Note: Descriptions are shown in the official language in which they were submitted.
'7~
The present invention relates to an improved form
of gravity separator for mixtures of immiscible liquids of
different densities, such as, for example, oil and water.
More specifically, the invention is an improved
gravitational separator of the type utilizing a collection
tank or housing for receiving a mixture of the fluids
to be gravitationally separated, the tank having a reaction
member preferably in the form of either a floating dome or
diaphragm element within the upper area of the tank which
serves as a reaction surface against which the volume of
lighter (less dense) fluid accumulated within the upper
portion of the tank exerts an upward, buoyant influence.
Separators of the type utilizing a floating dome
are known in the prior art, as exemplified in the sritish
Patent Specification No. 1,212,553 to Cornelis in'tVeld
published November 18, 1970 and U.S. Patent No. 3,628,~60,
also to in'tVeld, granted December 21, 1971. In separators
of this type, the mixture of lighter and heavier fluids
(oil and water, generally) is admitted to the interior of
the separator beneath the dome under positive pressure
or is inducted therein by suction of the heavier fluid from ~`
the heavier fluid discharge pipe of the separator, with the
separator being hermetically sealed. The mixtuxe of
heavier and lighter fluids gravitationally separates in
the separator, with lighter fluid rising up under the dome
and heavier fluid sinking to the lower part of the separator
vessel beneath the dome.
The gradual accumulation of lighter fluid beneath
the dome, which is counterbalanced so as to normally be
slightly negatively buoyant in the heavier fluid, causes
the dome to float upwardly in the heavier fluid within
the separator. It is customary to sense the high limit
position of the dome to produce a control signal useful to
instigate valve and pump actuations which enable the
:'~
-2-
. . . ~ ~: : : .: ~
~ ~ ~r~ 7~3
removal of less dense separated fluid from beneath the
dome.
Gravitational separators of this type that are
used to separate oil from an oily water mixture are
provided with filter or coalescer screens or elements
between the lower part of the separator and the water
discharge pipe to collect any lingering droplets of oil
carried to the lower part of the separator. Such screens
are backwashed periodically to remove the oil clinging
to the coalescers and, as described in the above-referenced
U.S. Patent No. 3,628,660, such backwashing of the screens
can be carried out quite efficiently during the oil
discharge mode of separator operation. That is, it is
customary procedure to remove the accumulated oil from
beneath the floating dome by pressurizing the clean
water discharge pipe of the separator to admit clean
water backwards into the lower end of the separator
through the coalescer screens, and into the area beneath
the dome to thereby force accumulated oil out of the
separator under positive pressure. Only the discharge
of oil is desired, of course, and the reverse inflow ~
of water is ceased when the accumulated oil has been `
discharged and the dome has sunk to its lower starting
level. -~
~5 . Several problem areas have been encountered with
the use of separators of the type just described. There
has arisen, for example, a need for a simple, efficient
and substantially fail-safe system to precisely counter- ;
balance the floating dome or the diaphragm beneath which
the separated oil is trapped and to accurately sense when
the volume of separated oil has reached an upper limit within
the separator so that removal procedures can be instigated.
.,. . :
'
LZ79
Also, the flow pattern of
water through the coalescer screens has been found to be
less than ideal both in forward and reverse flush senses.
Ideally, the flow pattern in a forward direction through
the coalescer screens should be uniform across all of the
-reens in the coalescer system and, when the screens are
backflushed, the backflush flow pattern should occur entirely
across the surfaces of the coalescer screens to remove oil
droplets therefrom. Furthermore, the discharge of oil from
between the coalescer screens should be as complete as
possible during the backflush operation. Finally, it has
been found to be highly desirable to prevent any accumulation
of oil above the separator reaction member during the
operating life of the separator, since accumulation of the
less dense fluid above the member causes an inaccurate
flotation response of the member to the accumulated oil
beneath the dome.
Another approach to the reaction member counterbalance
problem has been described in Patent No. 3,957,638 granted
May 18, 1976, and assigned to the assignee of the instant
application.
The present invention finds particular application ;
in a bilge water disposal system for a vessel, such as
described in U.S. Patent No. 4,018,683 owned by the assignee
of the present invention.
Other applications
of the present invention, of course, are envisioned
in industrial installations ashore for separating
mi~tures of immiscible fluids of different densities.
:
.
7'~13
The present invention contemplates the utilization
of a system of one-way check valves in the coalescer screen
assembly of the separator for ensuring efficient flow of water
through the coalescer screens both in a forward and backflush
mode.
Another inventive feature is the use of a particular
inlet conduit arrangement for preventing undue turbulence
within the incoming stream and to minimize disturbance of the
separation process taking place within a separator tank, parti-
cularly within the upper portion of the tank.
In addition, this invention contemplates constructingthe reaction member so that the buoyancy thereof can be more
precisely regulated during its manufacture.
Still another feature of the invention is a special
-construction of the reaction member whereby it cooperates with
the lighter fluid outflow conduit in a manner that minimizes or
eliminates the adverse effects of an air bubble trapped beneath
the reaction member.
Finally, the invention contemplates a special col-
lector hood over the coalescer for collecting backflushedmixture and carrying same beneath the reaction member during
each backflush operation.
Accordingly, the invention as claimed herein is an
improvement for a gravitational oil and water separator utili-
zing at least one coalescer screen within the lower area of the
separator for ~rapping oil particles entrained in a clean water
discharge flow from the separator, the water discharge from the
separator occurrin~ normally by suction of water from the
separator and the screen normally being backflushed by a
reverse flow of water through the screen under pressure, the
separator including a water discharge outlet and backflush inlet
means at the lower portion of the separator. The improvement is
f~
characterized by: a chamber, within the separator for con
taining the coalescer screen isolated from the interior of said
separator except through pressure responsive one-way valves; at
least one of said valves comprising an inlet pressure responsive
one-way valve for permitting flow of water into the chamber only,
and another of said valves comprising at least one pressure res-
ponsive one-way outlet valve for permitting flow of water out of
the chamber only. The water discharge outle-t/backflush inlet of
the separator communicate with the interior of the chamber. The
inlet one-way valve is located towards the lower end of the
chamber near the outer periphery of the coalescer chamber and
the outlet one-way valve is located at an upper end of the cham-
ber. The coalescer screen is disposed in the chamber so as to
extend entirely across the chamber with the water discharge
outlet/backflush inlet means being located towards one side of
the screen centrally within the chamber. Finally, the inlet and
outlet valves are located towards the opposite side of the screen.
There now follows a detailed description of a specific,
illustrative embodiment of the invention. Of course, the scope
of the invention is intended to be limited solely by the claims
set forth below, with the detailed description describing a
preferred em~bodiment of the invention in accordance with
statutory requirements.
. Sa -
With reference to the attached drawings:
FIGURE 1 is a schematic view of a floating dome
separator system incorporating one embodiment of the improved ~;
coalescer screen system of the present invention;
FIGURE 2 shows an alternate embodiment of the coalescer
screen arrangement and another embodiment of the separator
system used with the coalescer arrangement;
FIGURE 3 is a sectional view taken along line III~
in FIGURE 2; and ;
FIGURE 4 is a detailed view of the top area of the
dome in FIGURE 2 shown in its upper limit position.
With reference to Figure 1 of the drawings, a sPparator
system for separating oil from oily water includes a separator
tank 10 having an oily water mixture inlet conduit 12 that
continues internally of the separator tank 10 up to an upwardly `
extending extremity 14 which constitutes the actual inlet for
oily water mixture within the tank 10. Inlet conduit 12
includes a one-way check valve 15 at the source M of oily ~
water mixture to be processed. A water line 16 located towards ~ -
the lower end of the tank 10 serves as both a clean water dis-
charge line and a backflush-tank pressuri2ing inlet line~ as
will be more fully explained below. Line 16 is connected to
suction pump 18, through line 17, solenoid valve l9 and one-
way check valve 20, the pump 18 being connected to a control
panel 22 which provides a power supply for the pump and ~;
controls its operation through lead 24. The solenoid valve 19 `~
is connected to the control panel through lead 25. Line
26 is the outlet line for clean water processed by the
separator system. Conduit 16 is also connected to a clean
water s~upply under pressure through solenoid valve 28 which i: ;
is connected to control panel 22 through lead 29.;;~
Normally, the tank or housing 10 is initially filled ~ ~
with water or contains oil and water undergoing separation, ~ `
-6- ~
: :,
. ;` :~ .
f7~;~
the valve 19 is normally opened and valve 28 is normally ;;
closed. Actuation of pump 18 then draws a suction on line ~;
16 which, since the tank 10 is hermetically sealed, causes
discharge of water through lines 16 from tank 10 and in-
take of oily water mixture line 12 into the tank. Since
the mixture from source M is not agitated, emulsified or
homogenized by a pump located between the source M and the
se~arator tank 10, but rather quietly released at the top
of the upstanding column of conduit 12 in separator 10, sepa- - `
ration by gravity of oil and water proceeds rather rapidly ;
within the tank 10.
A dome-type reaction member 30 loosely fits within
tank 10 and may be provided with flotation chambers 32.
! The dome 30 will be counterbalanced to have slightly nega-
tive buoyancy in water (fresh or saIt water, as the situa-
tion demands) so that with no oil whatsoever in the separa-
tor the dome rests on lower stop means 34.
Oil discharge conduit 36 extends to a position at the
extremity 38 thereof within the tank 10 just beneath the
inner surface of the top of the dome 30 when the dome is in
its lower extreme rest position on the stop 34.~ The other
- end of conduit 36 empties into an oil storage tank 40 through
one-way check valve 41. Inlet line 12 discharges at 14 in
an area beneath the dome 30.
Thus, it will be evident that upon operation of pump
1~ in the normal manner, oily water mixture is sucked into
the tank 10 and discharged gently beneath the dome 30, with -
the water dropping down to the lower part of the tank and the
oil rising to the upper internal area beneath the dome 30. ;~
The dome 30 will then be influenced by the buoyancy of oil
trapped beneath the dome 30, which buoyancy wilI be a function
of the relative densities of the oil and water and the volume
of the oil-accumulated-beneath the dome.- The reaction of the
dome to the buoyancy force of the accumulated oil will be a
. '.''`.
-7-
,;,
tendency to float upwardly to the extent that the buoyancy
force is unbalanced. If the dome 30 were floating with
initial neutral buoyancy, for example, the presence of any
appreciable amount of oil under the dome 30 would cause it
to gradually rise to an upper limit in the tank 10. It will
be readily understandable that this is not desired, since -
the objective of the separator system is to cyclically ~
accumulate a certain volume of oil beneath the dome, and to ~;
discharge substantially all of this oil into a collection
tank with a minimum of interruption to the overall separa- ;
tory process. A balancing system for the dome is therefore
desirable to enable the accumulation of a predetermined
volume of oil beneath the dome and means for sensing the ` ~
occurrence of such predetermined accumulation in a precise ~ -x
manner. Once the accumulation of a desired volume of oil
has occurred, control means for the separator must sense
the occurrence of this accumulation and institute control
of the system to momentarily cease the inflow of oil and
water mixture, pressurize the interior of the tank with
water to cause the oil to be discharged from the separator
and finally to return the system to its original operating
mode when sufficient oil has been removed from the system.
A dome balancer system has been described in U.S.
- Patent No.4,032,444, ~entifi~ above. Upon shutting
off of pump 18, and with the closure of valve l9 and ~ ~
opening of valve 28, water under pressure is admitted `
quickly into the tank 10. The check valve 15 prevents outflow ~`
through conduit 12, with the consequent result that oil is dis-
charged through conduit 36, the only other outlet from the
separator tank. The inlet of conduit 36 is located beneath the
; dome 30 but closely adjacent the upper surface of the dome when ~ ` it is in its lowermost position. Oil will therefore be dis-
charged through conduit 36 as the interior of tank 10 is pres-
surized with clean water and the dome will gradually sink as ;
;:
the oil is discharged from the separator, since the volume
of oil causing the upward buoyant force on the dome is
gradually diminished. Tf the inflow of fresh water through
line 16 is continued indefinitely, of course the oil
would all be removed, the dome 30 would settle onto its
stop, and water eventually would be discharged through oil ;
discharge conduit 36. Obviously, this condition is never
intentionally allowed to occur.
Oil is indicated as 42, and water as 46. In Figure 1,
the dome is connected to the balancing and oil discharge
control mechanism within upper portion 51 of the separator ~ `~
tank 10. A magnet 52 connected by rod 50 to the dome 30
is used to trip relays 54, 55 for transmitting appropriate ~
signals to the control panel 22 via electxical lines 56 and ~ -
58, all as described in more detail in Patent No. 4,032,444.
In operation, the tank 10 is initially filled with ~`
water, preferably by closing valve 19 and opening valve 28 - -~
to cause clean water to be admitted into the tank through `,~
line 16. Check valve lS prevents outflow through inlet
line 12 beyond the valve 15, but line 12 can also be closed
by an appropriate shutoff valve. Line 36 is likewise closed~
! during the filling operation. The tank 10 is hermetically
sealed, with air being exhausted through an appropriate air
eliminator. Suitable switches at the control panel 22 are
then thrown to cause the system to operate in the automatic
; mode. Valve 28 is ciosed, valve 19 is open and lines~ 12 and
36 are in communication respectively with an oil and water ~ ;
mixture M and a storage tank 40. Operation of pump 18 can be
regulated in any suitable manner, such as, for example, where ~:
mixture M is located in a bilge of a vessel, by a swltch means -~
responsive to the bilge water level, and when functioning
creates a negative suction pressure in tank 10. As water is ~,
withdrawn through line 16 and discharged through line 26, oil
; ,.~
- g - : :, :
:
..
-` ~ ~.`"' .
- ~ :
~'7~
and water mixture is drawn into the separator through line 12. :
In the separator, oil will float towards the underside of the
dome 30, while water will gradually drop to the lower area of ~;
the tank. The volume of water displaced from beneath dome 30
will create an upward flotation force on dome 30 which force
will be a function of.the relative densities of the oil and
water, and the mass of the volume of oil accumulated between
the dome. Stated in a different manner, the force is a func-
tion of the relative densities of the oil and water and the
mass of the volume of water displaced by the oil beneath the
dome. Initially, upward flotation of the dome will be resisted
by the downward force of the balance mechanism on shaft 50,
and low dome position switch 54 will sense this condition and
transmit an appropriate signal to control panel 22. As the
mass of oil beneath the dome increases, the buoyance forces
acting on the dome increase and, when the resistance to up- :
ward movement exerted by the balance mechanism is overcome,
the dome will be allowed to rise until ~he high position switch
55 senses an upper limit position, at which time a signal
. 20 appropriate for this condition is transmitted to control
panel 22.
The high dome position, of course, is indicative of the ~:
accumulation of a predetermined volume or weight of oil beneath
the dome that must be discharged from the separator periodical-
ly. Control panel 22 includes appropriate circuitry to u~ lize
~` the signal transmitted by the high dome position switch ~ and
to send an appropriate signal to cease operation of pump 18,
: close valve 19 and open valve 28. This causes further mixture
input to the separator to cease, and forces fresh water under ;~
3~ pressure into the tank 10 to cause oil to be discharged from
line 36 to storage tank 40, as described above.
:.
.
-10- ;~
': ` : .' : : ' `
2~
Outflow of oil from beneath the dome will cause it to
sink towards its starting position until the low dome posi-
tion switches sense a low position of the dome and control
panel 22 responds to this condition. Circuitry within the
panel will then return the system to its original mode of
operation whereby valve 19 is opened, valve 28 is closed
and operation of pump 18 is enabled. Continued operation
of pump 18 will cause continued recycling of the system so
long as sufficient oil accumulates beneath the dome to cause
0 it to reach its upper flotation limit. For a suitable example
of a control panel and pump control system applicable to the
present invention, reference is made to U.S. patent No.
4,018,683.
In Figure 1, coalescer screens 100 (loosely referred to
as filters) are provided at the lower end of tank 10, the
screens being concentrically nested about a central conduit
102 which extends downwardly through the screen assembly and
slightly beyond the bottom of a lower screen support plate
104. Upper screen support plate 106 along with lower plate
0 104 extends transversely across the tank internal dimension,
and, along with the conduit 102, effectively seals the tank
10 from a filter chamber 110 which contains the screens 100 ~;
and which communicates with water outlet 16. ~-
Flow of water into chamber 110 is through lightly
loaded, pressure-responsive one-way valves 112 which allow ;
w~ater to be admitted to the chamber 110 from below the lower
plate 104. Inflow of water to chamber 110 occurs between the
duct 102 and the innermost coalescer screen 100 when pump 18
is operating. The water then passes radially outwardly through .
the successive screens 100 and finally out through line 16.
Oil droplets that may be entrapped in the sinking water
beneath the dome and not separated out in the main mass of oil
42 are caught up on the coalescer screens, which are prefer-
ably formed of an oleophobic, porous, fibrous material, woven
, . .
- ~''.
7~
or knitted, rough on one side and smooth on the other side,
the screens being supported on a vertical metal or plastic
framework. As illustrated, the screens preferably are con-
centric and cylindrical in form.
The screens 100 are backwashed during the oil dis-
charge operation when the tank 10 is pressurized by incoming
water through line 16. One-way valves 114 provided in the
top plate 106 provide the only outlets for chamber 110,
whereby, inflow of water to chamber 110 through line 16 will
reverse ~lush the screens 100 and discharge water and back-
flushed oil particles from the chamber areas between the
screens 100 into the tank 10 above plate 106. An oil detector
120 connected to panel 22 via lead 122 is provided within
tank 10 above the screens 100 to detect excessive oil at this
level of the separator. Actually, detector 120 can he located '~
at any desired position beneath the dome 30 and above the
screen support plate 106. If oil in an emulsion state with
water reaches the coalescers 100, oil could be passed through ~
the screens and into the water discharge line. Also, exces- ~ '
sive oil at this level of the tank 10 would be indica,tive of
a malfunction in the separator control system. If this situ-
' ation is sensed at the detector probe 120, appropriate cir-
cuitry at control panel 22 will shut down the separator system
and sound an appropriate alarm. ~ `
With reference to Figures 2, 3, and 4, another embodi-
me,nt of a coalescer screen unit is shown. The concentric ~;
screens 200 are arranged verticallybwithin a coalescer chamber
i ~ 202 having top and bottom walls ~4 and ~ ~ and a sidewall
208. The chamber 202 in this embodiment is sealed from the 'i
interior of tank 10 except through pressure responsive one-
way inlet valves 210 and pressure responsive one-way outlet ; -
~ valves 212. The chamber 202 is in communication at a bottom
`! central area with a water conduit 214 having an enlarged-area~
~ 216 where it is threadably connected at 218 to the bottom wall ~,
~',, `'~
. -12-
.: : .. ..-
'' " ;: :' '
204 of chamber 202. The enlarged diameter 216 is provided
to cause a velocity differential of fluid flowing through
conduit 214 when the fluid moves from the chamber 202 to the
conduit 214, or vice versa, depending upon whether the system
is operating in the suction mode or the backflush mode.
In this embodiment, water in the lower part of tank
10 from which most of the oil has been removed enters the-
coalescer through the lower wall 204 at the outside of the ~
area within chamber 202 and progressively moves towards the !'
inside water outlet conduit 214 which is centrally disposed
in this embodiment, within the innermost of the coalescer
screens 200. A maximum period of time is thus provided for -
effecting separation of oil particles from water and oil
mixture flowing through the system, since the water will be
required to travel to virtually the bottom of the separator
tank 10 before entering the chamber 202.
Accumulated oil particles on the screens 200 and `~
within the chamber 202 between the screens are removed by
backflushing the chamber 202. Water pressure and therefore
water flow is reversed through conduit 214 and valves 212
allow backflushed oil and water to exit out of chamber 202,
while valves 210 prevent backflush flow out through the
bottom of the chamber 202. Thus, backflushed oil is required
to exit from chamber 202 through valves 212 at the upper end
of the chamber.
Also in the embodiment of Figures 2-4, a collector
hood 230 is connected to the top of chamber 202 and is ;
sealed thereto. The hood, shaped generally like a funnel
that has been inverted, includes an upwardly~extending con~
duit portion 231 that terminates within the area encompassed
` by the dome reaction member 235, preferably the area just `
below the upper portion of the dome when the latter is at
its lower position. A deflector member 236 supported by a
suitable apertured spacer 238 is provided at the end of the
` 35 conduit 231 of the hood 230. ~
-13- `'
. ~, .
. . .
~iZ~27c3
:. :
The oily water mixture is supplied to tank lO through
inlet line 12 which includes a resilient sec~ion 240 and an
enlarged section 242 for reducing the flow velocity of incom-
ing mixture. Section 242 of inlet line 12, as seen in Figure
3, narrowly clears the inner diameter of conduit 231. Thus,
~ oily water mixture drawn into tank lO through line 12 is
; transferred to conduit 231 where it moves upwardly until de-
flected gently laterally by deflector 236 into the separation
area of the tank 10.
The oil outlet line 250 terminates within the uppermost
area bounded by the dome, just beneath its upper surface por-
tion. It also includes a resilient portion 251 to allow for -~
slight movement between the hood 230 and the ~ank sidewalls.
The dome reaction member 235 is provided with a ~`~
vertical flexible seal or screen 255 about its periphery which
' extends between the dome 235 and a deflector ring 256. Thus,
oil that may separate out from the water in the lower region -;
of the tank below the bottom edge of the dome cannot enter
the space in the tank above the dome. In this embodiment,
2C the screen 255 is non-porous, and a balance pipe 275 is -~
provided between the upper and lower regions of the tank, -
such balance pipe being filled with water in the manner `
described in our co-pending application S.N. 608,905.
A bellows seal 276 is provided to further prevent oil
contamination above the dome 235. Seal 255 may also be
formed so that it is impermeable to oil, but permeable to ~
water, in which case a balance pipe would not be necessary. ~;
The dome reaction member 235 is preferably formed of
resin-bonded fiberglass or the like, and is provided with a
flotation collar 260 that provides the dome with sufricient ~;
: buoyancy to make it effectively neutrally or slightly posi-
tively buoyant in water. The balance mechanism above the `~
dome and associated with rod 262-tsimilar to shaft 50 ln `-
Figure l) provides the precision buoyancy adjus~ment required
-14-
,,.
...,., ,~
'7~
,:
for the control system of the unit.
Dome 235 is provided with an auxiliary air trap
chamber 265 that represents a volume bounded by an upper
surface area of the dome 235. The volume of the air trap
chamber is carefully controlled during manufacture of the
dome for reasons that will be more fully explained momen-
tarily. The auxiliary chamber 265 includes a bottom open
area that is considerably smaller (less than half) than
- the total area of the underside of the dome that is reacted
upon by the lighter fluid (oil in this example) collected
beneath the dome.
The upper extremity of oil outlet duct 250 normally
extends into the air trap chamber 265 when the dome is
below its normal upper limit position as seen in Figure 2,
but lies approximately at the level shown in Figure 4 when
the dome is at its normal upper limit of travel.
With the dome in its upper limit position as shown
in Figure 4, the separator normally would shift over to
the oil discharge mode of operation, and therefore the ;~
separator would be pressurized with backflush water through ;
conduit 214.
: Any air trapped beneath the reaction member would
then collect in the air trap chamber 265 and the chamber
is dimensioned so that when there is enough air collected
to position the reaction member in the upper limit ~osi-
tion the upper surface of the oil layer is approximately
level with or below the upper opening in the oil discharge
conduit 250. The air trap chamber overcomes a problem in
prior art separators of the instant type that arises due to `;~
~ 30 an effective air lock condition that occurs beneath the
`- upper surface of the reaction member that is reacted
~ against by the lighter fluid. ~ `
.. ~ .
~',.
-15-
~12~79
When a relatively flat or slightly arcuate upper
reactor surface is used, as shown in Figure 1, for example,
air that accumulates beneath the reaction member gathers
in the form of a bubble. Due to the relatively small
volume of air required to displace liquid and thus to
cause the reactor to rise to its upper limit and the large
surface area over which the air is spread, the air-liquid
interface is above the upper opening in the oil discharge
conduit 250. Thus, when the system is cycling on air
~ 10 alone or a mixture of air, water and oil, a quantity of
! liquid is discharged during each cycle. Eventually the
minimum desired residual oil layer that is intended to
be preserved beneath the reaction member to make the
balance system operate properly will be discharged.
The air trap chamber 265 effectively prevents loss
of minimum desired oil layer thickness beneath the reac-
tion member while the air is being discharged, and allows
a volume of air to be compressed above the oil layer and
in communication with the oil discharge conduit. Even if
~,` 20 the system recvcles rapidly on air alone, the top of the ;
~; conduit 250 remains at or above the upper level of the mini-
` mum desired oil layer that is to be preserved beneath the `
reaction member.
The term "reaction member" is not intended to be
limited solely to a dome such as illustrated herein. It
applies equally well, and is intended to encompass, a
3 planar diaphragm member as well as an arcuate, flexible
diaphragm.
The above description is intended to be exemplary
of preerred embodiments of the present invention; modi~
fications of these embodiments and different arrangements
~" of specific structure falling within the scope of the ap-
pended claims are-intended to be encompassed by this
patent.
`` 35
, ;
-16- ~ -~
~: ":
