Patent Publication Number: US-3880178-A

Title: Hydraulic logic circuit with controlled delay

Description:
United States Patent 1 m1 3,880,  
 Panissidi Apr. 29, 1975 [54] HYDRAULIC LOGIC CIRCUIT WITH 2,262.99) 11/1941 Grove .t 251/26 X CONTROLLED DELAY 3241.804 3/1966 Bjorklund v. 251/41 Hugo A. Panissidi, Peekskill, N.Y.  
 International Business Machines Corporation, Armonk, N.Y.  
 Filed: Oct. 4/1972 Appl. No.: 296,498  
 Related U.S. Application Data Inventor:  
 Assignee:  
 Continuation of Scr. No. 85,852. Nov. 2, I972.  
 abandoned, Continuation-impart of Ser. No. 824.424. May 14. 1969, Pat. No. 3,726,190.  
 References Cited UNITED STATES PATENTS Prinmry Examiner-Arnold Rosenthal Attorney Agent. or Firm-Graham S. Jones, 11  
 [57] ABSTRACT A free piston, an orifice, and an independent valve are employed to provide multiple controls of the displacement of a control valve after a time delay provided by the orifice and free piston. The characteristics of the orifice and the free piston as well as pressure and resistance. determine the minimum time delay. Bleed circuits, when open, may delay the ultimate displacement of the control valve for an indeterminate period. The free piston assures that a high pressure pulse will hammer the control valve to its new position without stalling between positions. Several applications of the principle are provided.  
 18 Claims. 8 Drawing Figures PATENTEUmsims 3880.178  
 SHEET 10F 5 INPUT P PORT 1 38 R 1 INPUT P L MIN. PORT JDELAY 688 i I DELAY U I I PISTON ea 0 I I CONTROL 0 I VALVE 69 D l IN-SYSTEM BLEED 0 &#39;icmwrxs l c lm s LINE g \1 24 C I 25% i 1 74 R lx/ P OUTPUT OUTPUT OUTPUT II I TL 5 I ll I DELAY CONTROLLED DELAY CONTROLLED BY BLEED LINE BY DELAY PISTON TlME- Fl G. 2 INVENTOR Huso A. PANISSIDI ORNEY maze i975 IATEHTE&#39; SHEEF Q 0F 5 Nn MES as as; :3 mm:  
 on 6E PATENTEDA Z QY SHEET 5 BF 5 xumio MOI-m0 an QE 2 HYDRAULIC LOGIC CIRCUIT WITH CONTROLLED DELAY CROSS REFERENCE TO RELATED APPLICATIONS This is a continuation, of application Ser. No. 85.852 filed Nov. 2, I970.  
  This application is a continuation in part of US. Pat. application Ser. No. 824,424, now US. Pat. No. 3,726,190 by H. A. Panissidi entitled, Integrated Adder Drive Assembly Including. Damper, Hydraulic Power Supply and Paper Tape Feed, and is related to co-pending US. Pat. No. 3,575,301 based on application Ser. No. 694,94l by H. A. Panissidi, entitled Manipulator.&#34;  
 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to fluid time delay devices. More particularly, this invention relates to hydraulic time delay devices.  
 2. Description of the Prior Art In the prior art centering, i.e., stalling, of spool valves in a central position upon transfer in response to weak actuation pulses with oil passing upon both sides of the central land of the spool valve has been a prob lem. A spool valve should be hit with a pressure pulse comprising a hydraulic step function in order to eliminate stalling caused in the above way.  
  Prior art time delay devices have included a charging up of a pressure into a chamber, or displacement of a piston against a spring in such a manner that a strong pulse would not be produced at the end ofa time delay.  
 SUMMARY OF THE INVENTION In accordance with this invention means are provided for providing a sharp step function pulse at the end of a time delay with a fluid time delay device.  
  Also in accordance with this invention a device is provided for providing at least some fixed minimum delay time between the time of application of pressure to an input line and the time of the actuation of a spool valve. Oil under pressure is supplied through an orifice to a fixed volume cylinder which has a free sliding piston within it. The fixed time delay is provided by the time it takes to fill the volume of this cylinder when a given fluid passes through a given orifice size at a given pressure. Upon completion of filling of the delay cylinder, pressure will start to build up to actuate a spool valve unless the pressure is relieved via opening of a valve or bleed line. If a bleed line is open, actuation of the spool valve will be delayed an additional amount of time until the bleed line is closed. However, if the bleed line is closed to start with, the fixed minimum delay provided by the free sliding delay piston in its cylinder will still occur. The delay piston provides substantially no resistance or no back pressure until it reaches the end of its cylinder where it will provide substantially infinite resistance to further pressure.  
  Further, in accordance with this invention, a free piston and an orifice provide a minimum controlled time delay to produce a pulse to hammer a spool valve to its opposite position against a spring, with one or more bleed circuits to prevent operation of the circuit until closure of the bleed circuits.  
  Still further, in accordance with this invention, means are provided whereby transfer of a control valve is effected by closing a bleed line, unless the bleed line is closed before a minimum time delay, in which case transfer of a delay piston causes transfer of the control valve.  
  This invention includes a hydraulic element having at least one hydraulic input and a hydraulic output, the output having at least two states of operation, the input tending to drive the element towards one of the states of operation during pressurization of the input. The element is biased towards the reverse state, at least during pressurization of the input. First and second controlling ports are also included in the system. The first controlling port is connected to the inlet through an orifice. The second controlling port is coupled to the input through a chamber containing a freely reciprocable piston adapted to be displaced to the end by a predetermined quantity of hydraulic fluid. A third port is connected between the inlet and bleed valvev In addition this invention includes a hydraulic control system for providing a minimum time delay after a control input signal. The system includes a source of pressure responsive to control input signals, restrictive means for providing flow through a restriction into a common junction from the source, storage means for providing a volume for storage of hydraulic fluid substantially without resistance until a fixed volume of fluid has flowed within the storage means, having its input connected to the common junction, means for bleeding the junction connected to the junction, whereby the bleeding means can bleed fluid to prevent pressure from building at the common junction after the volume of fluid has filled the storage means. The restrictive means and the storage means provide a minimal time delay between the commencement of flow through said restriction and the filling of the storage means, whereby full pressure obtains at the junction subsequent to termination of bleeding by the means for bleeding.  
  An object of this invention is to vary hydraulic pressure in a controlled line when a desired position of a member of a hydraulic system has been realized, for at least a predetermined mimimum time.  
  Another object of this invention is to provide a minimum cost, positive interlock by eliminating the need for separate motion transducers.  
  The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawingsv BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a hydraulic circuit embodying the present invention.  
  FIG. 2 shows the displacement of various elements of the system as a function of time.  
  FIG. 3 shows the relationship between various segments of the composite diagram formed by FIGS. 3A-3D.  
  FIGS. 3A-3D show the overall connections between the various subsystems of the hydraulic drive control system employed in an embodiment of invention.  
  In FIG. 3E an additional detail of the system is shown.  
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a hydraulic control, spool valve 69 in cylinder 269 which includes end lands 250, and as well as central land 252. The control valve 69 is biased by spring 53 into a position in which the land 252 is above a central annular groove I6 in cylinder 269. Groove 16 is connected to pressure line 116 which is connected to a power supply line 47 by means shown in FIG. 33. With valve 69 in its upwardly biased position, with land 252 above groove I6 pressure line I16 is connected through groove [6 by central land 252 and passageway 253 to outlet 254. On the other hand with land 250 above return groove R and land 252 above groove 16 outlet 71 is connected through passageway 255 to return R or zero pressure. If sufficient pressure is applied to the top of valve 69 through common junction line 89, then the pressure on the top of band 250 will drive valve 69 down compressing spring 53, to connect line 71 to groove I6 as land 252 is driven below groove I6 and land 2S0 cuts off return groove R. The pressure in port line 38 is off when it is on in junction line 89 because two way valve 39 puts pressure on only line 38 or line 688. The purpose of this system is to drive the valve 69 down a selected time delay after valve 39 puts pressure on line 688 and to produce high pressure in junction 89 and after certain other events have occurred which are communicated to junction line 89 by means of simultaneous closing of all of valves 256, 36, and 258 which are connected to return 46, or closing of valve 36, when valves 256 and 258 are omitted.  
  The time delay referred to above is provided by means of free piston 68 in cylinder 268 which will be supplied with pressure on port line 688 through orifice 703 in orifice check 70. Orifice check 70 also includes poppet or check valve 702 which provides low resis tance for reverse flow from bleed line 24 to port 688. For example, when valve 36 is open, oil passing through orifice 703 bleeds through line 24 and valve 36 to return 46. When all of the valves 36, 256 and 258 are closed, then the piston 68 is driven down as quickly as possible because there will be no pressure in port line 38, which will be connected to zero pressure return 95. If bleed line 24 is shut by valves 36, 256 and 258, as soon as piston 68 hits the bottom of cylinder 268, a pressure pulse will hammer spool valve 69 down against spring 53 to connect pressure to line 7]. The size of orifice 703, the volume of displacement of the piston 68, and the pressure from source P will determine the time required between closure of the valves 36, 256 and 258 and the hammering down of valve 69 into its lower position.  
  In summary, the pulse operated hydraulic logic circuit includes the spool valve 69 which is spring biased up. A control port 688 is connected through orifice 703 to the upper end of the spool valve 69. The control port 38 is connected to the lower end of the spool valve 69. The free delay piston 68 is contained in a cylinder 268 connected between the two ends of the control valve 69. The bleed line 24 is connected through junction 89 to the upper end of the control valve 69. Port lines 688 and 38 are each operable to high or low (reservoir) pressure, in operation. so that when one is at high pressure, the other is at low pressure.  
  In operation, at the beginning of a cycle, the free delay piston 68 is at the upper end of its cylinder 268 as a result of previous pressure from port 38. Then pressure is applied to port 688 and the free delay piston 68 is driven downwardly by the flow of fluid through the orifice 703. If the bleed line 24 is closed by valves 36, 256 and 258 then a minimum time delay is provided as measured by the time for a regulated pressure to cause a volume of oil to pass through the orifice 703 to drive the delay piston 68 down. Since the delay piston 68 is connected at its lower end to atmospheric pressure, and since there is essentially no back pressure, there is a very low pressure downstream from the orifice until the delay piston 68 hits its lower end, even when the bleed line 24 is closed.  
  When piston 68 hits its lower end with bleed line 24 closed from return 46, the pressure will very suddenly build up to the pressure which exists upstream of the orifice 703, and as a result, the spool valve 69 will be hammered down by a pressure pulse. If on the other hand, the bleed line 24 is open to return 46, then the piston 68 will move down slowly without causing a pressure pulse. No pressure pulse will occur until the bleed line 24 had been closed. The advantage of the orifice and the free piston is that it will provide a controlled delay without any buildup of pressure above a very low threshold until the free piston 68 hits its lower end. With control pressure on line 38, the bypass poppet 702 in parallel with orifice 703 in the orifice check 70 assures rapid resetting of valve 69 while port 688 is exposed to the zero reservoir pressure.  
  FIG. 2 is a timing chart which shows the various changes in controlling and controlled pressures and the positions of the control valve 69 and delay piston 68 for two sample cycles applied to the configuration. In FIG. 2, abbreviations are used as follows;  
 P Pressure U Up 0 Open R Reservoir (zero pressure) D Down C Closed CONTROL SYSTEM This instant invention may be used in many ways. A few are exemplified by the system of my copending application Ser. No. 824,424 which embodies this invention in ways which are reproduced in abbreviated form herein. Usage of the hydraulic device of this invention includes several applications in the piston adder drive system shown in FIGS. 3A-3D. In each application. an orifice and delay piston ensures a minimum time interval before a specified action.  
  First, after a start valve 55 is moved up to cause transfer up of a flow valve 39 and a phase delay piston 67, one of the sweep sense valves 202 and 205 (FIG. 3D) must be closed before equal pressures can occur at both ends of the flow valve 39, which will then move down by reason of the spring force applied at its upper end,  
  Secondly, after the flow valve 39 moves up to cause transfer up of the delay piston 68 and to raise move valves 69, the move valve 69 (shown essentially as in FIG. 1) cannot be restored to its down position until the bleed line 24 to the move sense valve 36 is closed, indicating that the piston adder l5 and damper l8 have completed the move cycle of the adder drive system. In this case the biasing of move valve 69 is provided by pressure at point 64 which produces a greater force than spring 87 at the other end of valve 39. When pressure builds up down stream from orifice check 65, when free piston 67 has reached the opposite end of its cylinder, then when bleed line 25 is shut by exchange sense valve 35, the spring 87 pushes valve 39 down with a strong force overcoming centering in an alternative manner in accordance with this invention.  
  Reference is now made to the control system shown in FIGS, 3A-3D which is shown in greater detail in my copending U.S. application Ser. No. 824,424, now U.S. Pat. No. 3,726,190. The system shown there includes an air reader for reading a perforated tape which provides output pulses to a hydraulic control system by means of air lines 12 (FIG. 3C) connected to air hydraulic interfaces 13 which convert pneumatic pulses to hydraulic values. The air hydraulic interface transfers pulse input to hydraulic binary latch valves 14 which remember&#34; or retain a or a 1 condition, depending upon the sense or polarity of the input transmitted from the reader through the interface 13.  
  The outputs of the latch valves are in general connected via lines 141, 142 to extend or retract a corresponding one of piston adders 15 which comprise interconnected pistons and cylinders employed to provide binary displacement of load bearing shaft 156 by unit distances.  
  A set of variable orifices in a velocity control valve 17 are provided between lines 142 and 342 for the purpose of controlling the rate of displacement of the pistons. Valve 17 is shown in fragmentary form to indicate its extent in application Ser. No. 824,424, now U.S. Pat. No. 3,726,l90.  
  In order that the piston adders l and the output shaft 156 connected to one end thereof may be accurately located rapidly, a damper 18 is provided which permits the piston adders to cock it during an exchange interval.  
  The exchange interval is a time during which the output shaft 156 is firmly retained in position by braking means shown in part in FIG. 4 of my U.S. application Ser. No. 824,424, now U.S. Pat. No. 3,726,190 and in detail in my copending U.S. Application Ser. No. 694,94l now U.S. Pat. No. 3,575,301 entitled Manipulator and the piston adders 15 are reset and extended to the extent that certain pistons are retracted and certain other pistons are extended. During the exchange&#34; period the velocity control valve l7 will be held wide open to permit exchange at maximum permissable velocity, since the piston adders 15 will not be under load. The flow system 23 includes restrictive passageways 42, 44, 49 and orifices 50 and restrictive bypass valve 41 for varying the resistance of flow of fluid through the hydraulic circuit to the piston adder drive 15. A hydraulic logic unit 20 responds to an output of system 23 on line to close valve to increase the resistance to flow through system 23 to drive 15 and to release braking means controlled by aligner lines shown in Ser. No. 824,424. Exchange piston 35 and move piston 36 biased by springs 43 respond to decline of flow velocity below a predetermined level to cause lines 24 and 25 to sense such decline by disconnecting those lines from a zero pressure return line 46. The move piston oper ates with line 24 for sensing the termination of a step of operation of the arithmetic piston adder drive 15.  
  Referring again to the damper 18, when the load has been fully positioned where desired, the damper 18 provides hydraulic damping with minimum overshoot and is actuated via line by hydraulic logic unit 20 to provide mechanical positioning ultimately to a precise home position. Cocking minimizes overshoot and optimizes use of time for the steps of exchanging piston locations and driving the load.  
  In order to provide regulated hydraulic pressure to the system in my copending application Ser. No. 824,424 a hydraulic power supply is provided. It supplies pressure for latching of spool valves on lines 600 and 116 and to the central lands 16 of spool valves in the hydraulic logic until via line 6. Pressure is also supplied to the flow sensing system 23, via line 47, which controls two *bleed&#34; lines 24 and 25 to the hydraulic logic unit 20. The flow sensing system 23 operates as a function of the velocity of flow through line 47, the flow sensing system 23 and line 52 to the latch valves 14 which connect to the piston adders 15. When the flow or displacement of piston adders declines below a minimum value the bleed lines 24 and 25 are blocked by flow sensing system 23. A bypass control line 38 from the hydraulic logic unit 20 controls a port 40, 41 inside the flow sensing system 23 to control one of the flow sensing units therein.  
  The hydraulic logic unit 20 can be started and stopped. Since the logic unit 20 controls the toggle line 76 in FIG. 3A which powers the feed advance of the tape reader shown in my copending application Ser. No. 824,424 when switch 54 is operated, air is blocked from operating the logic unit 20 and, at the end of a displacement cycle operation of the system stops. Line 94 is adapted to connect to operate aligners not shown, which are similar to those shown in my copending United States patent application Ser. No. 694,94l now U.S. Pat. No. 3,575,301.  
  A set of sweep sense units 33 and a sweep cylinder 34 turn or sweep a load on support about an axis upon an input via line 198 or 200 from one of the latch valves 14. The sweep sense unit 33 is connected to bleed line 25.  
 EXCHANGE AND VARIABLE VELOCITY CONTROL The exchange and move flow sensing system 23 in cludes a cylindrical exchange sense piston valve 35, a cylindrical exchange move sense piston valve 36 and a bypass poppet 37. The bypass poppet 37 is controlled by pressure in a line 38 connected to the lower output offlow spool valve 39 in FIG. 3B. When pressure in line 38 is above return pressure, it drives piston 37 to the right to open valve 40 by moving it away from surface 41. When there is no pressure in line 38, which results when line 38 is connected to a zero pressure return line, as via groove 95, when valve 39 is down, then piston 37 moves left closing valve 40.  
  When the bypass poppet 37 is to the left, its valve 40 will seat on surface 41 to close off the inlet 42 to the exchange sense piston 35. It should be noted that the exchange sense piston 35 and the move sense piston 36 are each spring biased by springs 43, coaxial therewith in the larger coaxial bore 44 in the pistons 35 and 36. The pistons 35 and 36 have annular grooves 45 to connect the bleed lines 24 and 25 to the return 46 to the low pressure side of the hydraulic pressure supply 22.  
  When piston blocks bleed line 25 from return 46, as the result of a low flow rate through orifice 50 of piston 35, then after a time delay hydraulic logic 20 removes pressure from line 38, by driving flow spool valve 39 down which pulls piston 37 left to close valve on surface 41. Valve 39 connects line 38 to zero pressure, i.e., return pressure via groove 95. Pressure from a hydraulic pressure supply shown in Ser. No. 824,424 is supplied by line 47 to the inlet 48 on the upstream end of the valve 40 of the bypass poppet 37 which may or may not be open, as described above, and to the inlet 49 to the move sense piston 36.  
  Hydraulic line 47 is connected to hydraulic line 52 through system 23 via inlet 48, which connects via inlet 49, orifice 50, coaxial bore 44, and line 51 connected to line 52, and in parallel, when valve 40 is open, through inlet 48, through port 41, past valve 40, through inlet 42, through orifice 50, through coaxial bore 44, and through line 51 to line 52 also. Each of the exchange sense piston 35 and the move sense piston 36 is provided with a smaller axial bore 50 to the upstream end thereof confronting the corresponding inlet 42 or 49 thereof. The orifices 50 are selected so that when the pressure differential across the orifice S0 is above a predetermined level, then the pistons will be driven upwardly against the pressure of the springs 43 to align the grooves 45 with the bleed lines 24 and 25, thereby connecting the bleed lines to return 46. The bypass poppet 37 provides a means for selectively actuating the exchange sense piston 35. In this way, the flow sensing system may be operated in two modes depending on whether the piston adders 15 are being driven in the move or exchange mode of operation.  
  A further feature is that each orifice is of the same order of magnitude in diameter and length, so the resistance to fluid flow provided by each thereof is of the same order of magnitude. When both are connected in parallel. the resistance to flow provided by each thereof is of the same order of magnitude. When both are connected in parallel, the resistance to flow is nearly halved, or conversely, flow doubles, approximately. As will be noted, the outlets 51 of the two sense pistons are connected to line 52. Since the two sense pistons are in parallel, and therefore the orifices 50 are in parallel, if the bypass valve 40 is open, the quantity of flow through each of the two orifices 50 will be substantially equal and accordingly the rate of flow into the line 52, if sufficiently large and unrestricted will in general be approximately doubled. Accordingly, when the exchange sense piston 35 is permitted to operate by the bypass poppet 37, the quantity of fluid flowing from lines 51 through line 52 to the piston adder drive will be greater and the velocity of displacement in the exchange period will accordingly be far greater.  
 HY DRAULIC LOGIC UNIT The hydraulic logic unit contains many types of elements. These include a plurality of spool valves, delay pistons in cylinders which require a time delay for displacement from one end to the other end of the cylinder in which they are housed. orifice check units shown in FIG. 3E, interconnections and outlets which control other elements of the overall system. Certain spool valves are spring-biased into one position as indicated by helical springs in logitudinal cross section. Certain other of the spool valves are latch valves which are held in position by hydraulic latching means. Such a latching means comprises a passageway 600 tangential to one end of a land of a spool located so that it supplies fluid under pressure to the side of the land regardless of spool position. and contacts a small area on one side. The land thereby creates a laminar pressure gradient along that side which is coupled to the return lines through leakage. There is a ratio of pressure acrosss the land of several times the pressure on the low pressure side which pushes the land to one side and inhibits longitudinal sliding because of friction forces. Pressure can be relieved during movement of the spools to relieve friction forces.  
  When pressure at inlet 53 coupled from a tape reader via line 29 operates the start diaphragm 56 (assuming pneumatic toggle 54 is on) or otherwise provides input from a two way solenoid or valve 27, etc., then the start spool valve 55 moves up. This movement connects lines 57 to the right and to the left to higher pressure from the central annular groove 16 of valve 55 as the central land or ring passes thereabove. Pressure is applied at the junction 58 between the orifice checks (see FIG. 3E) 59 and 60 which connect to the probe spool valve 61., the probe delay piston 62, and the probe phase piston 63.  
  On the left side, the line 57 connects to the point 64 to supply the lower end of flow spool valve 39; and by connection through orifice check 65, point 64 connects to line 66 and phase piston 67. Note that orifice check 65 is located differently from orifice check 70.  
  It will be noted that line 66 connects to bleed line 25 and both connect to the upper end of the flow spool valve 39, which is spring biased down. However, pressure at point 64 biases the valve 39 up until line 66 is pressurized. When the flow phase piston 67 has moved fully to the top of its cylinder at the end of 60 milliseconds, and when exchange sense piston valve 35 disconnects bleed line 25 from return 46, the pressure on the line 25, and at the top of flow valve 39 increases and the flow valve 39 is pushed down hard to return to its position as shown in FIG. 3B under the force of the spring 87. The time delay is set by the orifice and piston 67.  
  Initially, after start valve 55 operates, flow valve 39 operates and pressure is placed on line 38. Then line 38 connects pressure to the bypass poppet 37, which remains open until the flow valve 39 returns to home position. Since line 38 is connected to the lower end of delay piston 68 and to the lower end of move spool valve 69, which is biased upwardly, the move valve 69 moves up fast shortly after the flow valve 39 moves up, by spring 53.  
  Later, when flow reverses, the delay piston 68 coop crates with the orifice check 70 to provide a long time delay before the move valve 69 can be reset down against the force of its spring 53. When the move valve 69 is driven up, the line 71 from the upper end of valve 69 has the pressure thereon released, thereby releasing pressure on the top of the exchange valve 72. Valve 72 has pressure on the lower end thereof applied on line 38. After the delay valves 68 and permit the pressure to build, valve 72 will then shift upwardly. The damp spool valve 73 has a spring bias at the lower end thereof, and will shift shortly after the exchange valve 72 shifts, thus releasing the pressure from its upper end. Line 75 is connected to the damper 18 including its pistons as shown in FIG. 3E secured to one end of the piston adders 15. Then in each displacement cycle of the drive, pressure is released from the damper postioning pistons 80. The damper 18 is released to be cocked during exchange.  
  After about 20 milliseconds to position pilot valves 85, the probe delay piston 62 reaches the opposite end of its cylinder. Then the pressure on the lower end of probe spool valve 61 reaches a high enough level to overcome the spring biasing force at its top to drive the valve 61 to provide pressure on probe line 81 from the central annular pressure source 82 as the central land passes thereacross and the lower land passes across the return 83.  
  The probe line 81 is connected to each of the inlets 84 of the pilot valves 85 to provide pressure to their central annular cavities. The probe pressure is employed to adjust the hydraulic binary latch valves 14 in accordance with the binary valves provided by a tape reader. The binary drive is reset by the most recent input data provided by the tape reader.  
  About 40 milliseconds after start, probe phase piston 63 rises to the top of its cylinder and causes a pressure build up at its lower end, connected to the top of probe spool valve 61 which is spring biased down. Since the pressures of the opposite ends of the probe spool valve 61 will be equal and opposite, the probe valve is moved down by its spring 86. Then pressure is removed from probe line 8!. This does not end the exchange motion of the piston adders which are controlled by hydraulic latch valves 14 which remain as positioned during the probe portion of the control cycle of the hydraulic logic circuit 20. While exchange continues, the exchange sense piston valve 35 remains against it spring like move sense piston valve 36.  
  When exchange velocity substantially ends resulting in elimination of substantial pressure differential the flow through the sense pistons 35 and 36 ends, substantially, they move down to their spring biased lower positions. Then Bleed line 24 closes momentarily and bleed line 25 closes for the remainder of each cycle of operation of the hydraulic logic unit 20. Line 25 then builds up pressure on the upper end of the flow valve 39 and its top spring 87 pushes flow valve 39 down. Pressure builds on line 24 and line 89 from lines 16 and 688 through the flow valve 39. However, the delay piston 68 and the orifice 703 in orifice check 70 defers the build up of the pressure in the lines 24 and the build up of the pressure in inlet 89 to a level sufficient to push move valve 69 down. Move valve 69 will not operate after exchange because, move sense piston 36 reconnects bleed line 24 to return 46 to bleed pressure from inlet 89 before sufficient time passes to build up enough pressure in inlet 89. Line 688 applies pressure immediately to the central cylindrical cavity 188 of the exchange spool valve 72 held up by pressure in line 38 to provide pressure on line 90 to the lower end of the aligner latch valve 74. Low pressure on line 75 and high pressure on line 90 drives the aligner latch valve 74 up.  
  The aligner latch valve 74 releases pressure on line 91 so spring 93 drives aligner valve 92 up. This applies pressure to line 189 resetting start valve 55, applying pressure from line 116 to reset line 88 to reset all of the pilot valves and will release pressure from line 94 which is to be connected to load aligners to move the output load. Line 94 also connects to the velocity control valve 17 to move it to reduce the orifice into the piston adders 15 during the period of driving of the load. Now the load can move so the piston adders can move and flow resumes in line 52. Thus the pressure drop across the move sense piston valve 36 resumes and move sense piston valve 36 moves up again to bleed pressure from the bleed line 24.  
  Pressure on the control line 38 for bypass poppet 37 is released since the flow valve 39 is down to connect line 38 to the return 95. Pressure on line 76 from aligner latch valve 74 in FIG. 3A is intended to operate a tape reader feed mechanism. In addition, in a purge control shown in my copending application Ser. No. 824,424, pressure on line 76, broken away will operate a pair of pistons so that the pressure will be connected down into the lines 101 which are connected to the purge inlets to the diaphragms 102 in the air hydraulic interfaces 13 in FIG. 3C. Air under pressure blows through the purge inlets 10] across the surface of the diaphragms of the interfaces 102 and out through the reader lines 12 to purge oil from the system and to clear chad and other material from the lines 12.  
  Pressure remains on line 76 until the piston adders l5 stop and move valve 69 moves when bleed line 24 closes as move sense piston 36 moves down. Then, line 71 drives exchange valve 72 down removing pressure from line and applying pressure to line 103 through the orifice of orifice check 104 and delay piston 105, after a time delay of 90 milliseconds, which pressure drives the damp valve 73 down against its spring. Valve 73 applies pressure on line 75 to drive the aligner latch valve 74 down and remove pressure from line 76 and to apply pressure to line 91 and through the orifice in the orifice check 106 and delay piston 107 require a time delay to pass before pressure drives aligner valve 92 down against its spring 93. The aligner delay piston 107 requires another milliseconds to drive downwardly.  
  However, referring again to the purge unit, when line 71 is pressurized, a piston is shifted so atmospheric pressure recurs inside the purge and reader lines 101 and 12 to return diaphragms 102 to atmospheric pressure. Then when pressure is removed from line 76 as a result of return of the aligner latch valve 74 to its lower position, the purge unit will act to shut off connections 101 to the diaphragms.  
  A perforated tape reader in my copending application Ser. No. 824,424, now US. Pat. No. 3,726,l90 will operate in ordinary machine shop air typical of industrial locations, which is contaminated with dirt, oil and water. Cyclic purging of lines 12 is necessary because the reader sense hoses are extremely thin, usually 0.030 inches [.D. making them vulnerable to clogging.  
  The ports of the air reader head are connected in my copending application by sense hoses to the 16 diaphragm driven hydraulic pilot valves. A hole in the tape pressurizes a corresponding diaphragm to actuate its pilot valve 13. Line 76 from the aligner latch valve lower outlet, is provided for starting operating of each cycle of the reader. Pressure applied to line 76, causes advancing of the tape two character positions. While probe pressure drives the air reader, probing does not occur until after the pressure on the purge line 76 is generated by driving aligner latch valve 74 up after ex&#39; change ends. Adjustment of the pilot valves during the probe cycle ends earlier and pressure on line 76, turns off pressure on the reader by means of the purge unit.  
  During a tape advance cycle described in above ap plication. the pilot valves 85 of the hydraulic system must be physically locked by pressure in line 88 from responding to the tape holes they move under the air reader head, and sense hoses 12, diaphragms 102 and air reader ports must be flushed out with a reverse air blast to purge the air sense system of any contamination from the previous read cycle, Line 76 to the purge control, causes valves to move to expose all of the purge lines 101 to pressure at the same time, shut off the air pressure to the air reader. The pressure blows air in reverse through the diaphragm chambers, sense hoses and the air reader. Foreign matter is expelled. Following this purge cycle, the entire reading circuit and diaphragms must be depressurized before releasing the locked diaphragm actuated pilot valves. To accomplish depressurization, the purge system is returned to its initial position and seals off all the purge hoses 101.  
  A time delay network consisting of an orifice in series with move delay piston 68 controls return of the purge system to its initial condition to expose all the purge hoses to the atmosphere. Again at the end of the tape advance cycle the aligner latch valve 74 is restored to its initial position with the removal of the hydraulic signal, exposing line 76 to the reservoir allowing the tape advance circuit and isolating valve to reset to their initial position.  
 Air Hydraulic Interface From the air reader of my copending application Ser. No. 824.424 connection is made, as described above. to the lines 12 to the diaphragms 102 in FIG. 3C. When pressure is applied to a line 12, then the corresponding diaphragm 102 operates to drive its pilot valve 85 left. This drives the associated latch valve 14 left, during pressure on probe line 81, as the line 84 connects to the right-hand side of the central land of the pilot valve 85. Pressure is applied to the right end of latch valve 14. Latch valve 14-16 on the left hand side of FIG. 3C, is connected to the 16 inch piston adder 140 by lines 141 and 142. The right hand one of the lines 142 has pressure applied to it when the pilot valve is actuated by the reader. Line 142 passes through the velocity control valve 17 in FIG. 3D, and pressure on line 94, drives spool valve 143 right and the orifice through the velocity control valve 17 is reduced for piston adders 15. As pressure is applied through line 142, the fluid flows through line 342 into the space in cylinder 145 to the right of piston 144. If the load is released from alignment or if other pistons are also being displaced at the same time, as during exchange then cylinder 145 probably is free to move relative to piston 144, and since pressure is on the right of the piston and cylinder, the cylinder 145 moves right. In the opposite case, piston 144 moves left, if the load is released. If it is desired to extend the 16 inch piston adder 144 and to collapse the 8 inch piston adder 444 during the exchange, then the orifice provided in velocity control valve 17 is held open and the pressures applied are on the right-hand ends of pistons 144 and 444. If at the same time damper 18 were released. with no pressure on pistons 80, then shaft 152 moves right until damper piston 153 rests at the right end of cylinder 154. During the exchange since damper 18 has a /2 inch displacement and since the difference between the 16 inch and eight inch pis ton adders is eight inches, the entire assembly from the piston adder cylinder 149, to the right, is moved the full distance of about one-half inch to the right. Very rapid exchange between piston adders occurs without motion of the load and with only motion of the damper 18, if desired. Exchange occurs fast; as described below. First, the load is braked and in essence disconnected from the piston adders 15 so no moving or collapsing of the heavy load occurs during exchange. Secondly, the orifices regulate the rate of flow of fluid to the adder drive 15. Such regulation is afforded in two ways, First opening or closing of the bypass poppet 37 controls the effective orifice size to control flow. Second, a velocity control valve 17 controls flow. Velocity control valve 17 is controlled through line 94 from hydraulic logic 20.  
 Damper In FIG. 3D, rod 152 is secured by a bar or plate 157 to a shaft 158 secured to a single damper piston 153. Shaft 158 is secured at its opposite end to a bar or plate 159. The plates 157 and 159 cooperate with the shafts 160 extending from a pair of positioning pistons carried inside cylinder 16] in the housing of the damper 18. The bars or plates 157 and 159 are aligned by guide rod 600 extending through plate 159. The pistons 80 position the damper piston 153 after it has damped the load, with minimal overshoot, near the end of its excursion. Pressure on line 75 is removed when the damper starts. Pins retract. Since pressure is removed therefrom, they permit the damper to move.  
  It has been found desirable to cock&#34; the damper 18 during exchange. Cocking of the damper at this time tends to speed the operation of the system. During the initial moments of each cycle of operation of the piston adder drive, the damper 18 is driven in the opposite direction from the one it will be traveling at the end of its cycle so that at the end of displacement of the entire system, the damper moves towards its central location (in which rods 160 position it). At the end of displace ment of the load by adder drive 15 inertia of the moving load urges the damper piston 153 towards the center of bore 154 and the force causes fluid flow through orifices 163 to slow the load smoothly to a stop to minimize overshooting of the target. When rods 160 operate again by pressure on line 75 transmitted to pistons 80, highly accurate positioning of the output shaft 156 of the piston adder 15 results, relative to a fixed reference point.  
  FIG. 3E shows a symbol for a hydraulic component referred to herein as an orifice check shown as a pair of slanted lines 700 forming an acute angle 701 pointing in the direction of low velocity flow in which the bypass check valve 702 is seated but the low velocity flow from 704 to 705 continues through an orifice 703 which permits flow at a low velocity.  
  Line 94 also provides a drain to a lower pressure thereby releasing any one of the different aligners shown in my copending application. By use of aligners under control of line 94, the shaft 156 carrying the load may operate the drive a member after exchange has been completed.  
 Sweep In FIG. 3C, the latch valve 14 on the right-hand side is labelled sweep l4-S indicating that it is employed for controlling a unit used for sweeping the entire manipulator which is being controlled by this system about a vertical axis. The support 190 for the sweep unit is shown in FIG. 3D in the lower left-hand corner. A support 190 is pivotable about an axis 191 under the driving force applied to pin 192 by shaft 193 by reciprocable sweep piston 194 in cylinder 195. Cylinder 195 has a counterclockwise input 196 and a clockwise input 197. When pressure is applied to line 198, it passes through orifice check 199 via line 196 to apply full pressure to the right side of piston 194 to drive the support 190 counterclockwise. Pressure on line 200 passes through orifice check valve 201 into the left-hand inlet 197 to drive the sweep piston 194 to pull the support 190 clockwise about the pivot 19]. The sweep sense valve 202 is connected to bleed line 25 in series with sweep sense valve 203. These sense valves perform two functions. one of which is to provide an auxiliary bleed exchange sense function. The move valve 69 may not operate until after the exchange sense piston valve 36 has closed its bleed line 24 at the termination of exchange. Similarly this series of sense valves requires that the sweep must be completed before the drive motion of the piston adders is begun. This is provided simply by locating a land on each of these sweep sense valves 33 which when neither one of the extreme sweep positions have been reached will provide a short circuit from line 25 to the return 204 via line 205.  
  Pressure on line 198 is applied to the right-hand end of the piston in the sweep sense valve 202 spring biased left, by damping spring 210, which piston provides longitudinal force to the shaft 206. Such force is transmitted to bar 207 carried on the edge of the support 190 to impulse it for counterclockwise rotation. This opens up the connection of line 25 to return 204. When support 190 reaches its extreme home position in the counterclockwise direction, the bar 208 drives shaft 209 down along with sweep sense valve 203 to close the bleed via 25 and 205 to the return 204 and also driving the unit down against the damping spring 210 contained in the end of the sweep sense valve. Thus, the port 2 will be closed by the land of the valve 203 as it would be in the case of the valve 202 in the reverse direction of rotation, and this will mean that the short circuit path through the end of the valve will be closed and that the orifice check valve 201, as would the orifice check valve 199, will provide reduced flow through the orifice therein which is indicated by the orifice check symbol shown. Actually, an adjustable orifice and check valve are connected in parallel for this purpose in order to provide a fairly low velocity flow rate of the sweep cylinder during its deceleration.  
  While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.  
 What is claimed is:  
  l. A hydraulic system including a hydraulic element having at least one hydraulic input circuit including a first input terminal and a hydraulic output circuit, said output circuit having at least two states of operation, said input circuit tending to drive said element towards one of said states of operation during maintenance of relatively high pressure at said first input terminal,  
 a source of hydraulic pressure,  
 a controlling inlet connected through a first port and a first conduit to said first input terminal,  
 a control valve connected between said source and said controlling inlet time delay means connected to admit fluid tending to provide pressure at said first input terminal for de laying a rapid increase of pressure at said first input terminal until at least a predetermined minimum time delay after application of pressure at said first input terminal and for delaying driving of said element, said time delay means including storage means for providing a substantial volume for storage of hydraulic fluid substantially without resistance to fluid flow until a fixed volume of fluid has been stored within said storage means thereby filling it,  
 a second port being connected between said first input terminal and a valving means connected to a low pressure outlet, said valving means being adapted for opening selectively to defer said rapid increase of pressure at said first input terminal beyond said time delay, and said system including conduit means for causing fluid flowing from said control valve and said controlling inlet to flow into said storage means and fill it thereby measuring said time delay during both open and closed positions of said valving means, whereby the valving means measures the time delay even when said valving means is open.  
  2. A hydraulic element having at least one hydraulic input circuit including a first input terminal and a hydraulic output circuit, said output circuit having at least two states of operation, said input circuit tending to drive said element towards one of said states of operation during maintenance of relatively high pressure at said first input terminal,  
 said element being biased towards the reverse state at least during the absence of application of pressure to said input terminal,  
 first and second controlling ports,  
 said first port being connected to said first input terminal through an orifice, said second port being coupled to said input first terminal through a chamber containing a freely reciprocable time delay piston adapted to be displaced to the end of said chamber by a predetermined quantity of hydraulic fluid, and  
 a third port being connected between said first input terminal and a bleed valve,  
 controlling valve means for connecting said first and said second ports oppositely and alternatively to a source of pressure and to a drain.  
  3. Apparatus in accordance with claim 2 wherein said input circuit has a second input terminal, said chamber being connected between said second input terminal and said first input terminal.  
  4. Apparatus in accordance with claim 2 wherein said input circuit has a second input terminal connected to one end of said chamber, said orifice being connected between said first port and the opposite end of said chamber.  
  5. Apparatus in accordance with claim 2 wherein said input circuit has a second input terminal, said orifice being connected between said first input terminal and said valve means, said element being spring biased at said second input terminal.  
  6. A hydraulic valve having two hydraulic inputs and a hydraulic output, said output having at least two states of operation, pressurization of a first of said inputs tending to drive said valve towards one of said states of operation, said valve being spring biased towards the reverse state,  
 first and second controlling ports, said first port being connected to said first input through an orifice in parallel with a check valve, said second port being connected to said second input and being coupled to said first input through a chamber containing a freely reciprocable time delay piston adapted to be displaced to the ends of said chamber by a predetermined quantity of hydraulic fluid, a third port being connected between said first input and a bleed valve, said first and second ports being connected to alternative outputs of a controlling valve,  
  whereby high pressure applied to said first port by said valve is delayed in application to said first input by said time delay piston. 7. Apparatus in accordance with claim 6 wherein said chamber is connected between said alternative outputs of said controlling valve.  
  8. A hydraulic control system for providing a minimum time delay after a control input signal, said system including a source of pressure, valve means responsive to control input signals for connecting said source of pressure to its output,  
 fluid flow measured time delay means having several terminals including an input terminal connected to said output and another terminal connected to a common junction to permit a buildup of substantial pressure at said junction after a predetermined time delay, said time delay means including storage means for providing a substantial volume for storage of hydraulic fluid substantially without resistance to fluid flow until a fixed volume of fluid has been stored within said storage means, thereby filling it, pressure reducing means for selectively reducing pressure at said junction connected to said junction, said pressure reducing means having an aper ture of limited size adapted to bleed fluid away from said junction selectively to prevent pressure from building at said common junction after said time delay has expired, and said system including conduit means for causing fluid flowing from said valve means to said common junction to flow into said storage means and fill it thereby measuring said time delay during any condition of said pressure reducing means,  
 whereby full pressure can obtain at said junction only subsequent to termination of reducing of pressure by said pressure reducing means and said pressure reducing means does not defer the measurement of the time delay when it is bleeding fluid away.  
  9. A hydraulic control system for providing a minimum time delay after a control input signal, said system including a source of pressure,  
 valve means responsive to control input signals for selectively connecting said source of pressure to its output,  
 restrictive means for providing flow through a restriction into a common junction from said valve means,  
 storage means for providing a substantial volume for storage of hydraulic fluid substantially without resistance until a fixed volume of fluid has flowed within said storage means, said storage means having its input connected to said common junction,  
  means for bleeding said junction having an aperture of limited size connected to said junction, whereby said bleeding means can bleed fluid while said volume of said storage means is being filled and operative to prevent pressure from building at said common junction after said volume of fluid has filled said storage means,  
 said restrictive means and said storage means providing a minimal time delay between the commencement of flow through said restriction and the filling of said storage means,  
 and said system including conduit means for fluid flowing from said common junction to said storage means and for filling it thereby measuring said time delay during both open and closed conditions of said means for bleeding,  
 whereby time delay is measured even while bleeding occurs, but full pressure can obtain at said junction only subsequent to termination of bleeding by said means for bleeding.  
  10. A hydraulic control system for providing a minimum time delay after a control input signal, said system including a source of pressure,  
 a control valve for selectively connecting said source of pressure to its output in response to control input signals,  
 restrictive means for providing flow through a restriction into a common junction from said control valve output,  
 storage means for measuring a time delay connected to said common junction via conduit means for providing a volume for storage hydraulic fluid sub stantially without resistance until a fixed volume of fluid has flowed within said storage means comprising a free piston in a cylinder, said cylinder having its input connected to said common junction,  
 means for bleeding said junction connected to said junction, whereby said bleeding means can bleed fluid from said junction without bleeding from said storage means to prevent pressure from building at said common junction after said volume of fluid has filled said storage means,  
 said restrictive means and said storage means providing a minimal time delay between the comma. ement of flow through said restriction and the filling of said storage means,  
 whereby full pressure can obtain at said junction only subsequent to termination of bleeding by said means for bleeding,  
 a biased valve spaced and separate from said storage means having a control input connected via a conduit to said junction, whereby a substantial pressure at said junction overcomes the bias on said biased,  
 and said system including conduit means for causing fluid to flow from said control valve through said restrictive means to flow into said storage means and fill it thereby measuring said time delay during both open and closed positions of said means for bleeding, whereby said means for bleeding does not defer the measurement of the time delay when said valving means is open.  
  1 l. A method of operating a switch system in a time delay mode consisting of at least a predetermined minimum delay time and a selectively variable delay time, said system including a hydraulic switch element having an actuating fluid input port, an actuating fluid source port, a conduit connecting said source port and said input port, means for selectively applying fluid pressure to said source port, a fluid reservoir connected to said conduit and operative to delay pressure buildup at said input port to provide said predetermined delay time, said reservoir providing a substantial volume for storage of hydraulic fluid substantially without resistance to fluid flow until a fixed volume of fluid has been stored within said reservoir thereby filling it, and a bleed valve selectively operable to open and closed states connected to said conduit to provide said variable delay,  
 said conduit being adapted to provide for fluid flowin g from said source port to flow into said reservoir and fill it thereby measuring said predetermined delay time during both open and closed states of said bleed valve,  
 said method of operating said system comprising the steps of:  
 applying a fluid pressure pulse to said source port while maintaining said bleed valve in said open state;  
 closing said bleed valve after a selected value of said variable time whereby said switch is operated after the expirataion of the later of said predetrmined delay time and said variable delay time.  
  12. A method of operating a system including a hydraulic switch which switch includes a switching input connected to time delay means for delaying a rapid increase of pressure at said switching input until at least a predetermined minimum time after applicatijon of pressure to said system and a bleed valve connected to said system for bleeding fluid pressure from said switching input, comprising the steps of:  
 applying a step function signal to said time delay means,  
 concurrently maintaining said bleed valve open to prevent operation of said switch while measuring said predetermined minimum time with said time delay means, and  
 closing said bleed valve after said predetermined minimum time to operate said switch immediately upon closing, whereby the operation of said switch is deferred beyond said time delay until a condition has been met as indicated by closing of said bleed valve.  
  13. A method of operating a hydraulic switch with a switching input operable after provision of a step function switching signal for at least a predetermined minimum time delay provided by time delay means and a bleed valve connected to drain fluid to remove pressure from said switching input at will, said time delay being substantially independent of the condition of said bleed valve including the step of opening said bleed valve and concurrently applying said switching signal to said switching input for delaying said hydraulic switch indefinitely beyond said time delay and then closing said bleed valve to operate said switch.  
  14. A method of operating a hydraulic element having at least one hydraulic input circuit including a first input terminal and a hydraulic output circuit, said output circuit having at least two states of operation, said input circuit tending to drive said element towards one of said states of operation during maintenance of relatively high pressure at said first input terminal,  
 a controlling inlet connected through a first port to said first input terminal, time delay means connected to said first input terminal for providing a time delay thereby delaying a rapid increase of pressure at said first input terminal unit at least a predetermined minimum time after application of pressure at said inlet and for delaying driving of said element, and a second port being connected between said first input terminal and a valving means connected to a low pressure outlet, said time delay being substantially independent of the open and closed states of said valving means, first applying a control pulse to said controlling inlet and maintaining said valving means open selectively to defer said rapid increase of pressure at said first input terminal beyond said time delay after application of said control pulse. 15. A method of operating a hydraulic control system for providing a minimum time delay after a control input signal, including a source of pressure, valve means responsive to control input signals for connecting said source of pressure to its output,  
 fluid flow measured time delay means having several terminals including an input terminal connected to said output and another terminal connected to a common junction to permit a buildup of substantial pressure at said junction after a predetermined time delay, said time delay means including storage means for providing a substantial volume for storage of hydraulic fluid substantially without resistance to fluid flow until a fixed volume of fluid has been stored within said storage means thereby filling it, pressure reducing means for selectively reducing pressure at said junction connected to said junction, said pressure reducing means having an aperture of limited size adapted to bleed fluid away from said junction selectively to prevent pressure from building at said common junction after said time delay has expired, and said system including a conduit means for causing fluid flowing from said valve means to said common junction to flow into said storage means and fill it thereby measuring said time delay during any condition of said pressure reducing means,  
 including the steps of applying control input signals to said valve means and maintaining said pressure reducing means open for a variable delay time,  
 whereby full pressure can obtain at said junction only subsequent to termination of reducing of pressure by said pressure reducing means and the minimum time delay is filled independently of the state of said pressure reducing means.  
  16. A method of operating a hydraulic control system for providing a minimum time delay after a control input signal, said system including a source of pressure,  
 valve means responsive to control input signals for selectively connecting said source of pressure to its output.  
 restrictive means for providing flow through a restric tion into a common junction from said valve means. storage means for providing a substantial volume for storage of hydraulic fluid substantially without resistance until a fixed volume of fluid has flowed within said storage means. said storage means having its input connected to said common junction.  
 means for bleeding said junction having an aperture of limited size connected to said junction. whereby said bleeding means can bleed fluid while said volume at said storage means is being filled and operative to prevent pressure from building at said common junction after said volume of fluid has filled said storage means.  
 said restrictive means and said storage means providing a minimal time delay beteeen the commencement of flow through said restriction and the filling of said storage means. and said system including conduit means for fluid to flow from said common junction to said storage means and to fill it thereby measuring said time delay during both open and closed conditions of said means for bleeding. including the steps of applying a control input signal to said valve means to open said valve means and operating said means for bleeding concurrently,  
 whereby time delay is measured even while bleeding occurs. but full pressure can obtain at said junction only subsequent to termination of bleeding by said means for bleeding.  
  17. A method of operating a hydraulic control system for providing a minimum time delay after a control input signal. said system including a valve for selectively connecting a source of pressure to its output in response to control input signals,  
 restrictive means for providing flow through a restriction into a common junction from said valve output. storage means for providing a volume for storage of hydraulic fluid substantially without resistance until a fixed volume of fluid has flowed within said storage means comprising a free piston in a cylinder, said cylinder having its input connected to said common junction to provide a first time delay.  
 drain means for bleeding said junction connected to said junction. whereby said bleeding means can bleed fluid to prevent pressure from building at said common junction after said volume of fluid has filled said storage means.  
 said restrictive means and said storge means providing said first minimal time delay between the commencement of flow through said restriction and the filling of said storage means.  
 whereby full pressure can obtain at said junction only subsequent to termination of bleeding by said means for bleeding.  
 a biased valve isolated from and separate from said storage means and said free piston having a control input connected to said junction, whereby a substantial pressure at said junction would overcome the bias on said biased valve.  
 including the steps of operating said valve to connect said source to said restrictive means. and concurrently maintaining said drain means open to defer full pressure occurring at said junction for a variable delay time. and also deferring operation of said biased valve commensurately.  
 18. A method of operating a hydraulic control system for providing a minimum time delay after a control input signal. said system including a source of pressure.  
 first means having first and second outputs for connecting said source to one of said outputs at a time responsive to control input signals for connecting said source of pressure to said first output.  
 restrictive means for providing flow through a restriction into a common junction through said first output from said source.  
 storage means for providing a volume of storage of hydraulic fluid substantially without resistance until a fixed volume of fluid was flowed within said storage means, said storage means having an input connected to said common junction for providing a first time delay.  
 second means for bleeding said junction connected to said junction, whereby said bleeding means can bleed fluid to prevent pressure from building at said common junction after said volume of fluid has filled said storage means.  
 said restrictive means and said storage means providing said first minimal time delay between the commencement of flow through said restriction and the filling of said storage means.  
 whereby full pressure can obtain at said junction only subsequent to termination of bleeding by said means for bleeding.  
 a control valve isolated from and separate from said storage means having opposite inputs, said second output and said junction being connected to opposite control inputs of said control valve.  
 the steps of applying an input signal to said first means to apply a pressure pulse via said first output to said restrictive means.  
 and concurrently maintaining said second means open to defer application of full pressure at said junction and operation of said control valve beyond said first time delay. for a variable delay time.