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Aerial Cableway Sheave Liner
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Introduction to the hazards and solutions of concrete pumping and shut-off
At present, helium pumps are widely used in the construction industry, particularly for concrete pumping. The most commonly used type is a two-cylinder driven helium pump, which often experiences a "shut-off" phenomenon during the pumping cycle. This issue poses two major risks: first, it can lead to segregation of the concrete mix, with some parts drying out and hardening, causing blockages—especially when pumping low-slump concrete. Second, the transient pressure changes during the commutation process can create stress on the hydraulic system, potentially damaging components and increasing energy loss. These effects become more pronounced when pumping vertically, especially at heights exceeding 50 meters.
The pump operates as a fully liquid-controlled system, where the main oil pump supplies oil to the main cylinders (10-1 and 10-2) and the distribution valve cylinder (9) through hydraulic valves (8-1 and 8-2). The main cylinder cartridge valve and the distribution valve cylinder send signals to control the reversal of the hydraulic valves, ensuring that the movement of the main cylinder and the distribution valve is synchronized, enabling the continuous pumping cycle. The main cylinder alternately draws and expels concrete, allowing for uninterrupted helium pumping. However, during each commutation, a flow-break-flow phenomenon typically occurs, known as the shut-off effect.
There are three primary causes of this turbulence. First, when the main cylinder reaches the end of its stroke, it sends a signal to reverse the direction, which requires at least 0.2 seconds to complete. Second, the concrete intake efficiency of the cylinder is generally between 85% and 95%, meaning a small amount of air may be drawn in. Third, differences in usage conditions between regions contribute to the severity of the issue. In Europe and the U.S., where pump trucks with large displacement and strict aggregate grading are common, the problem is less noticeable due to smaller building heights and better material control. In contrast, domestically used tow pumps typically have lower displacement (under 80 m³/h), and are often used for larger buildings, making the shut-off phenomenon more evident.
By carefully selecting and setting the control mode of the main oil pump, the issue of interrupted flow during helium transport can be significantly reduced. This not only minimizes the shock during commutation but also greatly enhances the overall performance of the helium pump, leading to smoother and more efficient operations.