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Fully Automatic Wet-Spraying Trolley with Multi-Pump Relay Connection Technology
Release time:
2026-09-16
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Summary:
In tunneling, mining, and other applications involving large cross-sections or long-distance shotcrete support, a single wet‑spraying rig is limited by the outlet pressure of its pumping system and pipeline friction losses, imposing an upper bound on the pumping distance. When the spraying front exceeds the capacity of a single unit, multi‑pump relay delivery—i.e., connecting multiple concrete pumps in series to ensure continuous concrete supply—becomes the preferred technical solution. The multi‑pump relay configuration for fully automated wet‑spraying rigs is not a simple “one pump feeding another”; rather, it constitutes a complex systems engineering task that encompasses selecting and positioning relay pumps, matching the pumping capacities of upstream and downstream units, calculating pressure losses, designing transitional connections for intermediate pumping stations, and conducting comprehensive safety verifications. JGJ/T 10‑2011, the Technical Code for Concrete Pumping Construction, explicitly stipulates that when relay pumping is required, the placement of relay pumps must ensure compatibility between the upstream and downstream pumping capacities, and that the structural components hosting the relay pumps must undergo load‑bearing capacity assessments, with reinforcement measures implemented where necessary.
I. Application Scenarios and System Configuration of Multi-Pump Relay Connections
Multi‑pump relay connections are primarily suited to the following two operating conditions: first, when tunnel shotcrete operations involve long working fronts and the concrete delivery distance exceeds the horizontal pumping capacity of a single wet‑spraying rig, requiring the installation of relay pumps along the route to sustain continuous conveyance; second, in vertical shafts, inclined tunnels, or on steep slopes, when the vertical lift required for shotcrete exceeds the static pressure resistance of a single unit, necessitating the placement of relay pumps at multiple levels to enable staged upward or downward transport.
A complete multi‑pump relay‑connection system typically consists of three components: the primary pump (lower pump), which is installed at ground level or on a lower working platform, receives material from the mixing station, and pressurizes concrete through pipelines to the relay point; the intermediate relay pump (middle pump), positioned on steps, platforms, or floor slabs, uses its suction capacity to draw concrete from the upstream pipeline into its hopper and, after boosting pressure, delivers it to the next section of the conveying line; and the terminal pump or nozzle pump, directly connected to the spraying boom, transports concrete to the nozzle to carry out the spraying operation. In the multi‑pump relay configuration of tunnel wet‑spraying rigs, both the primary pump and the relay pumps should be fully automatic wet‑spraying units of identical or similar specifications, facilitating power matching and coordinated control system integration.
II. Principles for Matching the Delivery Capacity of Relay Pumps
The core technical challenge of multi‑pump tandem‑connection lies in matching the delivery capacities of the upstream and downstream pumps. If the upstream pump’s output exceeds the downstream pump’s suction capacity, concrete will overflow and accumulate in the intermediate hopper; conversely, if the upstream pump’s output falls short of the downstream pump’s suction capacity, the downstream pump may draw in air or experience cavitation, leading to flow interruptions and pressure pulsations, which in severe cases can cause pipe blockages or equipment damage. From the perspective of the pumping system’s basic architecture, the wet‑spraying machine employs a three‑circuit, independent open‑loop hydraulic system—covering pumping, boom operation, and auxiliary equipment. Standard on‑board wet‑spraying rigs are equipped with multi‑pump, multi‑circuit configurations featuring constant‑power variable displacement combined with electro‑hydraulic proportional control, enabling precise adjustment of pumping parameters through advanced electro‑hydraulic proportional technology.
The matching degree shall be determined based on the pressure loss calculation results and the pump’s performance curve. In engineering practice, it is preferable to use wet‑spraying rigs of the same model for relay‑type connections, with the control system adjusting the upper pump’s displacement to 85%–95% of the lower pump’s rated suction capacity. This ensures that the intermediate hopper maintains an appropriate buffer stock, preventing the lower pump from running dry while also avoiding excessive feed from the upper pump that could lead to overflow and waste.
III. Erection and Structural Reinforcement of the Intermediate Relay Pump Station
The positioning of the intermediate relay pump directly affects its operational stability. The relay pump should be installed in a location with a level site, unobstructed access roads, convenient material supply, and close proximity to the concrete placement point, while also ensuring adequate provisions for power, water, and drainage. In tunnel construction using the bench method, the relay pump may be positioned on the completed invert platform or within the supported section of the upper bench; in shafts or on high slopes, it must be mounted on a dedicated platform or anchored to a support structure.
The code stipulates that structural members equipped with relay pumps shall undergo load‑capacity verification, and reinforcement measures shall be implemented where necessary. Impact loads during concrete pumping comprise the sustained vibrations generated by the hydraulic pump, hydraulic shocks associated with the directional change of the S‑pipe valve, and the backpressure exerted by the concrete column on the pipeline. Once the location of the intermediate relay pump has been determined, the load‑carrying capacity of the platform or floor slab must be rechecked; if insufficient, additional steel‑section support beams, supplementary support legs, or cast‑in‑place concrete piers shall be provided.
IV. Piping Connections and Transitions Between Upstream and Downstream Pumps
The delivery pipeline connecting the upper and lower pumps serves as the “blood vessels” of a multi‑pump cascade system, and its connection quality directly affects the suction efficiency of the cascade pumps and the overall system stability. Between the outlet of the upstream pump and the hopper of the downstream pump, a transition section of piping must be installed. This section should be laid out according to the principles of “gentle slope, straight alignment, and minimal bends,” with each meter of pipe maintaining a uniform, slightly downstream‑sloping gradient (0.5%–1%) to facilitate air venting and reduce hydraulic resistance.
At the inlet of the transition pipeline (the discharge port of the upstream pump), a gate valve or ball valve shall be installed to isolate the line during shutdown of the upstream pump or pipe replacement, thereby preventing concrete backflow from impacting the downstream pump. The outlet of the transition pipeline should extend 500–800 mm above the hopper of the downstream pump, allowing the concrete to fall into the hopper under gravity and minimizing impact and air entrainment during feeding. The pipeline outlet should not be inserted directly below the liquid level in the hopper; otherwise, vortices may form inside the hopper, drawing air into the pumping system.
The layout of transition pipelines should also avoid sharp S‑shaped bends or reverse bends. Each 90° bend is equivalent to a pressure loss of 9 to 12 meters of horizontal pipe; the fewer bends there are, the lower the pressure loss. In areas where bends change direction, stresses are significant, so supports should be spaced more closely. Support locations must be determined through structural calculations, and the supporting structure at each location must be verified. Pipe‑to‑pipe joints must be secured with clamps, and the sealing rings must be intact, ensuring that the transition pipeline remains leak‑free and firmly fastened under pumping‑induced impacts.
V. Pressure Calculation and Parameter Adjustment for Multi-Pump Relay Systems
The total pressure requirement of a multi‑pump relay system is not simply the sum of the individual pump pressures; rather, it necessitates calculating the pipeline friction losses for each pumping stage and adjusting the operating parameters of each pump accordingly.
The first pumping stage (from the mixing station to the intermediate relay pump) shall have its cumulative pressure loss calculated based on the horizontal delivery distance, vertical lift height, and the number of bends. Similarly, the second pumping stage (from the intermediate relay pump to the nozzle pump) shall also have its pressure loss determined according to the pipeline layout. By comparing the total calculated pressure loss with the pump’s rated discharge pressure, verify whether the selected pump meets the requirements. If the cumulative horizontal equivalent distance exceeds the maximum pumping distance of a single pump, an additional relay pump should be installed.
The theoretical outlet pressure of wet‑spraying rigs typically ranges from 6 to 9 MPa, with some high‑performance models reaching 10 to 12 MPa. In relay‑pump configurations, the operating pressure settings for each pump stage should be adjusted according to pipeline length and vertical lift, ensuring that all stages operate within their rated pressure ranges and preventing any single stage from running under prolonged overpressure, which could damage seals or overload the hydraulic system. During startup, it is advisable to adopt a low‑displacement, high‑pressure approach to gradually establish a stable flow regime.
VI. Precautions and Safe Operating Procedures for Multi-Pump Relay Connections
When implementing a multi-pump cascade connection, the following points should also be taken into account:
Impact of pressure losses in pump‑body accessories. In pressure‑loss calculations, the following pressure losses associated with pump‑body components should be accounted for: a V‑shaped pipe from 175 mm to 125 mm incurs a pressure loss of approximately 0.05 MPa; each distribution valve results in a pressure loss of about 0.08 MPa; and the internal losses incurred during startup of each concrete pump amount to roughly 2.80 MPa.
Provision for the anti‑pumping function. On the transition pipeline between the discharge outlet of the upstream pump and the hopper of the downstream pump, excessively long vertical risers with significant elevation differences should be avoided; otherwise, during back‑pumping, the upstream pump will be unable to effectively draw the concrete back from the pipeline. Where conditions permit, additional discharge ports should be installed at appropriate locations along the transition pipeline to facilitate pressure relief and pipeline cleaning in emergency situations.
Liquid level control for the intermediate hopper. The aggregate hopper of the lower pump shall be equipped with a liquid-level sensor that automatically triggers an alarm when the material level falls below the lower limit, prompting the upper pump to increase the feed rate or to stop the lower pump, thereby preventing air from being drawn into the lower pump. Operators of both the upper and lower pumps must maintain uninterrupted two-way radio communication, and the pumps must never be operated unless their control systems are interlocked.
Inspection of pipeline wall thickness wear and joint sealing. In relay pump connection systems, the pipelines experience uneven distribution of impact and wear; therefore, before and after each shift, the sealing integrity of transition pipe joints and the condition of pipe wall wear should be checked. Pipes with wear exceeding allowable limits must be replaced promptly, and any deteriorated joint sealing rings should be replaced immediately.
Electrical load and cable installation. For multi‑pump cascade connections, a power supply must be provided at the intermediate booster pump, and the electrical load shall comply with electrical safety standards. Cables shall not be routed in a manner that crosses or becomes entangled with the process piping, to prevent pipeline vibrations or leaks from damaging the cable insulation.
VII. Conclusion
The multi‑pump relay connection of a fully automatic wet‑spraying carriage is an effective technical solution for achieving ultra‑long‑distance or ultra‑high‑rise spraying operations. Its core lies in matching the delivery capacities of the upper and lower‑stage pumps, verifying the structural load‑bearing capacity of the intermediate relay stations, and optimizing the layout and adjusting the parameters of the transition pipelines. The design of a multi‑pump relay system should strive for simplicity; relay pumping should be avoided unless absolutely necessary, as the relevant codes recommend against using relay pumping for concrete pumps. When site conditions genuinely necessitate a multi‑pump relay configuration, the relay pumps must be selected strictly in accordance with the calculated pipeline pressure losses, and comprehensive safeguards—including structural reinforcement, pipeline sealing, interlock communication, and routine maintenance—must be implemented to ensure the continuity, safety, and stability of concrete spraying operations.
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