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Design Principles for Pipeline Slope in Fully Automatic Wet-Spraying Trolleys
Release time:
2026-09-10
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Summary:
The delivery pipeline of a fully automatic wet‑spraying carriage serves as the core conduit that transports concrete from the pumping system to the nozzle. The proper design of the pipeline’s slope directly affects pumping resistance, the risk of pipe blockage, and the continuity of spraying operations. An inadequately designed slope can lead to concrete deposition in low‑lying sections of the pipeline, exacerbate concrete segregation, increase pumping pressure losses, and, in severe cases, result in complete pipeline blockage. Based on the rheological properties of concrete and practical engineering experience, the slope of the wet‑spraying carriage’s pipeline should adhere to the following fundamental principles.
I. General Layout Requirements for Pumping Pipelines
The delivery pipeline of a wet‑spraying boom consists of rigid steel pipes and flexible hoses at the discharge end, ensuring continuous concrete flow throughout the system. Excessive or irregular pipe slopes can cause coarse aggregate to settle at the bottom, increasing the risk of blockages; conversely, too gentle slopes necessitate higher pumping pressure to overcome flow resistance. Standards stipulate that hose‑to‑hose joints on wet‑spraying machines must be securely clamped with ferrules, with intact sealing rings, and that the pipeline layout should minimize bends—preferably with bend angles of 90° or greater—to avoid sharp right‑angle turns that can lead to clogging. This underscores that pipeline slope design and bend configuration are interrelated systemic considerations: slope selection should prioritize smooth, unobstructed routing while meeting transport requirements, thereby minimizing unnecessary elevation changes and directional shifts.
In the design of horizontal pipeline sections, slope is not the sole determining factor; the straightness of the pipeline alignment and the number of bends are equally critical in influencing flow resistance. Horizontal conveying pipelines should be routed as straight as possible to minimize concrete‑flow resistance. When bends are unavoidable, the number of bends should be kept to a minimum, and large‑radius 90° bends with a radius of at least 1 m are recommended. Each additional 90° bend increases pressure loss, so slope design should be coordinated with the optimization of bend parameters.
II. Relationship Between Pipeline Slope and Pumping Pressure Loss
There is a direct positive correlation between pipeline slope and pumping pressure loss. Pumped concrete is a non-Newtonian fluid with relatively high yield stress and plastic viscosity. When conveying concrete upward through an inclined pipeline, it must overcome the hydrostatic pressure loss caused by its own weight; when conveying it downward, the concrete may accelerate under gravity, increasing the risk of segregation or “air suction” in the pipeline. According to the conversion criteria specified in JGJ/T 10, for vertical pipelines, every 5 meters corresponds to a pressure loss of 0.10 MPa, while for horizontal pipelines, every 20 meters corresponds to a pressure loss of 0.10 MPa. This indicates that the pressure loss per meter in a vertical pipeline is approximately twice that in a horizontal pipeline. When designing pipeline slopes, the length and angle of vertical lift sections should be minimized as much as possible to prevent a sharp increase in pumping pressure loss due to excessively steep gradients.
An optimal pipe‑slope design maintains a slight gradient along the entire length of the pipeline (1:100 to 3:100) to prevent localized depressions and arching. When the pipeline must cross obstacles or be routed along walls, supports should be adjusted to ensure a uniform upward or downward trend across the obstacle‑spanning sections, thereby avoiding the formation of local “V‑shaped” segments. After each concrete pour, the pipeline should be thoroughly cleaned with high‑pressure water or compressed air to prevent residual concrete from hardening in low‑lying areas of the slope and causing permanent blockages.
III. Anti-Segregation Measures for Inclined Pipelines
When concrete is conveyed through an inclined pipeline, it is continuously subjected to the component of gravity. When the pipe inclination is steep and the concrete flow velocity is insufficient, the coarse aggregate—due to its higher density—may accumulate at the bottom of the pipe, while the mortar layer flows toward the top, leading to segregation. Segregated concrete exhibits reduced uniformity upon discharge, directly compromising the strength of the sprayed layer; in severe cases, it can accumulate at pipe bends, causing blockages. Measured data indicate that when the pipe inclination exceeds 15°, the tendency toward segregation increases markedly.
To this end, on conveying sections with steep slopes (exceeding 10°), the pipeline should be laid out as a continuous single‑slope ascent or descent, avoiding alternating short undulations and sharp bends. When the concrete slump is too low, pumping resistance on uphill sections with large slopes increases sharply; therefore, prior to entering such steep grades, the concrete slump should be adjusted to the optimal range of 160–200 mm, and the pumping rate appropriately reduced to maintain a piston‑flow regime in the inclined pipeline. The pumping speed on uphill sections should be maintained at 60%–70% of the normal level to minimize the risks of segregation and blockage.
IV. Slope Requirements for the Transition Section Between Horizontal and Vertical Pipes
The transition section between horizontal and vertical pipes is a critical weak point in pipeline slope design. This transition should employ bends with a large radius of curvature (with a bending radius of at least 1 m) to ensure a gradual change in the concrete’s flow direction. If the bend radius is too small, localized turbulence develops on the outer arc of the bend, causing coarse aggregate to decelerate upon impact with the pipe wall and accumulate in the horizontal section downstream of the bend, thereby creating a potential blockage hazard.
According to the concrete pumping construction code, when conveying concrete vertically, the total equivalent length of straight and bent sections of the horizontal delivery pipeline should not be less than 20% of the vertical lift height, nor less than 15 meters. This means that a sufficiently long horizontal buffer section must be provided before entering the vertical run. The horizontal buffer section should be laid either horizontally or with a slight upward slope of 0.5% to 1%; downward slopes should be avoided to prevent the concrete from accelerating its slump and premature segregation under its own weight.
V. Control of the Slope and Angle of the Hose at the Nozzle End
The flexible hose at the nozzle end of the wet‑spraying carriage represents the final segment of the pipeline’s slope design. As concrete is conveyed through the hose to the nozzle, its flow characteristics directly determine the quality of the spray. The hose should generally be laid horizontally or with a slight downward gradient; upward bends should be avoided. When the hose is routed uphill, the concrete velocity decreases, and coarse aggregates tend to settle at the bends, resulting in uneven material discharge. The bend angle of the hose should not be less than 90°, the number of bends should be minimized, and sharp right‑angle turns that can cause blockages should be prevented. During operation, maintain an appropriate angle between the nozzle and the target surface; an excessively steep nozzle elevation angle can exacerbate intermittent material flow and increase the likelihood of blockages.
VI. Measures to Address Shutdown Periods and Temperature Variations
During downtime, moisture remaining in the pipeline tends to collect in low‑lying areas at the bottom, leading to concrete segregation and localized water accumulation. When pumping resumes, the highly water‑rich mortar that has pooled at the bottom is discharged first, compromising concrete quality. Therefore, the pipeline slope should be designed to enable self‑draining at idle positions—meaning that, once pumping ceases, residual concrete can flow out of the nozzle end under gravity without lingering in localized depressions. After each spraying operation, the delivery pipeline should be promptly flushed with high‑pressure water to prevent hardened concrete residues on the inner walls from causing permanent blockages.
Variations in ambient temperature can also affect the performance of pipeline slope design. During hot summer conditions, concrete slump loss accelerates, making uphill sections with steeper slopes more prone to blockages; therefore, the slope gradient should be appropriately reduced and the slope angle softened during design, while during construction, adequate shading and water‑spraying for cooling should be implemented. In cold winter weather, concrete workability decreases, and on downhill sections with steeper slopes, the concrete may freeze and adhere to the pipe walls due to slow flow. After construction, the pipelines should be thoroughly drained to prevent residual concrete from freezing and causing blockages.
VII. Numerical Values for Engineering Practice in Slope Design
Based on the aforementioned principles, the recommended range for the pipeline slope design of wet-spraying trolley systems is:
- Horizontal conveying section: The slope is maintained at 0.5%–1% to ensure the concrete flows naturally along the incline, thereby preventing dead zones in fully horizontal sections.
- Steep uphill sections (with gradients exceeding 10%): The pumping rate should be appropriately reduced, and the concrete slump adjusted to the suitable range of 160–200 mm.
- Transition bends between vertical and horizontal sections: bending radius not less than 1 m.
- Hose at the sprinkler head: Install it horizontally or with a slight downward slope, ensuring that the bend angle is no less than 90°.
- Pipeline emptying requirements: After pumping is completed, the concrete remaining in the pipeline shall be able to drain out by gravity.
The standard specifies that the horizontal level error of the wet‑spraying machine’s body must be no greater than 2 mm/m, and that the machine must remain stable. This underscores that slope control is a fundamental step in the overall installation process and should be carried out concurrently with the machine’s secure mounting. For a certain model of wet‑spraying machine built on a specialized chassis, the conveying pipe has a diameter of φ80 mm, serving as the reference baseline for matching slope and flow rate. In areas with excessively steep slopes, pressure monitoring devices can be installed at appropriate sections of the pipeline to promptly detect abnormal pressure fluctuations and implement counter‑pumping or venting measures to clear accumulated material.
The rational design of the pipeline slope for wet‑spraying boom systems requires balancing multiple factors, including smooth pipeline routing, control of pumping pressure losses, prevention of concrete segregation, and efficient emptying and discharge after shutdown. An improperly selected slope can directly result in reduced pumping efficiency, frequent pipe blockages, and inconsistent spraying quality. Prior to construction, a pipeline slope plan should be carefully developed based on site topography and concrete properties, with dynamic adjustments made during operation in response to changes in pumping pressure, thereby ensuring continuous and stable spraying performance.
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