История создания первого трубного захвата BREWIS
The Standard Towing Head was invented by Rod Brewis on 27th September 1984 as a result of a conversation about a contractor who had been seen trying to dead insert 63mm PE pipe into an old cast iron main.
Disillusioned with the timber hitch in the winch cable on his JCB slipping off the PE half way through his pull, he resorted to using a length of fencing wire slipped through the flow holes of a Brewis Live Head (above right), knotted and attached to the winch hook. Although the Live Head was held in the PE only by the friction and wedging action of expanded "O" rings, there was sufficient grip to pull in fifty metres or more of pipe. "What they need is something like a live head but with much more grip" was the simple statement which resulted in the product which has become an icon in the No-Dig industry.
The use of "O" rings to retain the grippers, the tooth profile, the configuration and manner of operation, and even its name have all been adopted as the industry standard. Its design is such that it will grip a range of wall thicknesses ( normally SDR11 to SDR17.6 in Europe ) but it is neither pressure tight nor mud tight. Available in sizes up to a metre in diameter, the Brewis Standard Towing Head has been the workhorse of the industry for the last nineteen years.
The Pressure Tight Towing Head
In the mid eighties British Gas decreed that all polyethylene pipe had to be pressure tested after installation to ensure that it had not been damaged in the process. The Pressure Tight Towing Head was quickly developed as an effective means of both pulling in the PE and of plugging the end. Used in conjunction with the Brewis Pressure Test End, it enabled the safe pressure testing of PE, even if inadvertently connected to an un-regulated site compressor. Sealing is effected on the inside of the PE by means of an expanding "O" ring and, for this reason, a dedicated Towing Head and test end is necessary for each wall thickness.
The Directional Drilling Towing Head As directional drilling became increasingly used for the installation of PE, it became obvious that the ingress of Bentonite into the PE was a problem, and a thriving industry in foam pigs developed. As it is far more logical to keep the bentonite out than to flush and pig it out afterwards, the Directional Drilling Towing Head was developed to seal the front of the pipe during pull-back.
The outside diameter of the PE is closely controlled in production and the manufacturing tolerance is on the wall thickness. This, together with the range of SDRs available means that, from a designers perspective, it is simpler to seal on the outside of the PE than on the inside. However, the resultant product, although it worked well and excluded bentonite, was not well liked by the drillers. The outside sleeve was, on larger sizes, considerably bigger in diameter than the PE, necessitating bigger back reamers, and the sealing mechanism incorporated external threads which seized if the unit was not cleaned and maintained regularly.
The Mudtight Gold Towing Head
Two occurrences triggered the invention of this product. Firstly, the increase in interest of Transco in the use of directional drilling to install new pipelines and its determination to exclude bentonite. No amount of flushing and pigging will remove all traces of clay dust from the walls of the pipe which "dusts" with the passage of gas. The minute particles clog the 15 micron filters in the transmission system which then require increased levels of cleaning to avoid unexpected disruption of supply. Secondly, the drive in the water industry to improve drinking water quality coupled with the use of pre-chlorinated pipe. There is no sense in using pre-chlorinated pipe if it is then contaminated with bentonite or ground water.
The Pressure Tight Towing Head had been used over the years to prevent ingress but it was only partially successful as it was designed to keep air in rather than mud out. It was also expensive as each size accommodated only one SDR of pipe, unpopular with contractors, who resorted to using Standard Towing Heads and a roll of Duck Tape.
It was in 2000, sixteen years after the invention of the Standard Towing Head that the problem of how to seal on the inside of the pipe, accommodate a range of wall thicknesses, and keep the outside of the unit to a minimum was finally solved. Mudtight Gold has the essentials of any towing head in the form of grippers, expander, and nose but it also incorporates a very slim outside sleeve to restrain the PE and, critically, a patented reversible cartridge. The reversible cartridge comprises three steel components and two sealing rings of different diameter. One end of the cartridge seals in one wall thickness (or range) of pipe whilst the other seals in a rebate in the nose. When the cartridge is reversed and the unit re-assembled, the second end seals in a second wall thickness (or range) of pipe whilst the first end seals in a second rebate in the nose.
In Europe, Mudtight Gold is available in sizes from 32mm up to 500mm diameter and normally seals on SDR 11 to 17.6. For the American market, it is available in IPS sizes from 1" to 12". There are up to eight wall thickness ( SDR 9.33 to SDR 33.5 ) for each size of pipe, all of which are accommodated by the reversible cartridge.
By replacing the eyebolt with a threaded hollow stem fitted with a ball valve, Mudtight Gold may be converted from a sealed towing head into a Pressure Test End, as shown in one of the attached photographs. In each configuration, Mudtight Gold will accommodate at least two wall thicknesses of pipe, thus effectively giving the purchaser four products for the price of one.