Iris-Stop is a method of carrying out flowstopping operation to facilitate maintenance or repair to distribution networks, whilst maintaining continuity of supply.
Developed by British Gas, Iris-Stop has been fully tested and in constant use since its introduction in 1972 and has proved itself in use to be safe, quick and economic.
Iris Stop is a technique for safe and reliable flowstopping of 100-1,200 mm (4”-48”) diameter live gas mains operating at pressures up to 2.0 bar (30 psi). The system has been proven in regular use for more than 30 years.
Iris Stop is based on the combination of structured barriers associated with high pressure pipeline working and small hole principle associated with low-pressure bagging-off operations. The “Iris” is a mechanically operated shutter, which is inserted through a small hole in the main and opened, providing the structural barrier across the pipe cross-section.
The seal is created by inserting a bag through a similar small hole, positioned on the pressure side of the Iris.
A secondary seal is provided by a semi-supported bag (E20A) (see flowstop bags) which is inserted gas-free using an ALH bagtube.
Once the operation has been completed, the equipment is removed and the small holes in the pipe are plugged using ALH non-tap-plugs.