CA1156935A

CA1156935A - Reverse osmosis liquid purification apparatus

Info

Publication number: CA1156935A
Application number: CA000364058A
Authority: CA
Inventors: Leslie P. S. Wilson
Original assignee: Sykes Ocean Water Ltd
Current assignee: Sykes Ocean Water Ltd
Priority date: 1979-11-05
Filing date: 1980-11-05
Publication date: 1983-11-15
Also published as: JPH0258968B2; EP0028913A1; US4367140A; EP0028913B1; AU540836B2; JPS5681108A; DE3068813D1; AU6410880A

Abstract

CANADA

ABSTRACT OF THE DISCLOSURE

In apparatus for the reverse osmosis purification of water or other fluid in a module containing a membrane, the water is forced into the module under pressure using two piston-cylinder assemblies mechanically interconnected with the pressurised fluid from the module applied to the rear face of the piston which, from its front face, is driving water into the module, a low pressure continuously operating pump providing a low pressure on the other piston to supply the necessary extra pressure.
Valve means automatically reverse the functions of the two cylinders at each end of each stroke.

Description

~ ~l3~

, ., , . ~ , . . . . .. . .... .... .... .... .
"R33VERSE OSMOSI5 L:[~)UII) PURIF:LCl~TION Al'PI :RATUS"

.. .. . .... .... . . . .. ...
5 BACKG:ROUI`JD OF TEIE II~VEN:TYON
1. Field of the Invention This inventi.on relates to appar~tus for the purif ication oE a l:tquid, sucli a6 water, by reverse osmosis .
10 2 r Pr iox Z~rt In the specification of U.S.Patent No.4,124 ,488 there is described an apparatus for the reverse osmosl.s purification o:E water or other ~luid comprising a module including a reverse osmotic mem~rane ~ a f luid ~ 15 inlet and fluid outlet for passage of fluid through the .- module over one surf ace of the men~rane and an oukle t for i:he passage of purified fluid out of the modu:Le from the oppo~ e surface of the rnembrane, together with a rarn having a piston or diaphragm i.n a cylinder Eor forc.incl 20 fluid from the front :Eace of the piston or diaphraym through a valve to the fluid Lnlet oE the module, the ram having an operating xod e~tendi.ng outwardly from th.e re~r fac~e or: the piston or dia~hracJm and mean.s, includ.i.n~ a first controlle.tl va:lve connect.lng ~;ai.d rlu:Ld outl~t rorn 25 the~ modul.t-~ to th~3 cyli.nder to admit returned f~luid '~

. ~

frolll tlle ]i~oc;-l1e ontG tl~c rear ~ce of the piston or diaphra~Jm and a second control yalve to cont~ol discharye ~rom the rear oX the piston or diaE)hragm. Such apparatus will be leferred to hereinalte:r as apparatus cf the kin~
described.
With this construction, a fluid such as seawater is ~orced by -the ram into the module. A valve is provided between the ram and the module to prevent return o:E llu.id from the module on the return stroke o~ the ram; this may be a non-return valve or it may be a valve which is controlled by the fluid pressure or by the movement of the ram or in synchronism thexewith.
On the forward stroke of the xam, some water may pass throuyh the mel~rane and the remainder of the fluid is retuxne~ to the rear face o the piston or diaphragm.
As is explained in the aforementioned specifioation, with this arrangement, fluid may be forced into the module at a very high pressure such that water purification can be obtained. For brackish water, a pressure of the order of 300 to 500 p.s.i. would be necessary whilst for seawater, since the osmotic pressure is higher, a pressure typically of 1:he order of 600 to lOOO p.s.i.
might be necessary~ The construction descrihed above enables l:hese high pressure~ to he obtained ~aonomiaally and efficierltly becctuse the return fluid from the rner~r~ne is applied l:o the rear surface o~ the piston or diaph~gm. This rear sur~ace/ because o~ the presence .

of the operating rod, ~las a sli.~ntly sm~ller ei.~ecti.~e ar.ea.
; l'he pxessllre i.n ~he system builds up ~Itil a ~ressure is reached at which water ~11 pass thxough t~e me~rane on each stroke in equivalent volume ~o the differerlce in vo].umc between the rear and .front ends of the cylinder due to tl~e presence of the operating rod. Power has to be su~plied to the operating rod and the required work ~ ;
~or each stroke depends only on the difference of the ~ront and rear f~ce axeas, the pressure and the lenyth of the stroke. The device is thus self regu].ating and tends to ope~ate in a condition w~lere the pr.oportion of water passing through the membrane to the total inlet ~luid is equal to the rati.o o~ the operating rod cros~-section to the piston or d.iaphragm front face area.
m er~ is thus no need for any pres.sure re~u'ation by relief valves~ No adjustment is required for ~ariations of salinity and the same equipment may be used for seawater as for slightly brac};ish water.
Althouyh it is convenient to refer to water, the apparatus may be used for reverse osmosis treatment of other fluids.

Reference may also be made ~o the following further United States Patents:- 1,909,145; 3,405,058; 3,493,495; 3,498,910;
3,875,122 and 3,558,242.
BRIEF SUMMARY OF THE INVENTION
It is one of the objects of the present invention to provide a reverse osmosis liquid purification me~hod and apparatus of the kind described above in which the necessity for a mechanical reciprocating drive system is avoided.
The invention provides a method of purification of a fluid by reverse osmosis comprising the steps of (a) continuously pumping fluid from a fluid to provide ' fluid at a first pressure;
(b) raising the pressure of the fluid at sa.id first ~ pressure to a second higher pressure by means of a plurality of ; cylinders with mechanically drivingly coupled movable .fluid barriers or diaphragms operating in cyclic sequence, each cylinder being divided by its movable fluid barrier into a front end and a rear end and the diaphragms or pistons having piston rods through the rear ends of the cylinders whereb~ the rear ends have smaller swept volumes than the front ends;
(c) feeding said fluid at said first pressure through separate non-return valves to the front ends of the cylinders whereby the fluid enters each cylinder on a rearward movement of the associated diaphragm or piston;
(,d) pumping said fluid at said second high pressure ~rom the front ends of the cylinders through further non-return valves to one side of a membrane in a reverse osmosis module, and;
(,e) extracting purified fluid passing through the membrane and feeding all the remaining fluid lea~ving the module through cyclically--controlled valve means, operating in synchronism with said pistons or di.aphra~ms, back to the rear ends of the cylinders during respective forward strokes of -the pistons, where-by said second higher pressure is stabilized at a value such that the extraction ratio in the module corresponds to the ratio of piston rod area to piston area, said controlled valve means being arranged to connect the rear ends of the cylinders to a discharge ou~let during rearward strokes of the pistons; whereby said continuously pumped fluid at said first pressure provides all the power to drive said pistons or diaphragms.
From another aspect, the invention provides apparatus for the reverse osmosis purification of water or other fluid com-prising a fluid supply, a module including a reverse osmotic membrane, a flui.d inlet and fluid outlet for the passage of fluid over one surface of the membrane and an outlet for the passage of purified fluid out of the module from the opposite surface of the membrane together with a plurality of similar cylinders each having a piston or diaphragm means dividing the cylinder into a front end a~d a rear end, the front end of each cylinder having a larger swept volume than the rear end, fluid connections connecting the front end of each cylinder to the fluid inlet of the module, a separate non-return valve in each fluid connection from the front end of each cylinder, each said cylinder having its piston or diaphragm means for forcing fluid at a pressure in excess of, at least, the normal osmotic pressure of water from the front face of the piston or diaphragm means through said separate valve to the fluid inlet of the module, operating rod means mechanically inter-~ ~ -5-connecting said piston or diaphragm means, which operating rod means extend from the rear faces of said piston or diaphragm means, said piston or diaphragm means mechanically operating in a cyclic sequence, separate fluid connections have a separate non~
return or controlled distribution valve for the front end of each cylinder means arranged for supplying fluid, under a relatively low pressure, compared with the normal osmotic pressure of water, from said fluid supply to the front end of each cylinder through said separate fluid connections with the separate non-return valve or controlled distribution valve therein, and controlled valve means being operative to connect the fluid outlet of the module to the rear ends of said cylinders in synchronism with said cyclic sequence so that all the fluid leaving said fluid outlet flows back to said cylinders into the rear ends thereof in cyclic sequence to drive the piston or diaphragm means towards the front ends, said controlled valve means furthermore being operative to connect said rear ends of each of the cylinders to a discharge in se~uence when the respective piston or diaphragm means are moving back towards those ends.
In this construction, pump means supply the fluid to be treated to the front ends of the various cylinders for subsequent forcing at high pressure into the module. ThiS fluid from the pump means provides the necessary driving power for operating the pistons or diaphragms in the various cylinders. There is thus no need ~or any gearbo~ or mechanical drive to the pistons or diaphragms. If there are three or more cylinders, the pistons or diaphragms may have their operating rods interconnected by a crank-shaft; this crank-shaft however is free-running, the drive power '~?
~ 6-coming from the pump.
In the simplest case however only two cylinders are employed and, in this case, the pistons or diaphragms may be directly connected hy an operating rod.
The invention also provides apparatus for the reverse osmosis purification of water or other fluid comprising a fluid ~; supply, a module including a reverse osmotic membrane, a fluid inlet and fluid outlet for the passage of fluid over one surface of the membrane and an outlet for the passage of purified fluid out of the module from the opposite surface of the membrane together with ram means comprising a pair of similar cylinders ` each having a piston or diaphragm having a front face and a rear face and dividing the cylinder into a front end a~d rear end, fluid connections connecting the front end of each cylinder to the fluid inlet of the module, a separate non-return valve operatively disposed in each connection, each cylinder with its piston or diaphragm being arranged for forcing fluid at a pressure in excess, at least, the normal osmotic pressure o~ water, from the front face of the piston or diaphragm through said separate valve to the fluid inlet o~ the module, a common operating rod, the cylinders being a~i.ally aligned with said common operating rod extending from the rear face of one piston or diaphragm to the rear face of the other piston or diaphragm so that the ront ace of each piston or diaphragm has a larger area exposed to fluid than the rear face, pump means with two separate non-return valves, said pump means being operative to supply ~luld, at a relatively low pressure, compared with the normal osmotic pressure, from said fluid supply through said separate-non-return valves to the front end of each ..~

said cylinder, and controlled valve means operati~e selectively to connect the fluid outlet Erom the module -to the rear end of one cylinder and to connect the rear end of the other cylinder to a discharge or to connect the fluid outlet Erom the module to the rear end of said other cylinder and to connect the rear end of said one cylinder to said dischar~e and control means for sa.id con-trolled valve means operative to change-over the connections when the pistons or diaphragms reach the end of a stroke.
~ith this apparatus, the pump means can be a continuously running pump, Gonveniently an impeller or gear or vane pump. The outlet from this pump need only be at a very low pressure compared with the pressure required in the module and might typically be 80 p.s.i. This output is applied through non-return valves to the front ends of both rams (considering a system with only two cylinders). One of these rams has its rear end connected to dischar~e. The other ram has its rear end connected to the high pressure outlet from the module. The two rams are interconnected by the common operating rod. Considering the ram with its rear end connected to discharge, the piston or diaphragm wil:L tend to move towards the rear end. The pump pressure, applied over the whole front face, will e~ert a force on the operating rod, which force is applied to the other piston or diaphragm and is additive with the return fluid pressure from the module Gn the rear face of that piston or diaphragm. Movement of the two pistons or diaphragms thus takes place iE the required module pressure is developed on the front face of the second piston or diaphragm, i.e. if the force in the operating rod is sufficient to overcome the effect of the different areas of the front and rear .~,~
~ -7a-3 ~

~aces ~h L C'll C~Xe hoth, s~b~c~ t;o tlle module ~-~xessure~ J
I~ wi.ll ~us be seen khat the re~uil-ed pumP pressure i5 a ~xaction of ~he re~uired modu:Le pressure ~etermined by the xa-tio of ~he cross~sectional ~reas of the operatiny xod 5 and o~ the piskon.
As described in the aforementioned U.S.Specification No.4~124,48S~ tlle ~pparatus will innexently operate at a ~odule pressure such that the extraotion r~tio is equal -to the ra~io of the cross-sectional areas of ~he operatin~
10 rod and piston. If the extraction ratio is less than this, - then the volume of return fluid fed to the rear face of a piston will be greater than can be accommodated by movemenk o~ th,e pis-ton to force the appropriate volume of fluid into -the module. The pressure inherentl~ builds up 15 to give the requlred extraction ratio. In the appaxatus of the present in~ention, no movement o~ the pistons will occur until the pump pressure has bu~lt up t~ the necessary pressure to pxovide the required operatiny orce. Although ' the pump is connected to the ~ron~ ends of both cylind~rs, tlle non-return val~e will be closed between the pump and th,~t one o~ the cylinders whi.~h i~ supplyin~ pressure f:Luid to the ~o~ule, The other non-xeturn yal,~e will ~e open bu~ ,~luid will only ~lo~ from the pump to the cylinder . .
~hen the r~ired pressure has deYeloped. It is thus 25 po~sible ~o USe any pump me~ns which will develop the _9_ .
xe~uii-ed ~luid pressure,' whichr ~s previously indicated wou].cl txpicall~ ~e a,bout ~0 p~5~io Flow will conmnence when t~e required pressure is reached. It will be seen ~hat the pressur~ throughout the system are self--5 regulatin~; hoth the ext~act:ion ratlo and the ratio of pump to module pressure are predetermined by choice of th,e ratio o.~ operati.ng rod cross-section to p.iston area. , t The controlled ~alves h~e to change-over at or near the end of eaGh stroke. These valves mi~ht be 10 electrically operated or mechanically operated or hydrauli.cally operated. Very conveniently hydrauli.c operation is employed~ makin~ use of the rise in pressure in the output from the pump a~ the end of a stroke (when flc~
must cease~. As soon ~s the valves change-over, the pressure ~5 will *all and thus there is a pressure-pulse at each'end of each stroke. Conveniently a reverslng actuator, e~g~
a semi-rotaxy ~low reversin~ device, is provided which~ on one pulse, sets the valYes in one position and, on the next , pulse, xeverses the valve positions. To avaid the pressure '~o pwlses, other means may be employed ~or detec-ting the end of a st~o]ce, e.g~ in~uctive sensing me~ns for detectin~
th,e pO5 ition of the piston; such me~m s wotlld conveniently be employcd to control. electricallv ~perated val-~es.
The ~ontro:lled valves ma~ be spool or piston valves.
~S q'he~ have to control fluid which may be at the moclule preSSUrr7~ To operate such valves frorn t}le pump outle~t fluid, i-t may be prefexxed to use. pres~ure intensifying means.
In a particularly conveni.ent arranqement, khe controlled val~res ar~ operated hydraulically by a spool valve and the rise in p.ressure at the end of each operatiny stroke of the main plstons i5 util.ised to effect revexsal of the spool ~alve The t~o main c~l:Lnder~ may ~e mounted ~ack-to-back. There wou].d ~e no need for any bearings for the operating rod betwe~n the cylinders and only one seal, on this operating rod, would be necessary.
There is no need for an~ tigh.t seal between the pistons and cylinaers because th.e pressures on the two ~ides of each piston are nearly equa]. if : 15 the cy].i.nder is su~ject to module pressure.
~ .
BRIEF DESCRIPTION OF THE DRAWINGS
__ _ ._ Figure 1 i5 a dia~ram illustrating one form o reverse osmosis li~uid purîfication apparatus;
Figure 2 is a diagralll sho~ing in furth.er detail another construction of the. apparatus;
Figures 3 and 4 are diagrams illustrating furth.er valve operating arrangement,s;

Figures 5 and 6 are diagram~ illustrating two further ~orms of rever,~e osmosis liquid purlfication ap~aratus; and Figures 6a and 6~ are di~grams illustrating part of the apparatus of ~igure'6 in different positions durïng a c~cle of operation.

, . . . .... . .. .... .. .... .... .... .... .... .... ....
DESCR:I:PTION OF THE PRE~FER`RI~D F.~lBOD:LMENT,~

10Referring to Fiyure 1, ~here Ls shown diagra~natically ; at 10 a reverse osmosis liquid purification module having a membrane 11 in a housing 12 with a fluid inlet 13 and fluid outlet 14 on one side of t~e memhrane and a puriEied li~uid outlet 15 on the other side of the membrane.
This module may be constructed in the known manner, for example haviny a sheet of cellulose acetate or polyamide membrane material wound spirally with a liquid-conductir,g backing sheet around a perforated tu~e which receives the purified liquid. As another example, the known hollow fibre construction may be employed.

A rotar,y p~urp 20, ~g, an impeller pump or ~ear pum~
or Yane pump driven hy an ei,~ctr~c mo~or feeds liquid to be pur,i~ierl at a p~essure typlcally of ~0 p.s~i to ducts 21, 22 leadin~ respectively'via non-xeturn ~alves 23r 5 2~ to the fxont ends of two cylinders 25, 2~ having pistons 27, 28 respecti~ely. In some cases ~he f]uid may be , "
available under a suitable pr ssure without a pump, ~g. a wat~r suppl~ from'a dam. These cylinders 25, 26 are aligned and the pistons are joined by a rlgid 10 connecting rod 29 extending between the rear faces o~ the two pistons. By means of va1ves 30, 31, the rear enA o~ -cylinder 25 is connected selectivel~ either to the module outl~t la or to a discharge 32. By means of ~al~es 33, 34, the rear end of cylin~er 26 is connected selectively 15 either to the module outlet 14 or to the discharge 32. The valves'30, 31, 33 and 34 are controllea in synchronic;m with the operation of the piStoQs so that they change-over at or near each end: of each stroke.
When fluid ~rom pump 20 is enterin~ the front end of 20 cylinder 25, the rear end o~ that cylincler i5 connected to ' disch~rge 32 ~nd thus the pwnp pressure on the piston appl.ies a ,~orce to the connecting rod 29. This ~orc~, as previous~,~ explained, supplements the forc~ on the xe~r ~c~ o~ piston 28 du~ to the module ~lul.d pressllre 25 and, provided the pump pressure'is suflcient, will cause ~luid to be f.rced frc)m the ~'ronl: end or c~llnder 26 through a nOI-- retUrll Ya1Ve 36 into the -module inle-t 13. A
~urther non-return valve 37, between the module inlet and the ~ront end of cylinder 25 pxe~ent.s the pressw~ised .~luid in the modul.e from ente.ring the fxont end o~
cylinder ~5.
At the end of the stroke, the valves 30, 31, 33 ~ld 34 are changed over by contx.ol means 40. These control "' m~ans ma~ be electrical r e.g. microswitches controlling solenoids operatln~ the ~alves, or mechanical or hydraulicO
10As previously explained, the appaxatus will develop a pressure in the module such as will give ~ extraction ratio corresponding to the ratio of the operating rod section to the plst,on area. This ratio will also detexmine the pressure which will have -to ~e developed by pump ~0 to effect measurement of the pistons. The apparatus i.s self-regula~ing in this .respect, inherently developing the ' rec~ulred pressures.
; Many types of valve c~ntrol means may ba used for controlling the valves 30, 31, 33 and 34. Figure 2 illustrates a hydrauli.cally operated system. In Figure 2 ~here is shown :a reverse os~osis system in many ways si~ r ~o that oP Fi~uxe 1 and th.e same reference characters are used to indicate corxespondill~ eleoent,s. In the , ~ollowing descript:ion mention will be made only of the distincti.~e ~eatures of th~,construct.ion of Figure ~..
~n t~hl~ arrangernent use is ~nacle of the pressure pulse which occu.rs in 'ch(3 out:put ~'rom tlle pump 20 at: the end of each :...................................................... .

. ~,,. .L~5~
.

stro~e. ~ e~ h,e p:is~ons s~op mov;ll~, the'pressuxe se ~ut, since ~he v~ll~es are l-hen immediatel~
actuated i.n a manner ~o ~e descrihed lat:er, the pressllre falls a~ain ~ld thus thexe 15 in ef.~ect a pressure pulse.
at each~ end of each stxoke~ This pressure pulse i5 app].ied to ~ pulse actuator 45 and has a spxing-loaded piston set so t~at ,it will jump open at a predetermined pressure.
~his pulse actuato1- operates a semL-rotary reversing switch 4~ which .s~i.k~h, in one I~osi~ion connec,ts the output of the pump 20 to one side ~7 of a pressure intensifier 48 and~ in the other position, connects the output o~ the pump to the ot~er side 4~ o~ the pressure intensifierO
The side o~ -t~.e pressure intbn~sifier to which the pump pressure is not employed is connected by the revexsing switch to a discharge 50. The intensi~iex pro~7ides output at typ.~cally 1000 p.s.i. on one or other of two lines 51, S2 according to the setting o~ the reversing switch. The ou-'cput on line 51 controls spool or pi,ston val~7e.s 53, 54 for the rear end of cylinder 25 whilst the output on l:lne 52 controls spool or piston val~es 55, 56 for the rear end o~ cyl~nder Z6. These valves are operated as previousl~
~escribed so that khe xear end o~ each cylinde.r is connected eith,e~ to t:he module outlet ox ~o the discharge 32 accoxdin~
to ~h~ xequire~ d.i.xect~on oi moVerll~nt o.~ t,he pistons.
The uC e oi~ l:he pxessu.re in tensl~ier in I~ ure 2 avoids the nec:essity i~ox h.-lvi~n~ larcJe ~ist:on areas operating the .

.

v~lves. 1-Io-~7ever thi.s pxoblem n~a~ be avoided hy ~ak.in~
use ~ an arrangement such as i.s shown in ,Figure 3 in which thexe ~s a low pressure-operated actu~tor 60'comprising'a pi.ston 61 in a cvlinder 62 ~it.h rods 63, 64 extendin'g througl seals in the cha~ex wall~ These xods serve to open baXl ~alves 65, 6~ respect:ively, th0 baJ.l val~es normall'y-:bei'ng held agal.nst th.cix seats by the fluid pr~ssu~e;t:o hë'-' controlled. It will be appreciated -Ihat two such:contxol devices would be requixed, one for each cy].:i.nder. - ---:-~i~ure 4 illustrates another arxangemerlt~in wh-i-ch ~
a solenoid 70 ha~in~ operatiny rods 7i, 72 actuates hall valves 74, 75 for controlling the connection of thë-~ear face of one cylinder eithex to the ~odule or to dis~,~arge ' as requixed. The solenoid is operat-.ed by: a sëriso'r:~6 which 15 might ~or example be,all inductive sensor sensing the -~-posi.tion of th.e piston. Separate induction coi~s may -be provided at each end of the cyli.nder to provide sensing si~nals indicative of when the piston has reached the en~s . o~ the cylinder. It will be appreciated that it is merely necessary to sense when the piston is approximately at the end o~ the cylinder. The actual len~th o~ travel for each stroke is not critical. HoweYer the valves on the two cylinde~s will have to be op~r~ted $imultaneously and'thus ol~e senC;in~ system will be used to contrQl the solenoid ~or opexat:l.n~ 1:he.yalves on bot:h.,cylil?ders.

ln l;'ic;ure 5 the~e.i~ illustr~ted a construction in which l.he pressure rise at the end of the stroke Is '' used not to opera-te d~r~ct].y valves controlling the ports for the mai.n cvlinder but to operate a spool valve controlling pi.loted valves for these ports.
In the following descrIption, the same refcrence, numerals will be used as .~n Figures 1 and 2 to~
ill.ustrate corresponding components and mentlon will only be rnade of the distin.ctive ~eatures o the Figure 5 construction.
' A pilot piston and cylinder 80 controls valves : 81 and 8~ such that one of thèse valves is opened when the other one is closed and vice versa. The valve 81 connects the rear end of cylinder 25 to dischar~e whilst the valve 82 connects the rear end of that cylinder to the outlet 14 from the module. A second pi].oted valve comprlses a piston and cylinder 83 operating valves 84, 85 such that one valve is open wherl the other is closed and vice versa. The valve 84 connects the rear end of c,vlinder 26 to the outlet 14 from the module 10 whilst the valve 85 connects the rear end of cylinder 26 to the discharge. The two piloted valves 80, 83 ar~ operated i.n syncllronism by applviny pressure, as will be described later, to lines 3~
-17~

8~, 8-,' leading ~o one. s~.ide of the pis.ton~ in the.s~
pi~oted valve.s and con~ecting the other sj.de.s 'V.id lines 88, 89~.o di.scharge or, by applying the~pressu.re to lines 8~r 8~ and connecting l~nes 86, 87 to disc~rge, forcing l:he pilo~ed va]~es into their opposite position.
This operation i5 achi.e.ved by-means of a spool- valve.
90 having th.rPe spools 91, g2, Y3 on a common conne.r.tor rod 94 which forms th~ axmature for a solenoid 95~
Inlet pressure from the. p~Ullp 20 is applied ~o an inlet port 96 and, according to the pos.ition of the spool valve, this pressure is appli.ed ei.ther vi.a an outlet port 97 to ~he aforementioned connectors 86, 87 or ~ia an outlet port 98 to the. aforemen~ioned connector leads 88~ 8~. Outlets 100, 101 from the spool valve lead to the discharge and serve ~o connect the:approprIate one o the ports 97, 98 to discharge when the other : port Is subjec~ed to the pump pressure. ~he solenoid is opexated by means of a timer or by means of a proximity .sensor on the main pistons 27, 28 or by a pressure-operated switch 105, as indicated diagrammaticall~ in Figure 5, this switch r~sponding to the lncrease in pressure at the outlet of the pump 20 at the end of the stroke .serving to e~ect an electrical connectlon ~ 3~

ellercJi~iny the ~oleno:Ld to le,~el.~e the spool valYe. ThQ
5pool valve may he movea in one dlrection or the, other electrlcall~, e r g ~ h~ proYidlng separa~,e solenoids or each d:Lrectlon o movement or the movement in one, direction may ~e effected hy th~'~o]enoId and movement in ~he opposi-te direction b~ a spring indicated diagramlnatically at 106.
Partlcularly with a large ~e~erse osmosis installation having a plurality of c~li`nders 25, 26 whicll are to ~e operated in a timed sequence/ it may be convenient to u.se a timing device for operatirlg the associated spool valve for each dou~le cylinder device.
Such an arrangement may also ~e used in a radial sy~tem, as previously descri~)ed havïng three or more cylinders operated in sequence.
' Figure 6 illustrates another construction i.n which the rise in pressure of the water from the pump 20 at the end of the stroke is utilised to effect operatioll o a spool valve controlling the piloted va,Lves. In Figure , ' 20 6, the spool valve 9Q and the piloted valves 80, 83 are similar to those descrihed with reference to Figure 5 and the same reference charactexs are used to indicate corresponding components. In Figure 6 however reve~rsing of the. spool va]ve 90 i~ effected ~,y means of a reversing mec}lan:L~;In compr i sing a f:i~ed cy-lin.der 110 h.~ing a p.iston :lll ~llich is u~Aged' in one di~ecti.on ~ nle~n~ o,~
a spring 112~ The pistc~n.i.s mova~le in the opposi~e clirec~::ioo. und.er the inEluence of the pressure from the pump 20 via line 113. The sprincJ 112 i5 arranged so that normally it holds tlie piston 111 at ~lle righ.1:-hand end of the cylinder as seen in the drawi:ng wh.en the.purnp 20 .is,providing the normal output pre.ss,ure ~hi.cF~ is,: in th..is particular embodiment, 60 p.s.i. As prev.~ousl~
eY~plained, at t~e end of the stroke. of th.e main pistons in the cylinde.r~. 25, 26, the output pres~ure from the pump 20 wi.11 rise. This output pressure is appli.ed : to the piston 111 and o~ercomes the sp~A.ing force to drive. the piston to the left.
The piston carries a fle~ible ne~edle 120, wh.ich is typically a stainle~s; steel. wire, stiffenc-,d along part .~ of its length remote from ~he piston 111, this stifening being effected by a thin bore metal tube 121 surroundi.ny the wire. The ~ixe ls terminated in a small ball or loop 123. The needle is ~,hus flexible only in the xegion clo~e to the piston 111. This needle co-ope.ra1:es wi~h , a cam 130 havin~ cam sur~aces in the ~orrn of a letter ~, the surfaces bein~ curved and havinc~ a cen~ral upstandinc,r part 131 ancl outer upstarldîng parts 132~ 133. The ~2~-cam is pivoted on a ~j.xec1 pi.vot 134 and .is rotatab:Le ~.~hrough. 45 iIl either d~ ^eCtiOIl. SO that it i~ mova~le into either one or other of t~e posi.t~ons shown in Figure~s Ga and 6b. Figure 6 shows the cam in a neutral position. In normal operation it is, as ~xplained l~elow, forced into on~ or other of the positions shown in Figure 6a or 6b. This cam has pi~oted there~o at 138, a connecting rod 13~ for effecting linear movement of the operating member 140 for the spool valve 90.
At the end of an operating stroke of the pistons in the main cy1.inders 25/ 26, the pressure at the output of the pump 20 rises and drlves the needle 120 fo~l.~dly.
This will engage one side or other of the central projection 131. and will ride around the curved cam surface so as to push that end of the cam 130 to the left in the drawing. If this is the upper part of the cam, then the spool operatîng rnember is drawn to the righ.t, the cam being set thus to the position shown in Fi.gure 6a. If OIl the other hand the needle engages the lower part of the cam, .it will push the lower part of the cam to the left and will force the operating member of the spoo]. to the left as sh.o~n. in F:igure. 6h.
Xt wi..l.l. he inlrrledi.ately apparent from Figures 6a and 6b 25 that, as 500n as the cc~n has ~een set on one side by an 3~

opexat~ cJ strc)]ce of the n~edle., it is po~itioned ~o that the needle will s~lect: the. opposite dlrect~on fox the next stroke. T~.us the system operates to reverse the spool valve ~0 each t.ime ~he pressure in the 5- output o:E t~e pump 20 ri:ses.
It will be noted that the alternate reversing ; thus achieved ~appens at the end of each stroke so that the pressure in the Eeed system 21, 22 will not ~all until the controlle~ valves 80, 83 have changed thei,r position and thus pe~rmitted the main pistons 27, 28 to reverse t,heir unction and commence movement in the opposite direction. At the end of the new stroke, the pistons 27, 28 wi.ll again stop, pressure will rise and overcome the sprlng ~orce of spring 112 to operate the mechanlsm agai~ to engage, the new section o~ the cam 130 and rotate the cam back.
The spool valve 9~ is preferably arranged so that the pressure port 96 o~ the spool does not ~dmit pressure to the chaml~ers on one. or other side of the central spool 92 unti.l the outer spools 91 r 93 have covered or uncovered : the ports 97, 98 leading to l:lle piloted valves 80l 8.~. ~his ensures that 0-rings or other seals on the spools are un~er ze.ro pressure, as they pass the ports in the ~alls of these chambers. Each port 97,98 is arranged as a number of small apertures extelldill~ around the circumfererlce of the bo~y of the ~S~3~

yal~e ;.n each port:ln~ position~ Thus very small holes c~ln be u~ecl so m~nimising the ~Ltxusion of such O-~rinc3s lnto thcse holes. The. centre por~ ~6 is under pressure from t11e pump 20 all t.he time and thus intrusion into the holes provid.inq the centre port Is impossI~:Le. The outermost port~s leading ~to d.ischarge are never under pressure anct so need not be protected in this wa~D

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for the reverse osmosis purification of water or other fluid comprising a fluid supply, a module including a reverse osmotic membrane, a fluid inlet and fluid outlet for the passage of fluid over one surface of the membrane and an outlet for the passage of purified fluid out of the module from the opposite surface of the membrane together with a plurality of similar cylinders each having a piston or diaphragm means dividing the cylinder into a front end and a rear end, the front end of each cylinder having a larger swept volume than the rear end, fluid connections connecting the front end of each cylinder to the fluid inlet of the module, a separate non-return valve in each fluid connection from the front end of each cylinder, each said cylinder having its piston or diaphragm means for forcing fluid at a pressure in excess of, at least, the normal osmotic pressure of water from the front face of the piston or diaphragm means through said separate valve to the fluid inlet of the module, operating rod means mechanically interconnecting said piston or diaphragm means, which operating rod means extend from the rear faces of said piston or diaphragm means, said piston or diaphragm means mechanically operating in a cyclic sequence, separate fluid connections have a separate non-return or controlled distribution valve for the front end of each cylinder means arranged for supplying fluid, under a relatively low pressure, compared with the normal osmotic pressure of water, from said fluid supply to the front end of each cylinder through said separate fluid connections with the separate non-return valve or controlled distribution valve therein, and controlled valve means being operative to connect the fluid outlet of the module to the rear ends of said cylinders in synchronism with said cyclic sequence so that all the fluid leaving said fluid outlet flows back to said cylinders into the rear ends thereof in cyclic sequence to drive the piston or diaphragm means towards the front ends, said controlled valve means furthermore being opera-tive to connect said rear ends of each of the cylinders to a discharge in sequence when the respective piston or diaphragm means are moving back towards those ends.

2. Apparatus as claimed in claim 1, wherein said apparatus has two cylinders which are in end to end alignment and the piston or diaphragm means are inter-connected by a common operating rod which constitutes the rod means.

3. Apparatus as claimed in claim 1, wherein said apparatus has three or more cylinders, each of said cylinders having an operating rod with said rods being interconnected by a free-running crankshaft and said rods constituting the rod means.

4. Apparatus for the reverse osmosis purification of water or other fluid comprising a fluid supply, a module including a reverse osmotic membrane, a fluid inlet and fluid outlet for the passage of fluid over one surface of the membrane and an outlet for the passage of purified fluid out of the module from the opposite surface of the membrane together with ram means comprising a pair of similar cylinders each having a piston or diaphragm having a front face and a rear face and dividing the cylinder into a front end and rear end, fluid connections connecting the front end of each cylinder to the fluid inlet of the module, a separate non-return valve operatively disposed in each connection, each cylin-der with its piston or diaphragm being arranged for forcing fluid at a pressure in excess, at least, the normal osmotic pressure of water, from the front face of the piston or diaphragm through said separate valve to the fluid inlet of the module, a common operating rod, the cylinders being axially aligned with said common operating rod extending from the rear face of one piston or diaphragm to the rear face of the other piston or diaphragm so that the front face of each piston or diaphragm has a larger area exposed to fluid than the rear face, pump means with two separate non-return valves, said pump means being operative to supply fluid, at a relatively low pressure, compared with the normal osmotic pressure, from said fluid supply through said separate non-return valves to the front end of each said cylinder, and controlled valve means operative selectively to connect the fluid outlet from the module to the rear end of one cylinder and to connect the rear end of the other cylinder to a discharge or to connect the fluid outlet from the module to the rear end of said other cylinder and to connect the rear end of said one cylinder to said discharge and control means for said controlled valve means operative to change-over the connections when the pistons or diaphragms reach the end of a stroke.

5. Apparatus as claimed in claim 4 wherein said controlled valve means are controlled in response to the pressure rise in the supply fluid at the end of a stroke.

6. Apparatus as claimed in claim 4 wherein said controlled valve means are controlled by sensing means sensing the position of the pistons or diaphragms.

7. Apparatus as claimed in claim 6 wherein said sensing means provide an electric signal.

8. Apparatus as claimed in claim 4 and having hydraulic means including a spool valve arranged for operating said controlled valve means and wherein means responsive to the pressure rise in the output of said pump means at each end of each stroke of said pistons or diaphragms are arranged to effect operation of the spool valve to thereby operate said controlled valve means.

9. Apparatus as claimed in claim 8 wherein said controlled valve means comprise two separate hydraulic actuators, associated respectively with the two cylinders, each actuator having two valves, one of which is open and the other closed in one state of the actuator, the actuator being operative to close the open valve and open the closed valve.

10. A method of purification of a fluid by reverse osmosis comprising the steps of (a) continuously pumping fluid from a fluid to provide fluid at a first pressure;
(b) raising the pressure of the fluid at said first pressure to a second higher pressure by means of a plurality of cylinders with mechanically drivingly coupled movable fluid barriers or diaphragms operating in cyclic sequence, each cylinder being divided by its movable fluid barrier into a front end and a rear end and the diaphragms or pistons having piston rods through the rear ends of the cylinders whereby the rear ends have smaller swept volumes than the front ends;
(c) feeding said fluid at said first pressure through separate non-return valves to the front ends of the cylinders whereby the fluid enters each cylinder on a rearward movement of the associated diaphragm or piston;
(d) pumping said fluid at said second high pressure from the front ends of the cylinders through further non-return valves to one side of a membrane in a reverse osmosis module; and;
(e) extracting purified fluid passing through the membrane and feeding all the remaining fluid leaving the module through cyclically-controlled valve means, operating in synchronism with said pistons or diaphragms, back to the rear ends of the cylinders during respective forward strokes of the pistons, whereby said second higher pressure is stabilized at a value such that the extraction ratio in the module corresponds to the ratio of piston rod area to piston area, said controlled valve means being arranged to connect the rear ends of the cylinders to a discharge outlet during rearward strokes of the pistons;
whereby said continuously pumped fluid at said first pressure provides all the power to drive said pistons or diaphragms.

11. A method as claimed in claim 10 including alternatively feeding the continuously pumped fluid into the front ends of two cylinders arranged back to back with pistons or diaphragms mechanically connected to operate in opposite phase.

12. A method as claimed in either claim 10 or claim 11 including operatively feeding said controlled valve means by a rise in fluid pressure of the continuously pumped fluid when the pistons or diaphragms reach the end of a rearward stroke.