When repairing an old sewer system, sometimes it becomes necessary to connect pipes made of cast iron and plastic. If the docking is done incorrectly, the tightness will be broken. The pipeline will begin to leak as the linear expansion rates of these materials differ.
Connection of a cast-iron sewer pipe with a plastic
Preparatory stage
First of all, prepare your workplace and select the right tools and consumables. Some of them are necessary for any connection method, but some depend on the connection method. It is necessary to think over the technology in advance.
To carry out the work you will need:
- plastic pipe of the required size;
- adjustable wrench;
- grinder or hacksaw for metal;
- mallet.
Depending on which joining method is selected, a hand press, thread cutter, or welding machine may be required. You should also select the elements for the connection: fittings, adapters, rubber seals.
When drawing up a diagram of a new wiring, do not forget to include inspection hatches in the project. They will make it easier to diagnose the system in the event of blockages and other problems. It should also be borne in mind that for a riser with a diameter of 110 mm, the best option would be to use pipes with a cross section of 50 mm.
Dismantling the old pipe
The joints of the old highways were sealed with tow and cement mortar. First you need to carefully remove all insulating materials, and then try to remove the pipe from the joint.
It is necessary to disconnect the pipes by scrolling, and in no case by swinging.
You can carefully use a mallet, but not a metal hammer, which can split cast iron. If there is a possibility of damage to the socket during undocking, you can carefully cut it with a cutting machine.
After making a cut in the cast iron pipe, do not try to break it off. The break will be uneven and you will have to cut again. It is best to make a cut around the entire circumference of the pipe.
Methods for joining plastic and cast iron pipelines
Methods for joining cast-iron and plastic lines:
- flanged;
- fitting;
- using rubber gaskets;
- caulking tow or sanitary flax;
- silicone sealing.
The latter method is used if the condition of the cast-iron section is good, and when a plastic product is inserted into it, a gap of less than 2 mm remains. The end of the cast-iron main is thoroughly cleaned and dried with a construction hairdryer. The connecting part of the polymer pipe is wrapped with plumbing thread and installed in the socket to a depth of 8–10 mm. The slots are filled with silicone sealant.
Until the silicone is completely dry, no impact on the joint is allowed. Curing takes about 5 hours, but it is better to start the system 24 hours after sealing.
Flanged method
The nuances of installing a flange connection:
- a strong docking can be achieved using a straight shoulder with a tapered transition;
- for highways with a cross section of more than 200 mm, take a free flange supported on a conical shoulder;
- for light pipes with a cross section of up to 150 mm from any materials and heavy polymer products of the same diameter, free flanges are used, supported on a free shoulder.
Before joining, cut the cast iron as evenly as possible in the area where the joint is planned. Put a loose flange with a rubber gasket on the edge with an overlap of no more than a centimeter. Then slide the flange piece onto the seal and secure with the bolts, tightening them evenly.
Fittings application
The connection of cast-iron and plastic sewer pipes using crimped or cast fittings is used if the cross-section of the products is not more than 110 mm. A molded PVC fitting with a thread on one end and a socket for connecting a plastic pipe on the other is preferable if the end had to be cut off on cast iron.
To create a transition, clean the cast iron from dirt and paint and cut a thread on it 30-50 mm. Re-clean from dust and metal filings and shavings, wind several turns of FUM tape or flax. Screw on the fitting and insert the end of the length of pipe into the collar.
If a cast threadless product is used, first an O-ring is installed into the socket, fixing it with special glue, and then a narrow fitting pipe is inserted into it.
You can also use crimp fittings that have a special split crimp ring. It avoids rapid failure of the connecting element and the appearance of leaks in the sewer pipes.
Application of rubber gaskets
The transition from a cast-iron sewer to a plastic pipe using a similar method is carried out if, after the elimination of the defective part of the old sewage system, there is an undamaged area with an even bell. First, a rubber cuff is installed, and then a piece of plastic is inserted into a cast-iron pipe to a depth of 5–8 cm.
Sometimes it happens that there is no required socket on the remaining section of the cast-iron pipe. In this case, an adapter is used. It is necessary to act as follows:
- Cast iron is thoroughly cleaned of dirt and rust, then dried, and a layer of sealing compound is applied to the inner part.
- The outer surface of the adapter is also coated with sealant and inserted into cast iron.
- Insert the end of the plastic pipe into the free end of the adapter until it stops.
At the end of the work, all joints must be additionally treated with a sealing compound.
Press-in technique
- In the place where the connection is supposed to be made, several layers of sealing material are wound around the end of the plastic pipe.
- The pipe is inserted all the way into the cast-iron bell.
- With a wide minus screwdriver or a narrow spatula, the winding is tamped tightly into the gap between the pipes to be joined.
- A mixture of cement, PVA glue and water is applied several times to the junction of cast iron with plastic.
After a day, the mixture is set, and you can start using the new pipeline. Such a connection of waste pipes has a limitation in terms of operating time up to 12 months. After this period, everything will have to be redone again or a more reliable pipeline installed.
With the right choice of joining technique and high-quality materials, a hybrid of old and new sewers will last for many years.
