IL34445A - Fluid flow control valve - Google Patents

Description

Fluid flow control valve Summary of the Invention In accordance with the invention, the second stage housing and spool are formed so that, when this spool is displaced from a reference position b a contr ol pre s sure from the first stage, a first passageway is opened which allow s fluid to flow from the fir st stage to the load port. This flow tends to reduce the control pre s sure '. An opposing bias pres sure, which may be ob-tained from the first stage or from the fluid supply for the se cond stage , cooperates with the control pre s sure to position the spool so that for any inp signal to the first stage , there is a corre sponding rate of flow of fluid from the first stage to the load port. The spool and housing are also formed s o that a second pas sageway is opened simultaneously with the first which allow fluid to flow from the second stage supply to the same load port. The two passageways have a predetermined, fixed ratio of cros s section areas and the control pres sure and the se cond stage supply pre ssure are made e qual with the result that the flow through the second passageway is proportional to that through the first. Accordingly, the rate of flow of fluid to the load depends solely on the input signal and is independent of load pre s sure .

Detailed De scription For a clearer understanding of the invention, reference may be made to the following detailed des cription and the accompanying drawing in which: Figure 1 is a schematic cross - section view of a flow control valve ' incorporating the invention; Figure 2 is a cross-section veiw taken on the line 2-2 of Figure 1; Figure 3 is a pictorial view of one of the elements of the valve of Figure 1 before its assembly with the remaining elements; - Figure 4 is a schematic cross-section view of another flow control valve incorporating the invention; Figure 5 is a fragmentary cross-section veiw of a modification of the valve shown in Figure 4} Figure 6 is a schemtaic. cross-section veiw of another valve incorporating the invention; Figure 7 is a cross-sectio veew taken on the line 7-7 of Figure 6; Figure 8 is a cross-section view taken on the line 8-8 of Figure 7; Figure 9 is a pictorial view of one of the elements of the valve of Figure 6 before Its assembly to the remaining elements* and Figure 10 is a cross-section view of an alternative form of pressure reducing valve which may be used with the Invention.

Referrrlng first to Figure 1, a housing 11 is formed with a hollow cylinder which, in turn, is formed with a centrally located port 12 and with prots 13 and 14 on either side thereof.' Within the cylinder is ,',5 | ' ·. . ' , -a spool 15 formed with a central land 16 which, when in the neutral pos ition, is "line on line " with the prot 12. The spool 15 also Includes lands 17 and 18 on either end thereof. Ports 13 and 14» which are positioned on either side of land 16· are connected by conduits 21 and 22 respectively to the second stage of the valve. The central port 16 is connected by means of a conduit 23 to a source flow occurs through, a passageway whose cross -sectional area is proportional to the distance A between the tongue members 47 and 48. At the same time, fluid will also flow from the chambers 51 and 52 to the port 31. This flow will be through a passageway whose cross-sectional area is proportional to the distance B. Since the pressure in chambers 51 and 52 is also equal to P2, the flow of fluid from the second stage supply will be in "the. ratio of these areas or will be equal to x B/A. The total flow to the load conduit 33 will be equal to plus x B/A regardless of the load pressure. For any input signal to the force motor 27 there is a definite corresponding flow of fluid through the first stage and therefore there is also a corresponding proportional flow throug the second stage.

It is to be noted that, as previously mentioned, the second stage spools are. automatically adjusted at the neutral position so that the leakage rate of the first stage is passed. Therefore, exact spacing of the various lands is unnecessary. Similarly, wear of the metering lands has little or no effect. Likewise, it is not necessary that the lands 44 and 43 open the ports 31 and 32 respectively at exactly, the same time because nothing can flow until both are open.

It is also to be noted that the pressure drop across the first stage land 16 is fixed and equal to the pressure drop across the valve 39 which is equal to PI - P2.' It is also to be noted that in this particular valve there is no "dead" space at all. As soon as there is a signal, fluid will flow .to the load device. extends from the left hand end, as viewed in Figure 4 as far as the land 82. The! section de signated A-A is identical to that designated 2 -2 in Figure 1 and is as! illustrated in Figure 2. A. stop ring 88 is placed to the left of the spool 71 to limit its leftward travel.

A second spool 71 ' is substantially identical to the spool 71 except i that it is turned end for end with respect thereto. The various parts are de signated by the same reference characte rs as those for spool 71 except that they are primed. ' The spool 71 ' operates in a similar cylinder formed with similar ports . Conduits 85 and 86 are connected to the left and right ends of the spool 71 respectively. The section designated B -B is identical to that de signated A-A.

The neutral position of the fir st stage is defined as that position of the flapper 67 at which the pres sure in the conduits leading to the orifice s i s' the same, provided there is no flow, or are equal rate s of flow, in the conduits 85 and 86. When these c onditions are met, the spools 71 and 71 ' will be in their neutral positions substantially as . shown. For example , if the spool 71 were displaced slightly to the right, then fluid would flow from the conduit 85 through the central bore to the port 76 thereby reducing the pres sure on the left end of the spool 71 and allowing the pre ssure in the conduit 86 to return the spool 71 to its neutral position. The stop 88 prevents the spool from going too far to the left. Similarly, if the spool 71 ' were unbalanced, a similar sequence of events would return it to the neutral position. At this position there is no flow of fluid to the load 77.

Let us designate the rate of flow of fluid from the source 61 to the I that ^l¾w¾g^'nrb.ugh the orifice 65 as Q,,that flowing through thej restrictor 63 as Q ; that from the source 61 to the restrictor 62 as Q ; that orifices 64 as Q4 2 flowing into. the right end of spool 71' Q^; and that flowing to the left end of spool 71 as spool Q^. Now, let us assume that the flapper 67 is displaced to the right. The pressure in the conduit 86 will tend to rise and this will dis¬ place the spool 71 to the left until it rests against its stop ring 88. The spool 71' will be displaced to the left and fluid will flow at the rate Q to the load port 76'. When this flow is sufficient to reduce the pressure in the. conduit 86 to that in the conduit 85 the spool 71' will come to rest. Since the source 61 applies pressure PI to both of the restrictors 62 and 63, and since the pres¬ sure in conduits 85 and 86 are the same, it follows that must equal Q^.

This being so, it likewise follows that Q. equals Q_ plus Qe. Therefore, for any position of the flapper 67 there is a corresponding flow rate.Q_ or Q, to D G the load regardless of. the load pressure. The spools are automatically posi-' tioned until this is. so. Then, to make the total flow of fluid to the load depend only on the position of the flapper, it is only necessary to adjust the pressure reducing valve 79 to make the pressure P2 equal to that in the conduits 85 and 86. This is done conveniently by adjusting valve 79 to make P2 equal to the pressure in conduits 85 and 86 when the flapper 67 is in its neutral position and there is no flow in these conduits. It is true that, as the flapper 67 is displaced from neutral causing fluid to flow in conduit 85 or 86, the pressure in these conduits falls. But it is also true that the output pressure of a valve D-2765 such as valve 79 falls as the rate of flow through it incr eas es . The s e two | W LH:hc changes occur at approximately the s ame rate and accordingly the above \ adjustment make s P2 aubstantially equal to the pr es sure in conduits 85 and 86 ' j > i throughout the entire range of operation. Then the total flow of fluid to the ; i load will be directly proportional to Q 5 or Q i as the case may be and this flow j rate is completely independent of load pres sure.

It is to be noted that in this embodiment of the invention the oppos ing pr es sures which position the spool are both taken from the first stage of the valve rather than taking one from the first stage and the other fr om the supply J I I to the s econd stage. It is also to be noted that there is no dead space in this [ embodiment e ither and that as soon as there is an input signal, fluid starts to flow to the load. It is als o to be noted that since the spools position them ¬ selve s in accordance with flow rates and pressure drops, there is automatic compensation for wear. i .15 When operating certain types of load devic es , it is de sir able that | there be a dead space, . that is that there be no movement of the load device until the input signal has reached a predetermined amount, positive or nega ¬ tive. The embodiment of Figure 4 can readily be modified to achieve such a condition. As shown in Figure 5, a spring 89 is placed in the spac e between the left end of the land 81' and the end of the cylinder and a similar spring | would be placed to the right of the land 81 of the spool 71. Then there would j i be no flow of fluid to the load until the input signal were sufficient to rais e the pres sure in one of the conduits 85 or 86 sufficiently to overcome the spring pres sure.

Referring now to Figure 6, there is shown another embodiment of the invention. In this'embodiement the pilot stage is also a flapper valve. A source of fluid 91 is connected to restrictors 92 and 93 which in turn are connected to nozzle s 94 and 95 respectively, which act on opposite sides of a vane or flapper 96 which. is positioned by a force motor 97. Conduits 98 and 99 lead from the nozzles 94 and 95 to the second stage.

The second stage includes a' ousing 101 in which is formed a hollow cylinder and which is also formed with ports 102 and 103 leading to the return; with ports 104 and 105 communicating with the load device 106; and with a port 107 to which is connected a conduit 108 leading to the low pressure side of a pres sure reducing valve 109, the high pres sure side of which is connected to the source 91.

Within the cylinder there is a single piston 111 formed with a land 112 on the righthand end, a land 113 on the left end, and with a central land 114. Both ends of the cylinder are stepped as shown, defining end spaces, in which washers 115 and 116 are placed. A pair of springs 117 and 118 are placed in the right and left end spaces respectively and bear against the washers 115 and 116 which in turn bear against the lands 112 and 113 so as to .. center the spool 111. The conduits 98 and 99 communicate with ports 119 and 120 respectively which in turn communicate, by means of internal pas sage-^ ways, with the end spaces containing the springs 117 and 118 respectively.

Let us assume that an input signal to the force motor displaces the ! i i flapper vane 96 to the right. This will tend to increase the pressure in the j I conduit 98 over that in the conduit 99 but nothing will happen until and unless the increase is large enough to overcome the spring 118. Then the spool 111 will be displaced to the left and fluid will flow from conduit 98 through the port 119 and through'the holes 126 and 127 and the load port 104 to the load device or actuator 106. The springs 117 and 118 are selected to have just enough strength to provide a usable dead space in the presence of very small signals. Once this threshold is exceeded, the strength of the springs is low enough in relation to the usual pressure differentials so as not to appreciably affect the equalization of pressures and the position of spool 111 is soon conduits stabilized with the pressures i -eemdywfcgry 98 and 99 substantially equal and ' onduit with a definite rate of flow from s-oad-Aoteg 98 to the load. As before, this rate of flow is determined solely by the signal to the force motor and is entirely independent of the back pressure of the load device 106. Also as before, the pressure reducing valve 109 is adjusted to make the pressure in the conduit 108 equal to that in the conduits 98 and 99. Then, the total flow to the load will be directly proportional to the flow from the first stage through the conduit 98 in an amount determined by the flow through conduit 98 and by the ratio of the lengths of the recesses 131-134 to the lengths of the slots 124-127, alias measured along the circumference of the cylindrical bore. More particularly, if the length of each recess be denoted by R, the length of each slot be denoted by S, and the flow through conduit 98 (and the slots) be denoted by Q , then, since there are four recesses and two slots, t I » total flow will be equal to Q plus Q x 2 R/S. As in the previously describe 7 7 embodiments, this flow likewise will be independent of load pressure.

An alternative form of pressure reducing valve is indicated generally by the reference character 141 in Figure 10. The valve comprises a piston 142, moveable in a cylinder, and formed with lands 143 and 144. The end space to the right of the land 143 communicates with a conduit 145 intended f connection to a source of control pressure. The end space to the left of the land 144 communicates, by means of internal passageways 146 in the piston 142, with the space between the lands 143 and 144. A conduit 147 is connect to this space. A port 148 is connected to a source of fluid pressure.

In operation, the. conduit 147 is connected to the device the pressure of which is to be controlled, that is, to port 78 of Figure 4 or to conduit 108 of Figure 6. The conduit 145 is connected to the reference pressure, that is, to conduit 86 of Figure 4 or to conduit 98 of Figure 6. Fluid from source PI starts to flow to conduit 147 but also shifts the piston 142 to the right, thereby shutting off the flow. When the pressure P2 in conduit 147 tends to fall below that of conduit 145, the piston 142 is shifted to the left, opening port 148. An equilibrium position is soon reached with the pressur in conduit 147. equal to that in conduit 145, without requiring any flow of fluid from the conduit 145.

Use of the valve 141 instead of. the valve 79 or the valve 109 makes the pressure P2 precisely equal to that in the conduits 86 or 98, thereby in- creasing the accuracy of the independence of flow rate from load pressure.

From the foregoing description, it will be apparent that Applicant has provided an improved and simplified valve in which the rate of flow of fluid to the load is independent of load pressure. The embodiment of Figure 6 is preferred, in some cases, especially if a dead space in the neutral position is desired, because it contains but one spool and is therefore somewhat simpler. However, the embodiment of Figures 1 or 4 may be preferred in some cases, because these embodiments may be made to have no dead space whatsoever and are much less affected by wear of the metering lands. In any case, however, the all important flow control chambers and passageways car-be formed either in the spools or in the surrounding sleeves, or housings.

It is to be understood that the showings in all of the figures of the drawing are highly schematic in order to show clearly the novel features of Applicant' s invention. Actual construction of valves in accordance with the invention will, of course, proceed along principals well known to those skilled in the art.

Although a number of embodiments have been described in considerabl detail for illustrative purposes, many modifications can be made within the spirit of the invention. It is therefore desired that the protection afforded by letters patents be limited only by the true scope of the appended claims. .

Claims (1)

1. P.A. 34445/2 1. A system for controlling the flow of fluid to a load* comprising, a control fluid circuit Including a conduit and inc uding first means responsive to an input signal for gener-ating a luid control pressure in said conduit, said control f¾uld circuit also including means defining a first restricted passageway interconnecting said condui and said load, a main fluid circuit including a main source of fluid under pressure and including^ means defining a second restricted passageway Interconnecting said, source, and said load, a source^/of biasing pressure approximately equal in pressure to that of said source, and second means' responsive to the difference in pressure betwee that of said control pressure i said conduit and that of said biasing pressure for varying the sizes of said first and second passageways iimuitaneouely in the same sense.. 2· A system for controlling 'the flow of fluid to a load, in . accordance with Claim 1, tn which said second means responsive includes a housing formed to define a hollow cylinder, a spool moveable in aaid housing and arranged to be urged in.opposite directions by said control. ressure and said biasing pressure, ' and in which said housing andspool are formed to define said ' first and second passageways*. 3. A system for controlling the flow of fluid to a load in accordance with Claim 2, in which said housing and Spool are both formed so that said first and second passagewpys are/closed when said spool is in a reference position but are opened simultaneousl when said spool is displaced therefrom by an excess of said control pressure over said biasing pressure* ' 4. Δ system for controlling the flow of fluid to a load in accordance with Claim 3 in which said housing and spool are formed P.A. 34445/2 regardless o the magnitude of the displacement of said spool* 5. A system fo controlling the flow of f luid^o a load in accordanc with Claim 4 > in which said housing and spool are > -formed so that s $-d second passageway is larger than said first passageway.. ' 6· A. system for controlling the flow of fluid to a load in accordance with Claim 3 in which said housing and spool aire formed so that said spool is displaced ftsom said reference position until the low of fluid through said first passagewa is suf cient to reduce said control pressure to equal said biasing pressure . 7. A system for controlling the low of fluid to a load in accordance with Claim 2 in which said first means responsive includes an additional hollow cylinder and spool* 8. A valve for controlling the flow of fluid to load in accordance with Claim 2 in which said first means responsive includes a f apper cooperating with a pair of nozzles discharging fluid. 9. A system for controlling the flow of fluid to a load in accordance with Claim 1 in which said source of . biasing pressure is said main source. LO. A system for controlling the f low of fluid to a load in accordance with Claim 1 in which said control circuit includes an auxiliary source of fluid under a pressure greater than that of said main source. 11. A system for controlling the flow of fluid to a load in accordance with Claim 10 in which said main source is supplied from said auxiliary source through a pressure reducing valve » P.A. 34445/2 12. A system for controlling the flow of fluid to a load in accordance with Claim 10 in which aaid biasing pressure is derived from said auxiliary source. 13. A system fo controlling the flow of fluid to a load in accordance with Claim 1 which includes means for deriving said source of biasing pressure from said control fluid circuit. 14. . i^ye em for controlling the flow of fluid to a load in accordance with Claim 1 in which said control fluid circuit includes an additional conduit and means for generating said biasing pressure as a fluid pressure in said conduit. 15. A system for controlling the flow of luld to a load i , accordance with Claim 8 in which said first means responsive includes a n additional conduit and in which said nozzles are . operatively connected to said first named conduit and to said addi ional conduit so that upon displacement of said flapper fcom a reference position in response to said input signal, the pressure in one of said conduits tends to increase while that in the other tends to decrease so as to constitute said control/' pressure and said biasing pressure respectively, and in which said second 'means responsive includes a further cylinder and: spoo similar - to the aforesaid, cylinde and spool, said sppools being operative y connected to be actuated in opposite senses by the difference of the pressures in said conduits. 16. A system for. controlling the flow of fluid to a load in accordance with Claim 7 in which said first means responsive , includes an additional conduit and means for generating said confisol pressuea in either said first named conduit or said additional conduit according to the sense of said input signal. Pw 34445/2 includes a furthe spool operating in the same hollow cylinder coaxially with the first named spool and in which said, first named conduit and said additional conduit are operatively connected to opposite remote ends of said coaxially arranged spools and inwhlch said source of biasing pressure is operatively connected V ' ' ■·'· . to the space, between said spools* 18. A system for controllin the flow o a luid substantially as' described with reference to and as illustrated in the accompanying drawings. ' COHEN ZEDEK & SPISBACH egd. Pafenl Attorneys Ρ.Ο οχ 33116, TEL-AVIV, ISRAEL