US3790101A

US3790101A - Combined transmit and receive terminal for pneumatic tube system

Info

Publication number: US3790101A
Application number: US00304754A
Authority: US
Inventors: A Weissmuller
Original assignee: Mosler Safe Co
Current assignee: Mosler Safe Co
Priority date: 1972-11-08
Filing date: 1972-11-08
Publication date: 1974-02-05
Anticipated expiration: 1991-02-05

Abstract

A pneumatic tube system terminal including a) a receive chamber in which a received carrier, in the course of sliding or rolling over an underlying spring-biased flap, deflects the flap to seal the vacuum line which connects to the receive chamber, enabling opening of the receive chamber door normally closed by the vacuum, the flap once being deflected remaining so under the action of the vacuum in the line which is now sealed by the flap in its deflected position, and b) a transmit chamber connected to a pressure line, having an actuator linked to a valve in the vacuum line, which actuator (1) upon insertion of a carrier into the chamber for transmission is tripped to momentarily close the valve in the vacuum line, in turn releasing the spring-biased receive chamber flap, and (2) upon passage of the inserted carrier into the transmit tube opens the valve in the vacuum line to restore vacuum/pressure in the system and transmit the carrier.

Description

United States Patent 91 Weissmuller Feb. 5, 1974 COMBINED TRANSMIT AND RECEIVE [57] ABSTRACT TERMINAL FOR PNEUMATIC TUBE SYSTEM A pneumatic tube system terminal including a) a recelve chamber in which a received carrier, in the [75] Inventor: Adam WeiSSmullel, Kinnelon, NJ. course of sliding or rolling over an underlying springbiased flap, deflects the flap to seal the vacuum line [73] Assignee' z gf g i biig Company which connects to the receive chamber, enabling opening of the receive chamber door normally closed [22] Filed: Nov. 8, 1972 by the vacuum, the flap once being deflected remain ing so under the action of the vacuum in the line [21] Appl' 304754 which is now sealed by the flap in its deflected position, and b) a transmit chamber connected to a pres- [52] HS. Cl. 243/19 sure line, having an actuator linked to a valve in the [51] Int. Cl. 865g 51/32 vacuum line, which actuator 1) upon insertion of a [58] Field of Search 243/2, 3, 4, 19, 23, 25, 26 carrier into the chamber for transmission is tripped t0 momentarily close the valve in the vacuum line, in

[56] References Cited turn releasing the spring-biased receive chamber flap,

UNITED STATES PATENTS and (2) upon passage of the inserted carrier into the 861,375 7/1907 Litchfield 243/23 transmit tube Opens the valve in the Vacuum line to Primary ExaminerAllen N. Knowles Attorney, Agent, or Firm-Wood, Herron & Evans restore vacuum/pressure in the system and transmit the carrier.

6 Claims, 1 Drawing Iligure COMBINED TRANSMIT AND RECEIVE I TERMINAL FOR PNEUMATIC TUBE SYSTEM This invention relates to a pneumatic tube system terminal, and more particularly to an improved terminal of the type which transmits and receives carriers via separate transmitting and receiving pneumatic tubes.

Pneumatic tube systems have long been proposed for transporting carriers between spaced terminals. In accordance with one such proposal, termed herein the dual tube approach, each remote terminal is connected to the system .by means of two separate carrier transport tubes, namely, a carrier receiving tube and a carrier transmitting tube. Each of these two tubes present is undirectional in the sense that each tube transports a carrier in only a single direction. The receive tube transports carriers toward the terminal, while the transmit tube transports carriers from the terminal. Such systems also include a source of vacuum, negative orsubstmospheric pressure, and a source of positive or superatmospheric, pressure, which are connected to the transmit and receive tubes, respectively, or vice versa, depending upon the design particulars of the system.

In any of the systems employing the dual tube approach, it is normally desirable to provide switch means of some type for terminating the pressure and vacuum upon receipt of a carrier at the terminal, which pressure and/or vacuum are then re-established when transmitting a carrier. Various-switching arrangements have been proposed employing both electrical and mechanical devices. Many of these proposed schemes have been unsatisfactory by reason of being too complex and, hence, costly, and/or unreliable in operation. Accordingly, it has been an objective of this invention to provide a combined transmit and receive terminal of the dual-tube type which is relatively simple in structure, and inherently reliable in operation. This objective has been accomplished in accordance with certain principles of this invention by providing, in a transmit/receive terminal of the dual tube type, the

unique combination of a) a receive chamber in which a received carrier, in the course of sliding or rolling over an underlying pivotal spring-biased flap, deflects the pivotal flap downwardly, interrupting the vacuum line, the flap once being pivoted downwardly remaining so under the action of the vacuum line which is sealed by the flap in its downwardly deflected position and b) a pressurized transmit chamber having an actuator linked to a valve in the vacuum line, which actuator l upon insertion of a carrier into the transmit chamber for transmission is tripped to momentarily close the valve in the vacuum line, which in turn releases the spring-biased receive chamber flap, and (2) upon passage of the inserted carrier into the transmit tube opens the valve in the vacuum line to restore vacuum and pressure in the system and effect transmission of the carrier.

The terminal of this invention, particularly by virtue of the fact that the carrier slides, or rolls, over the receive chamber valve flap, rather than passing through the flap, results in a terminal which is extremely reliable in operation. Specifically, the sliding receive chamber valve flap of this invention is responsive only to the weight of the carrier and, so long as the empty weight of the carrier exceeds the springbias of the flap, operation of the receive chamber valve flap is assured.

Since the weight of an empty carrier is predictable, reliable operation therefore results. This is in contrast to operation of a terminal of the break-through flap variety wherein valving occurs as a consequence of a carrier passing through a flap. In the pass-through flap scheme, operation depends not only upon the weight of the carrier, but also its speed. Since speed can vary, operation is unpredictable. For example, if for some reason the carrier is slowly moving, it may have insufficient force to pass through the break-through" flap, in which event a malfunction occurs.

Another important advantage of this invention resides in the fact that the door of the receive chamber through which the received carrier can be removed subsequent to receipt, is maintained in a closed position during transmission of a carrier as a consequence of the vacuum in the receive chamber. However, once 'a carrier is received in the receive chamber, and the pivotal valve flap lowered to seal the vacuum line, vacuum to the receive chamber ceases and the door is released. Thus, receive chamber door control is simpli- Finally, when the carrier is dispatched, there is no pressure in the system until the valve in the vacuum line, which is operated in response to insertion of the carrier to be transmitted, goes through its closing/opening sequence. Thus, complications of continuous pressurization are avoided.

In accordance with a preferred embodiment of this invention, the receive chamber floor and valve flap atop which a received carrier initially is located are constructed to be inclined such that a received carrier located atop the flap will roll out of the receive chamber for presentment to the operator. Such rolling carrier motion from the receive chamber as a consequence of the inclined structure of the receive chamber occurs, on an automatic basis, by virtue of the automatic release of the receive chamber door upon interruption of the vacuum line when the received carrier operates the receive chamber valve flap atop which it is located upon initial receipt in the receive chamber.

These and other advantages, features and objectives of the invention will become more readily apparent from a detailed description of a preferred embodiment thereof taken in connection with the drawings in which the single FIGURE is a front perspective view, partially cut-away, of a combined transmit and receive terminal embodying the invention.

The combined transmit/receive terminal of this invention, in a preferred form thereof, includes a housing 10 divided into an upper receive chamber 12 and a lower transmit chamber 14. Communicating with the receive chamber 12 is a receive tube 16 through which a carrier C passes in the direction of arrow 18 in the course of transmission from a distant station 20 to which the receive tube is connected at its remote end, and a vacuum line 22 which applies vacuum, negative, or subatmospheric pressure to the receive chamber from an intake port 24 of a blower 26 connected to the remote end of line 22. The transmit chamber 14 is in communication with a transmit tube 28 through which carriers C are transmitted in the direction of arrow 30 to a distant station 32 to which the transmit tube is connected at its remote end, and a pressure line 34 which applies pressure to the chamber 14 from an output 38 of the blower 26 to which the pressure line 34 is connected at its opposite end.

The receive chamber 12, which is generally elongated and horizontally disposed, includes oppositely disposed, spaced vertical

housing end walls

40 and 42; horizontal ceiling 44; an inclined floor 46; and a vertical side wall 48. A pivotal door 50 hinged along its upper edge to the ceiling 44 is provided to selectively close a receive chamber opening 52 provided in the housing opposite side wall 48. The internal dimensions of the receive chamber 12 are selected to accommodate receipt therein of a carrier C, and accordingly depend upon the size and shape of the carrier. Similarly, the opening 52, which is sized to enable a received carrier to pass out of the receive chamber 12, depends for its configuration on the size and shape of the carrier. End wall 40 is provided with an opening 40A, permitting the receive tube 16 to communicate with the chamber 12. Similarly, the floor 46 of the receive chamber 12 is provided with an opening 46A to permit the vacuum line 22 to communicate with the receive chamber. A rectangular planar flap 54 slightly smaller in size than the floor 46 is pivoted to the floor along an edge 54A thereof adjacent the end wall 40. A compression spring 56 located between the flap 54 and the chamber floor 46, in the absence of a carrier atop flap 54, biases the flap to an upward position (shown in the FIGURE) in which the lower surface of the flap does not seal the opening 46A in the chamber floor which communicates with the vacuum line 22. The spring constant of comrpession spring 56 is selected such that the fiap 54 will move to a lower position (not shown) wherein its lower surface seals opening 46A when a carrier C positioned in the receive chamber 12 is located atop the flap 54 and remains in sealing relation to opening 46A so long as vacuum exists in line 22 adjacent receive chamber 12. When the flap 54 is in its lower position, sealing vacuum line opening 46A in chamber floor 46, the vacuum line is interrupted at the receive chamber 12. Interruption of the vacuum line 22 permits the door 50, which is normally maintained closed by vacuum in chamber 12 to thereby seal opening 52, to pivot upwardly to its open position when a carrier received within the chamber 12 and resting atop flap 54 rolls in the direction of arrow 60 perpendicular to its longitudinal axis as a consequence of the floor 46 and, hence, the flap 54 being inclined or tilted.

Extending exteriorly from the edge of the floor 46 adjacent opening 52 is a downwardly angled or inclined ledge 62 which effectively forms an extension of the inclined floor 46 of the receive chamber exteriorly of the door 50 for storing a carrier (shown in phantom), which has been transmitted to the receive chamber 12 via tube 16 and passed outwardly through chamber opening 52 via pivotal door 50, in a horizontal disposition which facilitates convenient retrieval by an operator. An upstanding shoulder 64 integral with the outermost edge of the inclined ledge 62 functions as a stop member for arresting the motion of a received carrier as it rolls out of the receive chamber 12 onto the ledge 62.

The transmit chamber 14 is defined by opposite spaced vertical end walls 70 and 72, vertical rear wall 74, front wall 76, floor 78, and a ceiling established by the receive chamber floor 46 and the carrier supporting ledge 62. End wall 70 is provided with an opening 70A through which the vacuum line 22 passes. Floor 78 is provided with an opening 78A which connects the pressure line 34 with the interior of the transmit chamber 14, and an opening 788 through which the transmit tube 28 passes. The ledge 62 which establishes a portion of the ceiling of the transmit chamber 14 is provided with an opening 84 configured to permit a carrier C to be inserted into the transmit chamber 14 for transmission to a distant station 32 via the transmit tube 28. Located below opening 84 is a flap 86 which is mounted for pivotal movement about its edge 86A with a horizontally disposed shaft 88 between an upper position (solid lines) in which the flap 86 seals opening 84 and a lower position (dotted lines) in which the flap has been rotated approximately 90 to permit a carrier to be inserted into the transmit chamber via the opening 84.

Disposed below and in vertical alignment with the carrier opening 84 of transmit chamber 14 is the mouth or throat 89 of the carrier transmit tube 28. With the mouth 89 of carrier transmit tube 28 so located, insertion of a carrier C through opening 84, in addition to pivoting flap 86 to its open position (dotted lines) for reasons to become apparent hereafter, is also effective to cause the inserted carrier C to enter the mouth 89 of the transmit tube 28 for transmission to the remote station 32. A compression spring 90 connected to the flap 86 is provided to normally bias the flap 86 to its upper position (solid lines) sealing transmit chamber opening 84.

The vacuum line 22, as noted, passes through opening A in transmit chamber wall 70, terminating such that its upper end 92 communicates with the interior of the receive chamber 12 via opening 46A in floor 46 of the receive chamber. Disposed in the upper portion of the vacuum line 22 below the end 92 thereof is a wind gate or valve member 94 in the form of a circular disc configured and dimensioned such that when in its horizontal position (not shown) the vacuum line 22 is interrupted, or blocked, and when in its vertical position shown in the FIGURE, the vacuum line 22 is unblocked, or open. The wind gate disc 94 is fixed to the horizontal shaft 88, the shaft passing through suitable diametrically opposed openings in the wall of the upper end of the vacuum line 22, effectively mounting the shaft 88 for rotational movement about its longitudinal axis.

The orientation of the wind gate flap 94 with respect to the flap 86 is such that wind gate flap 94 is in its vertical, open position, unblocking vacuum line 22 when the flap 86 is in its upper, closed position, sealing opening 84; and is in its horizontal, closed position interrupting vacuum line 22 when the flap 86 is in its open position unblocking opening 84. By virtue of compression spring 90, flap 86 is normally in its closed position, sealing opening 84 and wind gate 94 in its vertical or open position, unblocking line 22. However, upon insertion of a carrier into tube 28 via opening 84, flap 86 is pivoted to its open or vertical position, in turn pivoting wind gate flap 94 to its horizontal or closed position interrupting vacuum line 22.

Under normal circumstances, that is, absent either receipt of a carrier or transmission of a carrier, flap 86 is in its upper position sealing transmission chamber opening 84 in which case wind gate flap 94 is in its vertical or open position. Additionally, door 50 is in its closed, vertical position, sealing opening 52 and flap 54 is in its elevated position, leaving opening 46A in the floor 46 of the receive chamber unblocked. With wind gate flap 94 in its vertical, open position and flap 54 in its upper position, an air flow path exists through the transmit/receive terminalhousing between the vacuum line 22 and the pressure line 34 withthe result that, assuming blower 26 is energized, receive chamber 12 is at subatmospheric pressure and transmit chamber 14 is at superatmospheric pressure. The subatmospheric pressure condition ,of rec'eive chamber 12 maintains the door 50 in itsclosed position, while the superatmospheric pressure in transmit chamber 14, in conjunction with spring 90, maintains the flap 86 in its upper, closed position sealing opening 84.

Now assuming a carrier Chas been transmittedfrom remote station to the terminal 10 via receive line 16, the carrier C is input to the receive chamber 12 via opening A as a consequence of the subatmospheric pressure condition of receive chamber 12. Upon receipt of the carrier C in receive chamber 12, the carrier initially rests on the flap 54 and by virtue of its weight overcomes the bias force of spring 56 to urge the flap 54 into its lower position sealing opening 46A in the receive chamber floor 46.The flap 54 is thereafter'maintained in this position by virtue of the vacuum existing in line 22 at receive chamber opening46A. With vacuum line opening 46A sealed by depressed flap 54, the subatmospheric condition of receive chamber 12 terminates, with the result that the door is no longer maintained in its closed position by the subatmospheric receive chamberpressure. Instead, the door 50 is free to pivot upwardly and open, and in fact does so, when the received carrier, which initially seats atop flap 54, rolls laterally in the direction of arrow 60 from a position atop the inclined flap 54 to a position supported by inclined ledge 62. When the received carrier has passed I through opening 52 onto ledge 62, door 50 pivots downwardly under the force of gravity to its closed position. At this point, the received carrier, now resting on ledge 62, can be removed by the operator. However, and independent of whether or not the received carrier is removed from the ledge 62 by the operator, the vacuum line 22 is interrupted by virtue of the flap 54 which is maintained in itslower position under the action of the vacuum existing in line 22. With vacuum line 22 interrupted, no pressure is applied to pressure line 34 by blower 26 since the inlet 24 to theblower is blocked.

Should it be desired to transmit a carrier C to a distant station 32 via transmit'tube 28, the carrier is inserted through the opening 84 into transmit chamber 14, and in particular into the underlying mouth 89 of the transmit tube 28. In the course of such insertion, the flap 86 pivots downwardly to the dotted line position in turn rotating the wind gate flap 94 to its horizontal or closed position. Placement of wind gate flap 94 in its closed position interrupts the application of vacuum from line 22 to the opening 46A in floor 46 of receive chamber 12 with the result that the flap 54, heretofore maintained in its lower position by the vacuum at opening 46A, is now released and returned to its upper position by compression spring 56. At this point vacuum line 22 is still interrupted by virtue of the horizontal closed position of wind gate flap 94 produced as a consequence of insertion of the carrier in opening 84 which pivots flap 86 downwardly. Thus, no pressure is present in line 34, and the carrier is not propelled to its destination.

After the inserted carrier has passed clear of flap 86, the flap is returned to its upper position by spring 90 sealing opening 84, and in turn rotating wind gate flap 94 to its vertical, open position. With wind gate 94 in its vertical, open position and flap 54in its upper, open position, the vacuum line 22 is uninterrupted .with the result that the blower inlet 24 is no longer blocked and the blower can apply super-pressure to line 3 4 and in turn to transmit chamber 14. With transmit chamber 14 subjected to superatmospheric pressure, the carrier Cf previously inserted into transmit tube 28 via opening 24 is now propelled to its destination 32 via, the transmit line. I t v The combined transmit/receive terminal described above affords a number of useful advantages. For example, since the received carrier slides over the receive chamber flap 54, rather than passing through the flap, reliability is improved. Specifically, the sliding flap 54 of this invention is responsive to only the weight of the carrier and so long as the weight of an empty carrier exceeds the spring bias afforded by spring 56 operation of flap 54 is assured. Since the weight of an empty carrier is predictable, reliable operation results. In contrast, were the carrier to pass through the flap, reliability is not assured. A pass-through flap depends not only upon the speed of the carrier but its weight. Since speed can vary, operation is unpredictable. For example, if for some reason the carrier is slowly moving, it may have insufficient force to pass through the pass-through flap, in which event a malfunction occurs.

Additionally, the door 50 of the receive chamber 12 through which the carrier slides'in the course of its travel to the external ledge 62 for presentment is maintained in a closed position during transmission of the carrier as a consequence of the vacuum in the receive chamber. However, once a carrier is received in the receive chamber 12, and the pivotal floor flap 54 lowered to seal vacuum line opening 46A, the vacuum into the receive chamber ceases and the door is released. Thus, receive chamber door control is simplified.

Also, when a carrier is dispatched, there is no pressure in the system until the wind gate flap 94 in the vacuum line 22 goes through its closing/opening sequence in response to insertion of a carrier into the transmit chamber 14. Thus, complications of continuous pressurization are avoided.

Further, if the blower 26 is for some reason inadvertently de-energized, the system is automatically reset since recieve chamber flap 54 is returned to its upper position unblocking the vacuum line 22 which in turn permits pressure to be applied to the transmit chamber 14 via pressure line 34.

Finally, the combined transmit/receive terminal of this invention provides a minimum number of moving elements which simplifies both the structure and operation of the unit.

What is claimed is:

1. A combined transmit and receive terminal for use with a pneumatically transported carrier, comprising:

a receiver having a receive chamber configured to contain a carrier received therein from a distant station via a pneumatic receive tube communicating therewith,

a vacuum line communicating .with said receive chamber,

a flap in said receive chamber underlying a received carrier located therein, said flap being movable between a first position in which said vacuum line is unblocked at said receive chamber and a second position in which said vacuum line is blocked at said receive chamber,

first means for biasing said flap to its first position to unblock said vacuum line prior to receipt of a carrier in said receive chamber atop said flap, said biasing means being inoperative to prevent said flap from moving to its vacuum line blocking position upon receipt of a carrier in said chamber atop said flap, said biasing means being further inoperative to return said flap to its unblocking position from its blocking position in the presence of vacuum in said vacuum line at said receive chamber,

a transmitter having atransmit chamber into which a carrier can be inserted for transmission to a distant station via a pneumatic transmission tube communicating with said transmit chamber, said chamber having an opening therein through which a carrier can be introduced for insertion into said transmission tube,

a closure for said opening and movable between a first position unblocking said opening upon insertion of a carrier therethrough and a second position blocking said opening,

second means for biasing said closure to its second position,

a valve member in said vacuum line movable between a first position unblocking said line wherein vacuum is present in said line at said receive chamber, and a second position blocking said line wherein vacuum is not present in said line at said receive chamber,

a pressure line communicating with said transmit chamber,

a blower having an air inlet and an air outlet connected to said vacuum and pressure lines, respectively, said blower being inoperative to produce pressure in said pressure line when said vacuum line is unblocked, and

means interconnecting said closure and valve member to position said valve member in its blocking position when said closure is in its unblocking position in response to insertion of a carrier in said opening for terminating vacuum in said vacuum line at said receive chamber and enabling said first bias means to return said flap to its normal position unblocking said vacuum line,

said inter-connecting means being further operative to position said valve member in its unblocking position when said closure returns to its blocking position when said closure returns to its blocking position following insertion of a carrier through said opening for enabling said blower to apply pressure to said transmit chamber to transmit said inserted carrier.

2. The terminal of claim 1 wherein said receive chamber has a floor provided with a port which connects to said vacuum line, and wherein said flap overlies said floor, said flap being normally spaced above said floor by said first bias means to unblock said port and vacuum line and being movable downward under the weight of a received carrier to block said port and vacuum line.

3. The terminal of claim 1 wherein said flap is mounted to be inclined when in its blocking position to enable said received carrier thereon to roll thereoff, and wherein said receiver has a pivotal door normally covering an opening in a side wall of said receive chamber, said door normally being maintained closed by vacuum applied to said receive chamber via said port when said flap is raised in the absence of a carrier on said flap, said door being released to enable pivotal motion thereof by said carrier to a position uncovering said opening as said carrier rolls off said flap through said receive chamber opening.

4. The terminal of claim 3 wherein said door is pivotally connected along an upper edge thereof to said receiver to enable said door to close under the force of gravity subsequent to receipt of a carrier which has rolled off said flap and out of said receive chamber through said receive chamber opening.

5. The terminal of claim 3 wherein said receiver is located above said transmitter and wherein said transmitter has a ceiling including a first section adjacent said receiver floor exteriorly of said receiver side wall opening for supporting exteriorly of said receiver a received carrier which has rolled off said inclined flap and out said receiver opening through said door.

6. A combined transmit and receive terminal for use with a pneumatically transported carrier, comprising:

a vacuum line communicating with said receive chamber,

a transmitter having a pneumatic transmission tube provided with a mouth into which a carrier can be inserted for transmission to a distant station when pressure is applied to said mouth,

a pressure line to apply pressure to said mouth,

a valve member in said vacuum line movable between a first position unblocking said line wherein vacuum is present in said vacuum line at said receive chamber, and a second position blocking said vacuum line wherein vacuum is not present in said vacuum line at said receive chamber,

a blower having an air inlet and an outlet connected to said vacuum and pressure lines, respectively, said blower being inoperative to produce pressure in said pressure line when said vacuum line is unblocked, and

actuating means to position said valve member in its blocking position in response to a carrier being inserted into said transmitter for terminating vacuum in said vacuum line at said receive chamber and enabling said first bias means to return said flap to its normal position unblocking said vacuum line, said actuating means being further operative to position said valve member in its unblocking position when said carrier has been inserted into said transmission tube for enabling said blower to apply pressure to said transmitter to transmit said inserted carrier.

Patent No. 3,790,101 Dated February 5, 1974 1nventor(s) Adam Weissmuller It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, Line 38 (Claim 1), "unblocked" should be -blocked--;

Column 7, Lines 50,51 (Claim 1), delete "when, saidclosure'. returns to itsblocking position";

Column 8, Lines 55,56 (Claim 6), ,funblocked" should be -blockec3.-.v

- Signed. and sealed this mm day of June 1974.

(SEAL) Attest:

EDWARD M.YFLETC I-IER,JR.- v V c. MARSHALL DANN Attesting Officer Commissioner of Patents

Claims

1. A combined transmit and receive terminal for use with a pneumatically transported carrier, comprising: a receiver having a receive chamber configured to contain a carrier received therein from a distant station via a pneumatic receive tube communicating therewith, a vacuum line communicating with said receive chamber, a flap in said receive chamber underlying a received carrier located therein, said flap being movable between a first position in which said vacuum line is unblocked at said receive chamber and a second position in which said vacuum line is blocked at said receive chamber, first means for biasing said flap to its first position to unblock said vacuum line prior to receipt of a carrier in said receive chamber atop said flap, said biasing means being inoperative to prevent said flap from moving to its vacuum line blocking position upon receipt of a carrier in said chamber atop said flap, said biasing means being further inoperative to return said flap to its unblocking position from its blocking position in the presence of vacuum in said vacuum line at said receive chamber, a transmitter having a transmit chamber into which a carrier can be inserted for transmission to a distant station via a pneumatic transmission tube communicating with said transmit chamber, said chamber having an opening therein through which a carrier can be introduced for insertion into said transmission tube, a closure for said opening and movable between a first position unblocking said opening upon insertion of a carrier therethrough and a second position blocking said opening, second means for biasing said closure to its second position, a valve member in said vacuum line movable between a first position unblocking said line wherein vacuum is present in said line at said receive chamber, and a second position blocking said line wherein vacuum is not present in said line at said receive chamber, a pressure line communicating with said transmit chamber, a blower having an air inlet and an air outlet connected to said vacuum and pressure lines, respectively, said blower being inoperative to produce pressure in said pressUre line when said vacuum line is unblocked, and means interconnecting said closure and valve member to position said valve member in its blocking position when said closure is in its unblocking position in response to insertion of a carrier in said opening for terminating vacuum in said vacuum line at said receive chamber and enabling said first bias means to return said flap to its normal position unblocking said vacuum line, said inter-connecting means being further operative to position said valve member in its unblocking position when said closure returns to its blocking position when said closure returns to its blocking position following insertion of a carrier through said opening for enabling said blower to apply pressure to said transmit chamber to transmit said inserted carrier.

6. A combined transmit and receive terminal for use with a pneumatically transported carrier, comprising: a receiver having a receive chamber configured to contain a carrier received therein from a distant station via a pneumatic receive tube communicating therewith, a vacuum line communicating with said receive chamber, a flap in said receive chamber underlying a received carrier located therein, said flap being movable between a first position in which said vacuum line is unblocked at said receive chamber and a second position in which said vacuum line is blocked at said receive chamber, first means for biasing said flap to its first position to unblock said vacuum line prior to receipt of a carrier in said receive chamber atop said flap, said biasing means being inoperative to prevent said flap from moving to its vacuum line blocking position upon receipt of a carrier in said chamber atop said flap, said biasing means being further inoperative to return said flap to its unblocking position from its blocking position in the presence of vacuum in said vacuum line at said receive chamber, a transmitter having a pneumatic transmission tube provided with a mouth into which a carrier can be inserted for transmission to a distant station when pressure is applied to said mouth, a pressure line to apply pressure to said mouth, a valve member in said vacuum line movable between a first position unblocking said line wherein vacuum is present in said vacuum line at said receive chambeR, and a second position blocking said vacuum line wherein vacuum is not present in said vacuum line at said receive chamber, a blower having an air inlet and an outlet connected to said vacuum and pressure lines, respectively, said blower being inoperative to produce pressure in said pressure line when said vacuum line is unblocked, and actuating means to position said valve member in its blocking position in response to a carrier being inserted into said transmitter for terminating vacuum in said vacuum line at said receive chamber and enabling said first bias means to return said flap to its normal position unblocking said vacuum line, said actuating means being further operative to position said valve member in its unblocking position when said carrier has been inserted into said transmission tube for enabling said blower to apply pressure to said transmitter to transmit said inserted carrier.