Patent Publication Number: US-5897482-A

Title: Rotor lid tie-down and vacuum venting system

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to centrifuge systems and more specifically to an apparatus for locking down rotor lids with a vacuum-tight closure and venting capability. 
     BACKGROUND 
     Large centrifugation systems typically use a rotor for holding sample containers which contain the sample to be separated. The rotor is covered by a rotor lid and then placed into an instrument chamber wherein the rotor is spun during centrifugation. Typically, the instrument chamber is evacuated for the centrifugation run to reduce the effects of windage and heat generation. 
     If the rotor lid is properly sealed, then the air within the interior chamber of the sealed rotor remains at atmospheric pressure and does not leak into the evacuated instrument chamber. Upon completion of the centrifugation run, the instrument chamber is vented back to atmospheric pressure and the rotor lid is easily removed from the rotor. 
     However, if the rotor lid seals are not properly maintained or if the seals have been compromised, then air from the interior chamber of the rotor will escape and leak into the evacuated instrument chamber during a centrifugation run. This creates a low pressure system within the rotor. When the instrument chamber is returned to atmospheric pressure, this pressure will push the lid tightly onto the rotor body thus creating a vacuum locked lid. 
     A good seal of the rotor lid is also desirable in order to prevent leakage of the material undergoing centrifugation. This is especially important where toxic and other bio-hazardous materials are concerned. If breakage occurs within the rotor chamber, the analyte may spill and/or release hazardous vapors, resulting in a positive pressure within the rotor chamber. Such vapors may release in a violent manner when the rotor lid is removed, exposing laboratory personnel to harmful material. 
     It is therefore desirous to have a rotor lid system which can provide venting in situations where a negative pressure is created within the rotor chamber. It is also desirable that the rotor lid system provide a safe venting direction in cases where a positive pressure develops within the rotor chamber so that venting of hazardous materials can occur without risk to the user. 
     SUMMARY OF THE INVENTION 
     A rotor lid assembly in accordance with the present invention comprises a lid having a centrally depending neck portion. A bore is formed through the lid and through the length of the neck portion. A tie-down stem is received within the bore and has a diameter less than that of the bore. One or more venting ports are formed in the neck portion, thus providing a fluid channel from within the bore. The tie-down stem includes a hermetic member disposed therealong, contacting a periphery of the bore and providing an air-tight seal therewith while at the same time allowing for a sliding action of the stem within the bore. When the tie-down stem is in a first position, the hermetic member is aligned with the venting ports thereby preventing fluidic flow therethrough. When the tie-down stem is in a second position, the hermetic member is displaced relative to the venting ports thus permitting fluidic flow through the ports. 
     In another embodiment of the invention, the lid assembly comprises a lid having a centrally depending shank and a bore formed through the lid and the shank. A safety knob is provided, also having a centrally depending shank. The shank of the safety knob is received in the bore of the lid. The shank of the safety knob has a bore formed therethrough which receives a tie-down stem in the manner as described above. Both shanks have venting ports aligned to allow fluidic flow from within the shaft of the second shank. 
     The hermetic member may comprise a protuberant annular portion of the tie-down stem, contacting a periphery of the bore. Alternatively, the hermetic member comprises an annular member made of material such as leather and disposed about the stem. Yet another alternative is a pair of spaced-apart O-rings which straddle the venting port(s) when the stem is in the first position, thus preventing fluid flow beyond the small volume enclosed by the O-rings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are cross sectional views of a rotor assembly. 
     FIG. 2 is a cross sectional view of a dual-locking lid version of the rotor lid assembly in accordance with the present invention. 
     FIG. 3 is a cross sectional view of a single-lid version of the rotor lid assembly in accordance with the present invention. 
     FIGS. 4A and 4B show alternate embodiments of the tie-down stem. 
    
    
     BEST MODE OF CARRYING OUT THE INVENTION 
     Referring to FIG. 1A, a rotor assembly 10 comprises a rotor 100 and a rotor lid assembly 200 which seals the contents in the rotor during centrifugation. Rotor 100 in turn comprises a rotor body 110 which has a rotor chamber consisting of a plurality of canister chambers 112 for receiving centrifugation sample containers (not shown) which hold the sample being centrifuged and an interior upper chamber 114. Interior chamber 114 is the volume which remains within the rotor chamber after insertion of the centrifugation containers. Rotor body 110 includes an axial bore 120 formed through the spin axis of the rotor body, extending from an open end 122 within interior chamber 114 to an open end 124 at the bottom of the rotor body. Axial bore 120 includes one or more locking pins 130 which project into the interior volume of the axial bore. 
     Setting up the rotor assembly for a centrifugation run includes placing rotor 100 into an instrument chamber (not shown). The instrument chamber includes a spindle 20 which is received in axial bore 120 of rotor body 110. The inserting end of spindle 20 is slotted to engage locking pins 130, thus locking the spindle into position relative to the rotor body. Spindle 20 is coupled to a drive motor (not shown) which provides the torque to spin the rotor. 
     Referring to FIG. 2, the rotor lid assembly 200 comprises a first lid 210 having an upper major surface 210U and an opposed bottom major surface 210B. A shank (neck portion) 211 depends from the bottom surface of lid 210. A bore 212 is formed through the lid, extending from upper surface 210U through the length of shank 211. A gasket member 204 such as an O-ring is disposed about the periphery of lid 210 to provide a seal with rotor body 110 (FIG. 1A). The length of shank 211 is such that when the rotor is sealed by the cap assembly, a distal end of the shank contacts a surface of open end 122 of axial bore 120. A gasket 206 is disposed at the distal end of shank 211 to provide a seal with the surface of the open end 122 when such contact occurs. 
     A safety knob 220 comprises an upper major surface 220U and an opposed bottom major surface 220B. Safety knob 220 includes a shank 221 depending from bottom surface 220B and a bore 222 extending from upper surface 220U through the length of bore 222. As can be seen in FIG. 2, the safety knob presses down onto lid 210 and serves to provide a dual locking function in conjunction with knob 202. This dual locking feature will be discussed further below. 
     Shank 221 of safety knob 220 is received within bore 212 of the first lid 210, thus forming a dual-locking lid combination. Bore 212 has a diameter D2 along its entire length which is sufficient to receive shank 221. Using a light coat of vacuum grease, an air-tight seal can be provided between shank 221 and bore 212 and yet permit a sliding action therebetween. 
     A distal end of shank 221 includes a threaded section 223. At the upper portion of threaded section 223 an annular notch is formed in shank 221 to receive a retaining ring 240. As can be seen in FIG. 2, retaining ring 240 serves to hold lid 210 in position along shank 221 to prevent the lid from sliding off the shank when lid assembly 200 is being transported. 
     A tie-down stem 230 is received within bore 222 of safety knob 220. Tie-down stem 230 has a diameter d that is less than a diameter D1 of bore 222. Bore 222 narrows to a diameter d along a portion proximate safety knob 220 in order to provide a slidable yet air-tight fit therebetween when a small amount of vacuum grease is applied. Tie-down stem 230 extends above upper surface 220U of the safety knob for attachment of a knob 202. Tie-down stem 230 includes a threaded end 233 distal to knob 202. 
     A washer seal 228 is disposed on bottom surface 220B and fits around shank 221. The seal is attached to bottom surface 220B. Similarly, a second washer seal 208 is disposed on a bottom surface of knob 202, and fits around tie-down stem 230. As will be explained below these washers provide a seal when lid assembly 200 is in a locked-down position. 
     Shank 211 includes a vent channel (venting port) 214 extending between the bore 212 and the outer surface of the shank. Similarly, shank 221 includes a vent channel (venting port) 224 extending from the outer surface thereof to the bore 222. Vent channels 214, 224 are co-aligned along their respective shanks, thus providing a fluid channel from within bore 222 to the external atmosphere. As can be seen in FIG. 2, additional vent channels 216 and 226 may be formed in shanks 211 and 221 respectively. 
     Tie-down stem 230 includes a piston-like portion 232 which contacts a periphery of bore 222. Piston-like portion 232 is disposed along tie-down stem 230 so that when the stem is in a first position the piston-like portion is co-located with vent channels 214, 224 so as to prevent continuous fluidic flow from bore 222 via the vent channels. Conversely, when tie-down stem 230 is in a second position, piston portion 232 is dislocated relative to vent channels 214, 224 thus allowing fluidic flow through the vent channels. 
     Referring to FIGS. 1A and 2, tie-down stem 230 is shown in the first position. Rotor lid assembly 200 is locked down to seal rotor 100 by engaging tie-down stem 230 with spindle 20, such as by screwing the stem into the spindle or by some similar interlocking method. It can be seen in FIGS. 1A and 2 that in the locked down position, interior chamber 114 is fully sealed off. First, there are the two gasket seals, one provided by gasket 204 at the periphery of lid 210 and the other by gasket 206 at open end 122 into axial bore 120. A second seal is provided by piston-like portion 232 of tie-down stem 230 to seal off vent channels 214, 224, 216, 226. A third seal is provided by washer seal 228 when safety knob 220 is tightened down upon lid 210. The washer seal serves to seal off the small gap between the bore 212 of lid 210 and shank 221 of the safety knob. A fourth seal is similarly provided by washer seal 208 when knob 202 is tightened down. In this case, washer seal 208 provides a seal of the small gap formed between the bore 222 through the safety knob and tie-down stem 230. 
     Recall that if air leaks from within rotor assembly 10 into an evacuated instrument chamber (not shown) during centrifugation, due to an improper or compromised seal at either of the two gasket seals for example, then lid assembly 200 will become vacuum locked onto the rotor 100 when atmospheric pressure is re-established in the instrument chamber. However, when the lid assembly is unlocked by disengaging tie-down stem 230 from spindle 20, as shown in FIG. 1B where the stem is moved to the second position, the vent channels are exposed. Thus, air from the instrument chamber enters the rotor via open end 124 at the bottom, flows along axial bore 120 and into bore 222 of shank 221, and vents into interior chamber 114, thus equalizing the pressure between the interior chamber and the instrument chamber. Once equilibrium is reached, lid assembly 200 can be easily removed from rotor 100. 
     Conversely, where breakage occurs within the rotor chamber during centrifugation, or some other process occurs which increases the pressure within interior chamber 114, the venting channels provide a fluidic path from the interior chamber to open end 124 at the bottom of the rotor. This is especially important where bio-hazardous material is involved. Rather than venting such material through the top of the rotor and exposing lab technicians to hazardous conditions, the lid assembly of the present invention vents the material safely into the instrument chamber. This is a safety feature not found in prior art rotor lid assemblies. 
     The lid assembly shown in FIG. 2 is a dual-locking lid variety which permits the lid to remain in a locked down configuration even when the tie-down stem is disengaged from the spindle. As can be seen in FIG. 1A a portion of shank 221 is received in axial bore 120 of the rotor body 110. Where shank 221 contacts rotor body 110, an interlocking interface (such as the threaded portion 223) is provided so that lid assembly 200 can be secured directly to the body of the rotor independently of whether tie-down stem 230 is coupled with spindle 20. The dual-locking lid assembly, therefore, provides two lock down mechanisms. 
     Referring to FIG. 3, a single-locking lid version 300 of the lid assembly in accordance with the present invention comprises the same elements as shown in FIG. 2 with the exception that there is no safety knob. Thus, lid 310 comprises upper and bottom major surfaces, 310U and 310B respectively. A neck portion 311 extends from bottom surface 310B. A central bore 312 extends from upper surface 310U through neck portion 311. A tie-down stem 330, received in bore 312, has a first diameter d&#39; that is less than the diameter D&#39; of the bore. A venting port 314 is provided along neck portion 311 to allow fluidic flow from within bore 312. One or more additional venting ports 316 may be provided in the neck portion. Tie-down stem 330 includes a hermetic member 332 disposed therealong and a threaded end 333. When tie-down stem 330 is in a first position, hermetic member 332 prevents fluid flow via the venting ports 314 and 316. When the tie-down stem is in a second position, hermetic member 332 is moved out of the way thus permitting flow through the venting ports. 
     Returning to FIG. 2, the piston portion 232 is depicted as a protuberant annular portion of tie-down stem 230, having a diameter sufficiently close to diameter D1 as to provide an air-tight contact with the periphery of bore 222 with an application of a light coat of vacuum grease and yet allow a sliding action of the tie-down stem within the bore. Moreover, the annular portion is positioned along tie-down stem so as to occlude vent channel 214 when the tie-down stem is in the first (locked down) position. 
     Refer now to FIGS. 4A and 4B for alternate embodiments of tie-down stem 230. In FIG. 4A, piston-like portion 232 of the tie-down stem comprises an expanded portion 402 circumferentially formed upon a segment of the stem. The expanded portion has a recessed channel 404 which receives an annular sleeve 420. Typically, the sleeve is of a non-metallic material such as leather for high vacuum pressure conditions (roughly 1/4 atmosphere within the rotor chamber) where a higher quality seal is required. FIG. 4B shows a pair of spaced apart O-rings 430 and 432, each received in a groove 406 and 408 formed in expanded portion 402 of the stem. Here, the O-rings are spaced apart so as to straddle the vents 224, 226 when the stem is in the locked down position. Thus, rather than directly occluding the vents as in the case of the other embodiments, the O-rings provide a seal occluding fluidic flow in bore 222 by sealing the bore slightly above and below the vents. The use of O-rings is appropriate for vacuum pressures less than 1/4 atmosphere within the rotor chamber.