The main swing system software of concrete pump trucks is mostly open-type hydraulic press system software, which has two structures: one is to use a gear oil pump, and the other is to use a constant pressure pump.

　　The operation of the gear oil pump oscillation system software involves the pump supplying oil into the accumulator via a one-way throttle valve. Once the accumulator pressure reaches the set pressure of the overflow hydraulic control valve, the overflow hydraulic control valve opens, followed by the opening of the overflow unloading valve. The oil from the pump then flows into the closed cooling tower and into the oil tank under extremely low pressure. When the electro-hydraulic directional valve controls the commutation, the oil-filled piston rod of the accumulator enters the already contracted oscillation cylinder, pushing the other oscillation cylinder to its extended position. At this time, the pressure gauge reading drops sharply, stopping after reaching a certain value (at this point, the cylinder has rotated to another endpoint). Due to the reduced system pressure, the overflow hydraulic control valve temporarily closes, and the gear oil pump immediately replenishes the accumulator until the system pressure reaches the set pressure before unloading. (The speed control valve is used to regulate the amount of oil entering the oscillation cylinder; the safety relief valve is designed to better reduce the destructive force on the oscillation cylinder; and the vacuum valve is designed to better release the pressure of the accumulator oil when the pump stops.)

　　Driven by a gear pump, the oscillating cylinder operates for short periods, with most of the time spent in an interrupted state. During these pauses, the gear pump is unloaded as much as possible, making the unloading valve an essential electronic component of this system. The absence of an unloading valve is also determined by the characteristics of the constant pressure pump. When the oscillating cylinder is interrupted, the flow rate from the constant pressure pump is generally zero. After the hydraulic directional valve opens, the constant pressure pump slowly supplies oil to the system. Both of these open-type structures achieve the same result. It is important to dispel a common misconception: that the oscillating cylinder of the constant pressure pump functions so that the oscillation pressure (gauge reading) does not decrease or drops less than that of the gear pump system during the oscillation process. Such an event is not easily caused because the swing system software, under the action of the accumulator, can swing in a very short time. Within that short time, the pressure of the constant pressure pump (the pressure after the one-way throttle valve) decreases to a certain value. This value drives the AC servo motor hydraulic cylinder, which then acts on the swashplate. Only then does the pump start to discharge oil. By the time this series of movements is completed, the swing cylinder has already swung immediately, and the pressure has already decreased to the lower limit of Z.

　　So, why use a constant pressure pump? I believe it's based on the following points: High-power concrete pump trucks (displacement > 80 m³/h) have a higher swash plate frequency and larger cylinder diameter. Increased swash plate frequency increases the amount of oil required for the swash plate (within a certain time period). Gear pumps are time-sensitive pumps; in rapid oil flow, the accumulator pressure must be maintained at the set value for a long time. If the diaphragm accumulator pressure doesn't reach the set pressure during swash plate commutation, it will undoubtedly affect the next swash plate movement, which is undesirable. Constant pressure pumps, due to their characteristics, allow the swash plate to be at a larger angle when the system pressure is low, discharging a large amount of oil to the system, enabling the system to quickly reach the set pressure. Therefore, using a constant pressure pump is suitable for high-power concrete pump trucks. If an expensive constant pressure pump is used because of the difficulty of swash plate commutation in concrete pump trucks, it won't provide sufficient pressure during the swash plate commutation process and won't solve the problem. In addition, because constant pressure pumps are gear oil pumps, their oil removal accuracy requirements are more stringent, which relatively increases costs. Constant pressure pumps operate under high pressure (gear oil pumps operate at very low pressure during unloading and are in an unloaded state most of the time), generating more heat. In contrast, the oil in a gear oil pump system during unloading flows entirely into a closed-circuit cooling tower, making the system much easier to dissipate heat. This is undoubtedly a significant advantage over constant pressure pumps.

　　To solve the problem of the swing system software failing to swing, we need to address the issues related to the swing cylinder's shaft diameter, the capacity and pressure of the accumulator, the swing valve design, the hopper structure, and the construction of the S-tube swing valve. It's important to note that due to the high-quality characteristics of a constant-speed pump, a speed control valve is unnecessary. However, currently, most manufacturers still include a small speed control valve, which functions as a gate valve, with a set pressure approximately 3 MPa higher than that of a constant-pressure pump.