JPH0368237B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oil-less mechanical pump,
The present invention relates to an oilless mechanical pump having at least two stages, each of which includes an intermeshing rotor within a pumping chamber.

One problem with such mechanical pumps arises from the significant differences in gas pressure that can occur between adjacent stages.

In such cases, a high incidence of back-leakage of pumped gas is likely to occur between stages. In particular, this high incidence of back leakage is likely to occur through the annular gap between the drive shaft and the hole in the inner wall of the stage separating adjacent pump chambers.

Back leakage of gas through the annular gap in the inner wall of the stage effectively causes a backflow of gas from the pump outlet to the pump inlet, effectively increasing the volume of gas to be pumped again, and reducing the volumetric efficiency of the pump. That is, the degree of vacuum obtained is significantly reduced.

Co-pending British Patent Application No. 2111126A discloses and claims a mechanical vacuum pump having multiple pump stages each including meshing rotors in separate pump chambers. The pump of this prior application is characterized by the absence of internal lubrication and the presence at the outlet end of the pump of at least two adjacent stages with interlocking melon-shaped rotors.

The relatively high gas compression associated with the absence of internal lubricant in the internal annular gap further increases the incidence of back leakage.

One object of the invention is therefore to reduce the negative impact that such back leakage has on the vacuum obtained, especially in dry mechanical pumps.

In its broadest aspects, the present invention has at least two pump chambers, each pump chamber containing a pair of mating rotors mounted on a pair of shafts, the pair of shafts being connected to one pump. passing through a hole in the wall separating one chamber from another pump chamber, thereby forming an annular space between the hole and the shaft; To provide a mechanical pump characterized in that a duct is provided for connecting the annular gap and the inlet side of the high-pressure pump chamber.

In a preferred embodiment of the invention, said duct connects the outlet side of the high pressure pumping chamber to the inlet port of said pumping chamber.

In this case, the invention relates to a mechanical vacuum pump of the type disclosed and claimed in the pending British patent application, namely a melon type in which two adjacent pump stages at the outlet of the pump are each mounted in opposite directions. The present invention exhibits particular advantages when implemented in a mechanical vacuum pump having an intermeshing pair of rotors.

Suitably said duct comprises an annular groove provided in the partition wall, at least partially circumscribing said shaft, and communicates with an inlet port of the high pressure pump chamber.

Gas leakage is thus directed back to the inlet side of the high pressure stage instead of entering the previous stage, ie the inlet side of the low pressure stage.

Embodiments of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings.

Referring to Figure 1 of the drawings, a mechanical pump, designated generally at 1, has a pump housing 2, with a pair of parallel drive shafts 3 extending from the pump housing 2.
penetrates through. The shaft 3 has three pairs of rotors 4, 5,
6 is supported so as to rotate together with the shaft 3.
The rotors 4, 5, 6 form complementary intermeshing pairs, as shown more clearly in FIG.
They are arranged vertically on each axis 3.

Referring again to FIG. 1, the pump housing 2 has three independent pump chambers 10, 11, 1 separated by partitions 8, 9 as shown.
Divided into 2, each pumping chamber
includes a pair of intermeshing rotors that produce the pumping of gas.

At one end of the pump housing, each of the shafts 3 carries a timing gear 13, and at the other end of the housing, one of the shafts is connected via a suitable coupling (not shown) of a type well known in the art. It can be driven by being connected to a motor.

As can be seen in FIG. 2, the pair of intermeshed rotors 4 in the pump chamber 10 are cocoon-shaped, well known in the art, and are one of the first high vacuum or inlet stages of the multistage pump 1. form a section.

The profile of the cocoon rotor 4 is such that the carry over volume of the pumped gas is minimized. This means that the cooperating rotors 4 are contoured such that during their interaction the volume of gas trapped on the exhaust side of the rotor and conveyed to the inlet side of the rotor is kept to a practical minimum. It means that. Gas carried over from the exhaust side to the inlet side of chamber 10 tends to expand, thus reducing the volumetric efficiency of the pump.

The gas exhausted from the pumping chamber 10 enters the inlet of the pumping chamber 11 via a suitable duct provided in the wall 9 forming the partition between the pumping chambers 10 and 11 and terminating in an inlet opening 54 of the chamber 11. .

Referring again to FIG. 1, the rotor 5 within the pump chamber 11 is of an interlocking melon shape as is well known in the art. From the inlet opening 54 to the intermediate pressure chamber 11
The entering gas is pumped to an outlet opening 22 provided in the wall 8 forming a partition between the pumping chambers 11 , 12 and which also acts as an inlet opening of the pumping chamber 12 . Although not shown, the inlet and outlet openings of the pump chamber are in the form of arcuate slots.

Gas entering pump chamber 12 at relatively high pressure is directed to an exhaust port 14 of chamber 12 by a pair of intermeshing rotors 6.
and is preferably, but not necessarily, pumped to the atmosphere via a one-way valve 16 effective to improve pump efficiency in the manner disclosed and claimed in pending British Patent Application No. 2111126A.

If the illustrated pump is a dry pump, ie, a pump that does not include internal fluid lubrication equipment, the gas compressed by the pair of meshing rotors 6 in the pump chamber 12 will mainly flow through the holes in the partition walls 8 and 9. There is a tendency for leakage back into the pump chamber 11 through the annular gap with the shaft 3.

Such reverse leakage of gas is caused by the pair of rotors 5 and 6.
Due to the opposite direction of
Since it expands toward the inlet side of 1, the volume has a particular effect on pump efficiency.

In order to improve the effect of this reverse leakage, the partition wall 8
As shown in FIG. 1, the shaft is provided with a continuous groove 51 in the circumferential direction in the region of the shaft. The grooves 51 communicate with each other via ducts or holes 52 which are also provided in the partition wall 8 and with the transfer opening (exit opening) 22 .

During operation of the pump, gas flows into the pump chambers 10, 11,
When being pumped from the low pressure end to the high pressure end through 12 , the gas compressed by the rotor 6 at the highest pressure outlet end of the chamber 12 passes through the annular gap in the partition 8 to the particularly high pressure delivery side outlet 14 . There is a tendency to leak into the pump chamber 11 through the gap closest to the pump (shown at the top of the figure).

Instead of leaking to the inlet side of the pump chamber 11, such back leakage gas is captured by the groove 51, passes through the duct or hole 52 and the cooperating groove 51, enters the transfer port 22, and enters the chamber. At 12, it is pumped again. The effect of gas diversion through groove 51 and duct 52 is to recirculate back leakage gas only to pump chamber 12 rather than to both pump chambers 11 and 12, significantly reducing losses in volumetric pumping efficiency.

Although the invention has been described with reference to a groove 51 in the shaft seal between pump chambers 11 and 12,
It will be appreciated that the invention is equally applicable to other adjacent pump chambers, and indeed to other areas of the pump where back leakage causes a loss of pump efficiency. Although the invention has been described with reference to a dry vacuum pump, it is understood that it is equally applicable to vacuum pumps and mechanical pumps that have internal lubrication facilities, but where the lubrication facilities are not sufficient to prevent back leakage of gas. Good morning.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional side view of a dry mechanical vacuum pump having three chambers each containing a pair of intermeshing rotors. 2 is a perspective view of a rotor incorporated into the pump of FIG. 1; FIG. 1... Mechanical pump, 4, 5, 6... Rotor, 3
...shaft, 10, 11, 12 ... pump chamber, 8, 9
... Partition wall, 51 ... Groove, 52 ... Duct, hole, 5
1... Inlet opening, 22... Outlet opening.

Claims (1)

[Claims] 1. has at least two pump chambers, each pump chamber housing a pair of meshing rotors mounted on a pair of shafts, the pair of shafts connecting one pump chamber to the other; a hole in the wall separating the two pump chambers, thereby forming an annular gap between the hole and the shaft; A mechanical pump characterized in that a duct is provided for connecting the inlet side of the high-pressure pump chamber and the inlet side of the high-pressure pump chamber. 2. The mechanical pump according to claim 1, wherein the duct connects an outlet side of a high-pressure pump chamber to an inlet port of the pump chamber. 3. The mechanical pump according to claim 1 or 2, wherein the duct includes an annular groove provided in the partition wall and at least partially circumscribing the shaft. 4. The mechanical pump according to claim 3, wherein the duct includes a hole connected to an annular groove provided in the partition wall and circumscribed to the shaft. 5. The mechanical pump according to claim 4, wherein the hole communicates with an inlet port of a high-pressure pump chamber. 6. The mechanical pump according to any one of claims 1 to 5, wherein the duct is provided in a high-pressure pump chamber at an outlet end of the pump. 7. The mechanical pump according to claim 6, wherein the high-pressure pump chamber at the pump outlet end receives a mating claw-type rotor.