As we have already mentioned, the concept of expansion tubes is important for a sustainable heating network, and this concept requires a fixed point. What are the characteristics and advantages of a fixed point?
What is it ?
The steel in the pipes of a heating network expands when it comes into contact with the hot water – the temperature can reach 109 ° C – that it is conveying. A straight pipe section expands at each of its ends. There is, therefore, a stationary section located at the centre of a straight section , known as a natural fixed point. This is a very important concept for the design of networks. Indeed, in some very specific cases, we may need to move the natural fixed point to artificially recreate it elsewhere. These cases arise at the specific request of the customer, in order to limit the expansion at the entry of substations or when the congested site does not enable a deflection arm of sufficient length to be installed to clear the movement.
The installation of a fixed point
This fixed or anchor point is a characteristic tube equipped section of a bearing surface. It is connected to the main pipe of the heating network. The assembly is then cast in a block of reinforced concrete, which makes it integral with this weight. After checking the block resistance, everything is covered with soil compacted before the commissioning of the pipeline. It should also keep in mind that to move a fixed point creates an imbalance at the other end and that the length of each deflection arm must be recalculated according to the constraint.
One particular, important constraint
The installation of an artificial fixed point can control the expansion movements. However, it also involves several constraints: the concrete block installed to solidify the installation weighs several tons; the whole of the drying time is 21 days; the cost of the book is important; the ring must be protected by a dielectric coating to prevent corrosion and the facility limit future work on the network.
Because of these drawbacks, equipping a heat network from a fixed point is recommended only in rare cases – when the customer requires. If this is not essential, it is best preferred installation lyre or bayonets which dissipate the movement naturally lever arm.
