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When the concrete delivery pump is interrupted during pumping?

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When the concrete delivery pump is interrupted during pumping?

Issue Time:2020-05-14
At present, concrete pumps have been widely used in the construction of concrete projects. By adopting the concrete delivery method, the construction party can not only reduce costs, but also save construction time and standardize the construction site. However, some problems will inevitably occur during the use process, such as the flow interruption during the pumping process, so why does the concrete delivery pump have a flow interruption? What harm will it cause? How to solve the interruption of current during construction? Now we simply analyze and introduce the reasons for the interruption and the methods to solve the interruption problem.
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1. Harm caused by interruption
First, it is easy to cause segregation of concrete, and some of the concrete is dehydrated into dry and hard concrete to cause pipe blockage, especially when pumping low slump concrete;
The second is the release of concrete pressure in the pipeline and the distribution valve at the moment of reversal, which has an impact on the hydraulic system of the concrete pump, causing damage to certain parts and increasing energy consumption. The interruption of the flow is particularly obvious when pumping vertically upwards, especially when pumping to heights above 50m.

2. Reason analysis
It is a hydraulic principle diagram of a double-cylinder driven concrete pumping system of an open hydraulic system. The pump is a fully hydraulically controlled concrete pump. The constant power main oil pump supplies oil to the main oil cylinders 10-1 and 10-2 and the distribution valve oil cylinder 9 through the hydraulic valves 8-1 and 8-2. The main cylinder insertion valve and the distribution valve cylinder send signals to control the commutation of the hydraulic valve, so that the action sequence of the main cylinder and the distribution valve cylinder are coordinated with each other, and the concrete pumping cycle is realized. The main cylinder 10 double cylinders alternately suck and discharge To achieve continuous pumping of concrete. The concrete flow usually has obvious flow-break-flow phenomenon during each commutation process, that is, the so-called flow cut-off phenomenon.

There are three reasons for the interruption of concrete flow:
① When the main cylinder runs to the end of the stroke, it sends a commutation signal to the commutation cylinder, and then the main system oil circuit is commutated, and the main cylinder 10 moves in the opposite direction. This process requires at least 0.2s;
② The suction efficiency of the concrete being sucked into the concrete cylinder is usually only 85% -95%, and it is inevitable to suck a short section of air, which will be a short section of empty stroke;
③ The pressure of the concrete sucked into the concrete cylinder during commutation increases when it is output outward, and has a certain compressibility, which is also a short period of empty travel. Due to the commutation and two sections of empty travel time, the problem of flow cut-off occurred during the concrete pumping process.
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3. Solution

The way to solve the flow interruption in the pumping process is to shorten the commutation time and speed up the operation speed of the main cylinder piston at the beginning of commutation, and to achieve continuous pumping of concrete before the concrete pressure in the pipeline and distribution valve is completely released. Reduce the backlash of the concrete due to the separation of the flow and the release of the concrete pressure in the pipeline and the distribution valve during the commutation process.

For most pumping systems, the current cutoff problem can be solved by using an electrical ratio. Since the electric proportional control + constant power control is the electric control variable takes priority over the constant power control, the displacement is controlled by the control current when the power is below the hyperbola, before the commutation process and after the commutation of the cylinder, the piston moves the concrete in the pipeline The system pressure is usually lower than the pumping pressure. You can increase the displacement of the main oil pump to achieve rapid commutation of the distribution valve, reduce the time after the commutation to start pushing the concrete, and realize the continuous flow of the concrete from the appearance.
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Generally, two proximity switches can be set in the water tank between the oil cylinder and the concrete cylinder, and the starting and ending points of the letter outlet are set according to the displacement of the main oil pump and the diameter and stroke of the main oil cylinder. In the control stage, the start and end positions of the message port are taken, and the distance between the proximity switches is usually 5% to 10% of the total travel. After the proximity switch gets the start signal, it is transmitted to the programmable controller or the holding relay. The controller or the relay sends out the current (usually several hundred mA) required to achieve the large displacement of the oil pump to the proportional solenoid of the main oil pump to realize the oil pump discharge. The volume soared, quickly changed direction and started to push the concrete in the distribution valve and pipeline. Adjust the cut-off proximity switch position to stop the electric control when the oil cylinder starts to push the distribution valve and the concrete in the pipeline, and continue to realize the constant power control of the oil pump. The actual start and end positions of the fetching port can be adjusted according to the actual situation of the concrete pump to ensure the continuity of the concrete flow during pumping to a large extent.

Once the concrete pump has a flow interruption during work, you can try to solve it from the above three aspects
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