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Alright, this is a detailed technical analysis on using high-pressure water jetting technology to remove residual cement from sewer pipes. This technique is currently one of the mainstream and highly effective methods for addressing such issues, but its success depends heavily on a deep understanding of the underlying principles, applicable conditions, operational skills, and risk management strategies.

I. Technical Principles and Advantages

The basic principle of high-pressure water jetting technology is to use a high-pressure pump to increase ordinary tap water to extremely high pressures—typically ranging from 10 to 35 MPa, or even higher—then direct it through specially designed nozzles to generate a high-speed, high-energy water jet.

Regarding the specific mechanism of action of cement blockages:

Impact and Chiseling Action: The high-speed water jet acts like a "water blade," directly striking the surface of the cement block. For cement structures that are loosely packed, incompletely cured, or relatively thin, this impact force can shatter and peel them apart.

Penetration and Splitting Action: Under high pressure, water forcefully penetrates even the tiniest cracks and pores in cement. The incompressibility of water causes the pressure inside these cracks to rise dramatically, effectively "popping" or "splitting" the cement block from within. This is the key mechanism behind the removal of large, hard chunks of cement.

Cutting and Clearing Functions: The nozzle is typically designed with both forward and backward jet holes. The forward holes are responsible for breaking down materials, while the backward holes (recoil holes) simultaneously provide propulsion to move the equipment forward—and also flush away the broken fragments and slurry, pushing them back toward the operator’s opening in a synchronized cleaning process.

Key advantages:

Highly efficient and thorough: It can effectively remove cement in various forms, ranging from slurry to fully hardened lumps.

Lossless Pipeline: Compared to rigid tools like mechanical picks and pneumatic hammers, water jets cause almost no damage to the pipe body—whether it’s made of metal, PVC, or other materials—and avoid scratches or cracking altogether.

Clean and environmentally friendly: The primary medium is water, which prevents chemical or dust pollution. The residual materials after crushing are directly flushed away, making them easy to collect and handle.

Wide applicability: Capable of handling pipes with varying diameters and different orientations.

II. Key Steps and Analysis for Technical Implementation

1. Preliminary Assessment and Diagnosis

This is the first step in determining the success or failure of the plan—and it’s absolutely critical.

Blockage Condition Assessment:

Cement state: Is it a semi-solid, still not fully set, or a completely hardened block? The semi-solid form is easier to handle, while the hardened block presents greater challenges.

Blockage range and location: The length of the cement blockage and its exact location within the pipeline (horizontal section, bend, or vertical pipe) can be precisely detected using an in-pipeline endoscope, allowing for a clear visual inspection of the cement's shape, thickness, and its adhesion to the pipe walls.

Pipe Material and Condition: Understand whether the pipe is made of cast iron, PVC, PE, or cement, as well as its service life and current strength. Old and brittle pipes require more careful pressure management.

2. Equipment and Accessory Selection

High-pressure washer:

Pressure: It is recommended to use equipment with a pressure of 20 MPa (approximately 200 bar) or higher when handling residual cement. The higher the pressure, the stronger the crushing capability.

Traffic: The greater the flow rate, the stronger the scouring and slag-discharging capability. For larger pipe diameters (such as DN200 and above), a high flow rate (≥15 L/min) is particularly important. Pressure is responsible for "breaking," while flow handles "cleansing." 。

Nozzle and Rod:

Nozzle type: You must choose a疏通 nozzle with forward-and-backward (or side) jetting. The backward jet provides forward propulsion as well as reverse冲 cleaning.

Nozzle Design:

"Concrete Crushing"-Specific Nozzle: These nozzles typically feature a conical or ball-tooth-shaped alloy steel head, combined with forward-facing nozzles of small aperture, which concentrate energy into a single point to achieve powerful chiseling and breaking.

Rotating nozzle: By rotating, the jet achieves wider coverage and cleaner, more even distribution.

Rod body: Use a rigid high-pressure hose or a rigid疏通 rod. For long-distance blockages, ensure you have a rod of sufficient length.

3. Operating Techniques and Procedures

Operation entry point: Choose the appropriate job opening, such as an inspection well, toilet outlet, or floor opening.

Gradual advancement:

Initial stage: Start at a lower pressure (such as 10–15 MPa), allowing the water flow to penetrate and test the strength of the cement.

Fracture process: Attach the nozzle firmly to the cement blockage surface, using a forward-directed jet for "targeted impact." Continuously strike at a single point, leveraging the principle of渗透劈裂 (penetration and splitting) to create an initial breakthrough. Once the breakthrough is achieved, the nozzle can be inserted, and then rotated while applying a backward-directed jet to further expand the opening—gradually breaking through each layer.

"From Outside In" Strategy: Avoid directly impacting the center of the pipe; instead, start from the junction between the inner pipe wall and the cement, carefully separating the cement from the pipe surface to create a circular gap. This will facilitate water penetration and help achieve overall fragmentation.

Simultaneous flushing: During the crushing process, ensure that the backflow jet continuously flushes out the debris. If drainage becomes obstructed, pause progress and repeatedly rinse to prevent debris from causing secondary blockages downstream.

III. Technical Limitations and Risk Analysis

Although efficient, this technology also has limitations and risks:

It is less efficient against fully hardened, massive cement blocks: If the cement completely fills the pipeline and forms a long, solid mass, the water jet may advance extremely slowly, consuming more time and water while reducing cost-effectiveness.

Improper operation damages the pipeline:

Direct breakdown: Under extremely high pressure, the nozzle being too close to the walls of soft pipes like PVC could potentially puncture the pipe directly.

Zhen Song Interface: Strong impact vibrations can loosen the socket joints of older cast-iron pipes, leading to leaks.

Damage the anti-corrosion layer: It may damage the anti-corrosion layer (such as asphalt coating) on the inner wall of metal pipes.

Risk of Secondary Blockage: If the large chunks of cement debris generated after breaking aren't promptly flushed out, they may accumulate downstream at pipe bends or narrow sections, leading to even more complex blockages.

Harsh working environment: It will generate large amounts of muddy water, so proper on-site protection and wastewater collection and treatment are essential.

Summary

High-pressure water jets are an efficient, environmentally friendly, and pipe-friendly technology for removing residual cement from sewer lines. At the heart of this method lies the use of high-pressure water’s kinetic energy to deliver powerful impacts, enabling deep penetration and effective splitting of hardened material.

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