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Switching Between Low-Pressure and High-Pressure Operating Modes of a Concrete Truck-Mounted Pump
Release time:
2026-10-15
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Summary:
During pumping operations, concrete truck‑mounted pumps face conflicting demands for pressure and flow rate depending on the specific construction conditions—whether handling high‑volume, short‑distance delivery or long‑distance, ultra‑high‑rise, high‑pressure pumping. To balance efficiency and performance, these pumps typically feature two operating modes: “low pressure with high flow” and “high pressure with low flow.” Switching between these modes essentially involves altering the hydraulic circuit configuration of the dual main cylinders, thereby changing the effective area over which pressurized oil acts.
I. Operating Principles of the Two Modes
The truck-mounted pump employs a twin‑cylinder piston‑type pumping system, in which two main hydraulic cylinders alternately drive the concrete cylinder pistons to perform suction and discharge. The distinction between high pressure and low pressure arises from the pressurized oil acting on different chambers of the main cylinders:
Low-pressure, high-displacement mode: The rodless chambers (the larger cavities on the back side of the piston) of the two pump cylinders are interconnected, while pressurized oil enters the rod-side chambers (the smaller cavities on the piston‑rod side). Because the effective area of the rod-side chamber is smaller, the pushing force generated under the same oil pressure is lower; however, the piston reciprocates at a higher speed. Consequently, the system delivers lower output pressure but a larger displacement.
High-pressure, low-displacement mode: The rod-side chambers of the two pump cylinders are interconnected, while pressurized oil flows into the rodless (large) chamber. Because the effective area of the rodless chamber is larger, the resulting pushing force is greater; however, the piston’s speed is correspondingly reduced. Consequently, this mode delivers higher output pressure but a smaller displacement.
Take the XCMG HBC9018VD truck-mounted pump as an example: in low-pressure mode, its theoretical flow rate is 90 m³/h at a pressure of 10 MPa; in high-pressure mode, the flow rate drops to 45 m³/h while the pressure rises to 18 MPa. The low-pressure mode excels in flow rate, making it suitable for horizontal or short-distance pumping, whereas the high-pressure mode prioritizes pressure, ideal for vertical or long-distance pumping.
II. Technological Evolution of Switching Methods
The switching mechanism between high and low pressure in truck-mounted pumps has undergone a technological evolution from manual to automatic, which can be broadly divided into the following three stages:
Manual hose replacement (traditional method): This involves disassembling and replacing hydraulic hoses to alter the oil circuit connections. However, this approach is slow, prone to oil leaks and contamination during switching, and the hose’s minimum bend radius limits the effective flow path.
Manual valve‑block switching (transition mode): By disassembling and reassembling the valve block, the oil‑flow path is redirected, which mitigates oil leakage and contamination. However, the switching speed remains insufficient to meet the demands of rapid mode changes.
Automatic switching (the mainstream approach): Modern vehicle-mounted pumps typically employ a two‑position, six‑way directional control valve or a logic valve block to achieve automatic switching. During automatic switching, once the preset pressure is reached, a pressure sensor sends a signal that activates an electromagnetic directional control valve, thereby routing the hydraulic circuit automatically. Operators simply press a button to complete the switch in an instant—no shutdown, no pipe disassembly, and no leakage.
The XCMG HBC9018VD employs a parallel dual-circuit high‑low voltage automatic switching system, which is a quintessential application of this technology.
III. Precautions for Switching Operations
In practical operation, the following points should be observed when switching between high and low voltage:
Switching should be performed at an appropriate time. It is advisable to carry out switching during pump‑off periods or under low‑load conditions, thereby avoiding hydraulic shocks that may occur during high‑load operation. Fully automatic switching systems can complete the transition in an instant, without requiring a shutdown.
Select the operating mode according to site conditions. Use low-pressure mode for short-distance, high‑flow pumping; switch to high-pressure mode for long distances, ultra‑tall structures, or pumping high‑grade concrete. Choosing the wrong mode can result in reduced efficiency or even pipe blockages.
Pay attention to power limitations. The power output of a given engine is finite, and operating in high-pressure mode inevitably results in a reduction in displacement. For ultra‑high‑rise pumping, a “high pressure, low speed” strategy is often required, with displacement appropriately reduced to maintain stable pressure.
Avoid frequent switching. Repeated transitions between high and low pressure can accelerate wear on the directional control valve and seals; switching should be performed only after confirming a change in operating conditions, rather than during continuous operation.
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