ends of the spiral sleeve 52 may be provided with an end cap 70 sealed to the spiral sleeve 52 as shown in fig7 to 9 the caps are preferably made of pe and contain an inlet 72 port and an outlet port 74 that may for example be in accordance with the u s pat no 7 168 743 or the u s patent application 2007 0018448 mentioned earlier seals such as for example u201c teflon u201d seals 78 are preferably provided between the end cap 70 and the spiral sleeve 52 and between the end cap 70 and the pipe 10 the end cap 70 preferably has a general form of a flexible split ring for fitting around the pipe 10 and secured by a connector such as for example a pvc or pe connector 76 as shown in plan view in fig1 the spiral sleeve 52 is dimensioned in diameter to form an annular chamber 80 between the pipe 10 and the spiral sleeve 52 as shown in fig1 and 12 that annular chamber 80 will typically range from 25 to 50 mm in radial extent between the outer surface of the pipe 10 and the inner surface of the spiral sleeve 52 the radial size of the annular chamber 80 will depend upon the.