FR2582741A1 - MULTI-STAGE MECHANICAL PUMP COMPRISING CENTRAL CONDUITS TO PREVENT GAS LEAKAGE - Google Patents

Abstract

MULTI-STAGE MECHANICAL PUMP WITH CENTRAL DUCTS TO PREVENT GAS LEAKS. PUMP 1 INCLUDES AT LEAST TWO STAGES INCLUDING EACH OF THE ROTORS ENGAGED WITHIN A CHAMBER 10; 11; 12 OF PUMPING, THESE ROTORS BEING MOUNTED ON SHAFTS 3, 3 THROUGH, BY DRY BEARINGS, PARTITIONS 8, 9 SEPARATING A BEDROOM 11 FROM THE ADJACENT BEDROOM 12. DUCTS 51, 52 ARE PROVIDED TO TRANSFER GAS ENTERING THE ANNULAR SPACE BETWEEN A SHAFT AND ITS BEARING, IN A REGION OF RELATIVELY HIGH PUMP PRESSURE, TO A REGION OF RELATIVELY LOWER PRESSURE OF THE PUMP IN THE SAME CHAMBER (RETURN THROUGH PORT 22). APPLICATION: VACUUM PUMPS RUNNING DRY.

Description

I

  The present invention relates to mechanical pumps

  oil-free operation and is more specifically aimed at

  the sealing of such mechanical pumps comprising

  at least two stages each comprising mutual rotors

  mentally rotating within a pumping chamber that

surround them.

  For such mechanical pumps, a problem is raised because of the large differences in gas pressure

  may appear between neighboring floors.

  We are in the presence of an increased risk

  leakage of the pumped gas, which gas then tends to

  dance to escape between floors and to go back; in particular, such an increased risk of occurrence of rising leakage may occur for gas tending to take the annular gap between the drive shafts and the hole in the internal stage wall separating

adjacent pumping chambers.

  The gas lift leak taking such a gap in the inner stage wall or elsewhere will actually produce a countercurrent flow of gas from the pump outlet to the pump inlet, which will actually increase the volume of gas to be repacked and greatly reduce the volumetric efficiency of the pump or vacuum

obtainable.

  In patent application GB-A-2 111 126, there is described and claimed a mechanical vacuum pump having a plurality of pumping stages each of which comprises rotors geared within an independent chamber or pumping compartment. The pump of this prior patent application is characterized by the absence of internal lubrication and by the existence, at the outlet end of the pump, of at least two adjacent stages having rotors of

  type in meshing or mutual cooperation by claws.

  The relatively high compression of gas thus produced, coupled with the absence of internal lubricant in the inner annular gap, further increases the risk

  appearance of a lift escape.

  An object of the present invention is thus to attempt to reduce the adverse effect exerted by such

  leakage recovery on the vacuum can be obtained, in particular

  in dry mechanical pumps.

  In its broadest aspect, the present invention provides a mechanical pump having at least two stages each comprising rotors intermeshed within a pumping chamber, the rotors being mounted on shafts passing through walls or partitions separating a chamber. or

  compartment or adjacent compartment, a system

  duct system being provided for transferring gas entering the annular space between a shaft and its trunnion or bearing in a partition located in a relatively high pressure region of the pump and to deliver this gas

  to a pump area where there is relative pressure

lower.

  In a preferred embodiment of the invention,

  The ducts are arranged to transfer gas from the annulus of a high pressure region of a pump chamber to a lower region.

pressure of the same chamber.

  According to other advantageous features of the invention: the ducts may be arranged to transfer the gas from the shaft seal to the high pressure region of a pump chamber to or into the orifice gas inlet in this room; the ducts can be arranged to transfer gas from the packer into the region

  at low pressure from a pumping chamber to or into the

  fice of gas admission in this room.

  The conduits may be arranged to provide communication between the shaft seals respectively at the high and lower pressure regions of the pumping chamber; the ducts may comprise an annular channel formed in a partition wall of the pumping chambers

  and at least partially surrounding the tree.

  The annular channel can completely surround the corresponding tree;

  ducts may include an additional hole

  in the partition wall and ensuring

  connection with the annular canal surrounding the corre-

laying;

  the extra hole can connect the annular canal

  surrounding the seals of a

  with the high and low pressure regions

the pumping chamber; -

  the extra hole can communicate with the ori-

  admission chamber of the pumping chamber; the ducts can be made in the pumping chamber at the outlet end of the pump; the pumping chamber located at the outlet end of the pump can enclose the type of rotors meshing or mutual cooperation by claws; and the pumping chamber at the outlet end of the pump can evacuate the gas through a

check valve.

  The general device of the present invention offers particular advantages when it is incorporated

  mechanical vacuum pumps of the type described and

  in the aforementioned GB-A-2,111,126 patent application, in which two adjacent pumping stages at the pump outlet respectively comprise intermeshing pairs of claw-type rotors which are mounted in

reverse orientation.

  Suitably, the ducts comprise an annular channel made at and ideally within the inter-storey partition wall; the channel wholly or partially surrounding the tree and communicating with a lower pressure region of the

pump.

  Conveniently the duct, in a stage of the pump, communicates with a similar annular channel provided

  in a partition wall in a region of relative pressure

  lower floor of the same floor and with the entrance to this floor.

  Thus, instead of entering the admission side of the previous stage,

  dent, any leakage of gas is short-circuited and returns to the intake side of the stage where this gas comes.

  An embodiment of the invention will now be

  in particular, as an illustrative example

  and in no way limiting, with reference to the accompanying drawings, in which: FIG. 1 is a side section of a pump;

  Dry-running mechanics, with three chambers

  chambers or compartments each containing a pair of intermeshing rotors; and FIG. 2 is a perspective side view

  rotors of the pump of Figure 1.

  Referring more particularly to Figure 1, we see that the mechanical pump, generally designated by the index 1, comprises a body 2 through which a pair of parallel shafts 3, 3 '. The shafts 3, 3 'bear, so as to rotate with, three pairs of rotors 4, 4'; , 5 'and 6, 6'. The rotors 4, 4 ', 5' and 6, 6 'as shown more clearly in FIG. 2, are arranged in complementary pairs of pairs and in tandem on their

respective trees 3, 3 '.

  Returning to FIG. 1 it can be seen that the body 2 of the pump is divided by separating partitions 8 and 9 into three spaced and independent pumping chambers 10, 11 and 12, each chamber comprising a pair of

  geared rotors for pumping gas.

  At one end of the pump body, each of the

  3, 3 'carries a transmission gear 13, 13, however,

  At the other end of the pump body, one of the shafts (eg 3) can be driven because it is connected to a motor via a coupling.

  suitable (not shown) of a type well known in the art.

  As seen in FIG. 2, the intermeshing pair of rotors 4, 4 'located in the pumping chamber 10 is of the "Roots" type, well known in the art and is part of the first stage at high vacuum or stage of pump inlet

1 to several floors.

  The profile Roots rotors 4, 4 ', is intended to ensure the minimum possible volumetric drive of the pumped gas. This is meant to indicate that the profiles of

  cooperating rotors 4, 4 'are such that during their interaction with

  tion, the volume of gas trapped on the output side of the rotors, which is driven back to the inlet side of the rotors,

  is kept to a minimum value as low as possible.

  Any gas drawn from the outlet side to the intake side of

  the chamber 10 will tend to expand and decrease the efficiency

volumetric flow of the pump.

  The gas extracted from the pumping chamber 10 enters the inlet of the pumping chamber 11 via a suitable duct formed in the wall 9 which forms the partition wall between the pumping chambers 10 and 11 and which

  terminates in chamber 11 at the inlet port 54.

  Referring again to Figure 2, it can be seen that the rotors 5, 5 'disposed in the pumping chamber 11 are of the interlocked claw type, also well known in the art. The gas entering through the inlet orifice 54 into the intermediate pressure chamber 11 is pumped to the outlet orifice 22 which is provided in the partition wall B between the pump chambers 11 and 12 and which plays also the role of intake port in the chamber 12 pumping. Although not shown in the drawings, the inlet and outlet ports of the

  pumping chambers have the shape of curvilinear buttonholes.

  The gas entering the relatively high pressure pumping chamber 12 is pumped by the pair of rotors 6, 6 'meshing towards the outlet orifice 14 of the chamber

  12 and to the atmosphere, preferably but not necessary-

  by using a non-return valve capable of improving

  effective pumping efficiency, as has been the case

  described and claimed in the aforementioned GB patent application

A-2 111 126.

  If the pump shown is a dry pump, that means

  that is, a pump that does not contain a device intended to ensure lubrication by internal fluid, the gas compressed by the pair of rotors 6, 6 'meshing within the chamber 12 for pumping will tend to leak to return to the chamber 11 pumping, especially by borrowing

  annular spaces between the shafts 3, 3 'and the holes

  in partition walls 8 and 9.

  Such a gas leak tending to go back into the pump will particularly affect the performance

  of this pump since, due to the

  the rotor pairs 5, 5 'and 6, 6', this gas will expand by penetrating into the intake side of the

chamber 11 pumping.

  In order to reduce the effects of this ascent slip, the separating partition 8 is, as represented in FIG. 1, provided in the region of each shaft 3, 3 'with channels

  51 continuous circumferentially surrounding the corresponding tree.

  The channels 51 communicate with each other by a conduit or hole 52 also formed in the wall 8 forming a partition

  or separation and with the transfer port 22.

  During operation of the pump, with gas pumped from the low pressure end to the high pressure end through the chambers 10, 11 and 12 pumping, the gas compressed by the rotors 6, 6 'at the end at greater pressure and at the outlet end of the chamber 12 will tend to leak in an attempt to enter the chamber 11 pumping by borrowing the annular space in the wall 8 forming partition wall and, in particular, in borrowing space, represented at the top end

  drawing, which is closest to Exit 14 on the side of

high pressure.

  Instead of fleeing to reach the inlet side of the pumping chamber 11, this upstream leakage gas will be trapped by the channel 51, it will pass through the conduit or hole 52 and into the channel 51 cooperating with it and will penetrate in the transfer orifice 22 to be pumped back into the chamber 12. The effect of the diversion of the gas passing through the channels 51 and the duct 52 is only leakage gas, which would tend, if not, to go upstream in the opposite direction. the pump will actually be recycled only in the pumping chamber 12 rather than borrowing the two pumping chambers 11 and 12, and it stays in the same chamber

  pumping, which will greatly reduce the loss of

volumetric flow of the pump.

  It will be understood that, if the present invention has been

  described more particularly with reference to channels 51

  In the shaft seals between the pump chambers 11 and 12, the invention can also be applied to other adjacent pumping chambers and, of course, to other pump regions where leakage occurs. recovery causes a loss of efficiency of the pump. It will also be understood that, if the invention has been described more specifically with reference to a dry vacuum pump, the invention is also applicable to vacuum pumps and, of course, to other pumps.

  mechanical devices, including devices for their lubrication

  internal arrangement but in which the lubricating device

  cation is not sufficient to prevent the gas from

lift-up leaks.

  It goes without saying that, without departing from the scope of the invention,

  Many modifications can be made to the duct system, described and shown, intended to improve the efficiency and overall tightness of a mechanical pump operating without lubrication by oil or with such lubrication but which is not sufficient.

prevent a gas leak.

Claims (13)

  1. Mechanical pump (1) comprising at least two stages, each of which comprises rotors (4, 4 ', 5, 5', 6,   6 ') intermeshed within a chamber (10; 11;   page, the rotors (4, 4 ', 5, 5', 6, 6 ') being mounted on shafts (3, 3') which pass through and are journalled dry in walls (8, 9) forming a partition wall a chamber with the adjacent chamber, pump characterized in that it comprises conduits (51, 52) for transferring the gas entering the annular sealing gasket between a shaft and its vortex or bearing in a region to relatively high pressure of the pump to a relatively high pressure region of the pump to a pressure region   relatively lower pump.   Mechanical pump according to Claim 1, characterized in that the ducts are arranged in such a way as to transfer the gas from the   shaft seal (3, 3 ') in the high-pressure region   from a pomanpage chamber (12) to a lower pressure region of the first room (12).   Mechanical pump according to Claim 1, characterized in that the ducts are arranged in such a way as to transfer the gas from the   shaft seal (3, 3 ') in the high-pressure region   pump chamber (12) to or into the port (22) for   gas supply in this chamber (12).   4. Mechanical pumping according to claim 3, characterized in that the conduits are arranged to transfer gas from the seal located in the region of low pressure of a chamber (12) of pcmpage to or in the orifice (22) for gas admission in this room.   5. Mechanical pump according to claim 4, characterized in that the ducts (51, 52) are arranged so as to provide communication between the shaft seals respectively in the regions with higher and lower pressure of the room (12) of pampage.   6. Mechanical pump according to claim 1, characterized in that the ducts comprise an annular channel (51) provided within a partition (8) separating the pan and surrounding chambers at   least partially the corresponding shaft (3, 3 ').   7. Mechanical pump according to claim 6, characterized   characterized in that the annular channel (51) surrounds the corresponding shaft (3, 3 ').   8. Mechanical pump according to claim 6 or claim 7, characterized in that the ducts comprise an additional hole (52) formed in the wall (8) forming a partition wall, this hole being connected   with the annular channel (52) surrounding the shaft (3, 3 ') corresponding to laying.   9. Mechanical pump according to claim 8, characterized   characterized in that the additional hole (52) connects the annular channel (51) surrounding the seals of the corresponding shafts (3, 3 ') respectively in the regions of greater and lower pressure of the chamber of pumping (12) corresponding.   Mechanical pump according to claim 9,   characterized in that the additional hole (52) communicates   only with the orifice (22) for admission into the chamber (12) pumping.   11. Mechanical pump according to any one of   preceding claims, characterized in that the con-   duits are arranged in the pumping chamber (12) at   the outlet end of the pump.   Mechanical pump according to Claim 11, characterized in that the pump chamber (12) at the outlet end of the pump surrounds rotors (6, 6 ') of the interengaged claw type.   Mechanical pump according to one of the claims   11 and 12, characterized in that the pumping chamber (12) at the outlet end of the pump discharges the gas by a non-return valve (16).