In addition to the high and low pressure mode, the concrete delivery pump also has two working modes: "forward pump" and "reverse pump".
Positive pump mode
Working principle: This is the normal pumping mode of a concrete pump truck for transporting concrete. In piston-type concrete pump trucks, there are two hydraulic cylinders at the bottom of the hopper, each with a piston that alternately performs reciprocating motion. When the piston moves backward, the concrete is passively drawn into the cylinder; when it is pushed forward, the concrete is pushed out by the piston. In the middle of the two cylinder openings, there is an S-shaped distribution valve that swings left and right, constantly connecting to the left or right cylinder opening and pushing the concrete out of this cylinder when connected to the cylinder opening. Finally, the concrete is sent into the delivery pipeline and transported to the target pouring location.
Applicable scenarios: It is suitable for various conventional concrete pouring construction scenarios, such as large-scale concrete projects in high-rise buildings, overpasses, expressways, etc., as well as secondary pouring construction in indoor projects, such as the pouring of structural columns and invisible columns, which can improve work efficiency, save time and costs. In bridge and tunnel construction, it can also effectively transport concrete to various parts of complex structures, ensuring the quality and progress of the construction. In addition, it is widely used in agricultural infrastructure construction, such as in mines, highways, railways, tunnels and culverts, providing reliable concrete transportation services. In slope care, small-scale reservoirs and water conservancy hydropower projects, and other small-scale outdoor or outdoor operations, it can also provide necessary concrete transportation support in various environments for construction.
Reverse pump mode
Working principle: The purpose of this working mode is to eliminate pipeline blockage faults and clean the delivery pipeline. The working process is to suck the concrete remaining in the delivery pipeline back into the hopper.
Applicable scenarios: When the concrete delivery pump encounters a pipeline blockage fault during pumping, it can switch to the reverse pump mode. By sucking the concrete in the pipeline back into the hopper, an attempt is made to clear the pipeline. After the construction is completed, the reverse pump mode can also be used to clean the delivery pipeline to prevent the concrete from solidifying in the pipeline and affecting future use.
The forward and reverse pump modes of a concrete pump truck represent two completely different working states. The core differences lie in functions, operational purposes, application scenarios, and the impact on the equipment. The following provides a comparative analysis from multiple perspectives:
I. Comparison of Functions and Working Principles
Mode Function Working Principle Hydraulic System Action Distribution Valve Action
Positive Pump Transport concrete to the pouring point Hydraulic cylinder pushes the piston forward, pushing the concrete from the hopper into the conveying pipeline, and achieving continuous pumping through the swinging of the distribution valve. No-load chamber of the main oil cylinder receives oil, the piston is pushed forward, and the displacement is large. S valve (or gate valve) synchronously switches with the pumping cylinder.
Reverse Pump Remove blockages or clean the pipeline Hydraulic cylinder pulls the piston backward, sucking the concrete in the pipeline back to the hopper, forming reverse flow. Loaded chamber of the main oil cylinder receives oil, the piston is pulled backward, and the displacement is small. S valve swings in the opposite direction, and is connected in reverse with the pumping cylinder.
II. Detailed Explanation of Core Differences
Direction and Purpose
Positive pump: Single-directional concrete transportation, the purpose is to transport concrete from the hopper to the pouring location, which is the main working mode of the pump truck.
Negative pump: Reverse pumping to suck out the concrete, the purpose is to clear blockages or clean the pipeline, it is an auxiliary function.
Hydraulic and Mechanical Differences
Hydraulic Pressure: During positive pumping, the hydraulic system pressure is high (usually 12-16 MPa), to overcome the resistance of concrete flow; during negative pumping, the pressure is low (8-12 MPa), only to overcome the frictional force in the pipeline.
Piston Stroke: During positive pumping, the piston works throughout its stroke, maximizing the displacement; during negative pumping, the piston stroke is shortened, and the displacement is reduced by approximately 30%-50%.
Distribution Valve Action
During positive pumping, the distribution valve synchronously switches with the pump delivery cylinder to ensure continuous concrete flow; during negative pumping, the distribution valve swings in the opposite direction, forming a reverse flow path. For example, when the left cylinder pushes the concrete forward, the distribution valve connects the left cylinder with the pipeline; during negative pumping, the left cylinder pulls backward, and the distribution valve connects the left cylinder with the hopper.
III. Comparison of Application Scenarios
Mode Typical Application Scenarios Operation Trigger Conditions
Positive Pump - Core cylinder pouring of high-rise buildings
- Construction of large-span bridge box girders
- Concrete transportation for tunnel lining - Normal construction stage
- Concrete slump meets requirements (120-180mm)
- No signs of pipeline blockage
Negative Pump - Pipeline blockage (pumping pressure suddenly rises above 18 MPa)
- Pipeline cleaning after construction
- Pipeline cleaning when changing concrete grade - Pumping pressure abnormally increases
- Pumping volume suddenly decreases
- No concrete flows out at the end of the pipeline
- Construction completion stage
IV. Impact on Equipment
Positive Pump Mode Impact
Wear: Components such as pistons, conveying cylinders, and distribution valves that are prone to wear experience high-pressure friction, with a lifespan of approximately 8,000 - 12,000 cubic meters of concrete.
Energy Consumption: Engine load rate is 70% - 85%, fuel consumption is approximately 0.3 - 0.5 liters per cubic meter.
Maintenance: Regular inspection of hydraulic oil cleanliness (NAS 1638 standard ≤ 9 grades) is required, and filter replacements are necessary.
Reverse Pump Mode Impact
Wear: During reverse pumping, the scouring effect of concrete on the inner wall of the pipeline intensifies, especially at the bends, and the wall thickness needs to be checked every 500 hours.
Energy Consumption: Engine load rate drops to 50% - 60%, fuel consumption is approximately 0.2 - 0.3 liters per cubic meter.
Risk: Frequent reverse pumping may cause concrete segregation, and the duration of reverse pumping should be controlled (no more than 3 minutes per time).
V. Operating Precautions
Positive Pump Mode
Before starting, check the amount of concrete in the hopper (not less than the rotating shaft of the mixer) to avoid air intake.
During pumping, maintain continuity. If the machine is shut down for more than 5 minutes, reverse pump 1 - 2 strokes to prevent blockage.
Monitor the pumping pressure (normal range 12 - 16 MPa), and switch to reverse pump immediately if it exceeds 18 MPa.
Reverse Pump Mode
Before reverse pumping, ensure there is sufficient space in the hopper (at least 1.2 times the volume of the concrete in the pipeline).
Reverse pumping should not exceed 3 times, with an interval of 10 seconds each time to avoid sedimentation of concrete in the hopper.
If reverse pumping is ineffective, immediately stop the machine, disassemble the pipeline for cleaning, and strictly prohibit forced pumping.
VI. Case Comparison
Positive Pump Mode Case
Project: Core tube pouring for a 30-story residential building
Parameters: Pumping height 98 meters, horizontal distance 150 meters, concrete strength C40
Result: The positive pump mode operated continuously for 12 hours, transporting 450 cubic meters of concrete, with the pumping pressure remaining stable at 14-15 MPa, and no blockage occurred.
Reverse Pump Mode Case
Project: Tunnel lining construction
Problem: When pumping to 500 meters, the pressure suddenly rose to 20 MPa, and the delivery volume dropped to 5 m³/h
Treatment: Switched to the reverse pump mode 3 times, each time for 2 minutes, successfully retrieved the blocked section of concrete, and resumed construction after restarting the positive pump.
VII. Summary and Suggestions
The Core Difference between Positive Pump and Reverse Pump
Positive pump is "one-way transportation", while reverse pump is "reverse suction"; positive pump pursues efficiency, while reverse pump focuses on fault handling.
Positive pump relies on a high-pressure system, while reverse pump relies on low-pressure high-flow; the wear of positive pump is concentrated at the front end, while the wear of reverse pump is concentrated in the pipeline. Operation Suggestions
Prioritize optimizing the concrete mix ratio (with a slump of 140 ± 20 mm), and reduce the demand for reverse pumps.
Perform a reverse pump - positive pump cycle every 500 cubic meters of concrete to clean the inner walls of the pipeline.
Equip with pressure sensors and IoT modules to monitor the pumping status in real time and automatically issue warnings for blockage risks.
By reasonably switching between the positive pump and reverse pump modes and combining with scientific maintenance management, the construction efficiency and equipment lifespan of the concrete pump truck can be significantly improved. In actual projects, operation strategies need to be dynamically adjusted according to the concrete performance, pipeline layout, and construction schedule.
