US 2760511 A
Description (OCR text may contain errors)
Aug. 28, 1956 C. E. GREEFF 2,760,511
PNEUMATIC CYCLE TIMER Filed March 4, 1955 INVENTOR CARL E. GREEFF BY /M/v/ WS ATTORNEY PNEUMATIC CYCLE TDi/1ER Carl E. Gree, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application March 4, 1953, Serial No. 340,355
4 Claims. (Cl. 137-102) This invention relates to an automatic cycle timing apparatus and particularly to a Widely adjustable, continuously operable pneumatic cycle timer.
It is frequently necessary in industrial manufacturing to control the performance of repetitive operations by the use of cyclic timers, the most common types of which are spring-actuated or electrical clock devices. Springactuated apparatus requires periodic winding, which is disadvantageous, and apparatus employing electrical energy as the power source is objectionable from the standpoint of re or explosion hazards.
An oject of this invention is to provide a continuously operable pneumatic cyclic timer which is infinitely adjustable over its full range to permit a wide choice of cycle intervals, which is adapted to use over a very wide timing range by suitably proportioning its capacity component and which may be readily adjusted during operation.
Another object of this invention is to provide a pneumatic cyclic timer which is completely pneumatic and is thereby free from inherent iire and explosion hazards.
Another object is to provide a pneumatic cyclic timer which is economical in air consumption, low in first cost, reliable in operation and which is adapted to use in any manufacturing building provided with air pressure service facilities.
The manner in which these and other objects of the invention are accomplished will be apparent from the detailed description and the following drawings wherein all gas ow conduits are shown in single line representation, in which:
Fig. l is a schematic representation of one embodiment of cyclic timer according to this invention,
Fig. 2 is a time-pressure diagram showing the characteristic variation of the signal pressure obtained with the timer of Fig. l, and j Fig. 3 is a modification of the three-way valve and actuating means for the timer of Fig. l, the showing of the timing circuit being omitted in this view.
Generally, this invention comprises a source of gas pressure and a timing circuit connected therewith through a three-way valve, which is actuated in response to the pressure existing in a gas storage capacity supplied with gas from the timing circuit, to cyclically vent or maintain an effective signal pressure in on-of sequence for intervals of time preselected by the operator.
Referring to Fig. l the gas supply is derived from a source not shown connected to supply line lil which, in turn, is connected to port 52 of the three-way valve indicated generally at 11. Usually the operating gas employed will be air, in which case line 1t) may be supplied from the building service air facilities commonly provided in industrial factories, although it may be derived from a separate compressor or gas cylinder if this is more convenient and, of course, any gas other than air may be utilized if conditions, such as tire hazards or the like, make the use of a non-combusting gas advisable.
trite rates attent of 21, which passes gas through check valve 22 without" Three-way valve 11 may conveniently include self-contained actuating mechanism, a commercially available design being the Brown Instrument Companys model RO49A provided with two spring-biased valve members, 40 and 41, and a snap-acting relay, indicated generally at 28, comprising a pivoted lever 42 which, when the lower end passes the pivot point of spring 43, rapidly tilts pivoted plate 44 to open and close Valves 40 and 41 in alternation. Lever 42 is actuated through a slide strap connection with piston rod 45, fixed at one end to diaphragm 46, in response to the ambient pressure in compartment 47, with which line 27 is in open communication. The opposite end of piston rod 45 is biased in oppositon to diaphragm 46 by spring 48, the compressive value of which can be adjusted to a predetermined set point by set screw 49.
Port Si) of three-way valve 11 is vented through line 12 while port 51 is connected to line 13 which communicates with line 14, from which the signal pressure is sensed, and with line 15, which communicates with the timing circuit. Ordinarily, line 12 vents to the atmosphere and the following description is based on such operation; however, it can vent to a receiver at subatmospheric or superatmospheric pressure providing the pressure range within which operation is desired is above the maximum vent back-pressure. Line 14 is in open communication with the diaphragm of pilot valve 18 which directly controls the ow of iiuid in line 19 and, secondarily, any other condition as to which control is desired. Thus, line 19 may be connected to an air-operated control valve in a process, or to two oppositely acting control valves, one of which opens to permit the iiow of one iluid while the other closes to discontinue the ilow of a different fluid. If the control is utilized for the proportioning of reflux to product takeoff in a distillation column, the variation in duid pressure in line 19 may be made to operate a threeway valve directing column condensate for one interval of time to product collection and during the other interval to reflux accumulation. Another useful application` might be the operation of a pressure switch controlling on-off electrical output for one of a myriad of purposes.
The timing circuit comprises the closed` gas flow path including line 20 provided with two gas ow throttling means 21 and 24, which may be conventional needle valves as shown in Fig. l, connected in parallel with line 15, after which are interposed check valves 22 and 23, which are adapted to permit flow in directions opposite one another (referred to the adjacent throttling valves) and prevent iiow in the reverse directions, as indicated byV the arrows adjacent each. A gas storage capacity 25, which may be any gas-tight chamber of sutiicient capacity to preserve the rate of rise and fall in pressure at levels to obtain the desired cycle intervals with the particular needle valves employed, is connected to the opposite sides of the check valves 22 and 23 by lines 26 and 29, respectively. Line 27 is provided to connect storage capacity 25 with the actuation means 28, which operates valve 11 in the manner hereinafter described. As shown in Fig. l, actuation means 28 may comprise a snapacting relay having a diaphragm responsive to the gas pressure existing in capacity 25, a suitable design being a relay having a 4-17 1bs./sq. in. adjustable set point and operating on a 2 lbs./ sq. in. differential.
In operation from the start-up condition the gas supplied through line 1t) enters valve 11 and discharges through valve member 40 into line 13 and thence into. lines 14, 15 and 20, imposing full source pressure on the diaphragm of pilot valve 18 and on the needle valves 21 and 24. However, since check valve 23 prevents flow in the direction of gas storage capacity 25, the rate at which pressure rises in 25 is determined by the setting interference therefrom. Thus, needle valve 21 controls the On" time for the apparatus and this interval of the cycle is represented as T1 in Fig. 2. When the preset upper pressure of relay 28 is attained, this pressure being appliedl to the relay diaphragm 46, relay 28 actuates valve 11 through llever 42, spring 43 and pivoted plate 44 of Fig. l and closes valve member 40, thus discontinuing the connection between line 1t) and line 13, at the same time opening valve member 41, thus opening connection between line 13 and vent 12. The signal pressure applied through line 14 to the diaphragm of pilot valve 18 thereupon almost immediately drops to atmospheric pressure, as indicated for the Off time interval T2 of Fig. 2, thus controlling the flow of duid through line 19, and any secondary devices (not Shown) responsive to such flow, in a manner different than the control imposed during the On interval T1. The pressure in capacity 25 decreases during the O11 interval by venting of gas through check valve 23 and needle valve 24 at a rate determined by the setting of the latter, the drop continuing until the preset lower pressure of relay 28 is attained, when relay 28, by operation of valve members 40 and 41, opens the connection between line and line 13, simultaneously closing the connection between line 13 and vent 12. The cycle then repeats itself `indeiinitely so long as operating gas supply-continues through line 14).
The controls effected by needle valve 21 for the On interval and by needle valve 24 for the Off interval are entirely independent of each other and thus the durations of Tr and Tz are controllable at the will of the operator. For purposes of representation solely the duration of VTr as compared to T2 in Fig. 2 is shown in the ratio of 3 :4; however, in a typical apparatus constructed according to this invention wherein the lower preset pressure of relay 28 was 7.5 lbs/in.2 and the higher preset pressure was 9.5 lbs/in?, the operating pressure diierential being then 2.0 lbs/sq. in., it was found practicable to obtain independent adjustments of the duration of Tr and T2 over a range greater than 200:1 using commercially available needle valves as the throttling means 21 and 24. The capacity 25 was 3.77 cu. in., and the inside diameter of the lines connecting the needle valves and the check valve was 555,-," while the length of the latter lines were limited to 2" to minimize the effect of the gas capacity contributed by the lines as compared to the volume of 25. This apparatus displayed completely satisfactory precision of control for absolute time intervals T1 and T2 ranging from 3 seconds to more than l() minutes over a wide series of ratios of durations up to and including 200:1. ratus constructed according to this invention can be irnproved by utilizing special types of high-precision throttling devices and in other ways known to persons skilled in the art, nevertheless the precision reported is ample for most manufacturing control uses and additional eX- pense in the appurtenances of the timing circuit is seldom warranted except for special situations. If greater or smaller ranges of operation are desired capacity 25 can be proportioned accordingly, which aiords the designer wide latitude in the accommodation of speciiic process requirements.
It is sometimes desirable to obtain a greater precision of preset high and low pressures and also a greater range of choice of `operating pressure differential than is afforded by a single relay of the type represented by 28 in Fig. l, and the system shown in Fig. 3 is therefore sometimes preferred. The timing circuit is omitted in the showing of Fig. 3, it being understood that it is identical in all respects with that hereinabove described for Fig. l, and the same reference numerals are utilized for elements common to both figures.
In Fig. 3 separate pilot valves with self-contained actuating mechanisms, such as the commercially available Moore Products Co. pneumatic precision relay Model 67, are provided for the preselection of the upper Obviously the precision obtainable with appa- A and lower operating pressures, respectively. Thus, the valve indicated generally at`34 is operated by the springbiased diaphragm actuating mechanism indicated generally at 32 to establish the upper pressure, while the valve indicated generally at 35 is operated by the spring-biased diaphragm actuating mechanism indicated generally at 33 to establish the lower pressure, although it will be understood that these functions can equally well be lreversed by suitable conduit connection.
The body 'of valve 34 is provided with a vent port 56, port 57 in open communication with line 36, and thus with gas supply line 10, and port 58 in open communication with line S9 leading to compartment 60 of double diaphragm pressure responsive three-way valve 37, which may be of the type marketed by the Valvair Corp. Similarly, the body of valve 35 is provided with a vent port 62, port 63 in open communication with lines 64 and 36, and thus with gas supply line 10, and port 65 in open communication with compartment 67 of threeway valve 37 through line 66. The valve sides of the diaphragms of actuating mechanism 32 and 33 are in open communication with capacity 25 through common line 27 and branch lines 38 and 39, which connect with ports 69 and 70, respectively, of the actuating mechanisms. The yopposite sides of the diaphragms are vented to the atmosphere through ports 53 and 54.
Valve 37'is provided with a double piston 72, attached at opposite ends to the diaphragme 73 and 74, and the central portion of the valve body into which the three ports hereinafter described open is 4sealed for the diaphragms by resilient O-rings 75, which also seal the two upper ports 7'7 and 7S from each other, while permitting connection of each of 'these ports in alternation with lower port 79 by virtue of the reduced diameter of the central portion of valve piston 72. Port 77 is in open communication with gas supply line 1l), port 78 is vented to the atmosphere and port 79 is in open communciation with line 13, and thus with line 14, leading to the diaphragm of pilot valve 18 and to line 15, leading to the timing circuit, in the same manner as hereinabove described for the embodiment of Fig. l.
The operation of the apparatus shown in Fig. 3 is similar to that described for Fig. l, venting of the system, or the Oli interval of the timing cycle, being `initiated by actuating mechanism 32 While pressure build-up, or the On interval of the timing cycle, is initiated by actuating mechanism 33. Thus, when the high pressure to which 32 is preset is imposed on its diaphragm, the valve member of 34 is momentarily moved to closed position against its upper seat, interrupting communication between vent port 56 and port S8 and establishing communication of the latter port with gas supply line 10 l through line 36 and port 57. Supply line pressure is thereupon applied to compartment and the left-hand diaphragm 73 of three-'way valve 37 through line 59, thus urging piston 72 toV the rightV and closing off cornmunication between supply line 10 through port 77 with port 79 and line 13. Inthe course of movement of piston 72 to the right, vent port 78 of valve 37 is opened to communication with port 79 and lines 173, 14 and 15, and the signal pressure applied to the diaphragm of pilot valve 18 almost immediately drops to atmospheric level. At the same time the valve member of 35 is retained in closed position against its upper seat, thus maintaining open communication between the right-hand compartment 67 ofvalve 37 and vent 62 through line 66. When the low pressure to which 33 is preset is imposed on its diaphragm, the valve member of 35 is moved-to closed position against its lower seat, interrupting cornmunication between vent port 62 and port 65 and establishing communication of the latter port with gas supply line 10 through lines 36 and 64. Supply =line pressure is thereupon applied to compartment 67 and the righthand diaphragm 74 of three-way valve 37, thus urging piston 72 to the left and closing off communication between vent port 78 and port 79 and lines 13, 14 and 15.'
it wiil be understood that the valve member of 34 is at this time against it-s lower seat, and atmospheric pressure exists in compartment 60. Similarly, the valve member of 35 is only momentarily closed against its lower seat, the valve members of 34 and 35 occupying the positions shown in Fig. 3 at all times except when initiating the respective cycle intervals assigned to each. In the course of the movement of piston 72 to the left, supply line 10 is placed in communication through ports 77 and 79 with lines 13, i4 and 15 and the On interval of the cycle begins, after which the complete timing cycle repeats.
From the foregoing it will he understood that this invention is capable of relatively wide modifications by those skilled in the art without departure from its essential spirit, wherefor it is intended to be li-mited only by the scope of the following claims.
What is claimed is:
1. A pneumatic cycle timer comprising in combination a gas pressure source, a three--way valve in gas supply connection through one port with said source, in vent connection through a second port and in gas delivery connection through the third port with a timing circuit, said timing circuit comprising a closed gas fiow path provided with a iirst throttling means, a rst check valve, a second throttling means and a second check valve, said first and second check valves being adapted to permit fiow of gas in opposite directions referred to their associated throttling means and :said third port being con nected to a point in said timing circuit opposite the sides of -said first and second throttling means adjacent said check valves, a substantially constant volume gas storage capacity in open communiction with said check valves on the sides opposite said throttling means, and means in open communication with said gas storage capacity for causing actuation of said three-way valve to permit gas iiow from said timing circuit through said second port at a preselected first pressure and from said source through said third port at a preselected second pressure lower than said first pressure, and a signal pressure sensing conduit in open communication with said third port.
2. A pneumatic cycle timer according to claim 1 Wherein said iirst and second throttling means comprise needle valves.
3. A pneumatic cycle timer according to claim 1 wherein said means for causing actuation of said three-way valve comprises a single pneumatic relay operating at the extremes of a preselected pressure differential.
4. A pneumatic cycle timer comprising in combination a gas pressure source, a three-Way valve in gas supply connection through one port with said source, in vent connection through a second port and in gas delivery connection through the third port with a timing circuit, said timing circuit comprising a closed gas iiow path provided with a rst throttling means, a first check valve, a second throttling means and a second check valve, said first and second check valves being adapted to permit flow of gas in opposite directions referred to their associated throttling means and said third port being connected to a point in said timing circuit Aopposite the sides of said iirst and second throttling means adjacent said check valves, a substantially constant volume gas storage capacity in open communication with said check valves on the sides opposite said throttling means, and means in open communication with said gas storage capacity for causing actuation of said three-way valve to permit gas ow from said timing circuit through said second port at a preselected first pressure and from .said source through said third port at a preselected 'second pressure lower than said first pressure consisting of a tinst pneumatic relay responsive to said preselected first pressure, a second pneumatic relay responsive to said preselected seco-nd pressure and valve actuating means controlled by said relays in response to each of said preselected pressures in sequence, and a signal pressure sen-sing conduit in open communication with said third port.
References Cited in the file of this patent UNITED STATES PATENTS 862,867 Eggleston Aug. 6, 1907 1,704,374 Stewart Mar. 5, i929 1,920,003 Chenaullt July 25, U33 2,620,825 Cannon Dec. 9, .1952