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Why is it necessary to lubricate the pipeline before pumping with a truck-mounted pump?
Release time:
2026-08-14
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Summary:
During the pumping operations of truck‑mounted concrete pumps, pipeline lubrication is an essential preliminary step that must be performed before formal concrete pumping. Inadequate or improper lubrication can, at best, increase pumping resistance and, at worst, lead to pipe blockages, resulting in equipment damage and work interruptions. A clear understanding of the underlying causes of pipeline lubrication is key to ensuring proper operating procedures, minimizing failures, and extending the service life of both the equipment and the pipelines.
I. Reducing Initial Pumping Resistance
Newly installed or cleaned concrete delivery pipelines have dry metal inner walls, resulting in a relatively high coefficient of friction. If concrete is pumped directly into the pipeline without prior preparation, it must overcome substantial wall friction to advance, leading to a significant increase in initial pumping pressure.
The inner surface of steel pipes in conveying pipelines, or the inner wall coated with mortar, can adsorb moisture. A dry pipe wall rapidly absorbs free water from the concrete and the mortar, causing the concrete’s workability to decline sharply. When the pumping pressure is insufficient to move the dehydrated concrete, it becomes lodged in the pipeline. Before pumping concrete, wetting the pipeline with water and then lubricating it with mortar creates a lubricating buffer layer between the pipe wall and the concrete, significantly reducing the initial pumping resistance.
Before pumping, first pump water to ensure the pipeline is free of foreign objects, then pump cement mortar with the same composition as the concrete. The amount of mortar should be sufficient to lubricate the entire pipeline. This step creates a smooth mortar‑based lining on the inner wall of the pipe, thereby establishing favorable conditions for the subsequent smooth passage of concrete.
II. Preventing Loss of Workability Due to Water Loss in Concrete
As concrete advances through the pipeline, water serves as the critical medium that maintains its workability. If the dry inner walls of the pipeline are not lubricated, they will continuously draw moisture from the concrete.
Water can wet the metal surface of the pipeline and the inner wall coated with mortar. Pre-wetting the pipeline with water helps reduce moisture loss from the concrete inside, thereby mitigating the reduction in workability, the increase in flow resistance, and the risk of blockage caused by dehydration. However, since water remains in the pipeline for only a short time, its wetting effect is inevitably incomplete; therefore, a secondary lubrication with mortar is required. The mortar contains fine sand particles, so even if some of the water is absorbed during conveyance and the consistency decreases, it is unlikely to cause pipeline blockage.
In long-distance pumping, the continuous absorption of water by the pipe’s inner wall can lead to concrete segregation, causing coarse aggregate to separate from the mortar and further increasing the risk of pipe blockage. Pre‑lubricating the pipeline with mortar effectively applies a low‑permeability protective layer to the pipe wall, thereby sealing off pathways for moisture loss from the concrete.
III. Inspect and verify the pipeline’s sealing integrity
Another important function of lubrication in piping systems is to perform leak‑tightness testing. In newly installed pipelines or in pipework that has been cleaned and reconnected, leaks may occur at the joints.
When the rubber sealing rings at pipeline joints are poorly sealed or the pipe clamps are not tightened sufficiently, grout leakage at the joints can easily occur. Once pumping‑aid material is introduced into the pipeline, any joint with inadequate sealing will immediately exhibit grout leakage, allowing operators to detect and address the issue promptly. Studies have shown that pumping‑aid materials not only reduce frictional resistance during the pumping of high‑strength concrete, ensuring smooth flow and minimizing the risk of blockages, but also enable verification of the pipeline’s sealing integrity, thereby reducing the likelihood of pipe blockages and bursts caused by loose or leaking joints. Conducting a sealing‑integrity check before commencing formal concrete pumping can effectively prevent concrete from spraying out through loose joints under high pressure, thus avoiding material waste and potential safety hazards.
IV. Lubrication Method and Material Selection
The conventional lubrication method employs a two-step procedure: first, pump one to two buckets of clean water to thoroughly wet the pipeline; then, pump cement mortar to achieve complete lubrication. The mortar mix typically consists of sand and cement in a 1:1 ratio, with an application rate of approximately 0.5 cubic meters per 200 meters of pipeline. Immediately after pumping the mortar, concrete should be introduced to begin pumping, thereby preventing the mortar from remaining in the pipeline for too long and losing its workability.
Lubricating mortar or clean water must not be pumped into the main structure; instead, it must be discharged outside the formwork for other uses. In recent years, polymeric pipe‑lubricating agents have gradually replaced traditional mortar. These pump‑truck pipe‑lubricating agents are formulated from polymeric materials such as polyacrylamide; when dissolved in water, they form a gel‑like liquid that adheres to the inner wall of the pipeline, creating a lubricating film that prevents the pipe wall from absorbing moisture from the concrete and maintains the concrete’s fluidity. Compared with conventional mortar, pipe‑lubricating agents eliminate the need for dedicated vehicles and associated costs for transporting mortar, reduce the number of construction steps, and shorten preparation time.
V. Safety and Standard Operating Precautions
Before commencing lubrication, operators must perform a thorough equipment inspection: verify that fuel, lubricating oil, and coolant levels are adequate; ensure the hydraulic system is functioning properly; and confirm that all pipeline connections are secure and leak‑free. Prior to formal pumping, set the main oil pump to its maximum flow rate, fill the料斗 with water, and run the machine at idle for 10 minutes to confirm that system pressure, the mixing mechanism, and the pumping operation are all normal. When starting to pump mortar, reduce the oil pump displacement to its minimum setting; once the mortar has been pumped and concrete has been discharged, adjust the displacement to an appropriate level.
The pumping rate should follow the principle of starting slowly and then accelerating gradually. Slowing down allows the mortar to adhere evenly to all sections of the pipe wall, ensuring a uniform and intact lubrication layer. At the start of pumping, the concrete pump should operate at a slow, steady speed, with close monitoring of pump pressure and the performance of all systems; only after confirming normal operation should pumping proceed at the designated rate. Once lubrication is complete, concrete supply must be continuous, maintaining a concrete level in the hopper no lower than the suction inlet to prevent air from being drawn in, which could cause concrete to spurt out of the discharge nozzle and injure personnel.
By standardizing the pipeline lubrication procedure, truck-mounted pumps can fundamentally reduce pumping resistance, minimize pipe‑clogging incidents, extend the service life of pipelines and pumping systems, and ensure construction continuity and operational safety.
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