Abstract: A pipe burster for cracking gas and other pipes preparatory to inserting a replacement pipe in the passage so formed. The burster comprises an elongated body tapering in the lengthwise direction and made up first and second parts 2,14 extending in said direction. The parts are connected by a transverse pivot pin 20. The first part 12 is received within the second part and carries a piston and cylinder 22 by which the parts are separable. The circumference of the body is substantially a closed curve and within the length of the first part the circumference is increased by said separation. Therefor the burster makes a clearance by said separation into which the burster can be advanced. In a modification more than one piston and cylinder is provided.

Abstract: The burster has a body in two parts 10, 12 separable by pistons 20, 22, 24 in cylinders 14, 16, 18 in the part 12. The pistons have piston rods 32, 34, 36 secured to the part 10 by screws 54. The relative rectilinear movement of the parts 10, 12 is guided by the sliding engagement between the internal cylindrical surfaces 58, 60, 62 of the rings 44 and 46 and of the cylinder 18 and the external surfaces of the piston rods 32, 34, 36. Separating movement is effected by fluid fed into the three cylinders via a passage 88 and is limited by engagement between stop surfaces 66, 68 on the part 10 and stop surfaces on the part 12. Approach movement is effected by fluid fed into two cylinders 14, 16 via a passage 90 and is limited by engagement between the inner surface 64 of the part 10 and the rings 44, 46.

Abstract: A ground boring tool known as a mole is fitted within its conical head (1) with a pneumatic-powered rotatory vibrator (8) which generates severe radial vibrations. As a result the progress of the mole through resistant ground is speeded or made possible. The mole also may be used for upgrading existing ducts with or without the destruction of an existing lining to such ducts. For destruction of existing linings elongate ridges (16) may be positioned on the surface of the cone.

Abstract: In an iris-stop arrangement for stopping-off a duct the secondary bag has a contact length with the duct of at least 0.7 times its diameter. The apparatus is such that the point where the inflation neck of the bag meets the remainder of the bag can adopt a position not substantially in front of the secondary bag support member. Thus the bag has improved functional grip on the duct and does not suffer severe flexing at the neck when it moves back to rest against the support member. Preferably the portion of the bag which contacts the duct in use is a single layer of fabric thick while the ends of the bag, which have to withstand the bag inflation pressure unsupported, are two layers thick. In this way the bag can have good performance characteristics while only needing a relatively small insertion hole in the side of the duct.