GB1589042A

GB1589042A - Fluid distributor operable by alternative pressure signals

Info

Publication number: GB1589042A
Application number: GB233478A
Authority: GB
Original assignee: Martonair Ltd
Current assignee: Martonair Ltd
Priority date: 1978-01-20
Filing date: 1978-01-20
Publication date: 1981-05-07

Description

(54) FLUTD DISTRIBUTOR OPERABLE BY ALTERNATIVE PRESSURE SIGNALS (71) We, MARTONAIR LIMITED, a British Company, of St. Margaret's Road, Twickenham, Middlesex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement The invention relates to a fluid distributor operable by alternative pressure signals and of the kind including a slide movable between two extreme operational positions in each of which the slide effects the connection of fluid inlet and outlet ports of the distributor in different arrangements, the slide being movable into one or other of its operational positions by the application to the slide of an appropriate end force in response to the application to the distributor of one or other of a pair of control pressure signals.

Tn sequence circuits incorporating one or more such fluid distributors, it is possible that in some or all the phases of the cycle of a sequence circuit, the simultaneous presence of incompatible signals may result in incorrect operation of the circuit. The effect of incompatible signals can be avoided by the use of functional relays in the circuit or by using logical or graphical mathematical methods or by operating the circuit in a systematical manner by using cascade or sequential components or bi-selectors.

These devices or procedures have the disadvantage that they necessitate the introduction of auxiliary components such as relays, joints and piping of which the design.

production and assembly are relatively expensive or require highly-trained personnel to perform. An object of the invention is to provide in a fluid distributor of the foregoing kind a control means by which the slide will be operated in response to a control signal regardless of the presence of another control signal.

According to the invention, a fluid distributor of the foregoing kind has at or adjacent each end thereof a control device operable to control the movement of the slide each time either one of the control pressure signals is applied to the distributor, each control device comprising a cylinder in which a first piston is movable between extreme end positions through a distance greater than the permitted travel of the slide between its two operational positions, a piston rod extending from the first piston, a second piston freely slidable with clearance on the piston rod and of smaller crosssectional area than the first piston, one of the control pressure signals being applied to the cylinder at the end of the first piston remote from the second piston and a further fluid pressure being applied to a chamber formed between the first and second pistons, and a valve member formed on the piston rod remote from the first piston and arranged to be engaged by the second piston to form a valve, the application of the control pressure signal and the further fluid pressure together acting to urge the first piston and the second piston as a unit in the direction in which the second piston is engaged with the valve member and also engages the adjacent end of the slide, the valve remaining closed until the second piston has reached the end of its travel, the first piston continuing to move until the first piston reaches the end of its travel, thereby to open the valve when the further fluid pressure in the chamber between the pistons will communicate through the open valve with an exhaust pressure, whereby the fluid pressure in the chamber between the pistons will fall, thereby permitting the slide and the second piston to be returned on the application of the other control pressure signal to the control device at the other end of the distributor irrespective of whether or not the first control pressure signal is still being applied.

By providing this control device at each end of the distributor, it is possible to obtain a control of the distributor by which the last control pressure signal to be applied always has priority, that is it is always the most recent control pressure signal which effects a change of position of the slide. A distributor provided by this invention therefore enables sequence control circuits to be provided without the added introduction of auxiliary control components or circuits which hitherto have been necessary to prevent incorrect operation as a result of incompatible operating signals being applied simultaneously.

Other characteristics and advantages of the invention will be better understood on reading the following description of several embodiments of distributor in accordance with the invention, given by way of example, in which reference is made to the accompanying drawings, in which: Figure 1 is a longitudinal section through the first distributor which includes a slide and is provided adjacent each end of the distributor with a device for controlling the movement of the slide in accordance with The application of a priority signal to the distributor; Figure 2 is a view in partial section on an enlarged scale showing the controlling device at one extremity of the distributor shown in Figure 1;; Figure 3 is a similar sectional view as in Figure 2 but showing a second embodiment incorporating a first modification of the controlling device, and Figure 4 is a similar sectional view as in Figure 2 but showing a third embodiment incorporating a second modification of the controlling device.

Figure 1 shows a fluid distributor including a body 1 within which is fixed a sleeve 2 having annular grooves 2a therein for the passage of fluid, where the sleeve 2 includes a bore 3 in which a cylindrical slide 4 is mounted to slide thus causing various ports in the body 1 and communicating with grooves 2a in the sleeve 2 to be put into communication with one another according to the design of the distributor. Although the drawing shows a distributor having a cylindrical slide the distributor could have a slide of any other convenient type, in particular a plane or plate-like slide.

In accordance with the invention, the distributor includes at each of its extremities a controlling device which is constituted (see also Figure 2) by a body 5, Sa inserted into a respective end of the body 1 of the distributor and including a cylinder 6, 6a closed at one end by a plug 7, 7a. In each cylinder 6, 6a there is a piston 8, 8a each dividing the respective cylinder into two chambers 9 and 10 and 9a and 10a. The plugs 7, 7a are provided, respectively, with control ports 11, 11a which open into the respective chambers 9, 9a and which allow control fluid to be fed to the chambers.

These control ports may, as is well known, lead from a connecting flange. Each piston 8, 8.a has a rod 12, 12a which carries at its extremity a valve 13, 13a with a seal 14.

The valves 13, 13a are arranged to close respectively a restricting annular orifice 15.

15a defined by the clearance between the rod 12, l2a and a bore in an auxiliary piston 16, 16a free to slide on the rod 12.

12a. The piston 16, 16a which includes a seal 17 is mounted to slide in the bore 3 which extends in the body 5, 5q in such a way that the piston 16, 16a is able to slide together with the slide 4 and to come into abutment against the adacent end of the slide 4. The piston 16, 16a has a smaller cross-section than that of the piston 8, 8a.

The valve 13, 13a is itself mounted in a bore 18, 1 8a provided respectively, in the two ends of the slide 4. Vents 19, 19a are provided in the slide 4 and communicate with the bore 18, 18a and a groove in the sleeve 2 which communicates with a port in the distributor leading to atmosphere or a return to a fluid reservoir from which fluid supplied to a port 23 is derived or they may instead communicate directly with atmosphere through a port provided for that purpose. The chamber 10, 10a is supplied from a source of pressure through a conduit 20, 20a, a calibrated restricting hole 21, 21a, a conduit 22, 22rl and the port 23 which is connected to a source of compressed fluid.

In the rest position, that is in the absence of a control signal at the ports 11 and 1 la, the pistons 8, 8a are withdrawn into the rear position, that is each piston 8, 8 < is held close to the respective plug 7, 7a as shown in Figure 2, by the internal pressure in the chamber 10, 10a, as the result of a differential effect, that is by the resultant of the forces applied to the piston 8 or 8u and to the piston 16 or 16a as a result of the internal pressure within the chamber 10, lGs. As the cross-section of each piston 8 or 8a is greater than the cross-section of the piston 16 or 16a, the resultant of these forces is such that the piston assembly 8, 16 and 8a. 16a is forced to the position shown in Figure 2 in which the piston 16 or 16a comes into abutment against a shoulder 24.

24a in the body 5, 5a and the piston 8 or 8a is close to the plug 7 or 7a. It should be noted that in this state and with the chamber 9, 9a being free from pressure, the action of the force applied to the piston 8 or 8.Ir causes the respective valve 13 or 13a and its seal 14 to be applied against the seat formed by the piston 16 or 16a, thus closing the orifice 15, 15a, the respective piston 16, 16a being applied against the respective shoulder 24, 24a.

If a signal, constituted by a fluid pressure, is applied for example to the port ila, and that signal has a pressure which is the same as the fluid pressure applied to the port 23, the resultant of the forces applied to the piston 16g and the piston 8a is such that it displaces the whole of the movable assembly, constituted by the pistons 8a, 16tri and the slide 4 towards the right, that is in the direction of the port 11 (assuming that the slide 4 is not already in the extreme right position). At the end of this movement, the slide 4 comes into engagement with the piston 16 which is pushed by the slide 4 against the shoulder 24, while the piston 8n continues to move to the right and effects the opening of the valve 13a, thereby allowing fluid to pass through the annular orifice 15a.The chamber 10a is thus put into communication through the annular orifice 15a, the bore 18a and the vents 19a with the port for connection to atmosphere or for return to the fluid reservoir. Thus, at this moment, fluid circulates from the port 23 through the conduit 22a, the restricting hole 21a, the chamber lOa, the annular orifice 15,a, the vents 1 9a to the port for connection to atmosphere or for return to the fluid reservoir.The restricting hole 21a and the annular orifice 15a together determine a level of pressure in the chamber 10a which is sufficiently low to ensure that the force exerted on the piston 16a is less than that required for resisting the displacement of the slide 4 if a signal should be applied at the port 11 but is sufficiently high to ensure the return movement of the piston 8a and of the valve 13a if the signal at the port 1 ia should be removed.

If, while the pressure signal is maintained at the port lla, there is now simultaneously applied at the port 11 a signal of the same pressure, the resultant of the forces applied to the pistons 8 and 16 is such that it is greater than the force applied to the piston I óa, because the valve 13a is open and therefore the pressure in the chamber 1 On is very low.

Thus the assembly constituted by the slide 4, the piston 16 and the piston 8 moves towards the left, that is towards the port 1 la carrying with it the piston 1 6a until the latter comes into abutment against the shoulder 24a of the body 5a.

Thus the slide 4 is inverted in spite of the previous production of the pressure signal at the port 1 la and which is still being applied.

If the pressure signal at the port 1 la is removed, while the pressure signal at the port 11 is still being applied, the residual pressure of the fluid in the chamber 1 On moves the piston 8a to the left, as viewed in Figure 1, until the valve 1 3a and its seal 14 come into engagement with the seat on the piston 1 6a and thus the annular orifice 15a for connection to atmosphere or for return to the reservoir is closed.

The pressure in the chamber 10a then returns to its normal value but the slide 4 does not move and remains in its same state because no force sufficient to displace it is present. Also the valve 13 is in the open position and the pressure in the chamber 10 is at its low level.

If a pressure signal is then applied to the port lla, the resultant of the forces produced by the pressure applied to the two faces of the piston 8a through the chambers 9a and 10n and to the piston 16a through the chamber 10n again becomes greater than the opposite force applied to the slide 4. At the other end of the slide 4, the valve 13 is open and the pressure in the chamber 10 is at its low level. Because of this, the movable assembly constituted by the piston 8a, the piston 16a and the slide 4 is moved towards the port 11 until the piston 16 comes into engagement with the right-hand end of the housing at shoulder 24.

It can be seen that, as a consequence of the foregoing operation, each time a control signal applied to the port 11 or 1 la changes from the state "0" to the state "1" which could for example be from "off" to "on", the control devices effect the displacement of the slide 4 of the distributor irrespective of the state "0" or "1" of the control signal applied to the opposite port 11 a or 11 respectively.

Figure 3 illustrates a second embodiment in which the annular orifice 15 or 15a need not be a restrictor and instead may allow a complete depressurising of the chamber 10 when the valve 13 is open. Instead of or additionally to a restricting orifice a helical spring 25 is positioned within the chamber 10 or IOn and acts between the body 5 or 5a and the adjacent face of the piston 8 or 8a, to ensure the return of the piston 8 or 8a towards the respective end plug 7, 7a.

Instead of the helical spring 25, another resilient member acting betwen the piston 8, 8a and the plug 7, 7a may be provided.

Figure 4 illustrates a third embodiment in which the annular orifice 15 is not a restrictor. Instead there is a partition 26 provided between the pistons 8 and 16, thereby creating a chamber 27 in communication with the chamber 10 through a restricting annular passage 28 defined between the rod 12 and the partition 26. As the annular orifice 15 is not a restrictor it allows, when open, the complete release of pressure in the chamber 27 producing a nil pressure therein, while the restricting annular passage 28 maintains while the valve 13 is open, a pressure in the charnber 10 which is greater than in the case of the first embodiment of Figures 1 and 2. The return of the piston 8 is more positive in the case of the embodiment shown in Figure 4. A similar arrangement between the bore 1 8a and the chamber 10a is provided at the left-hand end of the distributor.

In the three illustrated embodiments, the pressure signals at ports 11 and ila may be applied by any convenient means. For example, electro-magnetic pilot valves may be employed.

WHAT WE CLAIM IS: 1. A fluid distributor of the kind described having at or adjacent each end thereof a control device operable to control the movement of the slide each time either one of the control pressure signals is applied to the distributor, each control device comprising a cylinder in which a first piston is movable between extreme end positions through a distance greater than the permitted travel of the slide between its two operational positions, a piston rod extending from the first piston, a second piston freely slidable with clearance on the piston rod and of smaller cross-sectional area than the first piston, one of the control pressure signals being applied to the cylinder at the end of the first piston remote from the second piston and a further fluid pressure being applied to a chamber formed between the first and second pistons, and a valve member formed on the piston rod remote from the first piston and arranged to be engaged by the second piston to form a valve, the application of the control pressure signal and the further fluid pressure together acting to urge the first piston and the second piston as a unit in the direction in which the second piston is engaged with the valve member and also engages the adjacent end of the slide, the valve remaining closed until the second piston has reached the end of its travel, the first piston continuing to move until the first piston reaches the end of its travel, thereby to open the valve when the further fluid pressure in the chamber between the pistons will communicate through th open valve with an exhaust pressure, whereby the fluid pressure in the chamber between the pistons will fall, thereby permitting the slide and the second piston to be returned on the application of the other control pressure signal to the control device at the other end of the distributor irrespective of whether or not the first control pressure signal is still being applied.

2. A fluid distributor as claimed in Claim 1 in which the further fluid pressure applied to the chamber defined between the first and second pistons of each control device is derived from a compressed fluid source through a restricting orifice.

3. A fluid distributor as claimed in Claim 2 in which the compressed fluid source is common to the control device at both ends of the distributor and is arranged to be applied continuously when the distributor is operative.

4. A fluid distributor as claimed in any one of Claims 1 to 3 in which the clearance between the second piston and the piston rod in each control device defines a restricting annular orifice.

5. A fluid distributor as claimed in any preceding claim in which a spring or other resilient member acts betwen the first piston and a fixed part of the cylinder in each control device to urge the first piston in the outward direction with respect to the slide.

6. A fluid distributor as claimed in any one of Claims 1 to 3 in which in each control device there is a partition dividing the chamber between the first and second pistons into two parts, through which partition the piston rod passes with clearance, the clearance between the piston rod and the partition defining an annular restriction passage.

7. A fluid distributor constructed and arranged substantially as described herein with reference to Figures 1 and 2 or Figures 1 and 2 as modified by Figure 3 or Figure 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. be applied by any convenient means. For example, electro-magnetic pilot valves may be employed. WHAT WE CLAIM IS:

1. A fluid distributor of the kind described having at or adjacent each end thereof a control device operable to control the movement of the slide each time either one of the control pressure signals is applied to the distributor, each control device comprising a cylinder in which a first piston is movable between extreme end positions through a distance greater than the permitted travel of the slide between its two operational positions, a piston rod extending from the first piston, a second piston freely slidable with clearance on the piston rod and of smaller cross-sectional area than the first piston, one of the control pressure signals being applied to the cylinder at the end of the first piston remote from the second piston and a further fluid pressure being applied to a chamber formed between the first and second pistons, and a valve member formed on the piston rod remote from the first piston and arranged to be engaged by the second piston to form a valve, the application of the control pressure signal and the further fluid pressure together acting to urge the first piston and the second piston as a unit in the direction in which the second piston is engaged with the valve member and also engages the adjacent end of the slide, the valve remaining closed until the second piston has reached the end of its travel, the first piston continuing to move until the first piston reaches the end of its travel, thereby to open the valve when the further fluid pressure in the chamber between the pistons will communicate through th open valve with an exhaust pressure, whereby the fluid pressure in the chamber between the pistons will fall, thereby permitting the slide and the second piston to be returned on the application of the other control pressure signal to the control device at the other end of the distributor irrespective of whether or not the first control pressure signal is still being applied.