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.