GB1568671A

GB1568671A - Pneumatically operated tools

Info

Publication number: GB1568671A
Application number: GB3401576A
Authority: GB
Original assignee: BURTON I; Compair Industrial Ltd
Current assignee: BURTON I; Compair Industrial Ltd
Priority date: 1977-07-25
Filing date: 1977-07-25
Publication date: 1980-06-04

Description

(54) IMPROVEMENTS IN OR RELATING TO PNEUMATICALLY OPERATED TOOLS (71) We, COMPAIR INDUSTRIAL LIMiTED, a British Company, of P.O. Box 7, Broonwade Works, High Wycombe, Buckinghamshire, HP13 5SF and IAN STUART BURTON, a British Subject, of 23 Willoughby's Walk, Downley Heights, High Wycombe, Buckinghamshire, do hereby dedare the invention, for which we pray that a petent 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 pneumatically operated tools and provides a pneumatically operated tool of the kind comprising a reversible air motor having two inlet ports, an inlet passage for supplying compressed air to one of the inlet ports of the motor, an exhaust passage from the motor, manually operable first valve means normally urged into a position closing off the inlet passage and operable to open the inlet passage to supply air to the motor and a reversing valve for selectively connecting the inlet passage to one or other of the inlet ports, in which a second valve means is provided in a valve member of the reversing valve in fluid communication with the inletpassage between the first valve means and the inlet ports of the motor, said second valve means being operable to relieve the pressure in the part of the inlet passage between the first valve means and the inlet ports of the motor if said pressure rises above a predetermined maximum value.

The second valve means may be operable to connect the inlet passage to atmosphere or to the exhaust passage.

Preferably the second valve means is a ball-valve which is spring urged into a closed position.

A A preferred embodiment of a pneumati- cally operated tool according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which : - Figure 1 is a. section through a pneumatically operated tool according to the invention; Figure 2 is an enlarged end view of the reversing valve of the tool, looking in the direction of arrows 2-2 in Figure 1; Figure 3 is a section along the line 3-3 of Figure 2; and Figure 4 is a section along the line 44 of Figure 3.

Referring first to Figure 1, a pneumatically operated tool 10 is of the pistol type and comprises a body portion 11 and a pistol-grip handle 12. A reversible air motor 14 is located within the body portion of the tool and drives, in use an output shaft supporting an attachment (not shown) such as a screwdriver blade via an epicyclic gear box (not shown) located in housing 15.

Compressed air is supplied to the air motor 14 through a supply passage 17 in the handle 12 and exhaust air from the motor is discharged to atmosphere through an exhaust passage 18 in the handle. A filter 20 is provided in the supply passage and silencer elements 21 are located in the exhaust passage to reduce the noise level of the tool in operation.

A first trigger valve 22 is normally urged by air pressure into a first position closing off the supply passage 17 and is movable by finger pressure on a trigger 24 into a second position in which air is supplied to the motor via passages to be described below.

The above described parts of the air tool 10 are all well known in the art and are the main parts of a conventional reversible air tool with a pistol grip.

The system of passages etc. formed in the air tool 10 for the supply and return of air between the first valve 22 and the air motor 14 and means for controlling this supply will now be described with particular reference to Figures 2, 3 and 4.

An inlet passage 25 connects the supply side of valve 22 to a passageway 26 formed in the body 27 of a reversing valve which determines whether the air supplied to the motor causes forward or reverse rotation.

Passage 26 is in communication with a first motor inlet port 29a and thence with a working space 30 of the air motor 14.

In use, when the trigger 24 is operated, compressed air from the supply passage 17 enters through inlet passage 25, passes via passageway 26 into the motor inlet port 29a and thence into the motor working space 30.

Exhaust air from the outlet or exhaust side of the motor 14 is collected in chamber 32 and passes via passage 33 to the exhaust passage 18 and thence to atmosphere.

A passage 35 leads from passageway 26 and a second valve means 36 closes off passage 35. The second valve 36 consists of a ball valve member 37 resiliently urged by a coil spring 38 into a closed position.

A chamber 40 in communication with passage 35 is connected to a space 41 by ports 42a, 42b and passageways 43a, 43b formed in the valve body 27. A passage 45 connects space 41 to the exhaust chamber 32, so that the exhaust chamber 32 is in communication with chamber 40. Thus scavenge air from the exhaust chamber acts on the ball valve member 37 in addition to spring 38 to tend to close the second valve 36.

An extension of passageway 43b connects space 41 to a second inlet port 29b of the air motor so that scavenge air is also fed from the inlet port 29b via passage 45, chamber 32 and exhaust 18 to atmosphere.

The assembly comprising the reversing valve and ball valve as described above is located at the rear - of the body portion 11 of the air tool as shown in Figure 1. A reversing knob 47 comprising a domed member with a cylindrical bore 48 fits over a part of the reversing valve body 27 which protrudes from the body of the tool. The reversing knob is operable (in known manner) to rotate the reversing valve assembly between the position illustrated and a second position to be described below.

In use, when the trigger 24 is moved to the right as viewed in Figure 1, compressed air is supplied to the motor as described above and the output attachment of the tool starts to rotate. Air tools are inherently greedy when running free and thus when the tool is running free (that is with no load on the output attachment), the pressure in the passageways 25, 26 and 29 and 29 rises towards the supply pressure. As load on the output shaft increases (for example, as torque is supplied to a screw), the motor slows down and thus uses less air so that the pressure in inlet passage 25, 26 and 29 ries towards the supply pressure.As this pressure rises the force exerted on the left-hand side of the ball valve member 37 (as viewed in Figures 1 and 3) increases and at a predetermined value of this pressure (corresponding to a given output tor que), the force on the ball exceeds the force exerted by the spring 38 and exhaust air and the ball 37 is moved from its seat (to the right in Figures 1 and 3). Air is then dumped from passage 26 to chamber 40 and thence to exhaust via the passages and chambers described above. This ensures that the pressure at the motor inlet is kept at a fixed level and any excess pressure is dumped to exhaust.

This dumped air is connected to the exhaust chamber for convenience since it thus passes through the exhaust passage 18 and is silenced before emerging into the atmosphere. The dumped air represents only a fraction of the air fed to the motor but this is enough to bring about motor stall.

The above description and drawings show the air tool 10 arranged for reverse rotation. To operate in the forward direction, the knob 47 is manually rotated, to the second position referred to above, to rotate the reversing valve assembly so that the inlet passage 26 communicates with inlet port 29b (instead of 29a). The scavenge air passage 43a then communicates with the now spare inlet port 29a and the scavenge air passage 43b is isolated from inlet passage 29b. The other passages and chambers described above remain in communication in the way described and the device operates in precisely the same manner as described above. Thus, the output torque of the air tool is controlled during either forward or reverse rotation.

It will be realised that the invention is not limited to the preferred embodiment described above and various modifications may be made. For instance, the spring load on the pressure release valve 36 may be varied to vary the output torque characteristics of the tool.

Moreover, the air dumped from the pressure release valve need not be dumped to the exhaust chamber and may pass directly into the atmosphere.

The devices described above thus provide air tools in which the output torque is controlled accurately and by a simple means. In the past such control has often been achieved by clutches and these have many disadvantages in that they are noisy, heavy, relatively bulky, of limited working life, difficult to manufacture and prone to vibration. The pressure release valve described above has none of these disadvantages.

Attempts have also been made to control air tools by providing means to shut off the air supply under certain conditions.

Such devices are however usually complicated and lack versatility. The pressure relief valve described above may be incor porated in air tools which operate in any given pressure range.

WHAT WE CLAIM IS: - 1. A pneumatically operated tool of the kind comprising a reversible air motor having two inlet ports, an inlet passage for supplying compressed air to one of the inlet ports of the motor, an exhaust passage from the motor, manually operable first valve means normally urged into a position closing off the inlet passage and operable to open the inlet passage to supply air to the motor, and a reversing valve for selectively connecting the inlet passage to one or the other of the inlet ports, in which a second valve means is provided in a valve member of the reversing valve in fluid communication with the inlet passage between the first valve means and the inlet ports of the motor, said second valve means being operable to relieve the pressure in the part of the inlet passage between the first valve means and the inlet ports of the motor if said pressure rises above a predetermined maximum value.

2. A tool as claimed in claim 1 in which the second valve means is operable to connect the inlet passage to atmosphere.

3. A tool as claimed in claim 1 in which the second valve means is operable to connect the inlet passage to the exhaust passage.

4. A tool as claimed in any one of the preceding claims in which the second valve means comprises a ball valve spring urged into a closed position.

5. A tool as claimed in claim 4 when dependent on claim 3 in which the ball valve is located in a duct formed in the valve member of the reversing valve and seats on a valve seat formed by a restriction in the duct, one end of the duct communicating with the inlet passage and the other end of the duct communication with the exhaust passage.

6. A tool as claimed in claim 5 in which silencer elements are located in the exhaust passage downstream of the part of the exhaust passage with which the duct communicates.

7. A pneumatically operated tool substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. porated in air tools which operate in any given pressure range. WHAT WE CLAIM IS: -

1. A pneumatically operated tool of the kind comprising a reversible air motor having two inlet ports, an inlet passage for supplying compressed air to one of the inlet ports of the motor, an exhaust passage from the motor, manually operable first valve means normally urged into a position closing off the inlet passage and operable to open the inlet passage to supply air to the motor, and a reversing valve for selectively connecting the inlet passage to one or the other of the inlet ports, in which a second valve means is provided in a valve member of the reversing valve in fluid communication with the inlet passage between the first valve means and the inlet ports of the motor, said second valve means being operable to relieve the pressure in the part of the inlet passage between the first valve means and the inlet ports of the motor if said pressure rises above a predetermined maximum value.