Gas separation – With means securing or retaining separating media – Hinged or pivoted retainer or clamp on backing frame or in...
Reexamination Certificate
2000-12-01
2002-05-14
Smith, Duane (Department: 1724)
Gas separation
With means securing or retaining separating media
Hinged or pivoted retainer or clamp on backing frame or in...
C055S498000, C055S510000, C055S360000
Reexamination Certificate
active
06387142
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to air compressors, and, more particularly, to filters and air/oil separators.
BACKGROUND OF THE INVENTION
Oil-lubricated, rotary compressors are commonly used in industry and elsewhere to reliably produce large quantities of pressurized air. However, in these types of air compressors, the air, as it is compressed and passes through the compressor, comes into direct contact with the oil or other liquid (e.g., synthetic lubricant from a nearby reservoir) used to cool and lubricate the compressor's moving parts (e.g., a rotor with mounted vanes or a rotating screw). In doing so, an air/oil aerosol is formed, consisting of pressurized air interspersed with tiny particles or droplets of oil. To ensure that the pressurized air is relatively clean, as is required for most applications, the oil must be removed from the pressurized air prior to its being exhausted for use. Additionally, the separated oil can be channeled for re-use in the compressor.
In order to separate the oil or other lubricant from the pressurized air, most rotary vane or screw compressors are provided with an air/oil separator
20
, as shown in
FIG. 1
(labeled “Prior Art”). The air/oil separator
20
is a compound, cylindrical, coalescing element that separates the oil from the compressed air. The air/oil separator
20
is attached to the inside of a separator tank
22
, and is positioned such that the interior of the separator is in fluid communication with the compressor's air discharge or exhaust line
24
. The compressed air/oil aerosol is routed into the separator tank
22
and through the air/oil separator
20
, oftentimes after first passing through a baffle or other coarse separator that removes large particles of oil. The separator
20
is typically provided with an outer, tubular, coalescing separator
26
, and an inner, concentric, tubular drain separator
28
, the two being supported and/or separated by a concentric, tubular, perforated steel cylinder
30
(hereinafter referred to as the “cage”
30
). Additionally, other filter or separator stages (not shown) may be provided. It should be appreciated that the separator
20
acts like a filter in the sense of removing oil from air. However, unlike a filter, where particles are trapped in the filter elements, the separator
20
coalesces oil, which then drains to the bottom of the separator
20
.
The outer separator element
26
is typically composed of a fine fibrous separator media upon which the oil particles tend to coalesce. As oil particles build up, they move downwards, run together, and collect at the bottom end of the separator
20
. The inner separator element
28
is typically composed of a coarser fibrous media, and is provided to facilitate oil drainage and to collect oil that gets re-suspended in the air flow downstream the outer filter
26
. Oil that collects at the bottom of the separator
20
is collected for reuse via a scavenge line
32
extending into or through the tank
22
.
As should be appreciated, in order for the separator
20
to strip the oil from the compressed air/oil aerosol, the aerosol must pass through the separators
26
,
28
. For this purpose, the bottom of the air/oil separator
20
is provided with an end cap
34
. The end cap
34
blocks the bottom end of the separator's central cavity
36
, and seals the bottom ends of the separators
26
,
28
. Without the cap
34
, the aerosol would follow the path of least resistance by traveling directly through the separator's central cavity
36
and into the discharge line
24
without passing through the separators
26
,
28
.
Numerous methods have been used over the years to fasten the cap
34
to the bottom of the separator
20
. Originally, as shown in
FIG. 1
, and as also shown in U.S. Pat. No. 6,093,231 to Read et al., the cap
34
was simply glued on via an epoxy
38
or the like. The epoxy, besides acting as a connector, also provided a seal between the cap
34
and the bottoms of the separators
26
,
28
. However, although this would work for a while, the cap
34
would still tend to fall off after a relatively short period of time. This is because the components in an air compressor, and especially the separator
20
, are subject to a number of deleterious forces. For example, oil and other chemicals in the compressor tend to attack epoxy, especially if the compressor is left off for a while. Additionally, the separator
20
is subject to temperature changes during the compressor's duty cycle, and there is always the possibility of mechanical shock. Finally, when a check valve, a safety valve, or some other component of the compressor upstream from the separator
20
opens or fails (which happens relatively frequently), the separator is subject to a transient but high magnitude pressure differential or backlash. More specifically, in normal operation the pressure on the outer side of the cap is greater than the pressure on its inner side, helping the cap to stay in place. When the pressure suddenly drops on the outer side, the high pressure remaining on the inner side can literally blow the cap
34
off the end of the separator
20
.
In the case mentioned above, using epoxy by itself left the cap
34
especially vulnerable to all the aforementioned forces. If the oil did not cause the cap to fall off by gradually degrading the epoxy, temperature or pressure differentials would. Of course, when the cap
34
fell or blew off, the air/oil separator
20
would have to be replaced before the compressor could be used again. Additionally, with epoxy separating the cap
34
from the rest of the separator
20
, the cap would not be electrically grounded, raising the possibility of static discharge and fire.
To supplement the epoxy seal/connection, mechanical connectors or fasteners have been used in the past to connect the cap to the rest of the separator. For example, according to one method (not shown), the cage
30
was made wider and/or provided with end flanges, and the cap was riveted to the end of the cage
30
. Although this functioned better than only using epoxy, the rivets were still subject to failure via chemical attack, plus it was difficult to provide rivet connections, considering the limited space, that were strong enough to withstand significant or repeated pressure differentials.
According to another method (not shown), metal straps were welded between the separator's flanged ring top
40
and the bottom of the cap. Such straps would typically not work very well because their weld connections would tend to fail subsequent periodic temperature fluctuations. Additionally, the straps would tend to bow axially inwards, preventing secondary components (other filter units, separators, etc.) from fitting into the separator's inner cavity
36
, and it was effectively impossible to install such straps using an automated machine.
Other methods included using a central threaded rod, similar to the apparatus shown in U.S. Pat. No. 5,207,811 to Buonpastore, to connect the cap
34
to a cross brace placed across the ring top
40
; and, as shown in U.S. Pat. No. 5,605,555 to Patel et al., providing a gripping surface for the sealing epoxy via dimples or similar features in the end cap
34
and ring top
40
. Regarding the former method, secondary components could not be installed in the central cavity
36
, and, regarding the latter method, the interconnections were still reliant on the efficacy of the epoxy, plus there was no effective grounding connection between the cap and the rest of the metal parts of the separator.
A final prior art design (not shown) involved the use of an outer cage connected to the outer periphery of the ring top
40
and crimped or flanged over the bottom periphery of the cap
34
. Here, the cap
34
would still blow off from pressure backlash, mainly because the peripheral flange or crimping would fail, it generally being difficult to provide a cage strong enough to withstand large pressure differentials yet malleable enough to easily flange or crim
Pieciak David P.
Vogel John E.
Chicopee Engineering Associates, Inc.
Holland & Bozagni, P.C.
Kramer, Esq. John A.
Lawrence Frank M.
Smith Duane
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