US2130458A - Power control for pneumatic conveyer systems - Google Patents

Description

Patented Sept. 20, 1938 UNi'iED POWER CONTROL FOR PNEUMATIC CON- VEYER- SYSTEMS Application February 29, 1936, Serial No. 66,504 Renewed August 1, 1933 15 Claims.

This invention relates to power or motive fluid controllers for pneumatic conveyer systems and more particularly to the general type of controllers, the purpose of which is to reduce the total amount of motive fluid or power required to operate such systems. An early prior art controller of this type is disclosed in Patent No. 968,576 granted to Libby on August 30, 1910.

In the Libby type of controller a main motive l0 fluid valve opens for aperiod during which transmission is accomplished and closes at the end of the period, remaining closed until transmission is again desired. During this period of no transmission a so called minimum flow of fluid is maintained in the transmission line by means such as a by-pass around the main valve. For accomplishing the opening of the valve at the beginning of a transmission period, pneumatic means, designed to respond to pressure changes in the transmission line, opens a port to admit operating fluid to a motor which in turn opens the main ,valve. When the main valve reaches full open position, the pressure responding means is rendered inoperative whereupon the main valve closes by movement over a time interval determined by leakage of the operating fluid from the motor. As the main valve reaches closed position, the response means is reconditioned or restored for the next transmission cycle.

Heretofore the construction of a control mechanism in which the sequence of operation just described would be carried out with just the right interval and overlap to assure stable performance of the valve over long periods has been fraught with great difficulties. A particularly difficult sequence to carry out in the operation of this mechanism has been to close the main valve and restore the response mechanism without the latter responding to the transmission line pressure existing just prior to the complete closure of this valve, causing it to be reopened before complete closure.

The primary object of this invention is to provide a power control apparatus which will carry 0 out sequences of operation required in the Libby type of valve with certainty and over long periods of operation without readjustment.

Another object is to provide a means of restor- 50 ing the pressure response control valve to responding condition in a manner such that it will not respond to reopen the main valve before it has completely closed.

Another object is to produce a control valve 55 in which a very low minimum flow may be employed so that the power saving will be increased to a maximum.

Another object is to produce a control device employing a very low minimum flow and yet which is very sensitive to-the insertion of articles 6. to be conveyed which do not completely fill the conveyer line such as loosely fitting or badly worn carriers in a carrier system.

Still another object is to provide a control valve with means for quickly closing the same at the 10 end of its stroke.

A further object is to provide a control valve with means for increasing its speed of travel during the latter part of its closing stroke.

A further'object is to produce a control valve 15 which will operate as efiectively and economically on long lines as so called carrier closed valves, that is, closed by means responding to pressure variations incident upon carrier discharge.

A still further object is the construction of a 20 control mechanism of the type to which this'invention relates -in which the various operating parts are so located on the structure as to function in the best manner and at the same time provide a structure which is simple, having few parts, 2 and presenting a pleasing appearance.

These and other objects will be apparent from the following description taken in connection with the accompanying drawings in which:

Fig. 1 is diagrammatic view of a single conveyer 30 line showing where the control mechanism is usually placed therein;

Fig. 2 is a sectional view showing the parts when the main valve is in closed position;

Fig. 3 is a sectional view showing the parts in 35 the position they assume when the main valve is in full open position; and,

Fig. 4 is a fragmentary View showing a modified form.

While the use of this invention is not necessarily restricted to conveyer systemsof the pneumatic carrier type employing a tube through which carriers are transmitted by the flow of an air current through the line either under pressure or vacuum, this invention will be described for illustrative purposes as applied to the vacuum type of pneumatic carrier systems.

Referring now to Fig. 1 of the drawings, that portion of a pneumatic carrier system pertaining to a single conveyer line is diagrammatically illustrated. From a central station desk ill dispatch lines extend out to various substations. A single line employing a control device comprises a sending tube H having a dispatch terminal l2 and a return tube l3 provided with the usual delivery 5 terminal l4. From the latter terminal an extension tube l5 passes down through the central desk l6 and connects with the power control device |6 at what will hereinafter be referred to as the transmission line side of the device. From the suction line side of the device |6 a suction tube connects with the usual suction or header H3 in which a vacuum is continuously maintained by means of a suitable exhauster, not shown. In other words, the exhauster is the common power source and the device |6 controls the power expended in a single line. A continuous air passage or conduit is formed by the parts enumerated from the dispatch terminal I2 through the dispatch and return tubes II and I3 and the controller I6 to the exhauster.

Referring to Figs. 2 and 3, the controller I6 comprises a casing 2| divided by a septum 22 into two chambers, 23 and 24. Chamber 23 is in communication with the transmission line and chamber 24 is in communication with the suction header. The septum 22 is provided with two ports, a large port 25 which is controlled by a main valve 26 and a small port 21 which is controlled by an auxiliary valve 28. The auxiliary valve is opened by a screw threaded stem 29 and is set normally off its seat to provide a small air passage through which is maintained acontinuous stream of air flowing from the transmission line. This continuous flow of air will be hereinafter referred to as the minimumflow.

A motor 30 having a housing 3| is provided at the side of casing 2| for operating the main valve 26. This motor is comprised of diaphragm 32 connected to the main valve by means of a stem 33 which the motor reciprocates through a bearing 34 in the inner wall of the motor housing. The housing 3| comprises a saucer shaped base section 35 and a similar shaped cap 36 attached to the base with the rim of the diaphragm 32 held between these two elements.

The diaphragm divides the housing into inner and outer chambers 31 and 38. The inner chamber 31 communicates freely with the suction or low pressure chamber 24 through a relatively large unrestricted opening 39. The chamber 38 communicates with chamber '31 through restricted ports 4| and 42. The size of the opening of port 4| is regulated by needle valve 43. This port constitutes a continuous leakage connection between chambers 31 and 38 by means of which the closing time of the main valve is determined as will hereinafter appear.

The auxiliary port 42 and a connecting passage 44 provides a supplementary leakage connection between these two chambers. The passage 44 extends inwardly of the stem 33 from the outer end through the. diaphragm 32. This passage is formed at its outer end to admit a plug 45 which carries a reciprocating valve 46. Several air passage ways 41 extend through the plug to permit the passage 44 to communicate with the chamber 38 when the valve 46 is open but which are closed by the valve when it is seated upon the inner face of the plug. A spring 48 urges the valve toward seated position. The valve is opened when its stem 49 engages the inner face of the adjusting screw 5|. Although the supplementary leakage means is shown in stem 33 it could as well be located elsewhere and the valve 46 operated in accordance with the movements of the motor diaphragm in some other manner. 7

In Fig. 4 a modified form of the supplementary leakage connection between chambers 31 and 38 is shown. In this form the valve and plug at the outer end of the stem have been omitted. The port 42 is opened and closed by becoming covered and uncovered as it moves back and forth through bearing sleeve 34. The port 42 is positioned along passage 44 at a point such that during the closing stroke of the valve it will pass out at the right end of the bearing sleeve 34 at the point in the stroke where it is desired that increase in closing speed is to begin. This point may be varied by adjusting the sleeve 34 longitudinally in its supporting boss in wall 35.

As already indicated the stem 33 extends through the main valve 26. At its outer end the stem is carried in the central opening of a boss member 52 disposed at what is the rear of the structure viewed as it is ordinarily installed in service. This boss, as will presently be described, forms the base or seat element of a pilot valve which is employed to condition the mechanism for proper sequence of operation. The inner face of boss 52 carries a recess in which is seated the outer end of compression spring 53. The inner end of the spring is secured to stem 33 and exer'ts a force sufiicient to hold valve 26 normally on its seat.

The central opening of boss 52 forms a bearing for the outer end of stem 33 which extends through a sleeve 54 formed at the outer facing of the boss. A plate 55 is mounted to reciprocate upon this sleeve. The outer end of the stem 33 is turned down to a smaller diameter to form shoulder 56 thereupon. When the stem moves to its extreme left position, the shoulder 56 moves outwardly beyond the end of sleeve 54 a short distance as shown in Fig. 3. In valves constructed according to this invention for experimental use the shoulder moves out a distance of about of an inch or less. At the outer face of plate 55 is secured a disc 51 which surrounds the reduced portion of the stem. In the normal position of plate 55 this disc is positioned at the outer end of sleeve 54. When the stem moves outwardly, the disc is engaged by shoulder 56 moving plate 55 out a distance corresponding to the protrusion of the'shoulder portion 56. The outer end of the stem extends beyond disc 51 and carries an adjustable collar 58. This collar is set so that when the main valve 26 is moved to its seat, the plate 55 is brought against the face of the boss 52. It will be noted that shoulder 56 and collar 58 form a lost motion connection between the stern and plate 55. A spring pressed plunger 56 set in one side of plate 55 bears upon sleeve 54 to form a friction bearing for the plate to prevent accidental movement thereof when in its outer position as shown in Fig. 3.

The valve opening movement of motor 36 is determined by a control valve 6| disposed to normally close a passage 62 leading from atmosphere (see Fig. 1) through valve seat 63 to chamber 38. However, it might be spring loaded to vary gravity action or it might be so positioned that gravity does not act upon the valve at all. The valve is lifted by auxiliary motor 64. This motor comprises a casing which is divided into two chambers 65 and 66 by means of a small diaphragm 6?, the latter being connected through a suitable operating stem to valve 6|.

The lower chamber 66 is continuously open to the atmosphere through ports 68. The upper chamber 65 has two passages H and 12 leading therefrom. The passage 1| connects through tube 13 with chamber 23 on the transmission line side of the valve, communicating the pressure in chamber 23 to chamber 65. Adjustable restriction of this passage is provided by means of screw 14. The other passage 12 is connected by means of a tube 15, which may be a flexible hose such as rubber, and nipple T6 to a recess TI provided in boss 52. This recess has an atmospheric port which is preferably faced with a soft resilient ring 18 which may be live rubber or the like. The ring is preferably of suflicient thickness to be slightly compressed when plate 55 is brought into engagement with the face of the boss. Plate 55 acting as the valve and ring 18 acting as the valve seat on the atmospheric port form the pilot valve for opening and closing passage 12 in accordance with the position given to plate 55 by the movement of'valve stem 33 as already described. The pilot valve will be designated generally as 19. It is here to be noted that with the relatively large passage and valve opening, a very small movement of the valve face plate 55 is required to give full opening to the passage. It may be even less than A; inch, already given as the distance employed in experimental controllers.

Having described the construction of a controller embodying the invention, it is believed that a better understanding will be had of how this invention not only makes such a simple construction and operation thoroughly practical but also highly desirable by now examining the difiiculties heretofore encountered. While the dimculties of simple direct operation of the parts are inherent in substantially all arrangements where a portion of the main valve movement is employed to provide the movement of the pilot valve, these difficulties may be amply illustrated by pointing them out with relation to the type of valve chosen as the embodiment of this invention. This means, of course, that for this purpose the auxiliary leak port 42 with its associated closing apparatus and the special form of the pilot valve are to be considered as absent from the structure.

The operating difficulties grow primarily out of the inherent characteristics of the main valve of the prior art controllers to slow down in its travel as it approaches closed position. This is particularly true of the double chamber positive action type of motor where the chambers are separated by the movable operating wall or diaphragm and both chambers are normally under reduced pressure or vacuum and the forward stroke of the motor takes place upon the controlled admission of atmosphere or high pressure operating fluid to one chamber and the return stroke controlled in accordance with the resumption of equal pressures in both chambers accomplished by means of a controlled leak p-ort between the two chambers. The falling off of the closing speed at the end of the stroke is due to the decreased flow capacity of the leak port as the pressures on the opposite sides of the port approach the point of equalization. This follows the well known laws of orifice fiow.

that the main valve is opened by admitting substantially full pressure atmospheric air for the entire opening stroke. Consequently, the main valve is opened with a relatively quick movement. Yet, even though the pilot valve when opened directly must begin to admit atmospheric air to the operating chamber 65 of auxiliary motor 64 before the end of the stroke is reached, the time required to fill chamber 65 with the differential remainder of air from that admitted over that withdrawn through passage "H is quite sufficient to permit the main valve to reach full open position before the auxiliary motor drops the control On the other hand, it should be pointed out valve 6| closed cutting off the atmospheric pressure to the main motor. Furthermore it is to be noted that the full open position is not a critical one and whether it is completely attained will not affect the functioning of the valve.

on the other hand, as already pointed out the primary difiiculties in prior controllers accompany the closing stroke, particularly where, as in the present case, the speed of the entire closing stroke is slowed down by the employment of timed closing. When the pilot valve is moved by the main valve means, as it approaches the end of its closing stroke, the main valve is still partly open and even though the carrier has been discharged, sufiicient air is passing through the main valve to keep the pressure at the transmission side of the valve considerably below the minimum flow pressure. It should be noted that, even though in a decreasing amount, this low or sub-minimum-flow pressure continues until the main valve is-closed. And also that the increasing restriction upon the passage of atmospheric air through the pilot takes place reaching complete cut-oif as the pilot valve closes. However, in these closure movements, as soon as the amount of air entering chamber 55 through passage 72 becomes less than that withdrawn through passage ll, the pressure in chamber 65 tends to fall to the sub-minimmn-fiow obtaining on the transmission side of the main valve. Since the restriction of flow through the pilot valve varies between full flow and zero flow, and since the point at which the flow through pilot valve becomes less than that leaving the auxiliary motor chamber 55 is at some intermediate point of the pilot valve closing, therefore this point will be reached before. the valve is entirely closed; that is while it is still open and while the transmission side is still at sub-minimum-fiow pressure. The auxiliary valve does not open, however, simultaneously with the reaching of this point. On account of the reservoir effect of operating chamber of the auxiliary valve motor a moment is required for this sub pressure to accumulate. Now if the response of the auxiliary or control motor is made sensitive, as it must be if the amount of minimum flow is to be kept low so that a real saving is made by the use of power controllers, the control valve 6! will be opened up by the sub pressure before the main valve is completely closed, causing it to repeatedly open and never come to rest at closed position.

It is to be noted that the relation of the flow capacity of evacuating passage H and filling passage l'Z can be modified by an adjustable restriction means such as screw it to change the point at which the sub pressure is transferred to the chamber of the auxiliary motor. However, for the opening portion of the main valve cycle it is desirable to have the evacuating passage ll relatively wide open so that the diiferential build-up of atmospheric pressure takes place slowly in order to permit the main valve to open wide before the control valve closes. On the other hand, for the closing portion of the main valve cycle it is desirable that the evacuating passage it be considerably restricted in order to delay the build-up of the transmission iine pressure. It will be seen therefore that the adjustments favoring the two portions of the main valve cycle are in the opposite direction.

It is primarily because of these difficulties that a large number of the designs employed for minimum flow power controllers have proven difiicult of adjustment and maintenance and have become inefficient and obsolete from the standpoint of practical operation.

These difiiculties have been overcome by valves constructed according to this invention. It has been accomplished primarily by the provision of the supplementary leak port 42 opened as the valve approaches the end of its closing stroke thereby overcoming the tendency of the valve to slow down and instead speeding up the travel during this part of the stroke. By this means the passages controlling the auxiliary motor may be set for a median of adjustment, and no difl'iculties be encountered with a sensitively balanced control valve and motor. When fast closing of the main valve is provided, it has been found that the flow capacity of these passages may be adjusted to favor either the opening or closing stroke and still employ a sensitive control valve with ample margin of stability.

The operation of the controller constructed according to this invention including the auxiliary leak port, also the simple form of pilot valve, and its placement will now be set forth. When the system is in operation, chambers 24, 31, and 38 are all subjected to the vacuum pressure in the suction header l8. This is due to the fact that when no air is entering chamber 38, an equalization of pressures in chambers 37 and 38 is maintained through the port 4! and these chambers are in communication with the suction side of the valve through the large opening 39. Under normal conditions the valve parts take the position shown in Fig. 2. The minimum. flow of air through the transmission line takes place through the by-pass port 21 and is regulated by valve 28.

As already stated the control Valve SI and its operating motor '64 are so designed and balanced as to be very sensitive or, in other words, responsive to a relatively small vacuum. For the usual conditions it may be designed to respond to a vacuum of 3 to 3 inches of water. The minimum flow may then be regulated to a vacuum of from 1 to 2% inches of Water according to the type of line. At such minimum flow pressures it is obvious that the volumetric flow of air is small and that a real saving in power is accomplished. Although the minimum flow pressure is low and the margin of sensitivity of the control valve small, the control has proven to be very stable when adapted to widely varying conditions and has continued to function as set over considerable periods of time without readjustment.

The proper adjustments having been made according to line conditions, as soon as the head of a carrier enters the mouth of a terminal, it blocks the entrance of air to the line. Thereupon the air ahead of the carrier is exhausted through minimum flow opening 21 reducing the pressure in the transmission line and in chambers 23 and 55. As soon as a small pressure reduction occurs in chamber 65, diaphragm 61 acts to lift the valve SI from its seat admitting a rush of atmospheric air through the passage 62 into chamber 33. The rate of entrance of air through this passage exceeds by a considerable amount the rate of air leakage through both the leak ports 4! and 42. As the air fills chamber 38, diaphragm 32 and attached stem 33 are forced quickly to the left, moving main valve 26 to full open position and pilot valve plate 55 to the position shown in Fig. 3. As soon as the main valve cracks open, the pressure in the transmission line begins to be reduced and, as the valve opens, is rapidly reduced by an amount sufiicient to draw the carrier through the transmission line.

The reduced pressure in the transmission line, due to the opening wide of valve 26, draws air through passage 'H from the chamber 65 and would become established to hold the valve 6| continuously open but for provisions to admit air to the chamber through passage 12. However, to provide the timed closing of the main valve, control valve 6| must be closed to cut off atmospheric airto chamber 38 after the main valve has opened. This is accomplished by the. opening of passage '52 by means of the pilot valve :9 provided at the rear of the valve casing. The pilot valve is opened as the main valve approaches open position. The valve stem 33 near the end of its stroke moves the disc 55 slightly to the left uncovering the port in the bushing ring 18, thereby admitting a flow of atmospheric air through the pilot valve to chamber 65. It is to be noted that due to lost motion connection between stem 33 and plate 55 the latter is not moved until the very last portion of the opening stroke of the main valve. By providing a restriction in passage it through the medium of screw 14, air entering chamber 65 will not be exhausted through the passage into the valve casing as rapidly as it enters through passage 12. This differential of flow causes pressure in chamber 65 to rise within a short lapse of time to substantially atmospheric and since the pressure below the diaphragm is also atmospheric, the valve 6| will quickly close, due to gravity. During the above lapse of time, however, the main valve continues to move toward full open position. However, when the valve 6| has dropped upon its seat, and the admission of atmospheric air to chamber 38 has terminated, the opening movement of the main valve 26 ceases. It is preferable to so time the operation of the various elements that the main valve ceases its opening movement before it comes against any limiting stop member, thus giving the effect of cushioned opening.

The atmospheric passage to motor chamber 38 having been closed, the pressures in chambers 31 and 38 begin to equalize and at a rate determined by the setting of needle valve 43 controlling port M. As the pressure in chamber 38 drops, spring 53 acts to close the main valve by moving the stem 33 and parts having connection therewith toward their normal or closed position.

To offset the tendency of the travel of the main valve to slow down during the latter part of the stroke the auxiliary leak port 42 is opened up near the end of the stroke. The port is opened by the stem 89 of the leak valve is striking the inner end of screw or by the uncovering of the port in the modified form. The point in the travel of the main valve 26 and the motor diaphragm 32 at which the auxiliary port is opened is determined by the length of the stem 49. This point may be varied by the interchange of valves of various stem lengths. The same effect may be accomplished by setting the screw 5i (shown in Fig. 3) in or out.

Any desired characteristic of closure of the main valve may be had by varying the size and how capacity of the auxiliary leak port and interconnected passage and by determining the point in the closing stroke at which the port will be opened up. These may be chosen as just sufiicient to overcome the tendency of the valve to slow down at the end-of the stroke so that the speed of the closing travel' will be substantially the same for the entire stroke or they may be chosen so as to speed up the travel at the end of the stroke.

In order that the controller may be in readiness at the end of a transmission cycle for a succeeding cycle the auxiliary valve 6! and its motor 64 must be restored to its normal condition of sensitiveness to a drop of pressure in the transmis 1 sion line below minimum flow pressure. This .is accomplished by the main valve during the latter part of its stroke acting to close the pilot valve. As already explained in the examination of prior art difiiculties, the point at which the pressure in the operating chamber 65 of auxiliary motor M begins to assume the pressure in chamber 23 is when the air entering chamber 65 through passage F2 is restricted by the pilot valve to an amount less than that leaving through passage H. It was also pointed out that the point at which this begins is reached before completed closure of the pilot valve. However, when the pilot valve is constructed according to this invention with a large aperture seat 78 and large faced valve moving normal to the seat, the restricture of the flow therethrough takes place with a very small movement of the valve. This would take place in about one-half or less of the travel given the valve as shown in Fig. 3.

With a pilot valve having the above characteristics combined with the feature of increased speed of travel of the main valve at the end of the stroke, no diificulty is experienced with. the auxiliary motor building up to its condition of sensitivity to pressures on the transmission side of the main valve before the latter has completely closed and the transmission line pressure has come up to the normal minimum flow pressure. In this manner complete closure of the main valve is assured at the end of each cycle and repeated opening or pumping of the valve will not occur when there is no carrier in the transmission line.

The result of the fast closure of the main valve is that a simple form of pilot valve may be employed and may be operated directly from the stem of the main valve and yet stable and certain operation be assured and maintained over long periods of time.

Fast closing of the main valve enables the timing function to be restricted to the first portion of the stroke or the portion in which the valve has little or no restrictive effect on the flow of transmission line motive fluid. 0n the other hand, the restrictive portion of the stroke is traversed relatively quickly. This is advantageous in cases where the carrier is heavily loaded or worn or, for some other reason does not traverse the transmission line in the normal period requiring two or more time cycles to complete the transmission. In such a case the shortness of the restrictive travel time of the main valve causes only a slight hesitation of the carrier instead of a substantially complete stoppage with its attenciant delay.

These features of the power control give it operating characteristics equalling the so called carrier closed valves. It is well recognized that for short lines time control is adequate, the infrequent unusual condition being taken care of by a reopening of the valve. On the other hand, for long lines the valve may be set for two or more time cycles for the required travel period of the average carrier and the carrier will travel with substantially undiminished speed and be delivered in within substantially the same time period as if there were no intermediate valve closure. While at the same time the cuttingofi of the air flow shortly after carrier delivery is assured.

' It is to be observed that a controller has been provided with assured operation under all conditions and having a wide latitude of application and yet which is simple in structure and marked by an absence of a large number of interlocking and coacting parts. Further, due to the simpiicity of its operation, it has been possible to shift the pilot valve and its operating parts to the rear of the casing, whereas heretofore they have been placed in front or on top, very vulnerable positions for accidental damage to the parts. This arrangement also gives a more pleasing appearance to the eye.

It is to be understood that the form of the structure shown is merely illustrative and that while the invention has been shown in but two forms, it will be apparent to those skilled in the art that it may be embodied in many other forms and modifications without departing from the spirit thereof and it is desired, therefore, that only such limitations shall be placed thereon as are imposed by the prior art or by the appended claims.

What I claim is:

1. Power control apparatus of the minimum flow type for a pneumatic conveyer line having a transmission line tube and an exhaust line tube and a main valve between said tubes for controlling carrier propelling'air flow through the line, means for establishing a minimum flow of air through the line when the main valve is closed,

means for opening the main valve in response to means for establishing atmospheric pressure on said other side of the diaphragm at the end of the opening stroke of the main valve and maintaining the said pressure until the end of the timed closing stroke of said valve.

2. Power control apparatus of the minimum flow type for a pneumatic conveyer line having a transmission line tube and an exhaust line tube and a main valve between said tubes for controlling carrier propelling air flow through the line, means for establishing a minimum fiow of air through the line when the main valve is closed, means for opening the main valve in response to the presence of a carrier in the transmission line, and means for closing the valve after a period of time has elapsed, said response means including a pneumatic with a diaphragm continuously exposed on one side to aconstant pressure, means for sensitizing it to the presence f a carrier in the transmission line by normally exposing its other side to transmission line preshaving a transmission line tube and an exhaust line tube and a main valve between said tubes for controlling carrier propelling air flow through the line, means for establishing a minimum flow of air through the line when the main valve is closed, a main pneumatic for opening the main valve, an auxiliary pneumatic embodying a control valve for initiating the opening and closing action of the main pneumatic and a diaphragm for operating the control valve, said diaphragm and valve being biased toward the normal position of the valve, one side of said diaphragm being constantly exposed to atmospheric pressure, means for normally exposing the other side to transmission line pressure, said control valve being arranged so that a pressure drop due to the presence of a carrier in said line operates the control valve to cause said main valve to open, and means operated by movement of said main valve for establishing atmospheric pressure on said other side of the diaphragm at the end of the opening stroke of the main valve for equalizing the pressures on opposite sides of said diaphragm so that said bias means will restore the control valve to normal position and cause the main valve to close.

4. Power control apparatus of the minimum flow type for a pneumatic conveyer line having a transmission line tube and an exhaust line tube and a main valve between said tubes for controlling carrier propelling air flow through the line, means for establishing a minimum flow of air through the line when the main valve is closed, a main pneumatic for opening the main valve and including means for timing the closing of the valve, an auxiliary valve for controlling the operating fluid flow to the main pneumatic, an auxiliary pneumatic comprising two chambers separated by a diaphragm movable to operate said auxiliary valve, one of said chambers being constantly open to the atmosphere, first and second passages leading to the other chamber, the first passage being in constant communication with the transmission line, the second passage being normally closed, and means for opening the second to atmosphere at the end of the opening stroke of the main valve and for closing the same at the end of its closing stroke.

5. Power control apparatus of the minimum flow type for a pneumatic conveyer line having a transmission line tube and an exhaust line tube and a main valve between said tubes for controlling carrier propelling airflow through the line, means for establishing a minimum flow. of air through the line when the main valve is closed, a main pneumatic for opening the main valve and including means for timing the closing of the valve, an auxiliary valve for controlling the operating fluid flow to the main pneumatic, an auxiliary pneumatic comprising two chambers separated by a diaphragm movable to operate said auxiliary valve, one of said chambers being constantly open to the atmosphere, first and second passages leading to the other chamber, the first having a determined flow area, the second having a flow area larger than the first, the first passage being in constant communication with the transmission line, the second passage being normally closed, and means for opening the second to atmosphere at the end of the opening stroke of the main valve and for closing the same at the end of its closing stroke.

6. In combination, a valve for controlling the flow of motive fluid through a pneumatic conveyer line or the like. a resilient means tending to hold said valve closed, a fluid motor arranged to open the valve against the action of said resilient means; said motor comprising a housing embodying a motive fluid chamber having a movable side wall and means for operatively connecting said wall and the valve, a controlled inlet port for admitting motive fluid to said chamber for opening the valve, a continuously open regulatable leak port for bleeding the motive fluid out of said chamber at a determined rate for permitting the valve to close, a valve closed leak port and a rod reciprocated by the movement of the main valve for opening said port valve as the main valve approaches closed position to increase the determined leakage rate and closing the valve at increased speed, and an adjustable stop for the rod for determining the point in the closing stroke of the main valve at which the pOrt valve opens.

7. In a power controlling apparatus for a pneumatic conveyer line, a pneumatic motor having a chamber provided with a movable wall, a stem extending from said wall to said valve for operating the latter, a normally closed control valve in said stem arranged to provide a vent to said chamber for modifying the operation of said motor, and means operative by the inward movement of said wall and stem for opening said control valve.

8. In a power control apparatus for a pneumatic conveyer line, a main valve for controlling the flow of motive fluid in the line, means for opening and closing the main valve, an auxiliary valve for controlling the main valve, a pilot valve, opened and closed in accordance with the movements of the main valve, for conditioning the auxiliary valve, means for increasing the speed of travel of the main Valve as it approaches the end of its closing stroke, and means operated by the main valve for causing the pilot valve to be closed in accordance with the modified movement of the main valve.

9. Power control apparatus for a pneumatic conveyer line having a main valve for controlling the line fluid flow, meansfor opening and closing the main valve, a diaphragm normally sensitive to the pressure incident to the introduction of a carrier in the line for controlling the main valve opening means, a chamber enclosing one side of the diaphragm, means providing a pilot port in communication with said chamber for controlling the sensitivity of said diaphragm, means operated in accordance with the opening movement of the main valve at the end of its opening stroke for opening said port and desensitizing said control diaphragm, and means acting at the end of the main valve closing stroke including the portion in which the pilot port is closed to import a relatively quick movement to the main valve while the pilot port valve is being closed.

10. In a power control apparatus for a pneumatic conveyer line, a control valve disposed to travel between extreme open and closed positions for releasing and restraining the flow of motive fluid in the conveyer line, said valve being arranged so that in a first portion of its travel, which lies between an intermediate position and said open position, substantially no restraining efiect of the fluid flow occurs, while in a second portion of its travel, which lies between said intermediate position and said closed position, substantially all of the restraining efiect occurs, a motor having a motive fluid chamber including a wall movable between extreme positions by motive fluid, means for coupling the wall and the valve for moving the valve through its travel, said chamber being provided with regulated ports for the escape of the motive fluid for timing the closing of the valve, one of said ports being open a regulated amount throughout the closing stroke of the valve, an auxiliary valve for opening and closing another of said ports for speeding up the closing travel of the main valve, means for opening said auxiliary valve during the latter part of the closing stroke of said main valve, said valve opening means being adjustable so that the opening of the auxiliary may be regulated to include said second portion of its closing travel.

11. In a power control apparatus for a pneumatic conveyer line, a motive fluid power source, a valve casing being interposed therebetween, a motor for operating the valve and a controller therefor carried by the casing, a pilot valve for conditioning the controller, said pilot valve being embodied in a boss disposed at the rear of the casing and carrying a rearwardly extending sleeve, said boss having a port formed in its outer face and arranged to provide the seat portion of the pilot valve, a disc fitted to reciprocate upon said sleeve, the inner face of said disc being arranged to form the pilot valve face and acting when brought against the outer face of the boss to close said port by seating upon'the rim of the same, and a lost motion connection between said disc and said motor for operating the pilot valve.

12. In a power control apparatus for a pneumatic conveyer line, a motive fluid power source, a valve casing being interposed therebetween, a motor for operating the valve and a controller therefor carried by the casing, a pilot valve for conditioning the controller, said pilot valve being embodied in a boss disposed at the rear of said casing and carrying a rearwardly extending sleeve, said boss having a port formed in its outer face and arranged to provide the seat portion of the pilot valve, a disc being arranged to form the pilot valve face and acting when brought against the outer face of the boss to close said port by seating upon the rim of the same, a lost motion connection between said disc and said motor for operating the pilot valve, and means for applying a restraining friction between the disc and sleeve for guarding against untimely movement of the disc.

SIGGVE.

13. In a power control for a pneumatic conveyer line having a housing, a main pneumatic, a reciprocating stem extending therefrom and protruding through one side of the housing, a

sleeve extending from said housing parallel with the protruding portion of the stem, a disk pilot valve surrounding the sleeve, lost motionconnections between the stem and the pilot valve for giving a limited movement to the valve along the sleeve, a pilot port eccentric of said sleeve and arranged to be covered by the face of said disk at one extreme position of the valve; and means for providing frictional engagement between the pilot valve and the sleeve for restricting the movement of the valve to that imparted to it through said lost motion connections.

14. In a power control apparatus for a pneumatic conveyer line, a motive fluid power source, a valve casing being interposed therebetween, a motor for operating the valve and a controller therefor carried by the casing, a pilot valve for conditioning the controller, said pilot valve being embodied in a boss disposed at the rear of said casing and carrying a rearwardly extending sleeve, said boss having a port formed in its outer face, said port having a rim of resilient material and arranged to provide the seat portion of the pilot valve, a disc fitted to reciprocate upon said sleeve, the inner face of said disc being arranged 1 to form the pilot valve face and acting when brought against the outer face of the boss to close said port by seating upon and slightly compres-v sing the material forming the rim of the same, and a lost motion connection between said disc and said motor for operating the pilot valve.

15. In a power control for a pneumatic conveyer line having a housing, a, main pneumatic, a'reciprocating stem extending therefrom and protruding through one side of the housing, a sleeve surrounding the protruding portion of the stem, a pilot valve surrounding the sleeve and arranged to slide thereupon, means to set up frictional resistance to the sliding of said valve upon said sleeve for holding the valve in slid position and lost motion connections between the stem and the pilot valve for sliding the latter upon said HERMAN BUSCH.