of pistons and cylinders having a large diameter central portion, this end and both sides of the large diameter central portion providing three compression stages. , A new and improved oil-free multi-stage vacuum pump is provided in which these stages can operate in different modes in succession in at least three different ways.

Further in accordance with the present invention, there is a new and improved, single piston-cylinder assembly in which the inlet passages for the cylinder and each stage are formed in the casting that forms the housing of the pump. An oil-free multi-stage vacuum pump is provided.

According to the invention, there is also provided a single piston-cylinder assembly, the valve body means having a spring-clamped valve assembly and an opening smaller than the spring-clamped valve assembly. A solenoid valve or mechanical valve assembly arranged in parallel at the outlet of the first stage;
And an oil-free multi-stage vacuum pump including at least one valve assembly located at the outlet of the third stage, which may be either a spring-loaded valve assembly or a solenoid valve assembly. Will be provided.

Further in accordance with the present invention, there is provided a single assembly of a drive unit having a motor driven crankshaft within a cast aluminum housing and a multi-stage piston-cylinder operatively connected to said crankshaft. The drive unit housing is provided with a sealing means and a one-way valve connected to one stage of the exhaust unit for keeping the inside of the drive unit housing at atmospheric pressure or less. And the drive unit includes means for connecting an additional drive unit and integral internal passage means formed in the drive unit housing for communicating a plurality of exhaust units with each other. New and improved oil-free multi-stage vacuum pumps included There is provided.

Also according to the invention, it has at least two exhaust units connected to a common drive unit,
This evacuation unit provides a new and improved oil-free multi-stage vacuum pump, which is connected in series or in parallel to provide different evacuation capacities.

Further in accordance with the invention, there is a single piston and cylinder assembly with valves for controlling the individual stages of the pump, each valve being incorporated within a cylindrical cartridge. Provides a new and improved oil-free multi-stage vacuum pump that is inserted into the end faces of the housing parts upon interconnection to facilitate assembly of the pump and replacement of individual valve assemblies.

The above and other objects, features and advantages of the present invention will be made clear by the following more detailed description of the preferred embodiments of the present invention shown in the accompanying drawings.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENT A vacuum pump 10 whose outline is shown in FIG.
Is a drive unit 12 and two exhaust units 1 provided on opposite side surfaces of the drive unit 12.
4, 16 are mainly configured. The drive unit (module) 12 is an electric motor 20 having a drive shaft 22.
It includes a housing 18 that accommodates. The housing 18 is fixed to a drive housing 24, and the drive unit 24 has the exhaust unit (module).
14 and 16 are fixed.

A crankshaft 26 is rotatably supported by bearings 28 and 30 in the drive housing 24. This crankshaft 26
One end of the drive housing 24 extends through the peripheral wall 32 of the drive housing 24 and is sealed by the sealing material 34.
4 is hermetically sealed. The drive shaft 22 of the motor 20 is connected to the crankshaft 26 via a coupling 36.

In FIG. 1, two exhaust units 14 and 16 are shown.
However, only one exhaust unit may be used, or four exhaust units may be attached to the drive unit 12 so that a common motor 20 operates. .

As shown in FIG. 1, a pair of piston rods 38, 40 are connected to the crankshaft 26 at their base ends, and exhaust units 14, 16 schematically shown at the tips of the piston rods 38, 40. The pistons 42 and 44 respectively arranged inside are connected.

The drive housing 24 is made of cast aluminum material and has a respective exhaust unit 14,
A pair of integral passageways 46, 48 are provided to provide inlet and outlet passageways for 16. Appropriate inlet and outlet fittings (not shown) are connected to the passages 46, 48 for connecting to the device to be evacuated and to the appropriate vessel when accompanied by atmospheric or toxic gases. Such fittings extend through the cover or peripheral wall of the drive housing 24 so that fluid flows within the respective passages 46,48.

Each of the exhaust units 14 and 16 is an oil-free multi-stage vacuum pump, and since these exhaust units have the same structure, the exhaust unit 1 will be described below.
4 will be described in detail.

As shown in FIGS. 2-6, the exhaust unit 14 is coupled to the drive unit 12 by any suitable means (not shown) and is integrally formed with the different diameter cylinder during the casting process. It comprises a cast aluminum cylinder housing 50 having 52 and three passages 54, 56 and 58 which are parallel to this cylinder 52.

The relative position of the cylinder 52 and each of the passages 54, 56 and 58 is best shown in FIGS. 2, 5 and 6. The cylinder 52 is provided with two end portions 60 and 62 having substantially the same diameter at both ends thereof, and one end portion 62 has one end portion 62 for the drive housing 2 of the drive unit 12.
4 is located in the cylindrical protrusion 68. The cylindrical protrusion 68 projects into the drive housing 24 of the drive unit 12, as shown in FIG.

A similar cylindrical projection 69 is also formed on the opposite peripheral wall of the drive housing 24, and this cylindrical projection 69 is exhausted with respect to a second exhaust unit, for example the drive unit 12 shown in FIG. A part of the cylinder of the exhaust unit 16 installed on the opposite side of the unit 14 is formed.

Since the inside of the drive unit 12 must be kept under atmospheric pressure, in order to hermetically seal the inside, the opening 47 of the cylindrical protrusion 69 is covered with a suitable cover 49 to cover the lid. You can also do it.

The cylinder 52 has small-diameter end portions 60, 6
A central portion 70 having a diameter larger than those of the end portions 60 and 62 is provided in the middle of 2. The exhaust unit 14 has a hollow piston 42 having cylindrical ends 72,74 of approximately equal diameter and an intermediate portion 76 having a larger diameter than the ends 72,74.

The entire cylindrical surface of the piston 42 is covered with a low wear material 78 having a small friction coefficient. As the low wear material (coating material) 78, a material that does not cause any mechanical interference with the wall surface of the cylinder 52 even if the piston 42 expands is selected. The low wear material 78, the piston 42, and the cylinder housing 50 have the same expansion coefficient.

Piston 42 and cylinder housing 50
May be made of aluminum or other material such as stainless steel that can be used for pistons. The low wear material 78 is
It may be similar to that disclosed in U.S. Pat. No. 4,790,726 using a bronze filled polytetrafluoroethylene (PTFE) sleeve, and the filler used to reduce wear may be of another type. Anything is fine. As in this patent, a layer of low friction, low wear material on the cylindrical surface of the piston maintains a slight gap between the sleeve and the cylinder over the temperature range encountered during normal operation of the pump. However, this gap is at a level at which the leakage of gas through the sleeve is at a maximum corresponding to the degree of vacuum that the pump must hold.

A cup-shaped contact seal (sealing means) 80 made of similar material is provided on the cylindrical end 7 of the piston 42.
It is fixed to the end of No. 4 to prevent high pressure gas in the drive unit 12 from entering the working space of the pump.

The cylinder housing 50 is composed of two castings 51 and 53 separated from each other and an intermediate valve plate 55. These three parts 51, 53, 55
Are secured to each other by suitable means (not shown).

The main inlet passage (first passage) 54 of the pump
Penetrates through the cylinder housing 50 (see FIG. 2).
And FIG. 5). The end face 84 of the inlet passage 54 is shown in FIG.
Inlet passage 11 penetrating the peripheral wall of the drive unit 12 shown in FIG.
5 are arranged so as to communicate with each other, and as will be described later,
It is connected to the inlet that is attached to the exhausted object.

As shown in FIG. 5, the upper end of the inlet passage 54, as best shown in FIG. 2, extends around the small diameter end 60 of the cylinder 52 over a 270 ° circumferential passage. It communicates with the (first passage) 90. Piston 42
Is located at the bottom dead center position (see FIG. 3), the circumferential passage 90 is located above the tip end surface 94 of the piston 42 and is in radial communication with a large number of radial openings (first inlet port).
It is adapted to communicate with the inside of the end portion 60 of the cylinder 52 via 92.

As shown in FIG. 3, the valve plate (closure plate) 1
00 is fixed by any suitable means (not shown) so as to close the upper opening of the cylinder 52, and between the valve plate 100 and the tip end surface 94 of the piston 42,
The first stage exhaust chamber 61 of the multi-stage pump is partitioned and formed.

The valve plate 100 is provided with a pair of valves (first discharge valves) 101 and 103 that allow the gas in the cylinder 52 to pass when the piston 42 moves upward. The one valve 101 may be a solenoid valve, but the other valve 103 is a spring pressure type one-way valve.

A cover plate 99 is airtightly attached to the cylinder housing 50, and an outlet chamber 97 is defined between the cover plate 99 and the valve plate 100. The outlet chamber 97 communicates with the passage 58 of the cylinder housing 50 through the lateral passage 96.
As best shown in FIGS. 2 and 6, this passage (second passage) 58 constitutes the discharge passage of the first stage and the inlet passage of the second stage.

The passage 58, together with the lateral passage (second passage) 96 communicating with the outlet chamber 97, has a volume substantially equivalent to that of the first stage exhaust chamber 61 in order to minimize the accumulation of internal pressure. Is configured. This passage 58
Is also connected to the high pressure outlet via a one way valve 102 located in the drive unit 12 shown in FIG.

The passage 58 passes through a substantially arc-shaped passage (second passage) 59 (see FIGS. 2 and 6), and through a large number of openings (second inlet ports) 98, the center of the large diameter of the cylinder 52. It is connected to the part 70. The opening 98 is arranged along a cylindrical line located above the large-diameter intermediate portion 76 of the piston 42 when the piston 42 is at its bottom dead center position (see FIG. 3). The space above the middle portion 76 of the piston 42 and limited to the annular shape is the second stage exhaust chamber 63 of the multi-stage pump.

When the piston 42 moves from the bottom dead center position to the top dead center position, the opening 98 is closed and the gas in the second stage exhaust chamber 63 is fixed between the castings 51 and 53. It is forcibly discharged outward through a one-way valve (second discharge valve) 108 arranged in the valve plate 55.

Then, the gas is a spring pressure type one-way valve 1
08, and a passage extending parallel to the cylinder 52 (the third
It enters into a lateral passage (third passage) 109 connected to the passage 56. The lower end of the passage 56 communicates with a lateral passage (third passage) 57 that extends in the range of about 90 ° around the cylinder 52, as best shown in FIGS. 2 and 6.

The passage 57 is exposed when the piston 42 reaches the top dead center position (see FIG. 4) and has a large number of openings (third inlet port) 104 arranged radially on the circumferential line.
It communicates with the inside of the central portion 70 of the cylinder 52 via. As a result, the gas expelled from the second stage exhaust chamber 63 of the multi-stage pump is partitioned by the space between the large-diameter intermediate portion 76 of the piston 42 and the peripheral wall of the drive housing 24 of the drive unit 12. Enter the third stage exhaust chamber 65.

When the piston 42 moves upward from the bottom dead center position in FIG. 3 to the top dead center position in FIG. 4, the pressure in the third stage exhaust chamber 65 decreases, and the higher pressure gas in the drive unit 12 is discharged. In response, the one-way valve 114 is opened so that the gas in the drive unit 12 passes through the opening 116 and enters the third stage exhaust chamber 65, thereby maintaining the inside of the drive unit 12 at atmospheric pressure or lower. To be done.

As shown in FIG. 7, when the piston 42 moves from the top dead center position to the bottom dead center position, a spring pressure type one-way valve (third exhaust valve) 11 mounted inside the drive unit 12 is provided.
The gas in the third stage exhaust chamber 65 is expelled via the exhaust port (second port) 113 controlled by 0. Therefore, the pressure in the container to be evacuated connected to the inlet 126 of the drive unit 12 decreases due to the evacuating operation performed by the three stage evacuating chambers 61, 63, 65 of the multi-stage pump.

The normal arrangement of the drive unit 12 is shown in FIG. A lower chamber (first chamber) 152 for installing a drive mechanism that connects the motor 20 to the piston 42 is defined by the vertical partition wall 150. The opening 116 of the drive unit 12 provided in the peripheral wall 154 is controlled by a spring pressure type one-way valve 114 as shown in FIG.

As mentioned above, the crankshaft 26 is
It penetrates through the peripheral wall 32 of the drive unit 12 while being hermetically sealed by a sealing material 34. Therefore, even if the pressure in the lower chamber 152 is reduced as a result of the exhaust operation, it slides in the end portion 62 of the cylinder 52 in the cylindrical protrusion 68 (see FIG. 3) that enters the drive unit 12. Contact seal 8 fixed to the lower end of the cylindrical end portion 74 of the piston 42
0 reduces gas passage.

As shown in FIG. 7, the upper space of the drive housing 24 is divided by partition walls 143, 145 into three separate chambers 140, 142, 144. The drive unit 12 includes a cover 120 shown in FIG. 8, which is airtightly attached to the upper surface of the drive housing 24 by using a sealing material 122 that is provided around the entire periphery of the cover 120.

The similar sealing material 122 can be used for joining the upper surfaces of the partition walls 143 and 145 to the cover 120. This allows the three chambers 140, 142, 144 to be hermetically sealed to one another by fixing the cover 120 to the drive housing 24 by any suitable means (not shown).

In order to connect any device using a multi-stage vacuum pump so that any device can be evacuated,
A metal fitting 124 is fixed to the upper surface of the cover 120,
The inlet 126 penetrates the inside of the metal fitting 124 and the cover 120 and communicates with a Z-shaped chamber (second chamber) 140 shown in FIG. 7, which allows gas to pass through the first stage exhaust chamber 6
It communicates with the inlet passage 54 provided in the cylinder housing 50 of the exhaust unit 14 which leads to 1.

The exhaust port (first port) 111 of the first stage exhaust chamber provided in the drive housing 24 so as to communicate with the passage 58 inside the exhaust unit 14 is also inside the chamber (third chamber) 142. Installed spring crimp type one-way valve 10
2 communicates with the inside of the chamber 142.

The discharge port 113 of the third stage exhaust chamber provided in the drive housing 24 communicates with the third stage exhaust chamber 65 and also with the chamber 142 whose opening and closing is controlled by the spring pressure type one-way valve 110. is doing. Therefore, room 1
Reference numeral 42 denotes one discharge chamber, which is connected to the atmosphere via outlet passages 136, 132, and 130 as shown in FIGS. 7 and 8.

In order to locate the small diameter end of the piston inside the cylindrical protrusion 69 shown in FIG. 7, as shown in FIG.
If the second exhaust unit 16 is installed, the chamber (the third chamber)
144 also functions as an exhaust chamber, and the gas therein is also exhausted to the atmosphere via the outlet passages 134, 132, 130.
At this time, it is necessary to form the discharge ports 111, 113 and the inlet passage 115, which communicate with the chamber 144, on the peripheral wall provided with the cylindrical protrusion 69.

During operation, the cover 12 of the drive unit 12
When a container to be evacuated is connected to the metal fitting 124 above the gas, the gas enters the main inlet passage 54 in the drive unit 14 via the inlet 126, the chamber 140 and the inlet passage 115. Gas is
Then, when the piston 42 is near the bottom dead center, the opening (first inlet port) 92 arranged on the outer periphery of the cylinder 52 is provided.
And enters the compression space of the first stage exhaust chamber 61.

When the piston 42 moves away from the bottom dead center position shown in FIG. 3, the gas already in the compression space of the first stage exhaust chamber 61 reaches a high pressure and the solenoid operated valve 101
It is expelled to the outside of the first stage exhaust chamber 61 via either one of the spring compression type one-way valves 103 (first exhaust valve).

Then, the gas is discharged from the outlet chamber 97, the passage 96,
An opening (second inlet port) 98 exposed when the piston 42 is at the bottom dead center position by sequentially passing through the passage 58 and the passage 59.
Is transferred to the second stage exhaust chamber 63 via.

The gas in the second stage exhaust chamber 63 passes through the one-way valve (second exhaust valve) 108 and is expelled to the outside, and sequentially passes through the passage 109, the passage 56 and the passage 57,
As the piston 42 approaches the top dead center position shown in FIG. 4, it enters the third stage exhaust chamber 65 via the opening (third inlet port) 104 exposed. Third stage exhaust chamber 65
The gas therein passes through the one-way valve 110 (third discharge valve), is expelled from here, enters the chamber 142 of the drive unit 12, and is then discharged to the atmosphere from there.

If the gas is toxic, we would like to collect it in another container. Contact seal 80 fixed to the lower end of piston 42
If there is any gas leaking through the exhaust gas, it also enters the third stage exhaust chamber 65 and is expelled in the same manner.

Similarly, the pressure in the lower chamber 152 decreases while the piston 42 moves from the bottom dead center position to the top dead center position,
At that time, the pressure in the third stage exhaust chamber 65 is also lowered to open the one-way valve 114. Then, the gas passes through the one-way valve 114 and flows into the third stage exhaust chamber 65, and the pressure in the drive unit 12 is about 1/10 of the atmospheric pressure.
Fall to.

Since the pressure in the drive unit 12 is not so low, heat is prevented from being transferred by gas (convection) from the internal mechanism of the drive unit 12 and the exhaust unit 14 to the wall or surface of the aluminum housing. I can't.

The solenoid valve 101 for controlling the gas discharge from the first stage exhaust chamber 61 is normally spring-compressed in the closed position and has a relatively small opening with a diameter of about 1/16 inch (about 1.6 mm). is doing. Spring crimp type one-way valve 10
3 has an opening area about 100 times that of the solenoid valve. When the spring pressure type one-way valve 103 operates in the initial stage of exhaust, high-pressure gas from the first stage exhaust chamber 61 passes through the passage 58 and from the one-way valve 102 to the exhaust chamber 142 of the drive unit 12 and the first stage exhaust chamber 142. It flows into the two-stage exhaust chamber 65.

In order to secure the opening of the passage between the first stage exhaust chamber 61 and the second stage exhaust chamber 63 when the pressure gradually decreases as the piston 42 reciprocates.
A solenoid valve 103 is used. This solenoid valve 103
The piston 42 is opened before reaching the top dead center and closed before descending.

The outlet passages from the second stage exhaust chamber 63 and the third stage exhaust chamber 65 are connected to the normally closed spring pressure type one-way valve (shown) or the outlet of the first stage exhaust chamber 61. It can be controlled by either of the valve combinations similar to those described above.

In the operation of the dry multi-stage vacuum pump described above, the sliding speed (V) of the piston is 300 ft / min.
It is controlled to (1.5 m / s). The exhaust speed of the complete exhaust unit is 100 liters / min at the ultimate pressure of 20 mTorr. Considering the actual deterioration, the ultimate pressure is much lower than 20 mTorr at the new time.

As the motor 20 in the drive unit 12, a commonly available 1800 rpm motor can be used. The stroke of the piston 42 is preferably set to 25.4 mm or more in order to obtain sufficient compression in the high vacuum stage.

It is desirable to minimize the weight of the piston and related mechanical parts involved in consideration of vibration, noise and energy. To this end, it is important to make the piston as small as possible while preventing an abnormal increase in rotation speed.

As explained above, one piston having both narrow ends and a thick central part divides the space inside the cylinder into three compression spaces or stages which can be connected in three different ways. .

As shown schematically in FIGS. 2 to 6 and FIG. 10, all the first to third stage exhaust chambers can be continuously connected. Further, as schematically shown in FIG. 11, the first-stage exhaust chamber and the second-stage exhaust chamber are connected in parallel, and the third-stage exhaust chamber is continuously connected to the first-stage exhaust chamber and the second-stage exhaust chamber. As shown in
It is also possible to connect all of the third stage exhaust chambers to in parallel.

By changing the position and connection of the passages in the exhaust unit, different connections of stages can easily be achieved during the manufacture of the exhaust unit. If the first-stage exhaust chamber and the second-stage exhaust chamber are parallel to each other and continuously connected to the third-stage exhaust chamber, this multi-stage pump will be a pump with a medium exhaust speed and a medium ultimate pressure. It becomes possible to drive as. If all the stage exhaust chambers are connected in series, the pump can be operated at a low exhaust rate to a very good ultimate pressure. If the three stage exhaust chambers are connected in parallel, they can be operated at high exhaust speed and high pressure.

The above embodiment (first embodiment) shows an example in which a single exhaust unit is connected to the drive unit.
The following embodiments shown in FIGS. 13 to 20 show an example in which two exhaust units are connected to the same drive unit as described above.

As shown in FIG. 13, the multi-pump assembly is provided with a first exhaust unit 202 and a second exhaust unit 204 which are mounted opposite to each other. The motor unit 20 is provided on one side of the drive unit 200.
6 is detachably attached to the motor unit 20.
6 has two splines 214 and 216 interposed therebetween,
An electric motor M having a drive shaft 208 connected to a crankshaft 210 via a coupling unit 212 fixed to one shaft is provided.

The crankshaft 210 is rotatably mounted in the drive unit 200 via bearings 218 and 220. In addition, the crankshaft 210,
Two crank pins 2 that are 180 degrees out of phase with each other
22, 224 are provided.

The exhaust units 202 and 204 have the same structure, and in some respects are almost the same as the exhaust unit 14 shown in the above embodiment. The exhaust unit 202 is mainly composed of two castings 226 and 228 having a large number of fins extending in the circumferential direction for air cooling. These castings can be made of aluminum or other suitable material.

The casting 226 has a small first cylindrical hole (end portion of the cylinder) 230 for reciprocating the piston 242.
And a stepped cylindrical hole having a large-diameter second cylindrical hole (recess) 232 for accommodating a cartridge valve 234 described later.

The other casting 228 is provided with a cylindrical hole (center portion of the cylinder) 236 having a diameter larger than that of the cylindrical hole 230 provided in the casting 226. The casting 238 forms the housing of the drive unit 200,
A cylindrical hole (end of the cylinder) 240 having substantially the same diameter as the cylindrical portion 230 provided in the casting 226 is provided.

In this way, the three cylindrical holes 230,
236 and 240 form a different diameter cylinder similar to the different diameter cylinder 52 of the first embodiment, and the piston 242 is additionally received therein.

The two castings 226 and 228 are connected to each other by an appropriate means with the sealing ring 244 interposed therebetween.
While interposing 48, it is connected to the housing 238 of the drive unit 200 by an appropriate means such as bolts.

The piston 242 is a recessed piston similar to the above-described embodiment, and has two cylindrical end portions 250 and 2 having the same diameter.
52 and an intermediate portion 254 having a larger diameter than that.
Similar to the above embodiment, the entire cylindrical surface of the piston 242 is covered with a low wear material having a small friction coefficient. This material is selected so that no mechanical interference with the wall of the cylinder occurs when the piston expands. The low wear material (coating material), the piston and the cylinder housing have the same expansion coefficient.

Piston 242 and castings 226, 228, 2
38 is made of aluminum or other material. The coating material is polytetrafluoroethylene (PTF) filled with bronze.
It may be similar to that disclosed in U.S. Pat. No. 4,790,726 using a sleeve made from E). Fillers used to reduce wear may be of other types.

The layer of low friction, low wear material provided on the circumferential surface of the piston ensures that a slight gap is maintained between the sleeve and the cylinder over the temperature range encountered during normal operation of the pump. However, this gap is at a level where at most the leakage of gas through the sleeve corresponds to the permissible vacuum that the pump must hold.

One of the cylindrical ends 252 of the piston 242 slidably arranged in the cylindrical hole 240 of the drive unit 200 is provided with a cap-shaped contact seal 256, as best shown in FIG. The contact seal 256 is biased outwardly by an appropriately sized O-ring 258 to press against the surface of the cylindrical bore 240. The cap-shaped contact seal 256 is attached to the end of the cylindrical end 252 of the piston 242 by a threaded sleeve 260 having a lower flange 262.

The other cylindrical end 252 of the piston 242
A lateral hole 264 for accommodating a hollow cylindrical wrist pin 266 fixed by pressure fitting is provided in the. A pair of step-shaped closing members 268 having an O-ring 270 arranged in the central small-diameter portion is used to press-fit the wrist pin 266.
Side holes 26 of the cylindrical ends 252 of the piston 242 on both sides of the
It is fixed in 4.

The piston 242 is the offset connector 2
Through the bearing 276 interposed with the crank pin 22.
4 is connected to the crankshaft 210 by a cylindrical piston rod 272 connected to the shaft 4. As a result, the piston rod 272 of the exhaust unit 202 and the piston rod of the exhaust unit 204 are arranged in a substantially straight line. The crank pin 222 is connected to the crank pin 222 via the bearing 280.

By arranging in this way, it is possible to balance the device and reduce vibration. A short hollow sleeve 282 is secured to the upper end of piston rod 272 across the rod 272. The sleeve 282 is integrally cast with the piston rod 272 or formed separately from the piston rod 272 depending on the material, and is fixed by welding or other appropriate means.

A bearing sleeve 284 is disposed between the sleeve 282 and the rest pin 266, and the piston 242
A rest pin 266 and a piston rod 272 fixed to the cylindrical end portion 250 of the above are rotatably connected to each other. To achieve this rotatable connection, the piston 25
A suitable recess 286 is provided at the upper end of 0. As schematically shown by a broken line 288, the hollow inside of the rest pin 266 and the hollow inside of the piston rod 272 are configured to communicate with each other.

The cartridge valve 234 is the same as the first stage of the first embodiment, but the exhaust valve (first stage) of the first stage is used.
Exhaust valve). In the first embodiment, the solenoid valve 101 and the spring pressure type one-way valve 103 are the first
It is provided in a valve plate 100 that divides the stage. In this embodiment, the cartridge valve 234 is the first
It replaces the valve plate, cover plate and two valves in the example.

As shown in FIG. 13, a cartridge valve 234 is fitted in a cylindrical hole (recess) 232 and is fixed by a large number of bolts 233 (only one is shown in FIG. 13).

The details of the cartridge valve 234 are shown enlarged in FIG. The cartridge valve 234 has a large number of through holes 2
A hollow cylindrical sleeve 290 having 92 is provided. The first end plate 294 is integrally connected to the cylindrical sleeve 290, and the end plate 294 is provided with an umbrella-shaped valve seat 296. The second end plate 298 is also the same as the cylindrical sleeve 2
The end plate 298 is integrally connected to the plate 90 and is provided with a laterally extending flange provided with a hole for accommodating the mounting bolt 233.

The hollow cylindrical protrusion 300 extends downward from the center of the end plate 298, and the valve rod 302 of the valve body 304 is slidably fitted inside the protrusion 300 by the spline 305.

Almost the entire lower end surface of the valve body 304 is covered with the vinyl rubber molding 306, and the pressure in the first stage overcomes the elastic force of the spring 310 that presses the valve body 304 against the valve seat 296. Piston 242 when not present
The lower end surface of the valve body 304 is provided with a large number of projections or circumferential projections 308 that engage with the end surface of the valve body to open the valve.

Cylindrical recess 23 provided in casting 226
A pair of O-rings 312 are provided inside the container 2 to hermetically seal the cartridge valve 234. Such a cartridge valve 234 is pre-assembled to facilitate final assembly of the pump and facilitates valve replacement at any time during the life of the pump.

As in the previous embodiment, each exhaust unit 202, 204 of the embodiment shown in FIG. 13 is provided with three stages at the same positions as the three stages in the first embodiment. The connection between the inlet, the outlet and each stage is almost the same as in the first embodiment.
Of course, the types of valves used to control the various stages can be used.

As described above, the cartridge valve 234
Are used to control the exhaust of the first stage. The entrance of the first stage is similar to the first passages 54, 90, 92 shown in FIG. 5 of the first embodiment. However, instead of multiple apertures 92, a series of slits (not shown) are used, which slits are easier to fabricate than apertures 92.

FIG. 15 and FIG. 1 which are sectional views of the second embodiment.
The inlet passage 312 shown in FIG. 6 and FIG. 17 corresponds to the passage 54 shown in FIG. This inlet passage 312 is shown in FIG.
Is connected to a circumferentially extending passage 314 corresponding to the passage 90.

The passage 316 shown in FIGS. 15 and 16 constitutes a first stage exhaust passage (second passage) which is also connected to the second stage outlet 318. First stage exhaust passage 316
The second stage inlet passage 318 is shown in FIG. 2 of the first embodiment.
The first stage exhaust chamber passage 58 and the second stage inlet passage 59 of the embodiment shown in FIG. 6 are substantially the same.

The second stage inlet passage 318 communicates with the second stage through slits (not shown) or multiple openings as shown at 98 in FIG. The first stage outlet passage 316 communicates with the discharge chamber 320 of the drive unit 200 similar to the discharge chamber 142 shown in FIG. 7 of the first embodiment. Passage 32 that constitutes the third stage exhaust passage
2 is also connected to the discharge chamber 320 shown in FIG.

The passage 324 shown in FIG. 16 corresponds to the passage 56 connecting the second stage outlet and the third stage inlet shown in FIG. 6 of the first embodiment. However, in this embodiment, two identical exhaust valves 326, 328 are provided for the second stage instead of the one way valve 108 shown in FIG. 6 of the first embodiment.

The two exhaust valves 326 and 328 are shown in FIG.
Is connected to a passage 324 via a chamber (passage) 330 corresponding to the passage 109 shown in FIG. The other end of the passage 324 is
The opening 10 shown in the third stage of FIG. 6 of the first embodiment.
It is connected to the entrance opening or slit of the third stage corresponding to No. 4. A passage having substantially the same shape as the passage 330 but arranged straight and continuous in FIG. 16 is provided for connecting to the lower end of the passage 324 together with the opening of the third stage. Such a passage corresponds to or is substantially the same as the passage 57 of the first embodiment.

The exhaust valves 326 and 328 are drop-in cartridge valves similar to the cartridge valve 234 shown in FIG. However, this cartridge valve 326
As shown in FIG. 19 in detail, a hollow cylindrical sleeve 332 having an opening 334 on the end face is provided therein.
The valve body 336 is covered with a vinyl rubber molding and is slidably connected to the spring receiving plate 340 by a valve rod spline connector 342.

The valve body 336 and the spring receiving plate 340 are inserted into the sleeve 332, and the circular clip 344 prevents the valve body 336 and the spring receiving plate 340 from coming out of the sleeve 332. Disc 3
36 and a spring receiving plate 340, a coil spring 346 for constantly urging the valve body 336 outward is interposed, and the coil spring 346 locks the valve 336 to a valve seat around the opening 334. It is like this.

FIG. 13 shows one second stage exhaust valve 3
No. 26 is shown, the exhaust valves 326 and 328 are
The castings 226, 228 are quickly dropped into the opening of the casting 226 before they are connected to each other.

The third stage exhaust valve 350 shown in FIG. 13 is also a drop type cartridge valve similar to the cartridge valves 326 and 328, and the drive unit 200.
Before connecting the exhaust unit 202 to the drive unit 2
00 casting 238 into a suitable opening.

A valve similar to the discharge valve 350 is provided at the end of the first stage passage 316 reaching the discharge chamber 320 of the drive unit 200. In the exhaust chamber 320,
As shown in FIG. 15, an external metal fitting 321 is provided, and this metal fitting 321 is suitable for collecting the exhaust gas from the first and third stages even if the exhaust gas contains toxic elements. It is designed to be connected to a container.

As shown in FIG. 15, the inlet passage 312 is
It communicates with an inlet chamber 313 formed in the housing 238 of the drive unit 200. This entrance chamber 313 is the first
This corresponds to the inlet chamber 140 shown in FIG. 7 of the embodiment.

An inlet fitting 32 similar to the outlet fitting 322
3 is provided in the housing 238 and communicates with the inlet chamber 313 by a method not shown. The inlet fitting 323 is
It can be connected to any container to be evacuated.

As shown in FIG. 14, the third stage of the exhaust unit 202 communicates with the inside of the housing 238 of the drive unit 200 by a one-way valve 360 which is constantly biased to a closed position by a spring 368. The plate 362 is fixed to the lower end of the valve rod 364 by the screw 366, and the spring 3
68 is interposed between the housing 238 and the plate 362, and the valve 360 is urged to engage with a valve seat formed in the housing 238.

This valve 360 corresponds to the valve 114 shown in FIG. 4 of the first embodiment, and this valve 360
Allows the gas to flow into the third stage, which causes the pressure in the drive unit 200 to be about 1/1 atmospheric pressure.
Drop to zero.

Since the pressure in the drive unit is not so low, it is not possible to prevent heat from being transferred by gas from the internal mechanism of the drive unit and the exhaust unit to the wall or surface of the aluminum housing.

Housing 238 of drive unit 200
As shown in FIG. 13, a seal 370 is interposed between the bearing support 372 and the crankshaft 210, and an O is interposed between the housing 238 and the bearing support 372.
Airtightness is maintained by the ring 374.

Inside the housing 238 is the piston 242.
Communicates with the inside of. Cap-shaped contact seal 256
Seals between the end 240 of the cylinder and the lower end of the piston 242, and the upper end of the piston 242 has the rest pin 2
Seals 270 are sealed at both ends of 66.

The gas leaking inside the cylinder or inside the drive unit housing 238 raises the pressure, but the pressure is gradually lowered by the provision of the one-way valve 360 and the exhaust operation of the pump. As a result, even if the gas leaking into the piston 242 or the housing 238 is any toxic substance, this substance is discharged from the valve 360 to the third stage, and the third stage exhaust valve 350 and the exhaust fitting 3 are discharged.
It is discharged from 21 into a container.

In addition to the continuous interconnection of the respective stages of the pumps, the pumps shown in FIGS. 10 to 12, including those shown in FIGS. 10 to 12, may be connected in parallel or in combination.
The two pumps are connected for continuous or parallel operation with each other.

As shown in FIG. 7 of the first embodiment, the inlet chamber 140 of the drive unit 12 extends in zigzag from one corner of the unit to the other, and when the second exhaust unit is connected, each exhaust The entrance of the unit is the drive unit 12
Connected to a common entrance chamber 140. FIG. 7 shows two separate discharge chambers 142, 144, with the pumps operating in parallel with each other when the chambers are so arranged. Similarly, as shown in FIG. 15, the inlet chamber 31 of each exhaust unit
When three are interconnected, two exhaust units 20
2, 204 operate in parallel.

In order to continuously operate the exhaust units 202 and 204, it is necessary to interconnect the exhaust chamber 320 shown in FIG. 15 with the inlet chamber corresponding to the inlet chamber 313, but for other exhaust units. Associated with the entrance room of the. In this way, the exhaust chamber of one exhaust unit
The two exhaust units are connected in series by being connected to the outlet chamber of another pump unit.

When the two exhaust units are combined into a single drive unit and operated sequentially as described above, one
The sufficient ultimate pressure as a result of maintaining the exhaust speed of 00 liter / min is 20 mTorr or less.

As described above, when two exhaust units are connected in parallel, a higher ultimate pressure results, but a pump with an exhaust rate of 200 l / min can be created. The change between a continuous connection and a parallel connection is carried out in the factory, but it is necessary to make a foundry machine that molds the drive unit 200.

Although the preferred embodiments of the present invention have been particularly described, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic plan view of a drive unit in which two exhaust units, which are oil-free multistage vacuum pumps having a single piston / cylinder assembly, are connected.

FIG. 2 is an end view of an exhaust unit.

3 is a cross-sectional view of the exhaust unit taken along the line C-C in FIG. 2 in a state where the piston is at the bottom dead center position.

FIG. 4 is a view corresponding to FIG. 3 with a part thereof omitted, in a state where the piston is at the top dead center position.

5 is a cross-sectional view of the exhaust unit along line BB of FIG. 2 with the piston omitted.

FIG. 6 is a sectional view of the exhaust unit taken along the line AA of FIG.

FIG. 7 is a plan view of an exhaust unit with a cover plate omitted.

FIG. 8 is a side view of a cover plate for the drive unit.

FIG. 9 is an end view of a drive unit with an exhaust unit omitted.

FIG. 10 is a schematic diagram showing a fluid passage between a piston and each of three stages connected in series.

FIG. 11 is a schematic diagram showing a flow path between a piston and each stage in which first and second stages and a third stage that are continuously connected are connected in parallel.

FIG. 12 is a schematic view showing a piston and a flow passage between three stages connected in parallel with each other.

FIG. 13 is a cross-sectional view of another embodiment of the present invention showing two exhaust units connected to a common drive unit and an incorporated cartridge valve.

FIG. 14 is a left side view of the assembly shown in FIG. 13 with the drive unit housing omitted.

FIG. 15 is an end view of a drive unit in which an exhaust unit is omitted.

FIG. 16 is an end view of an exhaust unit in which a first exhaust valve (cartridge valve) is omitted.

FIG. 17 is an end view of an exhaust unit incorporating a first exhaust valve (cartridge valve).

FIG. 18 is a partially enlarged view of the first exhaust valve (cartridge valve).

FIG. 19 is a partially enlarged view of second and third exhaust valves (cartridge valves).

FIG. 20 is a partially enlarged view showing the piston assembly of the exhaust unit.

[Explanation of symbols]

 10 vacuum pump 12,200 drive unit 14, 16, 202, 204 exhaust unit 18 housing 24, 238 drive housing 26, 210 crankshaft 36, 212 coupling 42, 44, 242 piston 50 cylinder housing 52 cylinder 54, 312 passage ( First passage 56,324 Passage (third passage) 57 Passage (third passage) 58,316 Passage (second passage) 59,318 Passage (second passage) 60,62,230,240 Cylinder end portion 61 First stage exhaust chamber 63 Second stage exhaust chamber 65 Third stage exhaust chamber 68,68 Cylindrical protrusion 70,236 Center part of cylinder 72,74,250,252 Cylindrical end of piston 76,254 Middle of piston Part 80, 256 contact seal 90, 314 passage (first Passage 92 Opening (first inlet port) 94 Piston tip end face 96 Passage (second passage) 97 Outlet chamber 98 Opening (second inlet port) 100 Valve plate (blocking plate) 101, 103 Valve (first discharge valve) 104 opening (third inlet port) 108 one-way valve (second discharge valve) 109,330 passage (third passage) 110 one-way valve (third discharge valve) 111 discharge port (first port) 113,322 discharge port (Second port) 115 Inlet passage 126 Inlet 130, 132, 136 Outlet passage 143, 145, 150 Partition wall 140, 313 Chamber (inlet chamber) 142, 144 chamber (exhaust chamber) 152 Lower chamber (first chamber) 234 1st Exhaust valve (cartridge valve) 290 Sleeve 304 Valve body 326, 328 Second exhaust valve (cartridge valve) 332 Sleeve 336 Valve body 340 Spring bearing 350 third exhaust valve (cartridge valve) 360 one-way valve

 ─────────────────────────────────────────────────── —————————————————————————————————————————————— Inventors Eckhard Betz, USA 01863, North Chelmsford, Prescott Drive 83

Claims (12)

[Claims] 1. A cylinder disposed within the housing having a housing, an end having a substantially equal diameter and a central portion having a diameter greater than the end, and a cylindrical end having a substantially equal diameter and a diameter. Is a piston disposed in the cylinder, the first stage exhaust chamber being between the closed end of the cylinder and the end face of the piston. A piston having an axial length shorter than an axial length of the central portion of the cylinder, and partitioning and forming an annular second stage exhaust chamber and an annular third stage exhaust chamber on both sides of the intermediate portion; A first discharge valve provided in the cylinder adjacent to a tip end surface of the piston, an inlet and an outlet installed in the housing, the inlet and the outlet, and the first to third stage exhaust chambers to each other. Communicating A passage, a second and a third discharge valve disposed in the passage adjacent to the second and third stage exhaust chambers, and an operation of the piston for reciprocating the piston in the housing. Multi-stage vacuum pump including: a driving unit that is electrically connected. 2. The multi-stage vacuum pump according to claim 1, wherein the housing is made of cast aluminum, and the passage and the cylinder are integrally molded with the housing. 3. A first passage, wherein the passage constitutes a main inlet passage communicating the inlet with the first stage exhaust chamber, the first discharge valve, a discharge valve arranged in the outlet, and the The multi-stage vacuum pump according to claim 1, further comprising a second passage communicating with the second stage exhaust chamber and a third passage communicating between the second exhaust valve and the third stage exhaust chamber. 4. A first inlet port arranged in the cylinder so as to communicate with the first stage exhaust chamber when the piston reaches the bottom dead center position; and when the piston reaches the bottom dead center position, A second inlet port arranged to connect the second stage exhaust chamber and the second passage, and the third stage exhaust chamber and the third passage when the piston reaches the top dead center position. The multi-stage vacuum pump according to claim 3, further comprising a third inlet port arranged so as to communicate with each other. 5. The housing has a cylinder housing and a drive housing, and the drive housing has a peripheral wall having a cylindrical protrusion that projects into the drive housing and causes the rear end of the piston to reciprocate. A crankshaft that is fixed to the cylinder housing through the rotary housing, is rotatably disposed in the drive housing, and hermetically penetrates the peripheral wall of the housing, and one end of which protrudes outward.
2. The multi-stage vacuum pump according to claim 1, further comprising a connecting means for connecting the crankshaft to the piston, and a motor mounted outside the drive housing and connected to the crankshaft for rotating the crankshaft. 6. The drive housing has four chambers which are hermetically divided from each other by a partition wall, the chambers being the crankshaft, the connecting means and the piston, and the rear end portion of the piston and the chamber. A first chamber working together with a means for sealing the cylindrical projection of the drive housing, an inlet adapted to connect to a container to be evacuated, and a first passage in the cylinder housing on a peripheral wall having the cylindrical projection. Second having an inlet passage provided so as to communicate with each other
A chamber and a common outlet, a second chamber in the cylinder housing
A third chamber and a fourth chamber provided with a first port arranged to communicate with the passage, and a second port arranged to communicate with the third stage exhaust chamber and having a one-way valve;
The multi-stage vacuum pump according to claim 5, comprising: 7. The first exhaust valve is a hollow sleeve having a substantially cylindrical shape, the sleeve having first and second end plates and perforations extending in the sleeve, and the first end plate. An opening formed to define a valve seat, a valve body slidably held by the second end plate, and the valve body interposed between the second end plate and the valve body A cartridge having a spring for constantly urging the cartridge toward the first end plate, the cartridge being disposed in a cylindrical recess formed inside the cylinder adjacent to the tip end face of the piston. The multi-stage vacuum pump according to claim 1, which is provided. 8. The second and third exhaust valves are arranged in a hollow cylindrical sleeve having an opening for defining a valve seat in an end plate, and movably arranged inside the sleeve, and a valve rod is a spring. A valve body slidably held by the receiving plate and having a spring interposed between the spring receiving plate and the sleeve; and for maintaining the spring receiving plate and the valve body in the sleeve. The multi-stage vacuum pump according to claim 1, wherein the multi-stage vacuum pump is configured as a cartridge type provided with means. 9. A multi-stage vacuum pump comprising two identical multi-stage vacuum pump means and drive means operatively connected to each pump means for operating the respective vacuum pump means. The precursor drive means includes a drive unit having a rotatable crankshaft, a motor provided with a drive shaft and a coupling connecting the drive shaft to the crankshaft, and a motor attached to the housing, and the housing and the crankshaft. A first airtight means between the pump means and a second airtight means between the pump means and the driving means; a piston operatively connected to the crankshaft and having a hollow interior communicating with the interior of the housing; The stage of the stage vacuum pump means and the inside of the housing are connected to each other so that the inside of the piston and the housing is Multistage vacuum pump having a one-way valve to substantially decrease the pressure. 10. A multi-pump vacuum pump comprising first and second multi-stage vacuum pump means, and driving means connected to the respective vacuum pump means for simultaneously operating the respective vacuum pump means. The driving means includes a housing having a rotatable crankshaft, and a motor having a driving shaft attached to the housing and connected to the crankshaft, and each pump means has an inlet and an outlet. The housing includes an inlet chamber arranged in communication with each of the inlets of the pump means, and a discharge chamber arranged in communication with each of the outlets, and each of the inlet chambers and each discharge in the housing. A multi-stage vacuum pump provided with an inlet passage and an outlet passage that respectively connect the chamber and the chamber. 11. A multi-stage vacuum pump according to claim 10, wherein a first connecting means is provided between the inlet chambers and a second connecting means is provided between the discharge chambers so that the exhaust means operate in parallel. 12. The exhaust chamber of one vacuum pump means and the inlet chamber of the other vacuum pump means are interconnected with each other, and the exhaust means are connected so as to operate continuously. Multi-stage vacuum pump.