Service Connections for PVC Pipes
Only tapping saddles complying with AS/NZS 4793 – Mechanical tapping bands for waterworks purposes – and designed for use with PVC pipe should be used. These saddles should:
- Be contoured to fit around the pipe, have an “O” or “V” seal and not have lugs or sharp edges that dig in; and
- Have a positive stop to avoid overtightening of the saddle around the pipe.
Tapping saddles, which employ U-bolt fastenings, are not suitable for PVC pipes. Tapping clamps with full face flat gaskets have no diameter control and the high force required to seal may crush the pipe. Plastic and reinforced plastic units should be used only with specific recommendation from the supplier that they have been tested for use with the pipe material.
Local authority requirements for the maximum hole size that should be drilled in a PVC pipe for tapping purposes should be followed. A good rule of thumb is 50 mm, or 1/3 the pipe diameter, whichever is smaller. This does not prevent the connection of larger branch lines via tapping saddles, provided the hole size does not exceed the above requirements and the hydraulic loss through the restricted hole size is acceptable.
It is also recommended that holes should not be drilled into PVC pipe:
- Less than 300 mm from a spigot end;
- Closer than 500 mm to another hole on a common parallel line; or
- Where significant bending stress is applied to the pipe. Curved PVC pipes may be tapped, provided that the curve radius is not greater than 300 x DN.
For larger branches a tee is cut-in or an under-pressure cut-in using a flanged offtake clamp made (see below).
Various tools are available to allow live tapping of a line using a specially adapted tapping band.
The tapping band should be fitted to the pipe and correctly tightened, paying particular attention to the manufacturer’s recommended bolting torque. A specially adapted main cock for live tapping should be fitted to the tapping saddle using PTFE tape and a drilling machine fitted with a “shell” cutter or hole saw. The hole is drilled and the tapping flushed. The hole saw is then withdrawn and the main cock sealed. The tapping machine is removed along with the hole cut-out and the main cock plunger or cap is then fitted.
The procedure is the same as above except that the hole can be drilled before the main cock is fitted. It is also possible to dry tap using a twist drill with razor sharp cutting edges ground to an angle of 80°. Removal of the swarf, however, is more difficult and wherever possible the use of a hole saw is recommended.
Note: A spade bit is not suitable for drilling PVC pipes.
Vinidex does not recommend direct tapping (threading of the pipe wall) for PVC pressure lines.
Flanged Offtake Clamps
Under-pressure cut-in connections to existing PVC pipelines can be made using a flanged offtake clamp and a flanged valve. Using this technique, cut-ins up to and including the size of the host pipe can be achieved. A flanged offtake clamp is attached to the host pipe and a flanged valve installed. A hole is drilled through the valve using specialised equipment. Once the drilling equipment is withdrawn, the valve is closed and the new pipework connected up to the valve. Note that this is a specialised procedure to be undertaken by suitably trained personnel using Water Agency Guidelines and not to be confused with normal under-pressure tapping for providing property service connections.
For the Vinidex range of Service Connections for PVC pipes, please view our Associated Pipeline Components products.