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In concrete pumping operations, cleaning the concrete is an essential step that follows pumping. An effective cleaning method not only cleans the delivery pipes thoroughly but also ensures that all the concrete in the pipes is delivered to the pouring site, thereby avoiding waste of concrete and being both economical and environmentally friendly. There are mainly 3 common water-cleaning methods for S-tube valve concrete pumps, which are introduced as follows. 1. Direct water jet cleaning method: 1) Check the wear between the cutting ring and the eye plate; this is key to determining the success of cleaning using the direct water jet method. If the cutting ring and the eye plate are not severely worn, with a distance between them of <0.1 mm and no grooves or scratches larger than 1 mm between them, the direct water jetting method can be used. 2) After pumping the concrete, pump in 0.15–0.25 m³ of mortar with a water-cement ratio of 1:1.5 or 1:2. Then fill the distribution valve with water, start pumping, and convey the concrete to the pouring location until clear water flows out from the outlet end of the delivery pipe. If the pipeline is short and the cleaning effect is good, the cleaning process ends here. 3) When the pipeline is long or the cleaning effect is not good, open the hopper discharge door, start the reverse pump, and flush the hopper and distribution valve thoroughly. If pumping upward and the height is >20m, a wooden hammer can be used to strike the bottom of the elbow in the vertical section; if the sound produced by hitting it is dull, the elbow needs to be disassembled to remove any large aggregates that may have accumulated there. 4) Close the discharge door, and pump clean water until it flows out from the output end of the delivery pipe. The advantage of the direct water injection method is that there is no need to remove the discharge pipe or add cleaning balls, which saves time; pumping is more likely to succeed, and it is especially convenient for cleaning shorter pipelines. Its disadvantages: ① It requires a large amount of water, and pumping must be continuous; water easily accumulates at the pouring site ； ②If there are pipes running vertically upward, it is usually necessary to bend them ； ③When the delivery pipeline is long, residues are likely to remain inside it ； ④Strict requirements are placed on the sealing performance of the distribution valve. 2. Method of removing the discharge pipe: 1) After pumping the concrete, reverse-pump for 1–2 cycles to eliminate the pressure in the delivery pipe. If pumping upward, the stop valve must be closed first to prevent concrete from flowing back, and then the discharge pipe must be removed. 2) Open the hopper discharge door, and the reverse pump is used to flush the concrete out of the distribution valve, the concrete cylinder, and the hopper. 3) Remove some of the concrete at the outlet end of the first 6B or 5B delivery pipe, and insert a water-soaked cleaning ball or cylindrical cleaning piston. 4) Close the discharge door of the distribution valve; if there is a stop valve, open it, and pump clean water until the piston pumps it out from the output end of the delivery pipe. The advantage of the pipe removal method is that the pipes are cleaned more thoroughly, and the flow rate of the water source can be lower or even stopped. Its drawback is that it is difficult to reconnect the discharge port after it has been detached, which is time-consuming and laborious. 3 Piston addition method: 1) Roll 10–20 cement bags into a cylindrical shape with a diameter slightly smaller than that of the conveying cylinder, a slightly pointed tip, and a length of about 400 mm; tie it together with thin wire, and gently attach a cleaning ball to the rear end of the cylinder using wire, then soak it in water. 2) After pumping the concrete, reverse-pump for 1–2 cycles to relieve pressure in the delivery pipe, then press the button to move the piston of the concrete cylinder to its final position. If pumping upward and there is a stop valve, it must be closed first to prevent concrete from flowing back. 3) Remove the discharge pipe, open the hopper discharge door, and use a reverse pump to flush the concrete out of the distribution valve, concrete cylinder, and hopper. 4) Close the hopper discharge door and add water to the hopper. When the water reaches 2/3 of the height of the concrete cylinder’s diameter, insert the column-shaped object with its head facing the distribution valve into the concrete cylinder. Use a wooden lever that is about 1 meter long and 30 mm in diameter to push the column-shaped object in place, then continue adding water until it reaches the level of the centerline of the mixing shaft. 5) Remove the pry bar, quickly start pumping, and continue adding water until the column is pumped out from the output end of the delivery pipe. The advantage of the piston method is that it allows for a cleaner cleaning of the pipes; the flow rate of the water source can be kept low or even stopped, while also reducing the hassle of removing outlets and bends. The disadvantage is that it requires high operational skill, and the distribution valve can easily cut the cylinder. The three methods for washing concrete pumps mentioned above each have their own advantages and disadvantages. The most reliable method is removing the discharge pipe, the simplest is using a piston, and when the delivery distance is short, the direct water injection method is also a good option. The specific methods depend on the actual conditions of the construction; in any case, they must be both effective and cost-effective.