US3591308A

US3591308A - Rotor guard for centrifugal compressor

Info

Publication number: US3591308A
Application number: US830291A
Authority: US
Inventors: Ernest W Blattner; Arnold M Heitmann
Original assignee: Chicago Pneumatic Tool Co LLC
Current assignee: Chicago Pneumatic Tool Co LLC
Priority date: 1969-06-04
Filing date: 1969-06-04
Publication date: 1971-07-06
Anticipated expiration: 1988-07-06
Also published as: DE7013906U; CH512662A; FR2049821A5; GB1272512A; DE2018158A1; BE751276A; NL7007955A; SE361194B

Abstract

A safety device to protect a rotor impeller in a centrifugal compressor from damage that might otherwise occur when the impeller, because of some fault, engages an opposed wall of its chamber. The device includes a hollow tubular body supported in the walls of the compressor. It has one end connected with a pressure switch arranged in a power control electrical circuit, and has an opposite abradable thin end projecting into the impeller chamber. The device is pressurized with fluid and, when its thin end is caused to be abraded away by the impeller, the pressure fluid will be dumped, causing actuation of the switch and consequent discontinuance of power to the compressor. The pressure fluid for the device may be supplied from the compressor system or from an external source. In condenser steam turbines, the tubular body of the device may be connected with a vacuum element and arranged so that when the thin end is abraded away the tubular body will become pressurized by the process fluid to cause actuation of the pressure switch.

Description

United States Patent [72] Inventors Ernest W.Blattner Franklin, Pm;

Arnold M. Heitmann, Swampscott, Mass. [21] Appl. No. 830.291 [22] Filed June 4, 1969 [45] Patented July 6, 1971 [73] Assignee Chicago Pneumatic Tool Company New York, N.Y.

[54] ROTOR GUARD FOR CENTRIFUGAL COMPRESSOR 6 Claims, 2 Drawing Figs.

521 vs. Cl 415/9 [51] Int. Cl 4 F0lb 25/00 [50] Field of Search 41 5/30, 9; ZOO/81.8

[5 6] References Cited UNITED STATES PATENTS 1,326,867 12/1919 Junggren 415/9 1,498,096 6/1924 l-lerr.... 415/9 1,832,779 11/1931 Johnson. 200/8l.8 2,764,651 9/1956 Lang ZOO/81.8

3,207,473 9/1965 Madden 3,164,368 1/1965 Klein.....

Primary Examiner-Henry F. Raduazo Attorney-Stephen J. Rudy ABSTRACT: A safety device to protect a rotor impeller in a centrifugal compressor from damage that might otherwise occur when the impeller, because of some fault, engages an opposed wall ofits chamber. The device includes a hollow tubular body supported in the walls of the compressor. It has one for the device may be supplied from the compressor system or from an external source. In condenser steam turbines, the tubular body of the device may be connected with a vacuum element and arranged so that when the thin end is abraded away the tubular body will become pressurized by the process fluid to cause actuation of the pressure switch. I

ROTOR GUARD FOR CENTRIFUGAL COMPRESSOR BACKGROUND OF THE INVENTION This invention is concerned with a safety device for guarding against the damage that is likely to result in a centrifugal compressor unit as a consequence of loss of clearance developing between the impeller of its rotor and an opposed wall of the impeller chamber.

In centrifugal compressor units of the gaseous type having a rotor, the clearance of its impeller relative to the opposed walls of the rotor chamber is normally close. Accordingly, only a very limited loss of clearance could result in rubbing of the rotating blades of the impeller against one of the walls of the chamber with consequent damage.

The objective of the present invention is to provide a compressor unit with safety guard which extends slightly into its rotor chamber, and which is adapted, when a loss of rotor clearance develops sufficiently for the impeller of the rotor to contact the guard, to cause operation of a control circuit switch and consequent discontinuance of operating power to the rotor.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing wherein the invention is illustrated:

FIG. 1 is a view in section of a rotor safety guard embodying the invention installed in a pneumatic centrifugal compressor; only so much of the compressor being shown as needed for a proper understanding of the invention; and

FIG. 2 is a view similar to that of FIG. 1, but showing a modified form of the rotor safety guard.

DESCRIPTION OF A PREFERRED EMBODIMENT Reference is directed to the accompanying drawing, and now especially to FIG. 1 in which is shown a section of a scroll case of a conventional centrifugal pneumatic compressor. The case has the usual inlet passage 11 through which air is drawn by the impeller 12 of a rotor 13, and is compressively discharged through the case. The case defines a narrow space or chamber 14 between the opposed walls 15 and 16 of which the impeller rotates. The impeller is carried at one end of a rotor shaft 17 which is rotatably supported in conventional manner in a section of the compressor (not shown). The support of the rotor is such that a clearance 18 normally exists between the blade face 19 of the impeller and the opposed wall 15 of the impeller chamber. Undesirable damage to the rotor and to the scroll case is likely to occur if, because of some fault, the rotor should progressively take up the clearance 18 and carry the rotating blades of its impeller into contact with the compressor wall 15.

An advantageous solution to this problem is provided by means of a safety rotor guard 21. The guard is a unit that is separable from the compressor. It is supported in the compressor in such manner as to project at its forward end into the im peller chamber 14 opposite to and with some clearance from the blade face of the impeller. If the rotor should progressively take up the clearance 18, the impeller will cooperate with the guard 21 to cause actuation of a power control electrical switch 22. Actuation of the latter will shut off power to the rotor before the impeller can damagingly contact the wall 15.

The rotor guard 21 has a hollow body, generally designated 23, designed to be filled with fluid, such as air, under pressure. It is supported between the wall 15 and an outer wall 24 of the scroll case. The body includes an elongated tube 25. A front end of the tube is sealed by means of a cap 26. The cap is formed of readily abradable material, such as soft metal. Here. it is formed of leaded brass. The cap is fixed, as by welding, upon the end of the tube. The cap has a rear portion 27 of enlarged diameter which is received in an axial bore 28 of the scroll case wall 15 and is seated by means ofa shoulder 29 at the bottom of the bore. A terminal portion 31 of the cap having a reduced diameter is fitted in a complementary reduced extension of bore 23 and projects slightly beyond the wall 15 into the impeller chamber. A narrow passage 33 in the terminal portion of the cap is sealed at its outer or forward end by a thin web or wall 34. The opposite end of passage 33 opens into the relatively larger interior diameter of the tube 25. The terminal wall 34 of the cap is positioned in the impeller chamber substantially parallel relative to the blade face of the impeller. Its arrangement is such that the thin wall 34 will be ground or abraded away by the impeller's blades so as to vent the interior of the tube in the event of an undesirable loss of clearance developing between the rotating impeller and the opposed wall 15.

. The tube 25 projects at its opposite end through an opening 35 in the outer wall 24 of the scroll case. A sleeve connector 36 on the tube has a plug portion 37 threadedly engaged in the opening 35. An O-ring 38 seals against leakage of compressor air from the interior 39 of the scroll case around the periphery of the connector. A sleeve nut 41 threadedly engaged upon an oppositely projecting portion 42 of the connector cooperates with a sleeve seal 43 to seal against leakage around the tube 25 and to frictionally restrain the tube 25 against endwise displacement from the walls 15 and 24 of the scroll case. The tightened condition of the sleeve nut compresses the resilient seal 43 within the nut into tight frictional engagement with the surface of the tube.

A second sleeve nut 44 and a seal 45 connects the free end of tube 25 with piping 46. The latter is connected with the control switch 22 which is of a conventional pressure type. Here, it is defined by means ofa Bourdon Tube 47 connected at one end with the piping 46. The sealed terminal end 48 of the Bourdon Tube carries a switch spring contact 49 which it is adapted to close or open in an electrical control circuit 51, accordingly, as the terminal end 48 of the Bourdon Tube is caused to be extended or retracted.

The piping 46 is connected by means of an orifice 52 with a constant source of pressure fluid 53 whereby the interior of the rotor guard 21 is pressurized with fluid and maintained in a constantly pressurized condition at a predetermined pressure. In the pressurized condition of the rotor guard, the terminal end 48 of the Bourdon Tube is extended so that the switch contact 49 has a normally closed condition in the control circuit, as appears in FIG. ll.

In summary of the manner in which the rotor guard functions, if, because of some fault, the rotor 13 should progressively move toward the wall 15, the blades of its rotating impeller will eventually contact and abrade away the thin end wall 34 of the rotor guard to effect venting of the interior of the latter. The pressure fluid will in this action dump through the vented passage 33 faster than it wiil enter from the supply source 53 into the rotor guard through the relatively more restricted orifice S2. The internal pressure of the rotor guard accordingly relaxes causing the terminal end 48 of the Bourdon Tube to retract the switch contact 49 to open condition. The control circuit responds to this: action and shuts off operating power to the compressor.

The extent of the projection of the front end of the rotor guard into the impeller chamber 14 and the thinness of its end wall 34 is such that the latter will be ground away and the power to the compressor will be caused to be shut off before the impeller can come into damaging contact with the compressor wall 15.

The end of the rotor guard projects into the impeller chamber only slightly and approximately to the extent of the thinness of the end wall 34. Here, the latter has a thickness of about 0.005 of an inch. It is not necessary that the end wall 34 be fully abraded away. It is only necessary that a slight abrading action occur to weaken the end wall sufficiently for the pressurized fluid in the rotor guard to break through.

In FIG. I, it is noted that the cap end 26 of the tube is retained in its seated condition in the wall 15 against endwise displacement by means of the compressed condition of the sleeve seal 43 together with the connector 36. In FIG. 2, a

modified arrangement is provided for maintaining the seated condition of the cap end of the tube. In FIG. 2, a relatively shorter tube 25a is provided. Its rear end is enlarged by means of a collar or piston 54 fixed thereon. The collar has a slide fit in a corresponding internal enlargement 55 of the sleeve connector 36a. The rear portion 42a of the connector is coupled by means of a sleeve nut 41a and a sleeve seal 43a to piping 46a which connects with the pressure control switch. A space 56 normally exists between an internal shoulder 57 of the connector and the opposed end of the collar 54. By means of this arrangement, the pressure fluid in the rotor guard acting against the collar presses and holds the cap end 26a of the tube in its seated condition. An O-ring seals against leakage around the collar 54. An advantage of this arrangement is that it allows for thermal expansion of the tube 25a that might occur as a result of temperature changes developing during operation of the compressor. In this respect, the collar end 54 of the tube will move in the space 56 accordingly as the tube is thermally affected.

In a multistage centrifugal compressor in which intake fluid is drawn and compressively passed through successive stages, a separate rotor guard unit 21 may be associated with the impeller chamber of each stage; or the chambers of only certain selected stages may be equipped with rotor guards. In such arrangements, the several rotor guards would be connected in parallel with the piping 46. The latter would be connected by a single orifice 52 to the common source 53 of pressure fluid and would be connected to a single control switch 22. it can be seen in such an arrangement that the control switch would be actuated to shut off power to the entire compressor should anyone of the rotor guards be caused to be vented by the re lated impeller.

The rotor guard may be pressurized with air or liquid. The source for such may be bottled high-pressure fluid; the usual pneumatic or hydraulic control system of the compressor; the compressors lubrication system; or the fluid being processed by the compressor. in all cases, the pressure level of the fluid source should be distinctly above the pressures in the impeller chamber at the location of the rotor guard.

in some applications of the rotor guard unit, such as with a condensing steam turbine, the rotor guard could be connected to the usual condenser vacuum instead of to a fluid pressure source. In such an arrangement, when the end of the rotor guard is abraded away, the process fluid will rush into the rotor guard to fill the vacuum. The pressure switch in such a situation will respond to a sudden pressure rise in the rotor guard instead of to a sudden pressure drop.

The orifice 52, because of its restricted nature, is of further advantage in that it materially limits the quantity of fluid that can escape after the end wall of the cap is vented.

it is understandable that when a rotor guard unit has been acted upon by the impeller, it may be subsequently readily withdrawn from the compressor through the opening 35 for replacement after first disconnecting the connector 36 and sleeve nut4l.

We claim:

1. in a centrifugal fluid compressor including a rotor carrying an impeller having rotation in a space defined between a pair of opposed walls of the compressor, one of the walls having a recessed shoulder in a bore opening axially into the space in opposed relation to the blade face of the impeller, a rotor guard comprising a tubular body having a cap fixed over one end and seated upon the recessed shoulder and having a forward end projecting into the space, a connector supporting an opposite end of the tubular body in further wall of the compressor, a fluid pressure switch, piping means connecting the said opposite end of the tubular body with the pressure switch, an orifice connecting the tubular body with a constant source of pressure fluid, and a narrow passage in the cap sealed by means of a thin abradable wall at the forward end of the cap, the passage being relatively larger in diameter than the orifice, the pressure switch being responsive in a particular direction to pressurization of theinterior of the tubular body with fluid from the source and being responsive in an opposite direction upon the thin wall being abraded away to relieve the fluid from the tubular body through the narrow passage, the impeller being adapted upon losing axial clearance relative to said one wall to engage and abrade away the thin wall.

2. In a centrifugal fluid compressor as in claim 1, wherein the said opposite end of the tubular body has a collar disposed with a slide fit part way into the interior of the connector, the rear end of the collar being subject to fluid pressure within the interior of the rotor guard whereby the cap end of the tubular body is held seated upon the recessed shoulder.

3. In a centrifugal fluid compressor as in claim 2, wherein an O-ring seal is provided about the periphery of the collar having sealing engagement with the surrounding wall of the connector.

4. In a centrifugal fluid compressor as in claim 1, wherein a sleeve seal is fitted upon said opposite end of the tubular body, and a sleeve nut threadedly engaging a rear portion of the connector compressively engages the sleeve seal into tight en gagement with the tubular body.

5. in a centrifugal fluid compressor as in claim 1, wherein the level of the pressure in the rotor guard is greater than the ambient pressure in the said space of the compressor.

6. A safety guard comprising a hollow tubular body having a reduced passage at one end and a readily abradable thin wall sealing over the end of the passage, a pressure-responsive switch connected to the opposite end of the tubular body, an orifice the diameter of which is reduced relative to said passage connecting with the interior of the tubular body intermediately of the ends of the latter, the switch being adapted to respond in a particular direction in response to a relaxed pressure condition developing within the interior of the tubular body and to respond in the opposite direction in response to a pressurized condition developing within the interior of the tubular body, the tubular body being adapted to be supported in the housing of a rotor in a manner so as to have its abradable wall end project into a rotor chamber in opposed spaced relation to the blade face of the rotors impeller, the abradable wall being adapted to be abraded away upon being engaged by the impeller blades so as to open the interior of the tubular body through the reduced passage to pressures within the rotor chamber, and the orifice being adapted for selective connection with a suction device or a fluid pressure source.

Claims

1. In a centrifugal fluid compressor including a rotor carrying an impeller having rotation in a space defined between a pair of opposed walls of the compressor, one of the walls having a recessed shoulder in a bore opening axially into the space in opposed relation to the blade face of the impeller, a rotor guard comprising a tubular body having a cap fixed over one end and seated upon the recessed shoulder and having a forward end projecting into the space, a connector supporting an opposite end of the tubular body in further wall of the compressor, a fluid pressure switch, piping means connecting the said opposite end of the tubular body with the pressure switch, an orifice connecting the tubular body with a constant source of pressure fluid, and a narrow passage in the cap sealed by means of a thin abradable wall at the forward end of the cap, the passage being relatively larger in diameter than the orifice, the pressure switch being responsive in a particular direction to pressurization of the interior of the tubular body with fluid from the source and being responsive in an opposite direction upon the thin wall being abraded away to relieve the fluid from the tubular body through the narrow passage, the impeller being adapted upon losing axial clearance relative to said one wall to engage and abrade away the thin wall.

4. In a centrifugal fluid compressor as in claim 1, wherein a sleeve seal is fitted upon said opposite end of the tubular body, and a sleeve nut threadedly engaging a rear portion of the connector compressively engages the sleeve seal into tight engagement with the tubular body.

6. A safety guard comprising a hollow tubular body having a reduced passage at one end and a readily abradable thin wall sealing over the end of the passage, a pressure-responsive switch connected to the opposite end of the tubular body, an orifice the diameter of which is reduced relative to said passage connecting with the interior of the tubular body intermediately of the ends of the latter, the switch being adapted to respond in a particular direction in response to a relaxed pressure condition developing within the interior of the tubular body and to respond in the opposite directioN in response to a pressurized condition developing within the interior of the tubular body, the tubular body being adapted to be supported in the housing of a rotor in a manner so as to have its abradable wall end project into a rotor chamber in opposed spaced relation to the blade face of the rotor''s impeller, the abradable wall being adapted to be abraded away upon being engaged by the impeller blades so as to open the interior of the tubular body through the reduced passage to pressures within the rotor chamber, and the orifice being adapted for selective connection with a suction device or a fluid pressure source.