Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to an unidirectional
Eluid flow membrane useful as check-valve, overpressure
valve, purc~e valve, exhaus-t diaphragm, escape valve and
the like, and to a method of manu~acturing the same.
N~lmerous equipments, particularly underwater
equipments such as life- or sea- jackets, masks, snorkels,
regulators and filtering systems, include at least one check-
valve in their structure to allow a gas such as air to flow
in one direction while preventing water Erom flowing in the
other direction. Thus r every life- or sea- jacket incorporates
at least one overpressure valve to allow the pressurized gas
used for inflating it to escape over a threshold pressure of
about 1 lb. Most of the masks or snorkels used for diving also
each incorporate at least one purge valve to allow any water
entering inside the mask or snorkel to be expelled from the
same when the diver breathes out by the nose. Similarly, all
the regulators used by the divers each incorporate an exhaust
diaphragm to.allow air to escape and any water swallowed by
the diver to be spitted out by the same withou-t having to
remove the mouth piece from his or her mouth. In each case,
it is of course necessary that water be prevented from flowing
in the other direction and from entering into the inflated
life or sea jacket, the mask or the mouth.
All the check-valves used up to now in these under-
water equipments are of the mechanical type and include spring
or resilient means as return-means for the valve. After
several years of use or storing, the spring or the resilient
material generally becomes weak or it jams. In both cases,
this results in malfunctioning of the equipmentthat may be very
prejudiciable and even extremely risky when the equipment
is especially designed for being used in case of emergency.
In accordance with the present invention, it ha ~ ow
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been found that the abo~e mentioned drawback can be co~pletely
overcome by using an.u~idirectional fluid ~low~me~m~rane
allowing air or another gas to flo~ in.one directio~ ~hile
pre~enting water from flowing in the othex direction, instead
of using a spring valve. ~ndeed, as such a membrane does
not comprise any ~lechanical part, it cannot jam or be damaged
in any way.
The present invention therefore proposes a.n unidi-
rectional fluid flow membrane for use as overpressure valve, .
purge valve, exhaust diaphragm or escape valve, which membrane
is in the form of a sheet of porous plastics material havlng
a thickness ranging from about 1~16 to 1/2 inch and comprising
a multitude of interconnected pores that together deEine passages .
suitable to allow air or another gas to flow~ The sheet of
plastics material has one face heat treated to partially close
the passages tc an extent sufficient to prevent a liquid such as
water from flowing across the sheet toward the other face,
~hereby this sheet acts as a check-~alve with respect to the
liquid only.
Preferably, the interconnected pores of the sheet
o plastics material have a size ranging from about 8 to
250~.
When the unidirectional membrane according to the
invention is to be used as overpressure valve in a life-or
: sea-jacket, the sheet of plastics material preferably has a
thickness of about l/2 inch and the interconnected pores
have a size of 8 to 10 ~, the membrane thus having a
threshold pressure oE about Q.75 to l.0 lbs.
When the unidirectional membrane according to the ~;:
invention is to be used as purge val~e or exhaust diaphragm
in an underwater mask, snorkel or regulator, the sheet o~ :
plastics material preferably has a thiskness of a~out
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1/16 inch and the lnte~connected pores have a size of about
120~ to allow any water inside the mask, snorkel or regulator
to be unilaterally expelled therefrom when the diver breathes
out by the nose or the mouth.
When the unidirectional membrane according to the
invention is to be used as escape valve in a pumping filtering
system, -thc interconnected pores preferably have a size
of about 35ju.
In each case, the sheet of plastics material can
advantayeously be made from a material selected from the
group consisting of high density polyethylene, ultra-hic~h
molecular weight polyethylene, polypropylene and fluoro
carbon.
Suitable sheets of plastics material that can be
used, for example, as startiny material for the manufacture
of unidirectional fluid flow membranes according to the
invention are those sold under the trademark "POREX"
by the U.S. irm Glasrock Products Inc. of Fairburn, Georgia.
The sheets of plastics material supplied by this firm in
thicknesses varying from 1~16 to 1/2 inch or more, have
omnidirectional interconnected pore sizes varying from 8 to
500~ depending onthe polymers used. These sheets can be
used as disc filters or column chromatography, electrode
gel, ion-exchange resin or under-drain supports. To make
such sheets of plastics material unidirectional and therefore
useful in accordance with the present invention, it has been
found that it was necessary only to glaze one face thereof
at a temperature slightly inferior to, preferably less 1
or 2C than, the melting point of plastics material. Such a
glazing gives the sheet of plastics material a diffexential
porosity, that is a porosity that is different from one face
of the sheet to the other.
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Thexefore, the present invention also proposes
a method of manufacturing an unidirectional fluid flow
membrane of the type defined hereinabove, which method
~omprises the step of g]azin~ one face of a sheet of porous
plastics ma~erial comprising a multitude o interconnected
pores that together define passages suitable to allow
air or another gas to flow, at a temperature slightly
inferior to the melting point of the plastics material in
order to partially close the passages to an extent sufficient
to prevent water from flowing across the sheet from the one
face toward the other face.
As aforesaid, the purpose of this glazing which is
applied to an already formed sheet of plastics material is
essentially to reduce the porosity at the surface of one
face of the sheet to an extent sufficient to prevent water from
flowing across th~ sheet of plastics material from this one
face t~ the other. This reduction of porosity is obtained
as glazing causes shrinking of the pores in the vincinity
of the surface of this one face by non-reversible, thermical
expansion of the plastics cells forming the sheet and/or
slow melting of the ed~es of the same.
When use is made of "POREX" as porous plastics
material, glazing can be carried out in a single step, simply
by bringing the sheet of plastics material into contact
with a hot plate. If necessary, the hot plate may be
provided with hot air injection nozzles to diffuse heat
from the plate through the plastics material.
When use is made of another kind of porous plastics
materials, particularly non~hydrophobic porous plastics
materials, it is generally preferable to treat the material
with an inorganic acid in order to prevent wetting of the pore
surfaces and thus re-entry of water through the memhrane.
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Actually, if the plastics materials used in the membranes
according to the invention are not hydrophobic
they generally allow water, particularly soapy water, to
pass through -the memhranes as the -tiny pores at the surface
of tlle sheets of plastics material can no more "trap"
small buhbles of air or anyother gas tha-t prevents
water from flowing, as they can owing to their surface tension
when they are still dried. As soon as their pore surfaces
are wetted, the mernbranes thus allow water to continuously
pass therethrough in both directions.
In order to prevent such a drawback, the mernbrane
made of non-hydrophobic porous plastics material must
therefore be subjected to treatment with an inorganic acid
before glazing. This treatment can be carried out with, for
example, a solution of 40% HCl per volume. The acid makes
the surface of the pores non-slippery and thus renders the
material-completely hydrophobic~
The invention and its various advantages in use
will be better understood with re~erence to the following
description taken in connection with -the accompanying
drawings in which:
Fig. 1 is a schematic, enlarged view of an unidi-
rectional membrane according to the invention, shown in
cross-section;
Fig. 2 is a ~iew of an inflated life-jacket
provided with a membrane according to the invention as
overpressure valve;
F.igs. 3 and 4 are perspective and cross-sectional
views of the mernbrane used as overpressure valve in the
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life-jacket sho~n in Fi~, 2,
Fig. 5 is a cross~section view of a mask or snorkel
provided with a membrane according to the invention as
purge valve; and
Fi.g. 6 is a cross~sectional top plane view o~
a dried-regulator for use in diving, provided with a membrane
according to the invention.
The unidirectional fluid flow membrane l according
to the invention as shown in cross~section in Fig. l is
made of a sheet of porous plastics material 3 comprising
a multitude of interconnected pores 5 that together define
passages suitable to allow air or anyother gas such as CO
to flow therethrough. The sheet 3 has a thickness T `
that may vary from about l/16 to l/2 inch depending on its
use. The interconnected pores 5 have a size that may vary
from about 8 to 250 depending on the proposed use for the
membrane. ~-~
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The thickness of the sheet and the size of its
pores of course depend on its use. If the membrane is
to be used as overpressure valve, it will be necessary to use
a sheet 3 having a substantial thickness with pores 5 of
a very small size. If the membrane is to be used as purge
val~e, it will be necessary to use a sheet having a small
thickness with pores of bigger size.
The sheet 3 is preferably made of polypropylene as
this material provides better gas flow although other plastics
material such as high-density or ultra~high molecular weight
polyethylene or fluorocarbon could also be used.
The membrane l is generally made starting from an
omnidirectional sheet 3 of porous plastics material of the
type sold under the trademark "POREX" by the firm Glasrock
Products Inc. of Fairburn~ Georgia. To make it unidirectional,
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the sheet 3 is subjected to thermical treatment. More
especially~ one ~ace 7 of the sheet 3 is glazed at a tempera-
ture sli~htly inferior to the melting point oE the plastics
` material for a period of time sufficient to reduce the poro-
si.ty at the suxface o this one ace 7 to such an extent
that water is prevented from flowing across the sheet 3
from its one face 7 to its other ace 9.
Glazing of the face 7 of the sheet 3 causes the
particles oE plastics material adjacent to face 7 to
expand in a non-reversible manner or to slowly melt as is
shown in Fig. 1 and thus to reduce the size of the pores on
this face 7 only. As a result of this reduction in size, the
surface tension of the pores is substantially increased at
the face 7 and this surface tension increase prevents
water from entering into face 7 and flowing rom this face
7 to face 9.
.- As a matter of act, glazing here makes the sheet
3 completely hydrophobic, in a better manner than any
acidic solution could do.
The reduction in size of the pores 5 at the
surface of the face 7 of the sheet 3 however does not prevent
air or anyother gas to flow from face`~ to face 7 and water
or anyother liquid to be expelled under suitable pressure
in the same direction.
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The unidirectional structure of the membrane 1
with respect to water makes it particularly useful as check-
valve in many kind of underwater equipments in place of the
spring valves used up to now~
Figs~ 2 to ~ show a life~jacket 11 provided with
an unidirectional membrane 1 as overpressure valve.
As everybody knows~ the life-jacket 11 as every
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life-jacket must include at least one overpressure valve to
allow the pressurized gas contained in the cartridge 13
and used for inElating the bag 15 in case of emergency
to escape over a predetermined threshold pressure which is
generally of 1 lb. This overpressure valve is llecessary to
avoid that the bacJ lS be over-in1ated and eventually
dama~ed wi-th a:ir leaks or by complete explosion.
To re~lace the conventional overpressure spring-
valve that may become weak or jam, use is therefore made of
an unidirectional membrane 1. The membrane is glued and/or
sealed directly onto the surface of the reinforced edges 17
of an opening 19 provided in the bag 15 at a suitable location,
and protected by a grid 16. Of course, the heat-treated face
7 of the membrane 1 must be external to the bag 15 to prevent
water from entering into the same.
To ensure a suitable threshold pressure of about 1
lb, use,,can be made for example of a heat-treated, POREX
sheet of poly,ethylene having a thickness of 1/2 inch with pores
of about 8 to 10~.
,Fig. 5 shows a mask 2 of a conventional type,
comprising a rubber skirt 27, a strap 29 and a front glass
23 fixed to the skirt by a plastic trim 25. In accordance
with the invention, the mask 21 is advantaseously provided
- with an unidirectional membrane 1 acting as purge valve.
The membrane 1 is located just under the nose of the diver in
a hole provided in the rubber skirt 27 to allow any water
entering inside the mask to be expelled from the same when
the diver heavily breathes out by the nose~
Of course, the heat treated face 7 of the membrane
1 mus~ be external to the skirt 27 to prevent ex~ernal
water from extering into the mask.
To allow easy expulsion not only of air but also
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of water our o~ the mask, use can be made, ~or example of
a heat-treated, POREX sheet of polypropylene having a thickness
o~ 1/16 inch with large pores of about 120 ~.
Last of all, Fig. 6 shows a regulator 31 of a
convelltlonal type comprising a rubber mouth pieces 33, a
f~ont cap 35 made o~ plastics and/or metal and a low pressure
air-supply 37 in the form of a hose connected to a pressuriz-
ed air bot-tle via a pressure reducer (not shown). In
accordance with the invention, this regulator 31 is rendered
"dry" simply by using two separate membranes 1 and 1'.
The membrane 1 forms the back cap of the regulatox and allows
air together with any water having entered the regulator to
be expelled by the diver during his or her expiration. The
membrane 1' acts as a plug for closing the mouth piece 33
and is designed to prevent sea water from en-tering into the
regulator when the diver removes it from his or her mouth.
However, this membrane 1' must also be so designed as to
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allow water swallowed by the diver to be expelled by the same
during his or her expiration, that is under a certain overpres-
sure. Of course, the heat treated faces 7 and 7' of themembranes 1 and 1~ must be external to prevent sea water from
entering into the regulator.
As membrane 1, use can be made, for example, of a
heat-treated, POREX sheet of polypropylene having a thickness
~ of about 1/16 inch with large pores of about 120~u. As
membrane 1', use can be made, for example, of a heat-treated
POREX sheet of polypropylene having a thickness of about
1/16 inch with very large pores of about 250~u to prevent sea
water from entering into the regulator while allowing swallowed
water to ba expelled when strongly breathing out. Of course,
the unidirectional membrane according to the in~ention can be
used for other purposes in which unidirectionality is requested.
Thus, by way o~ example, the membrane according to the invention
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can also be used as a check~ e in a pumping filtering system
such as those used for the pool. In thls case, the pores of the :
membrane however must have a large size of, for example 35 ~u
'to avoid ~ener~tin~ too much loss of pressure lnsicle the system.
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