Why do we need to use rigid waterproof casing?

The superiority of rigid waterproof casing itself.
The casing through the wall. There are two kinds of rigid and flexible. After the installation is allowed to have the amount of deformation - flexible; do not allow the amount of deformation - rigid. Mainly the use of different places, flexible waterproof casing is mainly used in the human defense walls, pools and other demanding places, rigid waterproof casing is generally used in the basement and other pipelines need to wear the pipeline location.
 
The reason for choosing rigid waterproof casing.
General pool in order to prevent water leakage from the sidewalls, the water pipe through the pool are required to install waterproof casing, the side of the water stop wing ring, then the casing and the gap between the water pipe is not still leaking? Is there a rubber ring connection between the casing and the water pipe? How is this waterproof casing in construction?
 
The use of rigid waterproof casing.
Rigid waterproof casing is suitable for pipeline through the wall does not bear the pipeline vibration and expansion deformation of the building, suitable for pipeline through the wall space is limited or pipeline installation before the building or pipeline renewal and renovation. For areas with seismic requirements, such as the use of rigid waterproof casing, should be set up on the pipeline into the pool wall or building exterior wall near the flexible connection. type A for steel pipes, B,C for ductile iron steel pipes and cast iron pipes. The difference between rigid waterproof casing and flexible waterproof casing.
Rigid waterproof casing is a steel pipe plus wing ring, installed in the concrete wall, for general piping through the wall, for the waterproofing of the wall; flexible waterproof casing in addition to the external wing ring, there are internal gear ring and so on, the flange inside the wire, sold as a set, can also be processed, for the need for shock absorption pipeline, such as and pump connection of the pipeline through the wall. In other words, if you consider the waterproof performance of both sides of the wall, you should choose a flexible waterproof casing; if you just consider the pipeline through the wall, without considering the wall, the waterproof performance of both sides of the wall and the displacement of the pipeline deformation, you can choose rigid waterproof casing.