US2904073A - Instantaneously acting pneumatic timer - Google Patents

Description

States Patent r g 2,904,073 v INSTANTANEOU SLY ACTING PNEUMATIC TIMER v Robert C'owlierd, West Terre Haute, Ind. ApplicationNovember 27, 1957, Serial No. 699,238 j (Ch l y 620).

This invention relates to a pneumatically actuated timing device that is characterized by snap-acting load energizing and de-energizing features.

Electric controls, such as solenoids, information net works, relay's, timers, etc., cannot be either economically of safely used in areas where explosive vapors or gases exist. Optimum installations of these electrical com- Fig. 1 illustrates atypical exponential time-pressure curve A for a pneumatic system which includes air under pressure passing through a measured constriction into a closed system of finite volume. The curve B represents a time pressure curve for air under pressure passing from a closed system 'offinite volume, through a measured restriction to atmosphere. a

Referring to Fig. 2, the valves there shown aregenerally. of a similar construction, and, referring to valve A in particular, include the movable valve member 3 traveling between valve seats 4. and 5. Actuation of the valve is eflected by a diaphragm 6 connected through a push rod 7 to the valve member 3 and communicating at its upper surface or top with'a duct, such as conduit 8. A spring 9 biases the valve in one direction, oppositely to'the pressure exerted by the diaphragm. The common port '10 of the valve will communicate with either ports 11 or In, depending upon the presence or absence of pneumatic pressure at the valve ltop.

Referring again to Fig; 1, and keeping in mind the construction of valve A, it can be assumedthat when the pressure in the valve top reaches a value a the force exerted by the diaphragm 6 is exactly balanced by the initial upward force created by spring 9. When the pressure on diaphragm 6 reaches a value a the force on the diaphragm will not only overcome the upward force exerted by spring 9, but'will cause the valve member 3 ated valves utilize springs, which members cause them I x to throttle or move proportional to the pressure applied to their actuators, rather than to. move in a snap acting manner.

An object of the present invention is, therefore, to provide an improved control system employing fluid-actuated valves with a view to substantially eliminating the throtfling of the valve operators.

More specifically, the object of this invention is to provide a timing circuit consisting of an adjustable orifice,

a parallel connected volume and a suitable combination of pilot valves that will produce an instantaneous regenerativepressure and an instantaneous deenergized reduction in pressure of an extemally connected load, which may take the form of a process control valve, a cylinder actuator orother portions of an associated pneumatic circuit.

The nature of the invention will be understood from the accompanying drawings and the following description and claims:

Fig. 1 diagrammatically illustrates time pressure curves which are characteristic of a resistance-capacity combinationof elements.

Fig. 2 is a schematic diagram of a pneumatic control system embodying the present invention.

Fig. 3 is a diagrammatical illustration of the time pressure curves for certain of the components in the system of Fig. 2.

Fig. 4 is a time-pressure chart indicating the pressure at one of the load connections of the system in Fig. 2.

Fig. '5 is a time-pressure chart indicating the pressure at a further one 'of the load connections shown in Fig. 2.

Fig. 6 is a time-pressure chart of a further l'oad con nection shown in Fig. 2.

Fig. 7 is a chart indicating the positions of the various "valves during each step of an operating cycle.

While the invention will be herein described with reference-lto a pneumatic system, it is not to be restricted to pneumatic systems alone. By making certain simple modifications, the circuit will allow the use of an incompressible fluid-or liquid.

to traverse the distance between seats 4 and 5. The difference between the pressures a and a constitutes a range of pressure wherein valve member 3 may be at some intermediate position between the seats 4 and 5. This pressure range, associated with valves of this type, produces a regulating or throttling action instead of a snap action. The system to be subsequently described with reference to Fig. 2 provides a timing mechanism to provide the snap action effect.

Referring to Fig. 2, it may be assumed that the manifold or header 1 is supplied by a constant regulated pressure source capable of maintaining the pneumatic pressure within the manifold within a few percent of a predetermined level. Twenty-five pounds per square inch is typical of one source pressure commonly used in indus trial control circuits.

In the system of Fig. 2, the diaphragm top of a process valve H is coupled intothe control system. Operation of the valve by the system will provide non-throttling or on- 051 control of the medium flowing through the process v ve.

, Let it be assumed that the time sequence shall be initiated by momentarily depressing the push rod on'valve 20. The normally closed seat 27 is opened and the normally open seat 28 is closed, therebyadmitting a pulse of pressure from the port 21 which travels through the port 12 or pilot valve'A, thence through common port 10. From the common port 10 of pilot valve A the pulse is connected through normally openlvalve seat :22 of pilot valve E, thence through the common port 23 to the diaphragms of valves A and B. When the pressure wave reaches the actuation valve for the pilot valve' A, the seat 'Scloses and the seat 4 opens. This actio'njof pilot valve A closes off the initial air pulse from the portal of the push button 20, and by 'Way of the now openport 11 and the seat 4 admits an auxiliary source of pressure to the di'aphrag'ms of pilot valves A and B. The/push rod on the mechanism 20 may nowbe released without disturbin'g the pressured condition of the diaphragm-of valves Aand B. It will be noted that the foregoing has described the-exact pneumatic equivalentto the 'mbmentaryenergization of "an electrical hold-in circuit, sometimes re- Ierredto a'sa' lock tip.- .AWhen .pilot valve B. isactuated, its normally opened seat closes; Pressure is, therefore, admitted to the diaphragms of pilot valves C and D, to the normally closed seat of pilot valve F, and to the up-stream side of an adjustable restriction or orifice generally indicated at 24. Since'the normally open seat of pilot valv'e B has previously been closed, the reversal of the seats of pilot valve C will have 'no immediate effect on the system pressured by the now open normally closed seat of pilot valve B. When thepilot valveD is actuated, its normally open seat is closed so that the circuit down-stream from the adjustable restriction 24 becomes a closed volume which, in combination with the restriction 24, forms a resistance capacity time constant system. At this point in the sequence, a time delay has been initiated at the end of which the process 'valv e'H will be instantaneously energized.

Air may now be effectively metered through the restriction 24 and, depending on the flow area of the restriction and the down-stream system volume, the pressure on the diaphragm of pilot valves G, E and F will increase exponentially following curve A of Fig. 1, or along the line BC of Fig. 3. When the pressure in the now closed volume downstream from the adjustable restriction 24 reaches a value indicated at a in Fig. 3, pilot valves E, F and Gwill just being to overcome the force exerted by their respective loading springs. In particular, pilot F will be so affected.

When the pressure on the diaphragm of valve F slight- I ly exceeds the value a its normally closed port will open slightly, and in sodoing will admit a small amount of air around. the initial source flowing through the restriction 24. The auxiliary air pressure admitted to the top of valve F, caused by the flow of air through the slightly open normally closed seat of valve F, increases the opening of this seat still further, thereby admitting more air and hence opening the normally closed seat of valve F still further. This regenerative cycle causes the pressure on the diaphragms of pilot valves E, F and G to abruptly rise to the source pressure value. This increase in pressure on the diaphragms of valves E, F and G occurs along the line CD' of Fig. 3 instead of slowly reaching the same value along the line CD" of Fig. 3.

shut ofivwhen its top is pressurized.

When the diaphragm of pilot valve E is pressurized,

its normally open seat 22 closes and its normally closed seat 29 opens to atmosphere. The pressure on the dia-' phragms of pilot valves A and B is thereby vented to atmosphere through the common port 23 of valve E and its now open seat 29.

De-pressurizing the diaphragm of pilot valve A causes seat 4 to close. When seat 4 closes, the auxiliary air sup- :ply is eliminated and the pressure trapped between the i As the .diaphragm of pilot valve A is de-pressurized,

so also is that of pilot valve B, thereby causing its normally closed seat to close and its normally open seat to open. Since the diaphragm of pilot valve C is pressurized, the return to normal position of pilot valve B establishes communication for the trapped pressure in the timing cirouit to the adjustable restriction 25. Such communication is established through the common port and normally open seat of valve B and through the common port and the now open normally closed seat of pilot valve C.

-'I'he;-pressure in the timing section down-stream of the 'its' normally open seat 5 to open and its normally closed 7 common port of valve B, will therefore diminish along a line DE' of Fig. 3, the rate of pressure decrease depending on the timing circuit volume and the area of the restriction or orifice 25.

When the trapped pressure in the timing circuit reaches a value indicated at a in Fig. 3, the normally open seat of pilot valve C just begins to open and its normally closed seat just begins to close. With the slight opening of the normally open seat of valve C, air pressure is bled olf from the timing circuit more rapidly since the restriction 25 is by-passed. As a result, the decreased pressure on the diaphragm of pilot valve C causes it to open, its normally open port wider until the circuit is degeneratively de-pressurized in an abrupt manner along the line E'F of Fig. 3.

To aid in the degenerative action, the pilot valve D exhibits similar characteristics to those just described with reference to valve C. The dual action of pilot valves C and D thus cause an instantaneous drop in the timing circuit pressure.

Since the timing circuit pressure is also exerted on the diaphragms of pilot valves G and E, they too will snap to their depressurized positions as the timing circuit pressure drops. The air on the diaphragm of process valve H will therefore be vented to atmosphere in an abrupt manner through the common port and the now open normally open seat of pilot valve G. Process valve H will thereupon be snapped closed.

Fig. 4 illustrates a graph or chart of the pressure on the diaphragm of the process valve H. The time interval T T measures the time lapse between the closure of the normally open seat of valve D and the opening of the normally closed seat of valve G. The length of this timing period is dependent on the size of restriction 24 and upon the total volume of the timing circuit portion of the system. During the time interval T T the process valve H will be pressurized and the length of this interval will depend upon the adjusted size of restriction 25 and upon the timing circuit volume, as previously mentioned. Because of the degenerative action resulting from the return of valves C and D to their de-pressurized positions, the process valve H is abruptly de-pressurized at the end of the T T interval. The system connected as described in Fig. 2 thus provides an initial delay (T T adjustable by means of restriction 24, and a period (T T during which process valve H is pressurized, adjustable by means of restriction 25. The pressure rise and decline in process valve H occurs abruptly, rather than following the exponential curves A and B of Fig. 1.

The system of Fig. 2. has additional flexibility in providing alternate load connections. For example, if the diaphragm of the load pilot valve G is placed in parallel with the diaphragms of pilot valves A and B by connecting it to alternate load connection 36 in Fig. 2, it 'will be obvious that the resulting sequence of pressurization of process valve 1-1 will be as shown in Fig.5. Under these conditions the process valve H will be pressurized and de-pressurized between times T and T It may also be shown that if the diaphragm of load pilot valve G is placed in parallel with the diaphragms of pilot valves C and D, by connecting it to alternate load connection 35 of Fig. 2, the resulting sequence 'will occur as shown in Fig. 6. The process valve H will under these conditions be pressurized and de-pressurized between times T and T The present invention thus provides a non-electrical system for controlling a load, such as process valve H, that produces a snap action in the load valve instead of 4 the throttling action conventionally characteristic of pneumatic or hydraulic systems. The regenerative and degenerative effects produced by the pilot valves might be applied to control circuits of differing configuration and the specific example described is to be construed as illustrative only, the invention being limited only by the appended claims.

The invention claimed is:

1. In combination in a pneumatic control system, a valve with a valve seat and a valve member adapted to alternately open and close, with inlet and outlet ports communicating, respectively, with the two sides of said seat, and with pressure responsive means actuating said valve member; and means for rapidly actuating said valve comprising an unrestricted duct communicating with one of said ports, the other of said ports communicating with said pressure-responsive means, and a relatively restricted duct containing a predetermined volume communicating in shunt with said ports.

2. In a pneumatic control system having a pressure source and a pressure-responsive utilization device, two parallel lines between said source and said device, one line containing a series-connected constriction, and the other line containing a normally closed port of a pressureresponsive valve, and a feed-back line from the downstream side of said normally closed port to the pressureoperating chamber of said valve so that operating fluid through the valve regeneratively accelerates opening of the valve and the operation of said pressure responsive utilization device.

3. In a control system, a source of control pressure, a load device adapted to be operated upon the application of said control pressure thereto, a control pressure operated pilot valve having ports connected between said source and said load device operable to apply and relieve said control pressure on said load device, and means for operating said pilot valve with a snap action, said means including: a restricted passage 'from said control pressure source to the operator for said pilot valve, an unrestricted passage from said control pressure source to said pilot valve operator paralleling said restricted passage, in auxiliary pressure operated valve having its normally-closed port controlling said unrestricted passage, and a feedback passage from the downstream side of said normally closed port to the operator for said auxiliary valve, the resulting regenerative action of said auxiliary valve serving to operate said pilot valve with a snap action to abruptly apply control pressure to said load device.

4. A control system as claimed in claim 3 having additional auxiliary pressure operated valve means for dis- 6 connecting both said restricted and said unrestricted passages from said source of control pressure and venting said passages through an auxiliary restriction, and an unrestricted vent passage placed in communication with said restricted and unrestricted passages upon operation of said auxiliary pressure operated valve means.

5. A control system as claimed in claim 3 having additional auxiliary pressure operated valve means for disconnecting both said restricted and said unrestricted pas sages from said source of control pressure and venting said passages through an auxiliary restriction, an unrestricted vent passage placed in communication with said restricted and unrestricted passages upon operation of said auxiliary pressure operated valve means, and means for increasing the degenerative action thereby produced on the system including a further pressure operated valve means providing a further unrestricted vent passage placed in communication with said restricted and unrestricted passages upon operation of said further pressure operated valve means.

6. A control system as claimed in claim 3 having an additional pressure operated valve responsive to the pressure on the downstream side of said restricted passage, further pressure operated valve means for disconnecting both said restricted and said unrestricted passages from said source of control pressure and venting said passages through an auxiliary restriction, and an unrestricted vent placed in communication with said restricted and unrestricted passages upon operation of said further pressure operated valve means, said further pressure operated valve means being operated in response to operation of said additional pressure operated valve.

7. In combination in a control system of the class described, a pressure-responsive two-position valve hav. ing two ports and a pressure chamber, a restricted passage with a measured volume communicating with said chamber for moving the valve after a predetermined time, and an unrestricted passage communicating with said chamber through said valve ports so that fluid under pressure passing through the ports regeneratively accelerates the movement of the valve.

References Cited in the file of this patent UNITED STATES PATENTS 2,427,235 Smoot Sept. 9, 1947

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