GB2200185A

GB2200185A - Pneumatic percussive device

Info

Publication number: GB2200185A
Application number: GB08710872A
Authority: GB
Inventors: Jeremy Derek Fuller; Brian Aurther Robbins
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-05-09
Filing date: 1987-05-08
Publication date: 1988-07-27
Anticipated expiration: 2007-05-08
Also published as: GB8710872D0; GB2200185B; GB8611289D0

Abstract

A Pneumatic Percussive Device for use typically in pipe installation or replacement systems, ground boring and piling comprises a piston (111) within a tubular casing (11) in which air is fed to and exhausted from the chambers at both ends of the piston in controlled amounts without the use of portholes in the piston. Such control being achieved by a system of valves (vii, viii) caused to open and close either on a time based operating cycle and/or through the use of piston position sensors. In pipe replacement operations the device may be fitted with sensors to monitor the relative position of the pipe, the latter not being connected to the device. <IMAGE>

Description

PERCUSSIVE PNEUMATIC APPARATUS FOR THE INSTALLATION AND REPLACEMENT OF PIPES UNDERGROUND.

This invention relates to a percussive pneumatic apparatus for use in the installation or replacement of pipes underground.

Pneumatic percussive devices are known (eg. British Patent No.1,179,167) whereby a piston is made to reciprocate within a cylindrical housing by means of compressed air being fed alternately to chambers at either end of the piston through a system of port holes in the piston. A major disadvantage of such devices is that air is fed into the front chamber before impact causing the piston to decelerate before impact, thus reducing the power generated by the impact.

It is further known that one use for such devices, known in the art as "moles", is in the replacement of existing underground pipework as for example British Patent Specification No.2,092,701A.

Existing moles are designed primarily as devices for driving holes in the ground and are built in the shape of a long cylinder to enable them to maintain a straight bore through the ground.

Such length and weight is a disadvantage in pipe replacement operations where often it is difficult to handle them in the confined spaces of small access pits or manholes.

Without side wall friction from the ground around them to counter the reaction of air pressure on the piston, existing moles become erratic and unreliable in operation. Commonly in pipe replacement operations, a towing winch attached to the front of the mole is used to simulate the ground friction effect but they still lack the essential requirement of reliable and positive means of starting and stopping them, particularly when they are being operated with long air supply lines. Existing moles are also unreliable when submerged which is a situation often encountered in pipe replacement operations.

Because of the inefficient use of compressed air inherant in the basic design of existing moles it is necessary to use much larger compressors and air supply lines than is desirable for pipe replacement operations.

In pipe replacement operations there is the need to co-ordinate the progress of the mole with that of the pipe being inserted behind it so that mole/pipe seperation cannot occur. Commonly this is achieved by physically attaching the pipe to the mole, but this reduces the effective power of the mole to break the existing pipe and spread the ground, and can cause damage to the new pipe, thus limiting the type of pipe that can be used, and the method of inserting it. It is preferable, therefore, that the power and rate of stroke of the mole should be variably controlable to enable co-ordination without physical connection of the mole and pipe.

The new invention seeks to remedy all these defects in existing moles by providing a means of causing the piston to reciprocate without using port holes in the piston. Instead air is fed to and exhausted from the chambers at both ends of the piston in controlled amounts, with control being achieved by a system of valves caused to open and close either on a time based operating cycle and/or through the use of piston position sensors. It is possible to create such a system by mechanical means, for example by using a rotating cam shaft, but the preferred embodiment is to use an electronically controlled, pneumatically actuated system as described below.

Reference is made to Figures 1.

Figure 1 is a schematic representation of the new device in which a piston (1) is movable within a sealed casing (2). At either end of the piston is a chamber (3) & (4) into which air may be fed and exhausted through air lines (5) & (6) which are connected to the air valve assembly (7). Compressed air is fed to the air valve assembly (7) from a compressor (8) preferably by way of a pressure regulating valve (9). Air is exhausted to atmosphere from a port (10) in the valve assembly (7). A remote control device (11) may be used to control the operation of the air valve assembly (7) via a communications link (14) which may be electrical cable, ultra sonic sound, fibre optics, radio control, infra red, or other suitable medium.

The valve assembly (7), typically contains one or more air valves (12) & (13) which control air to each of the air chambers (3) & BR< (4). A timing device within the remote control unit (11) controls the operation of the air valves (12) & (13). Typically the valves are controlled in, but not limited to the following #equence:- Step (a) Vent (12) Vent (13) stop position Step (b) Vent (12) Open (13) forward stroke Step (c) Open (12) Vent (13) rearward stroke Step. (d) Vent (12) Vent (13) stop position For multiple strokes of the piston steps (b) & (c) are repeated with the timing adjusted to suit the piston movement required.

For example in forward operating mode the timing of cycle (b) would be such to ensure the piston (1) impacted the front of the sealed casing (2) while the rearward stroke would be set to ensure the piston (1) returned without striking the rear of the sealed casing (2). Reverse operation can be achieved by adjusting the timing to ensure the piston (1) impacts the rear of the sealed casing (2). Within the cycle would typically be set a delay phase so that the rate of stroke can be adjusted. The preferred embodiment incorporates a timing device within the remote control unit (15) which is electronically operated.

The valve assembly (7) in Figure 1 could be made up with only one valve (13) which would feed chamber (4) with pulsed high pressure air, the frequency of pulse being controlled by the remote control unit (11). A constant low pressure would be fed into chamber (3) to return piston (1) to the rear of casing (2). The chamber (3) could be made so that it has a smaller effective area than chamber (4) which would enable the same pressure to be used to return the piston (1) as the pulsed pressure which is used to power the piston (1) forward.

The alternative using piston position sensors requires sensors to be mounted in the sealed casing (2) in such positions that as the piston passes the sensor it triggers a response to the remote control unit (11) which then activates the air valves (12) & (13) in the sequence as defined above.

Below is a detailed description of one possible embodiment of the new device and makes reference to Figure 2.

The new device consists of a sealed casing made up of the nose (i), the outer tube (ii) and the rear plug (v). The sealed casing is held together by the central feed tube (iv) which is threaded at each end. On the central feed tube (iv) slides the piston (iii) which has sealing rings (xi) & (xii) for positive sealing.

These components make up the main part of the new device.

Fixed onto the rear plug is the valve assembly comprising an adaptor plate (vi), two valves (vii) & (viii), an inlet manifold (x), and a vented sleeve (ix).

The two valves (vii) & (viii) are solenoid operated and are controlled by a remote electronic time based control unit. The comunication link between the control unit and the valves (vii) & BR< (viii) is by electric cable.

In order to ensure that the new invention cannot seperate from the pipe in pipe replacement operations the new invention can be fitted with a system of proximity sensors to monitor the relative position of the pipe. The information from these proximity sensors would be linked into the remote control system to signal to the operator that seperation is imminent or that the pipe progress is satisfactory. The operator can then control the new invention as required. The remote control system could be made to interpret the signals from the proximity sensors and control the new invention automatically.

Because the new device has significant improvements in performance over existing moles it makes it ideal for pipe replacement operations. It also makes it suitable for all other operations that moles are traditionally used for in creating bores through the ground, driving steel tubes, piling and many other applications.

The invention is not restricted to the above described embodiments but modifications and variations may be made without departing from the scope of the invention.

Claims

CLAIMS 1) A Pneumatic Percussive Device comprising of a piston within a tubular casing in which air is fed to and exhausted from the chambers at both ends of the piston in controlled amounts. Such control being achieved by a system of valves caused to open and close either on a time based operating cycle andlor through the use of piston position sensors.
2) A Pneumatic Percussive Device comprising of a piston within a tubular casing in which air is fed to and exhausted from the chambers at both ends of the piston in controlled amounts. Such control being achieved by a system of valves caused to open and close either on a time based electronically controlled, pneumatically actuated operating cycle andlor through the use of piston position sensors.
3) A Pneumatic Percussive Device comprising of a piston within a tubular casing in which air is fed to and exhausted from the chambers at both ends of the piston in controlled amounts. Such control being achieved by a system of valves caused to open and close on a time based electronically controlled, pneumatically actuated operating cycle. In which the operating cycle can be altered for either or both frequency and characteristic.
4) Pneumatic Percussive Device comprising of a piston within a tubular casing in which air is fed to and exhausted from the chamber at one end of the piston in controlled amounts. Such control being achieved by a system of valves caused to open and close either on a time based operating cycle andlor through the use of piston position sensors. The piston being made to recipricate by a continuous air supply to the other chamber.
5) A Pneumatic Percussive Device comprising of a piston within a tubular casing in which air is fed to and exhausted from the chamber at one end of the piston in controlled amounts. Such control being achieved by a system of valves caused to open and close either on a time based electronically controlled, pneumatically actuated operating cycle and/or through the use of piston position sensors.

The piston being made to recipricate by a continuous air supply to the other chamber.
6) A Pneumatic Percussive Device comprising of a piston within a tubular casing in which air is fed to and exhausted from the chamber at one end of the piston in controlled amounts. Such control being achieved by a system of valves caused to open and close either on a time based electronically controlled, pneumatically actuated operating cycle and/or through the use of piston position sensors.

The piston being made to recipricate by a continuous air supply to the other chamber. In which the operating cycle can be altered for either or both frequency and characteristic.
7) A Pneumatic Percussive Device as described in any of claims 1 to 6 which is adapted for pipe instalation and/or replacement.
8) A Pneumatic Percussive Device as described in claim 7 which is fitted with one or more sensors to monitor the position of the pipe relative to the device.
9) A Pneumatic Percussive Device as described in claim 7 which is fitted with one or more sensors to both monitor and automatically control the position of the pipe relative to the device.
10) A Pneumatic Percussive Device substantially as described herein with reference to the accompanying drawings.