Reverse osmosis water purification system with improved pressure relief valve

An improved pressure relief valve is provided in a reverse osmosis water purification system to prevent the pressure of produced purified water from exceeding a predetermined pressure limit. In the water purification system, ordinary tap or feed water is supplied to a reverse osmosis module which produces a purified water supply coupled for flow to a pressurized storage reservoir to await dispensing, and a reject water supply coupled through a backpressuring restrictor for flow to a drain. The relief valve comprises a valve head with differential surface areas exposed respectively and directly to the pressure of the purified water supply and to the pressure of the reject water supply upstream of the restrictor, wherein the differential surface areas are chosen for valve head movement to open a purified water relief port when the purified water pressure reaches a selected proportional limit relative to the reject water pressure. A diaphragm operates in conjunction with the valve head to positively prevent reject water leakage into the purified water supply.

BACKGROUND OF THE INVENTION 
This invention relates generally to water purification systems of the 
reverse osmosis type for producing a supply of relatively purified water 
for drinking, cooking, etc. More particularly, this invention relates to 
an improved pressure relief valve for use in such water purification 
systems, wherein the pressure relief valve is designed for accurate and 
reliable operation to prevent the pressure of produced purified water from 
exceeding a predetermined pressure limit. 
Reverse osmosis water purification systems in general are relatively well 
known in the art for producing a supply of purified water from an incoming 
supply of ordinary feed or tap water or the like. In such systems, the 
feed or tap water is coupled to a reverse osmosis module including an 
appropriate membrane for separating the feed water supply into a 
relatively pure water supply and a relatively impure or reject water 
supply. The purified water supply is normally coupled for flow into a 
suitable pressurized storage reservoir to await dispensing through a 
conventional faucet valve or the like. Conversely, the reject water supply 
is coupled for flow to and discharge as waste through a suitable drain 
path. As is known in the art, for proper operation of the reverse osmosis 
module, the reject water drain path includes a restrictor which functions 
to maintain a substantial backpressure acting upon the membrane. 
In many water purification systems of the general type described above, the 
storage reservoir comprises a compact tank or vessel having an internal 
flexible bladder which separates the tank interior into two distinct 
chambers. The produced purified water is coupled for flow into one of 
these chambers, whereas the other chamber contains a compressible gas such 
as air. As the tank fills with produced purified water, the compressible 
gas is reduced in volume to progressively increase the pressure acting 
through the bladder upon the purified water for dispensing purposes. 
However, this increasing pressure applied to the purified water reduces 
the pressure differential across the reverse osmosis membrane to 
correspondingly reduce the operational efficiency of the reverse osmosis 
module. That is, as the pressure of the purified water approaches the 
pressure of the reject water supply upstream of the restrictor, the 
operational efficiency of the reverse osmosis module progressively 
diminishes. If the purified water pressure is allowed to reach equilibrium 
with the reject water pressure, the desired pressure differential across 
the membrane is eliminated to result in potential migration of impurities 
through the membrane to the produced purified water. 
In the past, pressure relief valves have been proposed to prevent 
pressurization of the produced purified water beyond a selected pressure 
limit relative to the pressure of the reject water supply. That is, such 
pressure relief valves are designed to maintain a minimum pressure 
differential across the reverse osmosis membrane during all conditions of 
system operation, including a substantially filled condition for the 
purified water reservoir. Such relief valves function by the use of 
complex valve structures designed to bleed produced purified water into 
the reject water supply when the predetermined pressure limit is reached. 
See, for example, U.S. Pat. Nos. 3,542,199; 3,568,843; and 4,077,883. 
However, such prior pressure relief valves have not provided reliably 
accurate pressure control of a purified water supply. Moreover, such prior 
relief valves have utilized valve structures and related seal components 
which undesirably leak pressurized reject water into the produced purified 
water supply during certain failure mode conditions. 
There exists, therefore, a significant need for an improved pressure relief 
valve for use in reverse osmosis water purification systems, wherein the 
improved pressure relief valve is designed for accurate pressure limiting 
operation with respect to produced purified water, without permitting 
inadvertent leakage of reject water into the produced purified water 
supply. The present invention fulfills these needs and provides further 
related advantages. 
SUMMARY OF THE INVENTION 
In accordance with the invention, a reverse osmosis water purification 
system or the like is provided with an improved pressure relief valve for 
preventing pressurization of a produced purified water supply beyond a 
predetermined pressure limit. The pressure relief valve comprises a valve 
head with differential surface areas to provide a fixed proportional 
comparison between the pressure of a produced purified water supply and a 
pressurized reject water supply. The differential surface areas on the 
valve head are designed to insure valve head movement to open a purified 
water relief port whenever the purified water pressure reaches a 
predetermined proportion of the reject water pressure. A diaphragm 
cooperates with the valve head for positively preventing reject water flow 
into the produced purified water supply. 
The reverse osmosis water purification system includes a reverse osmosis 
module adapted for connection to an incoming supply of ordinary feed or 
tap water or the like. The reverse osmosis module includes a membrane 
which functions, as is known in the art, to separate the feed water supply 
into a relatively purified water supply and a relatively impure reject 
water supply having impurities concentrated therein. The purified water 
supply is coupled for flow to a suitable pressurized storage reservoir, 
whereas the reject water supply is coupled through a backpressuring 
restrictor to a suitable drain. 
In a preferred form, the pressure relief valve comprises a relatively 
simple and compact valve assembly mounted within the reverse osmosis 
module in flow communication with the purified and reject water supplies. 
The valve assembly includes means for supporting the backpressuring 
restrictor in the form of an elongated narrow tube or the like for 
coupling the reject water supply with substantial pressure drop for flow 
to the drain. A pressure port formed in the valve assembly communicates 
the pressure of the reject water supply at a position substantially 
upstream of the restrictor to a pressure chamber. The valve head is 
movably carried within the valve assembly and defines a first surface area 
exposed to the reject water pressure within the pressure chamber, and a 
second surface area exposed to the pressure of the produced purified water 
supply. When the pressure of the produced purified water reaches a 
selected proportion of the reject water pressure, as determined by the 
proportional sizes of the first and second surface areas on the valve 
head, the valve head is displaced to open a relief port communicating 
excess purified water to the drain. 
In accordance with further aspects of the invention, the valve head is 
physically separated from the pressure chamber by a flexible diaphragm. 
Reject water within the pressure chamber acts through the diaphragm 
directly upon the first surface area of the valve head. However, the 
diaphragm positively isolates the pressurized reject water supply within 
the pressure chamber from the relief port or the purified water supply to 
prevent inadvertent reject water flow into the purified water supply when 
the relief port is closed. 
Other features and advantages of the present invention will become more 
apparent from the following detailed description, taken in conjunction 
with the accompanying drawings which illustrate, by way of example, the 
principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the exemplary drawings, a water purification system of the 
reverse osmosis type is referred to generally in FIG. 1 by the reference 
numeral 10. The purification system includes, in accordance with the 
invention, an improved pressure relief valve 12 (FIGS. 3 and 4) for 
limiting the pressure of a produced purified water supply contained within 
a storage reservoir 14 (FIG. 1). By limiting the pressure of the produced 
purified water supply, the pressure relief valve 12 insures reliable and 
efficient operation of a reverse osmosis module 16 (FIGS. 1-3). 
The water purification system 10 is constructed and operates generally in 
accordance with reverse osmosis purification systems known in the art. 
More particularly, the system 10 includes the reverse osmosis module 16 
coupled to a feed or tap water supply conduit 18 for receiving an incoming 
supply of feed or tap water for purification purposes. The reverse osmosis 
module 16 comprises a housing 20 encasing a reverse osmosis membrane 22 of 
a type known in the art for separating the incoming feed water supply into 
a substantially purified water supply having suspended and/or dissolved 
impurities removed therefrom, and a reject or brine water supply having 
the impurities concentrated therein. In general terms, the produced 
purified water supply is coupled through a conduit 24 for flow into and 
storage within the reservoir 14 to await dispensing, whereas the reject 
water supply is coupled through a drain conduit 26 for discharge as waste 
to an appropriate drain. Importantly, as is known in the art, the drain 
path for the reject water supply includes a restrictor (not shown in FIG. 
1) for maintaining a fluidback pressure on the reverse osmosis module 16 
to insure proper and efficient module operation. In accordance with one 
aspect of the invention, as will be described, the restrictor is 
conveniently integrated into the improved pressure relief valve 12. 
Although the construction details for the reverse osmosis module may vary, 
the illustrative drawings show the reverse osmosis membrane 22 wrapped 
about an upstanding perforated support tube 28 to define a cartridge 29 
adapted for simple replacement installation as a unit into the module 
housing 20. Incoming feed water flows through the membrane 22 for 
separation into the purified and reject water supplies. The purified water 
supply passes into the support tube 28 for flow through an outlet port 30 
in the module housing 20 and further passage through the conduit 24 to the 
storage reservoir 14. The reject water supply is discharged to the drain 
conduit 26 through the restrictor shown in FIG. 3 in the form of an 
elongated tube 34 carried by the improved relief valve 12. 
The produced purified water supply flows through the pure conduit 24 into a 
pure water chamber 36 within the storage reservoir 14. This reservoir 14 
comprises a suitable storage vessel or tank having an internal flexible 
barrier or bladder 38 which separates the tank interior into the pure 
water chamber 36 and a second chamber 40 adapted to receive a supply of a 
compressible fluid such as air through an appropriate fill valve 41 or the 
like. As is known in the art, supply of purified water into the pure water 
chamber 36 causes the bladder 38 to deform in a manner expanding the pure 
water chamber 36 which decreases the volume of the second chamber 40. Such 
volumetric changes are accompanied by compression of the fluid in the 
chamber 40 to apply a progressively increasing pressure to the stored 
purified water. This fluid pressure applied to the purified water is 
effective to deliver a flow of the purified water through a dispensing 
conduit 42 and a faucet valve 44 when the faucet valve is opened. 
The improved pressure relief valve 12 of the present invention is designed 
to limit the pressure applied to the produced purified water within the 
storage reservoir 14 as the pure water chamber 36 is filled. More 
specifically, the purified water produced by the reverse osmosis module 16 
is coupled to and gradually fills the pure water chamber 36 within the 
reservoir 14, resulting in increased pressure applied to the stored 
purified water unless and until the faucet valve 44 is opened for 
dispensing purposes. The pressure of the purified water acts through the 
pure conduit 24 and the perforated support tube 28 upon the pure side of 
the membrane 22. Accordingly, the differential pressure across the 
membrane 22 defined by the reject and purified water supply pressures 
progressively decreases. This decrease in differential pressure is 
accompanied by a progressive reduction in the operational efficiency of 
the reverse osmosis module. Moreover, if this pressure differential were 
permitted to reach an equilibrium condition, impurities in the reject 
water can migrate through the membrane to contaminate the produced 
purified water supply. The pressure relief valve 12 is designed to limit 
the pressure of the purified water supply to a predetermined proportion of 
the reject water pressure, thereby maintaining acceptable module 
efficiency at all times and preventing contamination of the purified water 
supply. 
As shown best in FIG. 3, the relief valve 12 comprises a compact valve 
assembly seated within the base or lower end of the module housing 20 in a 
position disposed in direct flow communication with the reject water 
supply surrounding the membrane 22 and the produced purified water supply 
within the membrane support tube 28. Specifically, the valve assembly is 
defined by a generally cylindrical valve body 46 having an external upper 
annular groove 48 for receiving a seal ring 50 such as an 0-ring or the 
like to seal against the interior of the module housing. A reject drain 
port 52 is formed in the valve body 46 to couple the reject water supply 
within the module housing 20 for in-line passage through the elongated 
tube 34 wrapped loosely about the valve body 46 within a lower external 
annular groove 54. A downstream end of this support tube 34 opens freely 
into the lower groove 54 for reject water drainage downwardly around the 
valve body 46 and passage through a housing drain port 56 coupled to the 
drain conduit 26. Accordingly, as previously described, the tube 34 
defines a restrictor through which the reject water supply is discharged 
to the drain while maintaining a satisfactory operational backpressure on 
the reject water side of the membrane 22. The specific backpressure 
applied by the restrictor tube 34 may be accurately chosen and controlled 
by selection of the tube diametric size and length. 
The relief valve 12 further includes a pressure port 58 having an upstream 
end open to the reject water side of the membrane 22 and thus 
communicating with the pressurized reject water supply. This pressure port 
58 in turn has a downstream end opening into a pressure chamber 60 within 
the valve body 46. A resilient diaphragm 62 lines one side of this 
pressure chamber 60. More particularly, as viewed in FIGS. 3 and 4, the 
valve body 46 includes an upwardly open counterbore 64 with an annular 
shoulder 65 surrounding an upper margin of the pressure chamber 60. The 
diaphragm 62 comprises a resilient disk of elastomer material or the like 
and is seated with its peripheral edge resting upon the shoulder 65. A 
retainer ring 66 is installed into the counterbore above the diaphragm 62 
and functions in cooperation with the shoulder 65 to hold the diaphragm 
firmly in place. 
A plug-like valve head 68 is mounted within the retainer ring 66. This 
valve head 68 has a lower surface area 70 of precision selected dimension 
rested or abutted directly against the diaphragm 62. In addition, the 
valve head 68 includes an upper or opposite surface area 72 of relatively 
precision dimension defined by the upwardly presented area circumscribed 
by a seal ring 74 seated within a valve head groove 75. A valve seat 
cylinder 76 in turn has a lower edge seated upon the retainer ring 66 and 
an upper end projected into the support tube 28 of the reverse osmosis 
cartridge 29. A lower shoulder 77 of the cylinder 76 is positioned to abut 
the lowermost end of the support tube 28, and a seal ring 78 on the upper 
end of the cylinder 76 engages the interior of the support tube. An upper 
plug 80 of the valve head 68 conveniently guides into the cylinder 76 to 
permit upward valve head movement to a position engaging the seal ring 74 
with a valve seat 82 on the cylinder 76. When such engagement occurs, as 
viewed in FIG. 3, relief flow of purified water is prevented, as will be 
described. 
More specifically, during normal operating conditions when the pure water 
chamber 36 of the reservoir 14 is below a substantially filled condition, 
the pressure of the reject water within the pressure chamber 60 is 
sufficient to maintain the valve head seal ring 74 engaged with the valve 
seat 82. The reject water pressure acts through the diaphragm 62 directly 
upon the lower surface 70 of the valve head in direct opposition to the 
pressure of the purified water acting against the upper end of the valve 
head 68 as defined by its effective upwardly presented surface area 
including the seal ring 74. Notably, the pressure chamber 60 is sealed 
against flow such that the reject water is supplied thereto substantially 
without pressure drop and further without risk of inadvertent flow into 
the purified water supply. 
When the reservoir 14 reaches a substantially filled condition as 
represented by a predetermined maximum purified water pressure relative to 
the reject water pressure, the valve head 68 displaces away from the valve 
seat 82 to open the relief valve. In this mode of operation, a bleed flow 
of purified water is permitted from the support tube 28 into the interior 
of the valve body 46. This bleed flow passes further through a port 84 in 
the retainer ring 66 and a port 86 in the valve body 46 for leakage flow 
past the restrictor tube 34 to the drain. Importantly, the purified water 
bleed flow is maintained in parallel with the reject water drain flow path 
until a low pressure region downstream of the restrictor tube 34 is 
reached for purposes of preventing undesired mixing of purified and reject 
water in the event of failure of seal components. 
The improved relief valve 12 thus provides a relatively simple structure 
designed for reliable control of purified water pressure in a reverse 
osmosis purification system. The purified water pressure is limited to a 
set maximum proportion of the reject water pressure, wherein the limit may 
be controlled with great accuracy by precision formation of the 
differential upper and lower valve head surface areas. In a preferred 
design, the purified water pressure will be limited to about two-thirds of 
the reject water pressure to maintain an efficient pressure differential 
across the membrane 22. Importantly, the diaphragm 62 provides a safeguard 
against failure mode mixing of the purified water and reject water 
supplies. 
A variety of modifications and improvements to the improved pressure relief 
valve and related water purification system will be apparent to those 
skilled in the art. For example, for ease of assembly, the retainer ring 
66 and valve seat cylinder 76 may be formed as single component for 
suitable mounting into the valve body 46 as by threading. Accordingly, no 
limitation on the invention is intended by way of the foregoing 
description and accompanying drawings, except as set forth in the appended 
claims.