JPH0433997B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to mechanical pumps, and in particular to large, oil-free, high-vacuum, multi-stage vacuum pumps.

In certain industries, such as the food processing industry, air and other gases supplied by mechanical pumps or compressors must be free of oil and particles.

In known oil-free mechanical rotary pumps, a pair of cooperating dynamically balanced rotors having complementary profiles are each mounted within a pump chamber on a corresponding pair of parallel shafts. Each shaft has a timing gear that synchronizes the rotary motion of the rotor.
In use, one shaft is driven by a motor and a timing gear rotates the shaft and associated rotor, thereby pumping fluid from the inlet to the outlet of the pumping chamber.

However, conventional rotary pumps cannot effectively prevent backflow of fluid at the outlet, and such undue backflow of fluid causes problems such as a decrease in pump efficiency.

It is an object of the present invention to provide a multi-stage vacuum pump which is capable of achieving high vacuum without the use of lubricants in the pumping chamber and which is capable of compressing the pumped fluid to at least atmospheric pressure.

According to the invention, a multistage vacuum pump comprises a pump chamber having an inlet and an outlet through which the fluid to be pumped flows, and at least two pairs of rotors extending through the pump chamber and having different contours for rotational movement. the pair of rotors closest to the outlet of the pump chamber; has a claw-shaped profile and the outlet of the pumping chamber is provided with a one-way valve for controlling the flow of fluid to be pumped through the outlet.

Referring first to FIG. 1, a pair of parallel shafts 3
1 shows a known mechanical pump 1 with a pump chamber 2 (only one shown) passing through it; Each shaft 3 supports a rotor 4 rotating together. The rotor 4 has a substantially figure-eight complementary contour, ie, a roots-shaped contour, as shown by the dotted line. At its right end, each shaft 3 carries a timing gear 7 , and at its left end one shaft 3 is driven by a motor 5 via a fluid coupling 6 .

In use, when the motor 5 drives one shaft 3 via the fluid coupling 6, the other shaft 3 is rotated synchronously with the one shaft 3 by the timing gear 7. The contour of the rotor 4 is selected such that the fluid to be pumped is sucked into the inlet 8 of the pumping chamber 2 and exits the pumping chamber 2 via an outlet (not shown).

This known mechanical pump is extremely useful and is widely used in processing equipment, furnaces, wind cylinders, space simulators, large volume rough pumping, packaging, diffusion pump support, and oil vapor booster pumps, etc. ing.

Referring to FIGS. 2-4, the multi-stage vacuum pump 21 of the present invention is suitable for high vacuum applications and has a pair of parallel shafts 23 (only one shown).
It is the same as the known pump of FIG. 1 in that it has a pump chamber 22 through which it passes. Each shaft 23 supports four rotors 34A, 34B, 34C, and 34D such that they can rotate together. Each pair of rotors 34A to 34D has complementary rotor profiles and is arranged for tandem drive on a respective shaft 23. One axis 2
3 is driven by a motor (not shown) via a joint 26. A timing gear 27 is mounted on each shaft 23 adjacent to a joint 26.

The pump chamber 22 has four partition walls 28, 29, and 30.
It is divided into two separated sections, and a pair of rotors 34A to 34D are located in each section.

The pump chamber 22 has an inlet 31 that directly communicates with the compartment occupied by the rotor 34A, and outlets 32A and 32B that directly communicate with the compartment occupied by the rotor 34D.
It has The flow of fluid pumped from the outlet 32A is controlled by a one-way valve 33A made of a thin elastic member such as a known flap valve.
Fluid pumped from 2B is controlled by a similar one-way valve (not shown). That is, in the illustrated example, as shown in FIGS. 2 and 3, the one-way valve 33A is disposed with the outlet closed in the wall of the outlet 32A opposite to the pump chamber section in which the rotor 34D is located. When receiving a predetermined pressure of the fluid from the pump chamber, the outlet 32A is opened to allow the fluid to flow out (second
The arrow in the figure) prevents the fluid from flowing back into the pump chamber from the outlet 32A, and is a kind of check valve. The one-way valve 32B associated with the outlet 32B may also have the same configuration.

Passages 36, 37, and 38 are passageways for fluid flow that is pumped from one section of pump chamber 22 to the next adjacent section.

The outline of the rotor 34A closest to the inlet 31 indicates that the rotor 34A has the "minimum remaining amount" (minimum clearance volume)
It is defined as having the following. The same is true for rotor 34B in a compartment directly adjacent to the compartment in which rotor 34A is located. The "minimum remaining amount" here means that during the interaction of the cooperating rotors, the amount of gas retained between the rotors is effectively the minimum when the rotors are rotated back to the inlet side of the rotors after exhausting. This means forming the contours of the cooperating rotors so that When the remaining fluid after exhaust returns to the inlet side of the rotor, the fluid expands and
This contouring of the rotor is extremely important as it reduces the volumetric efficiency of the pump. The profile of a rotor having such a "minimum residual amount" is, for example, a roots-shaped profile as shown in FIG.

Each rotor 34D closest to the outlet 32A, 32B
has a known so-called claw-type profile as shown in FIG. The same is true for rotor 34C in a compartment directly adjacent to the compartment in which rotor 34D is located. When a rotor with a claw-shaped profile performs a pumping action in cooperation with the inlet of its pumping chamber, as is known, the fluid in the clearance volume of the rotor is prevented from re-expanding through direct communication with the inlet. This makes it possible to obtain a pressure ratio of approximately 30:1 across one pump chamber.

In use, when the motor drives one shaft 23, both shafts 23 are driven synchronously by the timing gear 27, thereby driving the pair of contoured rotors 34A-34D synchronously. The fluid to be pumped enters inlet 31 and is continuously pumped through passages 36, 37, 38 until it exits via outlets 32A, 32B as indicated by the arrows.

When the pump 21 is used for high vacuum applications, the stroke volume of the rotor 34D is mainly at low pressure, so the gas exiting from the outlets 32A and 32B will flow back into the stroke volume unless measures are taken to prevent backflow. Resulting in. Gas flows back into the stroke volume through the outlets 32A, 32B and also through the rotor 34.
If the gas is allowed to re-expand from the gap volume D, it will be repeatedly compressed, which will consume excessive power, increase pump temperature, and increase pump noise. increases, limiting the degree of vacuum that can be achieved. The rotor 34D thus has a claw-shaped profile which cooperates with the inlet to its pump chamber to prevent gas in the interstitial volume from re-expanding into the inlet, and prevents gas from entering the stroke volume. A one-way valve (e.g. 33A) is provided to prevent backflow of.

The two spaced apart outlets 32A, 32B are positioned to avoid pre-compression. Precompression is also undesirable because it consumes power, since the valve action does not occur at the pressure of the gas being pumped, but at the rotor 3.
Occurs when triggered only by 4D geometry and motion. One of the one-way valves is therefore adapted to operate under the pressure of the pumped gas.

The pump described with reference to FIGS. 2 to 4 is capable of achieving high vacuums and can be constructed as a simple unit. The pump can achieve high vacuum (well below 0.1 mbar) without the use of lubricants in the pump chamber. The pump can maintain a large pumping capacity at low pressures and compress the fluid being pumped to at least atmospheric pressure.

In the embodiments described above, only the rotors 34A and 34B are described as having a "minimum residual volume," but the rotor 34C may have a profile that provides a "minimum residual volume" depending on the application of the pump.

[Brief explanation of drawings]

FIG. 1 is a partially exploded perspective view of a known mechanical pump, FIG. 2 is a vertical cross-sectional view of a four-stage mechanical pump of the present invention, and FIG. 3 is a machine shown in FIG. Figure 4 is a cross-sectional view adjacent to the outlet of the pump.
FIG. 3 is another cross-sectional view adjacent the inlet of the mechanical pump shown; 22...Pump chamber, 23...Shaft, 28, 29, 30
...Partition wall, 31...Entrance, 32A, 32B...Exit,
33A...One-way valve, 34A, 34B, 34C, 3
4D... Rotor, 36, 37, 38... Passage.

Claims (1)

[Claims] 1 a pump chamber having an inlet and an outlet through which the fluid to be pumped flows, and a pair of parallel parallel rotors extending through the pump chamber and supporting in series for rotational movement at least two pairs of rotors having different contours; axis and
In a multistage vacuum pump comprising a device for synchronizing the rotational movement of the rotor and a device for driving at least one of the shafts, the outlet 3 of the pump chamber 22
The pair of rotors 34D closest to 2A, 32B have a claw-shaped profile and are connected to the outlet 32 of the pump chamber.
A, 32B have the outlet 32A for the fluid to be pumped;
One-way valve 33A to control flow through 32B.
A pump characterized by being provided with.