Molecular sieve abstract
A molecular sieve bed container provides a plurality of molecular
sieve bed chambers. The chambers are formed by tubular wall members
concentrically located within a tubular outer housing and are closed
at their ends by end closure members. One end closure member incorporates
valves (not shown in FIG. 1) for controlling supply of charge gas
to the sieve bed chambers and venting of purge gas from the sieve
bed chambers. The other end closure member incorporates valves for
controlling passage of product gas from the sieve bed chambers to
an outlet (not shown) and portways for permitting some of the product
gas to flow back through the sieve bed chambers as purge gas during
a purge/vent phase. In the illustrated embodiment three sieve bed
chambers are filled with a molecular sieve material which is given
to removal of nitrogen from air supplied to the container as charge
gas while two chambers are filled with a molecular sieve material
which is given to removal of oxygen whereby supplies of oxygen-enriched
air and nitrogen-enriched air are delivered as product gases.
Molecular sieve claims
What is claimed is:
1. A molecular sieve bed container including concentric tubular
members and end closure members closing respective opposite ends
of said concentric tubular members to form discrete chambers, at
least three separate molecular sieve beds including molecular sieve
material for retaining nitrogen in air supplied to said sieve beds,
said molecular sieve material filling said discrete chambers, each
said chamber being of substantially constant cross-sectional area
in extending between the end closure members, annular resilient
sealing elements sealing the inner concentric tubular members with
at least one of said end closure members, filter plates located
at each end of each sieve bed between the molecular sieve material
and the end closure members, springs acting between the end closure
member and the filter plates at one end of said container to retain
the molecular sieve material in a compact condition, valve means
in one of said end closure members for passing a supply of charge
gas into the sieve beds and for venting purge gas from the sieve
beds comprising an individual pair of valves associated with each
respective sieve bed, and means in said other end closure member
for delivering a supply of product gas and for passing some of said
product gas back through said sieve beds as purge gas.
2. A molecular sieve bed container in accordance with claim 1
wherein each said individual pair of valves comprise diaphragm valves.
3. A molecular sieve bed container in accordance with claim 1
further comprising solenoid operated valve means controlling opening
and closing of each valve in a pair of said valves.
4. A molecular sieve bed container in accordance with claim 1
wherein the container comprises three discrete chambers filled with
molecular sieve material for retaining nitrogen in air supplied
to said three sieve beds, and two discrete chambers filled with
molecular sieve material for retaining oxygen in air supplied to
said two sieve beds, whereby in operation separate supplies of oxygen-enriched
gas and nitrogen-enriched gas are delivered as product gasses from
said container.
5. A molecular sieve bed container comprising,
three concentric tubular members;
a respective end closure member closing respective opposite ends
of the tubular members;
three discrete chambers defined by said tubular members and said
end closure members, each said chamber being of constant cross-sectional
area in extending between said end closure members;
three molecular sieve beds provided one in each of said three discrete
chambers by molecular sieve material for retaining nitrogen in air
supplied to the sieve beds;
annular resilient sealing elements sealing the inner concentric
tubular members with at least one of said end closure members;
springs acting between the end closure member and the filter plates
at one end of the container to retain the molecular sieve material
in a compact condition;
an individual pair of valves associated with each sieve bed provided
in one of said end closure members for passing a supply of air to
said associated sieve bed and for venting purge gas therefrom;
valve means in said other end closure member for delivering a supply
of oxygen-enriched product gas from said container and for passing
some of said oxygen-enriched product gas back through said sieve
beds as purge gas.
6. A molecular sieve bed container comprising,
five concentric tubular members;
a respective end closure member closing respective opposite ends
of the tubular members;
five discrete chambers defined by said tubular members and said
end closure members, each said chamber being of constant cross-sectional
area in extending between said end closure members;
three molecular sieve beds provided one in each of three of said
five discrete chambers by molecular sieve material for retaining
nitrogen in air supplied to the sieve beds;
two molecular sieve beds provided one in each of two of said five
discrete chambers by molecular sieve material for retaining oxygen
in air supplied to the sieve beds;
annular resilient sealing elements sealing the inner concentric
tubular members with at least one of said end closure members;
filter plates located at each end of each sieve bed between the
molecular sieve material and the end closure member;
springs acting between the end closure member and the filter plates
at one end of the container to retain the molecular sieve material
in a compact condition;
an individual pair of valves associated with each sieve bed provided
in one of said end closure members for passing a supply of air to
said associated sieve bed and for venting purge gas therefrom;
valve means in said other end closure member for delivering a supply
of oxygen-enriched product gas from said three molecular sieve beds
comprised by nitrogen retaining molecular sieve material and for
passing some of said oxygen-enriched product gas back through said
sieve beds as purge gas;
valve means in said other end closure member for delivering a supply
of nitrogen-enriched product gas from said two molecular sieve beds
comprised by oxygen retaining molecular sieve material and for passing
some of said oxygen-enriched product gas back through said sieve
beds as purge gas;
whereby in operation separate supplies of oxygen-enriched product
gas and nitrogen-enriched product gas are delivered from the container.
Molecular sieve description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to molecular sieve bed containers and is
more particularly concerned with the form and construction of molecular
sieve bed containers for gas separation apparatus.
2. Description of the Prior Art
It is current practice in molecular sieve type gas separation apparatus
and systems having multiple sieve beds for each sieve bed to be
provided in an individual container. Examples of such systems, which
are particularly suited for the production of oxygen-enriched air
for breathing by aircrew in an aircraft application, are disclosed
in EP-A-0080300 and EP-A-0129304 (Normalair-Garrett). However,
as with all ancillary equipment required to be carried by an aircraft,
it is of great advantage for molecular sieve beds to be of minimum
size and weight compatible with required performance and physical
integrity.
GB-A-2013101 (Bendix) discloses apparatus for producing oxygen-enriched
air wherein pressurised air is passed through a molecular sieve
bed which removes nitrogen from the supply air and through which
a portion of the oxygen-enriched product gas is passed as a purge
gas for regenerating the molecular sieve material. The sieve bed
is defined by a housing or container which provides a larger flow
area at the inlet face of the bed than at the outlet face thereof.
In one disclosed embodiment a sieve bed is formed by an annular
portion having one flow area disposed around a tubular core of a
lesser flow area and arranged so that flow through the bed reverses
its direction under an end cap at one end of the container in passing
from the annular part to the tubular core. In another disclosed
embodiment of simpler form the sieve bed is of a frusto-conical
shape having a single pass flow-path from an inlet end of one flow
area to an outlet end of a smaller flow area.
Thus, GB-A-2013101 is concerned to provide a container for an
individual molecular sieve bed which matches velocity of product
gas output from the sieve bed with that of supply gas input to the
sieve bed thereby compensating for the gas element of the supply
gas which is adsorbed by the molecular sieve material.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a molecular
sieve bed container which embodies a plurality of molecular sieve
beds whilst being compact in size and low in weight so as to be
particularly suited for use in an aircraft on-board gas separation
apparatus.
Accordingly, the present invention provides a molecular sieve bed
container comprising a plurality of concentric tubular members,
a respective end closure member closing respective opposite ends
of the concentric tubular members, a plurality of discrete chambers
defined by the concentric tubular members and end closure members
and each being of substantially constant cross-sectional area in
extending between the end closure members, a plurality of separate
molecular sieve beds provided by molecular sieve material filling
the discrete chambers, one of the end closure members providing
means for passing a supply of charge gas into the sieve beds, and
means for venting purge gas from the sieve beds, the other end closure
member providing means for delivering a supply of product gas from
the sieve beds and means for passing some of said product gas back
through the sieve beds as purge gas.
The inner concentric tubular wall members may be sealed with at
least one of the end closure members by annular resilient sealing
elements.
Preferably, filter plates are provided at each end of each sieve
bed between molecular sieve material in the bed and the end closure
members for retention of the molecular sieve material and any dust
associated therewith.
Springs may be provided between the end closure member and filter
plates at one end of the container so as to act on the filter plates
and thereby retain molecular sieve material in the sieve beds in
a compact condition. Each end closure member may incorporate valve
means for controlling the flow of gas into and out of the sieve
beds, the valve means incorporated in the end closure member providing
passage means for flow of charge gas into the sieve beds and venting
of purge gas from the sieve beds comprising an individual pair of
valve associated with each respective sieve bed.
The valve means incorporated in each end closure member may comprise
diaphragm valves. Opening and closing of each valve in a pair of
such valves controlling supply of charge gas to a sieve bed and
venting of purge gas from a sieve bed may be controlled by solenoid
operated valve means.
Alternatively, each valve in a pair of such valves may be controlled
by gas operated servo valve means carried on the exterior of the
end closure members.
Solenoid operated valve means or gas operated servo valve means
may be actuated by an electronic timer which may provide a single
overall cycle time with the ratio of charge period to vent period
being fixed at a predetermined value such as 1:1 or 2:1 or it may
provide two or more different overall cycle times with the ratio
of the charge period to vent period for each cycle time being fixed
at a common predetermined value such as 1:1 or 2:1. The two or more
predetermined overall cycle times may be switched from one to another
by a control loop sensing a parameter of the system gases, such
as the concentration value of the product gas, or by an external
parameter, such as altitude.
A molecular sieve bed container in accordance with one embodiment
of the invention has each sieve bed chamber filled with a molecular
sieve material suited to retaining nitrogen in air supplied to the
container so that oxygen-enriched air is delivered as product gas
from the container.
A molecular sieve bed container in accordance with another embodiment
of the invention has some of the sieve bed chambers filled with
molecular sieve material suited to retaining nitrogen in air supplied
to the container whilst the others of the sieve bed chambers are
filled with a molecular sieve material suited to retaining oxygen
in air supplied to the container so that both oxygen-enriched air
and nitrogen-enriched air are delivered as product gases from the
container.
In this latter embodiment of the invention those chambers containing
nitrogen retaining molecular sieve material all have the same individual
volume, as do those chambers containing oxygen retaining molecular
sieve material but each of these latter chambers is of larger volume
than the chambers containing nitrogen retaining molecular sieve
material.
The concentric arrangement of discrete sieve bed chambers allows
the interior wall structures to be of minimal thickness appropriate
to the required physical integrity, only the outer wall of the container
requiring to have a thickness providing normal rigidity and protection
to the container as a whole. This enables a large proportional reduction
in overall weight relative to a set of comparable molecular sieve
beds provided in individual containers and, also, a reduction in
the space envelope required to accommodate the container housing
the discrete chambers.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be further described by way of example with
reference to the accompanying drawings in which;
FIG. 1 shows a fragmented longitudinal cross-sectional view of
a molecular sieve bed container in accordance with one embodiment
of the invention;
FIG. 2 illustrates a sealing and vent feature of the container
shown in FIG. 1;
FIG. 3 is a fragmented end view of the container shown in FIG.
1;
FIG. 4 shows a fragmented longitudinal cross-sectional view of
a molecular sieve bed container in accordance with another embodiment
of the invention; and
FIG. 5 is a cross-sectional view of a solenoid operated valve and
two diaphragm valves controlling supply of charge gas to and venting
of purge gas from a molecular sieve bed chamber.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings a molecular sieve bed container 10 includes
a tubular outer housing 11 manufactured from rigid impervious material
having a thickness dimension in the order of 1.5 mm and sealingly
secured at one end to an endplate or closure member 12. Four tubular
wall structures 13 14 15 and 16 each having a wall thickness
dimension in the order of 0.8 mm are positioned concentrically within
the housing 11 and are also sealingly secured to the closure member
12. This concentric structural arrangement provides four discrete
annular molecular sieve bed chambers 18 19 20 21 and a central
cylindrical molecular sieve bed chamber 17. The three chambers 17
18 19 are filled with a molecular sieve material which is given
to nitrogen removal and the two chambers 20 21 are filled with
a molecular sieve material which is given to oxygen removal from
air passing through the container. The central chamber 17 and the
two annular chambers 18 19 each have the same individual volume.
The two annular chambers 20 21 also each have the same individual
volume, but their volumes are greater than the volumes of the chambers
17 18 19.
The sealed securement to the closure member 12 of the outer housing
11 and the four wall structures 13 14 15 16 is obtained by forming
the foot of each of these as an annular flange 22 23 24 25 26
respectively, these flanges being brazed, welded or bonded as appropriate
to the closure member 12.
At the junction of the closure member 12 and the wall structure
15 which separates the chambers 17 18 19 given to nitrogen separation
from the chambers 20 21 given to oxygen separation, an annular
gas drainage chamber 27 is provided. This is obtained by means of
the annular flange 26 at the foot of the wall structure 16 having
a returned section 28 so that the foot is in the form of an annular
channel. A transition section 29 from the flange 26 to the returned
section 28 is made over a short distance at an angle of, conveniently,
45.degree. whereby the gas drainage chamber 27 is formed as an annular
channel defined by surfaces provided by the transition section 29
the wall structure 15 and the closure member 12. Vent ducts 30 are
provided in the closure member 12 connecting the gas drainage chamber
27 with ambient atmosphere.
The closure member 12 comprises two plate elements 31 32 which
are integrated in facial contact such as by electron beam welding.
The two plate elements are appropriately ported, a port 33 from
chamber 17 being shown in FIG. 1 to provide for emission from each
of the chambers 17 18 19 and 20 21 of the respective product
gases thereof. Annular mesh guards 34 are trapped in recesses between
the two elements 31 32 for prevention of the egress of molecular
sieve material from the discrete chambers into the ports. Small
portways are provided within the closure member 12 and entered by
way of ports 50 one of which is shown in FIG. 1 leading from chamber
17 for enabling some oxygen product gas to pass as purge gas from
and to any of the discrete chambers 17 18 19 which are given to
nitrogen separation. Similar portways and ports (not shown) are
provided to pass some nitrogen product gas as purge gas from and
to the two discrete chambers 20 21 which are given to oxygen separation.
The end of the outer housing 11 remote from the closure member
12 terminates in an annular V flange 35 which provides a closing
and sealing contact with a mating flange on an end cap closure member
36 and is retainable therewith by means of an associating resilient
clamp ring 37 of known form.
The end cap closure member 36 is provided on its inner side with
concentric grooves 38 39 40 41 which are arranged to receive
the other ends of the wall structures 13 14 15 16 respectively,
these ends being fitted into slotted annular resilient sealing elements
42 having peripheral sealing relationship with the walls of the
grooves 38 39 40 41.
Referring to FIG. 2 the sealing element 42 associated with the
wall structure 15 which separates the discrete chambers 19 20 that
are given to obtaining different product gases is so formed as to
provide an annular gas collecting duct 43 extending from and beyond
the end of the inserted wall structure 15 for enabling any collected
gas seepage to pass to ambient atmosphere by way of apertures 44
in its end wall and vent ducts 45 provided at the bottom of the
groove 40.
The end cap closure member 36 is also provided with a series of
pockets 46 equally spaced around the mean pitch circle diameter
dimension of each chamber 18 19 20 21 and around a suitable outer
diameter dimension of the core chamber 17 for the location of compression
springs 47 arranged to urge perforated pressure plates 48 onto the
molecular sieve material in each of the chambers so as to hold the
material in a predetermined lightly compacted and firm condition.
The end cap closure member 36 also provides, for each chamber 17
18 19 20 21 an inlet/outlet port (not shown) for charging the
molecular sieve bed in the chamber with pressurised air and for
venting an effluent gas from the bed. Each inlet/outlet port connects
with an annular groove 49 positioned between two adjacent spring
pockets 46 and opening into a respective one of the discrete chambers.
The closure member 12 is adapted to carry valve means for control
of the delivery of product gas from each sieve bed chamber 17 18
19 20 21 and whilst various valve types are functionally acceptable
this embodiment utilises simple diaphragm valves 51 each of which
is peripherally sealed and retained in a housing 52 and has a central
area that cooperates with a valve seat 53 that circumscribes an
inlet 54 connecting with the interio of the chamber by way of the
port 33 in the closure member 12. An annular space 55 around the
valve seat 53 that is defined on one side by the outer portion of
the valve 51 provides the outlet therefrom which communicates with
a respective product gas collection chamber 59 60 and delivery
connection 61 62 (reference FIG. 3).
The diaphragm of the valve in its outer portion, is pierced by
a small orifice 56 which enables collection chamber pressure to
be effective in a manner for closing the valve 51 on to its seat
53. These product gas control valves 51 open and close automatically
according to pertaining working pressures of the system so that,
for example, during a charging phase when the pressure in a sieve
bed chamber is above that in the product gas collection chamber,
owing to withdrawal of gas therefrom by a user, the associated valve
51 lifts; conversely, while the pressure in the sieve bed chamber
is below that in the product gas collection chamber during a regeneration
phase, the valve 51 is held closed by the greater pressure of the
collection chamber gas.
The application of purge gas to each sieve bed chamber is also
automatic, being made by relative gas pressures during overlapping
cycling of the sieve beds as they alternate through charging and
regenerating phases. The inclusion of small portways in the purge
flow paths (an entry to which is seen at 50) obviates the need for
any valved control thereof.
The end cap closure member 36 is adapted to carry valve means for
admission of pressurised air to charge the molecular sieve beds
of the chambers of the container 10 and alternately for release
of effluent gas therefrom. Whilst various valve types are functionally
acceptable, such as pad, spool, gate and other valves, this embodiment
favours an arrangement including simple diaphragm valves (not shown)
that respond to supply and to bed pressure and which are controlled
by sequentially operating pneumatic servo-valves 57 switched by
an electronic timer 58 also mounted on the end cap closure member
36 that has two or more predetermined overall cycle times within
each such cycle time there are two periods of fixed ratio, determining
the charge and regeneration phases respectively. The electronic
timer may be caused to switch from one overall cycle time to another
by such means as altitude switches or by sensing a parameter of
the working gases, preferably the concentration value of an element
of the product gas.
A molecular sieve bed container providing a plurality of molecular
sieve bed chambers, in accordance with this embodiment of the invention,
is particularly suited for use with gas separating apparatus in
an aircraft application. The oxygen-enriched product gas is available
for breathing by aircrew, whilst the nitrogen-enriched product gas
provides a substantially inert gas which may be used for such purposes
as preventing explosive gas mixtures from collecting over fuel in
the fuel tanks of the aircraft.
In another embodiment of the invention, illustrated in FIG. 4
a molecular sieve bed container 80 provides three molecular sieve
bed chambers 81 82 83. When filled with molecular sieve material
these chambers provide molecular sieve beds which are suited for
retention of a constituent gas (for example nitrogen) in a gas mixture
(for example air) supplied to the container as a charge gas, so
that, for instance, oxygen-enriched air is delivered as product
gas. The container 80 comprises a tubular outer housing 84 having
a wall thickness dimension in the order of 1.5 mm and two inner
tubular wall structures 85 86 of different diameter dimensions
and each having a wall thickness dimension in the order of 0.8 mm,
concentrically located within the outer housing, this assembly being
closed by respective end closure members 87 and 88. In this embodiment
the tubular wall structures 85 86 are sealed with each of the end
closure members 87 88 by resilient sealing elements 89 which seat
in annular grooves in the end closure members.
Molecular sieve material in the chambers 81 82 83 is held in
a compacted condition by springs 90 located in pockets 91 provided
in the end closure member 87 and acting on a disc shaped filter
plate 92 in the case of the central chamber 81 and annular filter
plates 93 94 in the case of the annular chambers 82 and 83 respectively.
The plates 92 93 94 are manufactured from sintered aluminum filter
material which allows gas to pass whilst retaining the molecular
sieve material and any dust associated therewith. Similar filter
plates 95 96 97 are provided between the molecular sieve material
and the end closure member 88.
End closure member 87 is provided with a threaded union 98 for
attachment of a hose (not shown) whereby charge gas is supplied
to the container 80. Charge gas flows from ports 99 in the union
98 into a passageway 100 provided in the end closure member 87 and,
following the path shown by the solid arrows, flow past diaphragm
valve 101 (shown closed in FIG. 4) when this valve is open to enter
the sieve bed chamber 81 by way of passageway 102 and filter plate
92.
A similar diaphragm valve 103 closes an outlet port 104 connected
with passageway 102 and, when open, allows purge gas to vent from
the sieve bed chamber 81 to ambient atmosphere following the path
shown by the broken arrows.
Pairs of diaphragm valves (not shown) similar to diaphragm valves
101 and 103 are provided for the sieve bed chambers 82 and 83. Opening
and closing of the respective pairs of diaphragm valves of the respective
sieve bed chambers 81 82 83 are controlled by solenoid valves
105 106 and 107 associated one with each pair of diaphragm valves.
Operation of a solenoid valve and a pair of diaphragm valves will
be further described hereinafter.
End closure member 88 is provided with a threaded union 108 for
connection with a hose (not shown) by which product gas is delivered
to an end user. Product gas flowing from the sieve bed chambers
81 82 83 flows through the filter plates 95 96 97 into passageways
in the end closure member 88 such as passageway 109 associated
with sieve bed chamber 83 and then by way of outlet ports, such
as outlet port 110 associated with passageway 109 to a gas collection
chamber 111 having connection with the threaded union 108 by way
of ports 112 in the union 108. Each outlet port is adapted for closure
by a diaphragm valve, for example diaphragm valve 113 closing outlet
port 110 operation of these diaphragm valves being similar to that
hereinbefore described for the diaphragm valves 51 of the end closure
member 12 provided for the container 10 shown in FIG. 1 of the drawings.
Also, application of purge gas to each of the sieve bed chambers
81 82 83 is automatic, being made by relative gas pressures during
overlapping cycling of the sieve beds as they alternate through
charging and regenerating phases, in similar manner to that hereinbefore
described for the container 10 shown in FIG. 1.
Configuration and operation of solenoid valve 105 and associated
diaphragm valves 101 and 103 of sieve bedchamber 81 will now be
described with reference to FIG. 5. The solenoid valve 105 comprises
an armature 114 and double acting valve member 115. An elastomeric
pad valve 116 is provided in one end 117 of the valve member 115
for cooperation with a valve seat 118. The valve seat 118 surrounds
an orifice 119 connecting with a passage 120 which in turn communicates
with a chamber 121 in the end closure member 87. One wall of the
chamber 121 is provided by that surface of the diaphragm valve 101
which faces outwardly away from molecular sieve bed chamber 81.
An elastomeric pad valve 122 in the other end 123 of the valve
member 115 cooperates with a valve seat 124 provided on one end
of a union assembly 125 having a central orifice 126 extending therethrough
to open at the valve seat 124. At the other end of the union assembly
125 the orifice 126 connects with a passage 127 which communicates
with a chamber 128 in the end closure member 87. One wall of the
chamber 128 is provided by that surface of the diaphragm valve 103
which faces outwardly away from the molecular sieve bed chamber
81.
Chambers 121 and 128 are each provided with a bleed flow of charge
gas supplied to the container 80 this bleed flow being provided
by an orifice 129 which communicates between passageway 100 and
one end of a passage 130 in the end closure member 87. Orifices
131 and 132 communicate between the other end of the passage 130
and the respective chambers 121 and 128.
Thus charge gas pressure is effective in one or the other of the
chambers 121 and 128 to retain the respective diaphragm valves 101
or 103 in a closed position, dependent upon the position of the
double acting valve member 115. If the double acting valve member
115 is positioned so as to bring the pad valve 116 into a position
where it seats with valve seat 118 then chamber 121 will be closed
and charge gas pressure will be effective therein to retain diaphragm
valve member 101 in a closed position. With the valve member 115
in this position the pad valve 122 at its other end will be lifted
off valve seat 124 and the chamber 128 will be communicated to ambient
atmosphere by way of passage 127 orifice 126 in union assembly
125 and an outlet (not shown). The pressure of purge gas in the
molecular sieve bed chamber 81 will act upon the diaphragm valve
103 to cause it to open and communicate the chamber with ambient
atmosphere for venting of the purge gas.
Similar solenoid valve and diaphragm valve arrangements are provided
for each of the molecular sieve bed chambers so that by sequentially
operating the solenoid valves under control of an electronic timer
(not shown) the sieve beds are caused to cycle through charge/supply
and purge/vent phases in overlapping sequence. This ensures that
a continuous supply of product gas, such as oxygen-enriched air,
is made available by the molecular sieve bed container.
A molecular sieve bed container in accordance with the present
invention provides a plurality of molecular sieve beds in a compact
arrangement which accomplishes considerable savings in both weight
and space envelope required to accommodate the container when compared
with molecular sieve beds provided in individual containers. The
wall thickness of the inner wall structures is reduced by at least
half compared with the wall thickness of the outer housing, this
thickness reduction being limited mainly by the requirement to provide
some rigidity for ease of handling during assembly of the container.
Also, substantial weight saving is effected by the requirement for
only two end closure members as compared with the total number of
end closure members required for the same number of sieve beds provided
in individual containers. |