Concrete pump technology development Today, the concrete pump (car) has been towards the direction of high pressure and large displacement in the high-rise building construction, we must consider the pump (car) in the park when the pump back to the concrete and preventive measures. 1 Concrete backflow and its effect The so-called "stop pump" refers to the concrete pump (car) in the pumping intermittent (non-stop host) or after completion of the cleaning work to stop pumping. In the normal operation of the main cylinder to stop the pump (non-start, stop point) Vertical slump in the vertical pipe (18-22mm), under its greater gravity through the horizontal pipe and concrete distribution valve backflow back to the return The back pressure is transmitted back to the concrete distribution valve, and back pressure is transmitted back to the end surface of the concrete piston, which is then transmitted to the master cylinder piston of the oil cylinder through the live rod, as shown in FIG. 1. If there is no anti-concrete backflow structure, then this back-pressure back to concrete will be forced to reverse the scouring concrete stopper limit stopper (or tube), while the master cylinder piston in its role also produce reflux pressure , And return to the starting point A of the movement. When the pumping is stopped, the main system's oil pump is under unloading condition, and the larger reflux pressure generated in the A-tank when the concrete is flowing back has a greater harmful impact on the oil pump. At the same time, Rod chamber is closed communication, when the left cylinder piston to stop the pump position (dashed line) to return to point A, the closed loop volume increases, the following two situations occur: ①due to the volume increase Under the action of a larger negative pressure, the oil in the closed circuit will float, that is, the distance between the oil molecules is widened, and the air in the oil is separated to form bubbles. At the same time of emulsification, the external circuit will leak into the closed loop until the negative pressure of the closed loop is less than the seal contact stress of all NASA's. The result is mainly inward leakage, oil emulsion times, resulting in closed loop oil increase (in extreme cases are two master cylinder are retracted at the starting point A, B Department). In the second pumping, the master cylinder in addition to overcome the pumping resistance of concrete files outside the room, but also to overcome the rod cavity due to increased oil through the closed circuit safety valve or check valve to produce a larger back pressure. If the sum of the above two reaches the overflow pressure of the main system, the main system will stop pumping pound. ② If the closed circuit sealing effect is better, then the circuit changes in the oil is mainly hydraulic emulsion, inward leakage times. That is, the negative pressure of the closed circuit quickly reaches a state of less than the minimum contact stress of all the sealing elements (in the extreme, only the oil in the original circuit is emulsified and doubled). During the pumping again, during the period when the master cylinder runs to the fast commutation, the oil in the emulsified state returns to its original state after being pressurized and the pumping pressure will not increase. Continue to travel to the end of the campaign; due to the infiltration of a small amount of excess oil to be completely discharged, then the pumping pressure suddenly increased, pumping pressure and back pressure will occur and the main system to achieve the safety of overflow pressure, Main system pumping failed. 2 Prevention Structure Design Principle and Its Application (1) In the main inlet and outlet of the main tank, the use of three-way four-way valve surface energy to achieve when the main pump off the main oil tank in the off state of the main system of oil cut off, as shown in picture 2. This structure is used in Schwing's concrete pump (vehicle) series. Control of the master cylinder, anti-pump three-way four-way valve with liquid-controlled spring on the reset structure, slide valve function for the M-type. Its working principle is: stop pump, hydraulic pressure pk disappear. Three four-way spool in the displacement spring on both sides in the middle, then the valve outlet is in the off state, the main oil pressure p is back to the unloading state. Closed by the backflow valve. In some closed main pumping system, digging control master cylinder reversing four-way valve also uses the three-way four-way valve structure shown in Figure 2, but the slide valve function is used "H" type. Although it meets the requirements of the closed circuit system for oil return, it can not prevent the reverse flow of concrete. The author thinks it is better to use M type function. Can meet the requirements of closed systems, but also to prevent concrete backflow. Figure 2, one of the backflow prevention structure of concrete (2) using shuttle valve plus one-way valve shown in Figure 3. Figure 3 back to prevent the structure of concrete back two one-way valve closed to lock the back flow of concrete back pressure generated by the cylinder. This structure applies to IHI companies and similar products in the pump (car). Its working principle is: stop pumping, the solenoid valve is located in the position shown in the figure, concrete back to the cylinder back pressure pk through the master cylinder four-way valve (two), the shuttle valve core to the right position and Flow through the shuttle valve, solenoid valve after the role of the one-way valve spring chamber. Because the one-way valve is a DF type right angle type, the master cylinder back pressure can be separated from the main system being unloaded. (3) the use of sequential valve main core off the main oil. Sequential valve sequence in the main system, the use of sequence valve main pump closed at shutdown, the master cylinder into the oil road and unloading system, as shown in Figure 4. This structure applies to IHI companies and similar products in the pump (car). The principle is: in the present structure, the check valve 2 and its control circuit f does not exist. Stop pumping, the solenoid valve 3 is located in the work on the map, the pilot valve of the external control and return oil road connected to the pilot valve immediately closed. The main spool will also close. The back pressure generated by the concrete backflow to the cylinder is cut off by the main spool. But because of the sequential valve main core is a tapered Vernal line seal, its inlet and outlet are also at right angles. Therefore, there is always an effective pressurized annular area for the main core to open on the sealing cone surface. When the back pressure reaches a certain value, the force exerted on the pressurized annular area will be greater than that of the main core spring, Open, back pressure back to overflow tank. Therefore, the height of the structure against concrete backflow is limited and needs to be improved. The improved principle is: the use of external control sequence valve outside the oil on the solenoid valve of the extra plugging oil to control the addition of the main oil on the check valve, as shown in Figure 4 and f f frame. Its working principle is: When the pumping stops, the solenoid valve as shown in the working position, from the accumulator pressure distribution valve holding pressure circuit through the solenoid valve, f oilway to the spring chamber of the check valve 2, so that the single Close the valve. Due to the pressure area of ​​the spring cavity is much larger than the effective annular compression area of ​​the sealing cone. Therefore, the one-way valve 2 can be placed effectively back to the concrete back pressure generated by the cylinder cut-off. (4) In the main pumping system of the cartridge valve (as shown in Fig. 5) Fig.4 Four of the backflow prevention structures of the concrete rely on the cartridge valve 2 to realize the anti-backflow. Through the pilot valve control valve 1 on the main plunge back pressure reference and control, respectively, the return flow back pressure acting on the spring loaded cavity components, the master cylinder back pressure and the main system in the unloading off. Its principle of action is essentially the same as the first and second kinds of structures, all of which use the reverse pressure back pressure or the external control pressure reverse direction (spring cavity) to close the one-way valve. Cut off the main cylinder back pressure back. Through the principle model shown in Figure 6, p back to the concrete back to the master cylinder back pressure, S is the effective area of ​​the spring cavity, S ring is the effective area of ​​the loop by the p loop role. Figure 6 check valve or the back pressure seal plug device 3 actual pumping concrete backflow phenomenon to avoid the phenomenon and treatment has been put into use without any reverse flow of concrete pump (vehicle), in case of vertical pumping During construction, special operations may be performed on the main system to avoid the backflow of concrete, that is, when the concrete distribution cylinder has just completed reversing, pumping will stop immediately. In this case, the concrete backflow pressure in the vertical direction presses the concrete piston against the wash stopper (or tube). If concrete backflow has occurred and the (excess) oil infiltration into the closed circuit of the master cylinder is confirmed, turn off the shut-off valve or adjustable restrictor valve that regulates the amount of oil in the circuit after a period of pumping operation for a while to clear It contains too much oil, but then it should be shut down immediately.