US3769996A

US3769996A - Fluid timer and method

Info

Publication number: US3769996A
Application number: US00135317A
Authority: US
Inventors: M Norman; E Holbrook; W Gripe
Original assignee: Amot Controls LLC
Current assignee: LOW TECH AUTOMATION Inc A CORP OF
Priority date: 1971-04-19
Filing date: 1971-04-19
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06

Abstract

A timer apparatus and method wherein a fluid signal is produced at a predetermined time in a passage at the downstream side of a choked fluid pressure supply line by the opening and/or closing of a vent connected to such passage, and wherein such vent opening and/or closing is a function of the change in fluid pressure in a chamber occasioned by fluid flow through a predetermined size orifice connected to the chamber.

Description

United States Patent [1 1 Holbrook et al.

[451 Nov. 6, 1973 1 FLUID TIMER AND METHOD 75] Inventors: Edward L. Holbrook, Pinole;

William B. Gripe, Concord; Melvin [-1. Norman, Oakland, all of Calif.

[73] Assignee: Arnot Controls Corporation,

Richmond, Calif.

22 Filed: Apr. 19,1971

211 App]. No; 135,317

[52] U.S. Cl 137/102, l37/624.14, 251/28, 251/50 [51} Int. Cl. Fl6k 31/145 [58] Field of Search 137/624.14, 102, l37/505.4l, 505.42; 251/50, 127, 28, 41;

[56] References Cited UNITED STATES PATENTS 1,269,721 6/1918 Kuntny 251/37 3,326,237 6/1967 Frick 137/624.14

2,722,234 1l/l955 MacGeorge 251/33 X 2,887,123 5/1959 Bccker..... l37/505.4l X

3,030,064 4/1962 Taylor 251/127 1,480,909 1/1924 Johnson... 137/505.41 3,601,148 8/1971 Jeffrey 137/505.36 X 2,949,128 8/1960 Carter 137/505.42 X

FOREIGN PATENTS OR APPLICATIONS 1,068,965 11/1959 Germany 251/127 Primary Examiner-Arnold Rosenthal Att0rneyWarren, Rubin, Brucker & Chickering [57] v ABSTRACT A timer apparatus and method wherein a fluid signal is produced at a predetermined time in a passage at the downstream side of a choked fluid pressure supply line by the opening and/or closing of a vent connected to such passage, and wherein such vent opening and/or closing is a function of the change in fluid pressure in a chamber occasioned by fluid flow through a predetermined size orifice connected to the chamber.

6 Claims, 12 Drawing Figures PAIENIEBunv ems 3369396 saw m 4 INVENTORS Edward L. Holbrook BY Wi B. Gri 1 Me H. No an WW,W

PAIENTEnnnv 6:915 3369.996 sum an; 4

F i g. 8

.INVENTOR5 Eqvqard L. Holbrook F I. g. 2 73 BY WIIham B. Gripe Melvin H. Norman PAIENTEUnuv slam 3,759,996 SHEET 30F 4 IINVENTORS Edward L. Holbrook BY WiI/iam'B. Gripe Mlvin H. Norrpan mml M V mneys FLUID TIMER AND METHOD The invention relates to time measurements or determinations made or obtained by the employment of fluid flow through fixed orifices into and out of chambers, cylindersand the like to obtain a change in pressure as a function of time.

An example of the foregoing are pneumatically operated timing valves wherein air pressure from a regulated source is fed into the cylinder of a pneumatic pilot for the valve through a predetermined restricted orifice. When the pressure builds up to a predetermined amount, the valve will shift, the latter movement frequently being made against the resistance of a spring. The orifice may be embodied in a needle valve so that it is adjustable thereby obtaining a time relationship between the setting of the needle valve and the shifting of the piloted valve. While the foregoing arrangement is common, it is not very accurate due to the problem of controlling orifice size, friction of valve movement, spring constants and the like. An accuracy of between about percent and percent can with reasonable care be expected.

The concept of the present invention is to produce a timed fluid signal in a passage at the downstream side of a choked fluid pressure supply line by opening and closing of a vent connected to the passage wherein such opening and closing is a function of the change in fluid pressure in a chamber occasioned by fluid flow through a predetermined sized orifice connected to the chamber. The vent opening and closing of the passage produces an abrupt change in pressure in the control passage which can be read or used in a variety of ways. For example, a preferred arrangement is to connect the control passage with the fluid pilot of a piloted valve so that the abrupt pressure change will be accompanied by an instantaneous shifting of the valve. Another important feature of the present invention is the measurement of the change in fluid pressure in the chamber by a'predetermined displacement of pressure responsive means against a spring and wherein time is adjustably selected by adjusting the magnitude of resistance offered by the spring. In the foregoing arrangement the inaccuracies and variables encountered in former structures are avoided with the result that the apparatus and method of the present invention can be made and practiced with dependable and repeatable timing accuracies within a range of less than 1 percent.

Another object of the present invention is to provide a fluid timer of the character described in which the timing range over which the. unit functions may be extended or shortened by simple modification and without affecting the basic accuracy of the device.

A further object of the present invention is to provide a fluid timer of the character above which may be rapidly recycled at the end of each timing period so that successive timing periods may be obtained in very closely following relation.

Still another object of the present invention is to provide a fluid timer of the character above which may be produced in mass production from a minimum number of ruggedly constructed parts designed to afford dependable trouble-free operation over a long period of time.

The invention possesses other objects and features of advantage, some of which of the foregoing will be set forth in the following description of the preferred form of the invention whichis illustrated in the drawings accompanying and forming part of this specification. It is to be understood, however, that variations in the showing made by the said drawings and description may be adopted within the scope of the invention as set forth in the claims.

Referring to said drawings:

FIG. 1 is a side elevation of a timer constructed in accordance with the present invention;

FIG. 2 is a vertical sectional view on an enlarged scale and taken substantially on the plane of line 2-2 of FIG. 1;

FIG. 3 is a plan view of the timer shown on the same scale as FIG. 2;

FIG. 4 is a cross sectional view of the timer on the larger scale, taken substantially on the plane of line 4-4 of FIG. 1;

FIG. 5 is a cross-sectional view of the timer on the larger scale, taken substantially on the plane of line 5-5 of FIG. 1;

FIG. 6 is a cross sectional view of the timer taken substantially on the plane of line 66 of FIG. 2;

FIG. 7 is a schematic representation of the timer and associated fluid piloted control valve;

FIG. 8 is a fragmentary cross sectional view on an enlarged scale of a modified structure used with the timer; FIG. 9 is a fragmentary side elevation of a modified form of the invention;

. FIG. 10 is a longitudinal cross sectional view similar to FIG. 2 but showing a modified form of the invention;

FIG. 11 is a cross sectional view taken substantially on the line 11-11 of FIG. 10; and

FIG. 12 is a schematic representation of the timer of FIGS. 10-12 in combination with a fluid piloted valve. The fluid timer of the present invention comprises briefly a fluid pressure chamber 16 and an orifice 17 connected thereto for providing a variable fluid pressure versus time characteristic; pressure sensing means 18 connected to chamber 16 and movable in response to change in pressure therein; resilient means 19 connected to sensing means 18 for resisting pressure displacement thereof; and manually controlled means 21 adjusting the magnitude of resistance offered by resilient means 19 to sensing means 18 thereby selectively determining the time interval occurring for a predetermined displacement of means 18. In accordance with the present invention there is further provided a control passage 22 adapted for connection to a source of fluid under pressure and a vent passage 23 connected thereto; and a valve 24 mounted to control fluid flow in vent passage 23 and being connected to sensing means 18 to closevent 23 at the aforementioned predetermined displacement of means 18 thereby causing an abrupt change in pressure in control passage 22. The timing signal thus produced may be taken from outlet port 26 connected to control passage 22.

In order to obtain maximum sharpness in the pressure change in control passage 22, an orifice 27 is provided in the passage upstream from vent passage 23; and another orifice 28 is provided in vent passage 23 but of a somewhat larger size than orifice 27 so as to maintain the pressure in control passage downstream from orifice 27 near ventpressure in the open position of valve 24 with the pressure abruptly increasing to approach source pressure upon closing of valve 24.

In the present construction the several parts are mounted within a housing having a base section 31 and a top section 32; and pressure sensing means is composed of a diaphragm peripherally supported between

sections

31 and 32 here clamped together by screws 33, and is surmounted by a perforated plate 34 which supports diaphragm 18 in the latters lowermost position, see FIG. 2. Mounted on the opposite side of diaphragm 18 is a bearing plate 36 which in turn supports a spring rest 37 for one end of helical spring 19 here forming the aforementioned resilient means. Also with reference to FIG. 2, it will be noted that vent passage 23 and more particularly orifice 28 thereof terminates in a downwardly opening valve seat which is positioned for engagement by valve 24 here mounted on plate 36, valve 24 being thus carried by diaphragm 18 for movement from seat 38. Spring 19 is here mounted in compression between lower spring rest 37 and an upper spring rest 39 which is threadably attached to a screw forming the aforementioned manually controlled means 21. The latter is journaled in housing section 32 for rotation but is retained by

clips

41 and 42 against relative longitudinal displacement. Rest 39 is mounted within a spring cavity 43, see FIG. 4, so as to retain the spring rest against rotation and for longitudinal displacement upon rotation of screw 21. This is here effected by making the spring rest and interior bore of chamber 43 of polygonal form so as to prevent relative rotation.

In accordance with the foregoing, it will be understood that variations in the timing cycle can be directly and precisely produced by changing the compression of spring 19 and the threaded engagement between screw 21 and spring rest 19 affords an extremely fine adjustment of spring tension. Preferably the distance of travel on valve 24 to and from its seated position is kept small so that variations in the spring constants which may be encountered in mass production will have a negligible effect on the operation of the device. Where both adjustment and read out of the time is required, we prefer to attach a vernier counting dial 46 to the outer end 47 of screw 21 so that the number of turns and degress of rotation may be easily manually set and read. Such vernier turn counters are readily obtained and one providing approximately turns is desired. The counter will be set in zero position on screw 21 after the latter has been turned to take up slack in spring 19. Thereafter rotation of the counter through its maximum number of turns will adjust the device to maximum time setting.

Where the device is to be merely set to a desired time and left in such setting for protracted periods, screw end 47 may be turned by a tool engaging part 48, such as screw driver slot, and a guard 49 fastened in place over screw end 47 to obstruct access to the screw. Such a guard is here shown in FIG. 9 and may be secured by screws 51 to the outer end of housing section 32.

As another feature of the present invention, means is provided for rapidly resetting the timer after each timed operation. As here shown in FIG. 2, a second passage 52 is connected to chamber 16 in parallel flow relation to orifice 17; and a pressure responsive check valve 53 is mounted to control fluid flow through passage 52, and in the form of the invention illustrated in FIG. 2 to also effect a venting of chamber 16 at the end of each timing operation. As here shown, base section 31 is formed with a cylindrical valve chamber 54 which is connected at its lower end 56 to a fluid inlet passage 57 having an exterior port 58 adapted for connection to a source of fluid under pressure, and is connected at its upper end with passage 52 leading into chamber 16.

A vent passage 59 is provided in section 31 leading between a side of cylinder 54 and the atmosphere. Valve 53 is here fitted at its upper end with a sealing ring 61 which seats on a tapered valve seat 61 at the upper end of cylinder 54 so that in the upper position of valve 53, as seen in FIG. 2, chamber 16 will be sealed off from vent passage 59. On initiation of timing operation by application of fluid pressure to port 58, valve 53 will be elevated to close chamber 16 while fluid under pressure passes into the chamber through orifice 17 to start the pressure build up in the timing cycle. After valve 24 is closed and the timing signal is produced at port 26, a momentary venting of port 58 will cause valve 53 to immediately shift to its downwardly displaced position, as seen in FIG. 2, and thus open vent passage 59 to chamber 16 to effect rapid discharge of pressure therein. Thereupon pressure may again be applied to port 58 to start the next timing cycle.

Timing orifice 17 is here formed in a plate 63 mounted in an orifice chamber 64 formed in base section 31. Chambers 64 is communicated at its base with an air chamber or manifold 66 communicating with inlet passage 57 and at its upper end is ported as at 67 to the interior of chamber 16. Plate 63 is here supported in chamber 64 by a short tube length 68 notched at its base for fluid communication with manifold 66, the upper side of plate 63 thus being sealed against a O-ring 69 compressed between plate 63 and the upper end of chamber 64. The orifice 17 needs be drilled with precision in plate 63 and for best results jeweled orifices are preferred.

As a feature of the present invention, chamber 64 is made of sufficient size as to accommodate a plurality of orifice plates 63a, 63b and 630 which may be assembled in stacked relation, as seen in FIG. 8, with O-

rings

69a, 69b and 69c mounted between the plates, the assembly being supported in mutually sealed relation in chamber 64 by a base tubular piece 68a which is appropriately notched for admission of fluid from manifold 66 to the several superimposed apertures. We have found that the arrangement of the aperture plates in this manner provides effective expansion chambers between the plates thus providing an accumulated effect of the stacked aperture plates in prolonging the time period for charging chamber 16.

In the form of the invention illustrated in FIG. 2, control passage 22 and its orifice 27 are connected to inlet passage 57 so that the same source is used for timing and control operations. Accordingly, base section 31 is provided with a second orifice chamber 71 which communicates at its base with manifold 66 and connects at its upper end to control passage 22. Orifice 27 may be fashioned in an orifice plate 72 mounted in chamber 71 by a notched tubular section 73 and O-ring 74 in the manner described in connection with orifice plate 63. In this arrangement fluid under pressure entering port 58 passes into manifold 66 and then through aperture 27 to control passage 22.

Manifold 66 is formed at the bottom of section 31 by specially formed passages in the section and a gasket 76 formed, as seen in FIG. 6, and attached to the bottom of section 31 by base plate 77. With reference also to FIG. 5, it will be seen that passage 57 turns downwardly in base section 31 to discharge at its lower end 78 into a manifold chamber 66 formed by an open portion in gasket 76. With refemece to FIG. 6, it will be seen that this open portion communicates with the lower end 56 of valve cylinder 54; with the lower end of orifice chamber 64; and with the lower end of orifice chamber 71. An opening 79 in base section 31 is provided for use with an optional base plate (not shown) replacing plate 77, to enlarge the size of chamber 16 where more time is required or which may be closed when only chamber 16 is used for the timing action. An excellent embodiment of the invention is illustrated in FIG. 7 wherein port 26 of the control passage is connected to the pilot of a piloted control valve 81. The latter may typically be constructed in accordance with the showings in US. Pat. Nos. 3,516,442 and 3,542,073 to perform a multiplicity of logic or control functions. A simple three-way single piloted valve is here shown for purposes of illustration and comprises briefly inlet and

outlet ports

82 and 83; a valve member 84 movable to positions opening and closing communication between

ports

82 and 83; a spring 86 biasing valve 84 to closed position; and a fluid actuated pilot 87 (piston on valve member working in cylinder) operable when energized to move the valve member to open position against the action of spring 86. Inlet port 82 is connected to a fluid pressure line 88 which may or may not be taken from the samesource as connected to timer port 58. Port 89 connecting pilot cylinder is here connected by conduit 91 to timer control passage port 26 whereby upon closing of valve 24 in the timer, fluid pressure will be transmitted through conduit 91 to energize pilot 87 and shift valve member 84 to open communication between

ports

82 and 83 thus producing a pressure signal at outlet port 83. The latter may be connected to a pneumatic actuator or other operating or read out device.

Timing ranges up to a minute or so may be provided depending upon the orifice arrangement used. Where a longer timing period is required, an additional volume may be added to chamber 16. For this purpose an additional opening 60 is formed in the base section 31

adjacent ports

58 and 59, see FIG. 1, connecting chamber 16 and which may be connected to an additional chamber. When not used, opening 60 will be closed with a plug.

The operation of the form of the invention illustrated in FIG. 7 follows. The timing operation is initiated by the application of fluid pressure to port 58. This will ordinarily be done manually or automatically by the use of a piloted control valve of the type illustrated at 81 and which is connected to a regulated source of pressure and the atmosphere to alternately apply fluid pressure to port 58 at the start of timing operation and to vent port 58 at the end of timing operation to recycle the device. Where air is used, working pressures up to about lOO psi are suggested and we have found that the timer will operate reliably over a very wide temperature range of about 35 F to [50 F. Pressure entering port 58 passes into manifold 66'causing valve 53 to move to position closing chamber 16 and to pass fluid under pressure through orifice l7 and into the chamber to start the pressure build up therein. Orifice 27 function to maintain fluid pressure in manifold 66 and to cause the pressure in control passage 22 at the downstream side of orifice 27 to approach atmospheric pressure so long as vent passage 23 is open. To ensure this relationship, the restriction 28 inlet passage is made somewhat larger than orifice 27. As pressure builds up in chamber 16, diaphragm 18 will be displaced against the action of spring 19 until valve 24 moves into engagement with seat 38 at the mouth of vent passage 23 thus closing off the vent passage and causing pressure in passage 22 to abruptly rise. The magnitude of this pressure change and energy contained therein causes an instantaneous shifting of the piloted control valve 81 and the appearance of a fluid pressure signal at the outlet port 83 of valve 81 to signal the end of the timing period. The valve supplying pressure to port 58 will then be shifted manually or automatically to vent port 58 thereby causing check valve 53 to shift and discharge the pressure in chamber 16 through port 59. Valve 24 will then open to vent control passage 22 which will in turn cause valve member 84 to shift under the urge of spring 86 and discontinue the pressure signal at outlet port 83. The parts are thus returned to starting position when the timing cycle may be reinitiated.

A modified form of the invention is illustrated in FIG. 10 wherein the fluid flow with respect to pressure chamber 16a and orifice 17a is reversed for developing the timing period. In this form of the invention, the pressure in chamber 16a is first raised to the pressure of the regulated source to close valve 24a and then fluid is metered from chamber 16a through orifice 17a to effect a timed reduction in pressure in chamber 16a terminated by the opening of valve 24a. To obtain a rapid charging of chamber 16a, the operation of check valve 53a is reversed so as to open communication between manifold 66a and chamber 16a immediately upon application of fluid pressure to the intake passage 58a (FIGS. 11 and 12) communicating with manifold 66a in the same manner as the first described embodiment. However, in this form of the invention vent passage 59ais not used and is closed by a plug 94. With reference to FIG. 10, it will be seen that a tubular valve seat member 96 is mounted in the bottom of valve chamber 54a and is formed with a base opening 97 communicating the interior of the valve chamber with the manifold 66a. A sealing ring 98 is mounted on the lower end of valve member 53a to seat against member 96 and normally the valve member is pressed downwardly onto its seat by a spring 99 mounted in compression between the upper end of the valve member 53a and the top of the valve chamber which is ported at 52a to chamber 16a. Valve member 53a is formed with a peripheral longitudinally extending slot 101 which is dimensioned for ample fluid conduction from-manifold 66a to chamber in the open position of valve 53a to provide a rapid charging of the chamber.

In this form of the invention, as seen in FIGS. l0, l1 and 12, the control passage 22a and the flow restriction orifice 27a are provided externally of the timer housing. With reference to FIG. 12, it will be seen that the control passage 22a is in the form of a separate supply line adapted for connection to a source of fluid under pressure and which need not be a regulated source as in the case of the supply to port 58a. Orifice 27a is preferably mounted in a separate choke member connected on one side to supply line 22a and on the other to pilot passage 89a of pilot control valve 81a described in connection with the above embodiment. It will be noted that the piloted control valve as here illustrated is made up of a plurality of sections with a pair of diametrically arranged ports for each section to facilitate circuit plumbing. Ports not used are closed by plugs. In the arrangement shown the second pilot passage 8% is connected by conduit 102 to port 26a which is in turn connected to vent passage 23a and flow restricting passage 28a opening to valve seat 38a engaged by valve 24a. In this form of theinvention, gasket 76a is formed, as seen in FIG. 11, to close off communication between manifold 66a and the orifice chamber 71a which is not used in this form of the device. Manifold 66a is formed as an open cutout in gasket 76a as in the first embodiment but, as seen in FIG. 11, the opening is confined to the downwardly discharge opening of passage 52a, the base of valve chamber 54a and the base of orifice chamber 64a. As in the first embodiment, a single orifice plate may be used as well as the stacked orifice plate arrangement, as illustrated in FIG. 8.

Operation of the form of the in the invention illustrated in FlGS. 10, 11 and 12 follows. A regulated fluid pressure is first applied, manually or automatically, to inlet port 580 causing check valve 53a to shift, charging of chamber 16a and closing of vent valve 24a. Closing of valve 240 produces an instantaneous rise in pressure at pilot 87 causing valve 84 to shift and open communication between inlet and

outlet ports

82a and 83a. lnlet port 82a is connected to supply line 22a so that virtually instantaneously with the closing of valve 24a, a fluid pressure signal will appear at port 83a. To initiate the timing cycle, the control valve supplying regulated fluid pressure to port 58a will be manually or automatically changed to vent port 58a to the atmosphere. When this occurs valve 58a will be held in its seated position by both the pressure differential across the valve as well as by spring 99. However, fluid may now meter out of chamber 16a through orifice 17a through manifold 66a and out of port 58a. A predetermined reduction in pressure in chamber 16a will signal the end of the time period by opening valve 24a thereby venting the pilot chamber, causing the return of valve member 84 (see FIG. 7) to its original position by spring 86 (FIG. 7) and cutting off the fluid pressure signal at port 83a.

We claim 1. A fluid timer comprising:

a housing and a diaphragm carried thereby defining a fluid pressure chamber, said housing having a fluid flow (first) passage connected to said chamber;

means providing a fluid metering (first) orifice in said passage and providing a variable fluid pressure in said chamber and displacement of said diaphragm as a function of time; means resiliently biasing said diaphragm against displacement by increasing pressure in said chamber;

said housing having a control (second) passage adapted for connection to a source of fluid under pressure and providing a vent port for said passage and a valve seat surrounding said port positioned in proximate confronting relation to the side of said diaphragm exterior to said chamber;

means providing a flow restricting (second) orifice in said control passage upstream from said vent port and being smaller than said port so as to maintain a pressure in said control passage near vent pressure in the open position of said port; and

a valve member carried by said diaphragm at said side in alignment with said port and movable with said diaphragm into and out of engagement with said seat, said valve member moving to said seat and functioning to close said vent port thereby causing an abrupt pressure change in said control passage upon increasing pressure in said chamber to a predetermined amount and moving away from said seat to open said port upon decreasing pressure in said chamber below said predetermined amount.

2. A fluid timer as defined in claim 1:

said first named means comprising a plate demountably positioned in sealed engagement with said first passage and having an apertur of predetermined size determining the rate of displacement of said diaphragm.

3. A timer as defined in claim 2:

a plurality of said plates being mounted in said first passage and a plurality of sealing members sealing said plates in longitudinally spaced relation therein and providing accumulated reduction in the rate of displacement of said diaphragm.

-4. A timer as defined in claim 1:

means providing a third passage connected to said chamber in parallel flow relation to said first named orifice; and

a pressure responsive check valve mounted in and controlling the flow through said third passage.

5. A timer as defined in claim 4:

said housing being formed with a fluid inlet (fourth) passage adapted for connection to a source of fluid under pressure and being connected to said first, second, and third passages; and said check valve being constructed to close flow through said third passage upon application of fluid pressure to said fourth passage thereby restricting fluid flow entry to said chamber through said first orifice, said valve being constructed to open said flow in said third passage upon venting of said fourth passage to thereby vent said chamber.

6. A timer as defined in claim 41' said housing being formed with a fluid inlet (fourth) passage adapted for connection to a source of fluid under pressure and being connected to said first, second, and third passages;

said check valve being constructed to open flow through said third passage upon application of fluid pressure to said fourth passage thereby rapidly charging said chamber and to close said flow in said third passage upon venting of said fourth passage for timed reduction of pressure in said chamber by fluid flow therefrom through said first orifice.

UNITED STATES PATENT OFFICE CERTIFICATE OF CURRECTION Patent No. 3,7 9 ,99 Dated Ngxgmhg; 6, 1,973

'lnvent fl Edward L. Holbrook, et a1,

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 50, after "as" insert -a-., Column 4, line 4, change "61" to -62--; line 21, change "Chambers" to -Chamber-; line 27, change "a" to -an--; line 66 change "refernece" to ref erence-. Column 5, line 59, change '"tion" vto -tions-. Column 8, line 18, change "apertur" to --aperture--.

Signed and sealed this 23rd day of April 1971;.

(SEAL) Attest:

C MARSHALL DANN EDWARD M.FLETCHER,JR.

Commissioner of Patents Attesting Officer USCOMM-DC 6037 G-PBQ I FORM P0-1050HG-69) 1% us. GOVERNMENT FRINUNG OFFICE uses o-ass-au

Claims

1. A fluid timer comprising: a housing and a diaphragm carried thereby defining a fluid pressure chamber, said housing having a fluid flow (first) passage connected to said chamber; means providing a fluid metering (first) orifice in said passage and providing a variable fluid pressure in said chamber and displacement of said diaphragm as a function of time; means resiliently biasing said diaphragm against displacement by increasing pressure in said chamber; said housing having a control (second) passage adapted for connection to a source of fluid under pressure and providing a vent port for said passage and a valve seat surrounding said port positioned in proximate confronting relation to the side of said diaphragm exterior to said chamber; means providing a flow restricting (second) orifice in said control passage upstream from said vent port and being smaller than said port so as to maintain a pressure in said control passage near vent pressure in the open position of said port; and a valve member carried by said diaphragm at said side in alignment with said port and movable with said diaphragm into and out of engagement with said seat, said valve member moving to said seat and functioning to close said vent port thereby causing an abrupt pressure change in said control passage upon increasing pressure in said chamber to a predetermined amount and moving away from said seat to open said port upon decreasing pressure in said chamber below said predetermined amount.

2. A fluid timer as defined in claim 1: said first named means comprising a plate demountably positioned in sealed engagement with said first passage and having an apertur of predetermined size determining the rate of displacement of said diaphragm.

3. A timer as defined in claim 2: a plurality of said plates being mounted in said first passage and a plurality of sealing members sealing said plates in longitudinally spaced relation therein and providing accumulated reduction in the rate of displacement of said diaphragm.

4. A timer as defined in claim 1: means providing a third passage connected to said chamber in parallel flow relation to said first named orifice; and a pressure responsive check valve mounted in and controlling the flow through said third passage.

5. A timer as defined in claim 4: said housing being formed with a fluid inlet (fourth) passage adapted for connection to a source of fluid under pressure and being connected to said first, second, and third passages; and said check valve being constructed to close flow through said third passage upon application of fluid pressure to said fourth passage thereby restricting fluid flow entry to said chamber through said first orifice, said valve being constructed to open said flow in said third passage upon venting of said fourth passage to thereby vent said chamber.

6. A timer as defined in claim 4: said housing being formed with a fluid inlet (fourth) passage adapted for connection to a source of fluid under pressure and being connected to said first, second, and third passages; said check valve being constructed to open flow through said third passage upon aPplication of fluid pressure to said fourth passage thereby rapidly charging said chamber and to close said flow in said third passage upon venting of said fourth passage for timed reduction of pressure in said chamber by fluid flow therefrom through said first orifice.