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How to adjust the working pressure of the vehicle-mounted pump’s hydraulic system
Release time:
2026-01-27
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Summary:
As a critical piece of equipment in construction projects, the working pressure of the core hydraulic system in a vehicle-mounted pump directly determines the overall performance, efficiency, and reliability of the machine. If the working pressure is too high, it will accelerate component wear, cause oil temperatures to soar, and even lead to safety hazards such as seal failure or pipe rupture. Conversely, if the pressure is too low, the pump will lack sufficient power, resulting in weak pumping performance and sluggish operation, thereby affecting the construction schedule. Therefore, correctly and safely adjusting the working pressure of the hydraulic system is a core skill that operators and maintenance personnel must master.
Adjusting working pressure essentially involves modifying the setpoint of the relief valve in the hydraulic system. The relief valve acts as the system’s “safety sentinel”—when the pressure attempts to exceed its preset limit, the valve opens and diverts a portion of the hydraulic fluid back to the reservoir, thereby stabilizing the system pressure within the predetermined range. The entire adjustment process should follow a rigorous sequence of steps, always prioritizing safety above all else.
I. Necessary Preparations Before Adjustment
1. Confirm the necessity of adjustment: Do not adjust blindly. Only when the equipment exhibits clear symptoms of pressure abnormalities—such as a pressure gauge reading that deviates from the rated value, insufficient actuator performance, or abnormal heating in the system—and after preliminary troubleshooting has ruled out other simple faults like low oil level, clogged filter elements, or pump damage, should you consider adjusting the relief valve.
2. Familiarize yourself with equipment documentation: Before operation, be sure to carefully read the equipment’s instruction manual and hydraulic schematic diagram. Clearly identify the location, model, and manufacturer-specified rated pressure range of the main relief valve and secondary relief valves (such as the overload valve on directional control valves) within the system. Setting values vary depending on the manufacturer and model of the equipment.
3. Equipment Status Preparation: Place the equipment on a flat, stable surface, turn off the engine, and firmly engage the parking brake. For electric pumps, be sure to disconnect the main power supply and hang up a warning sign reading “Under Maintenance—Do Not Close Circuit.” Ensure that the hydraulic system is completely depressurized (achieved by repeatedly operating the directional control valve handle) and that the system has cooled down.
4. Tool and Personnel Preparation: Prepare a qualified precision pressure gauge (with a range higher than the system’s rated pressure), appropriate wrenches, screwdrivers, and safety equipment such as protective goggles and gloves. It is recommended that two trained personnel work together: one person is responsible for adjustment, while the other monitors the pressure gauge and ensures on-site safety.
II. Specific Steps for Pressure Regulation
1. Connect the monitoring instrument: Locate the system’s main pressure measurement point (typically near the main pump outlet or the main relief valve), and securely connect a reliable, high-precision pressure gauge to the pressure-measurement interface. This is the sole basis for obtaining accurate pressure data; you must not rely solely on the pressure gauge built into the equipment for precise adjustments.
2. Start the equipment and allow it to preheat: On the premise of ensuring safety, start the engine or connect the power supply, and let the hydraulic pump run at low speed under no-load conditions for 5–10 minutes. Allow the hydraulic oil temperature to rise to the normal operating range of 40–60℃, as the oil temperature affects the viscosity of the fluid and, in turn, influences the pressure readings.
3. Load the system and observe the initial pressure: Create loading conditions to raise the system pressure. For on-vehicle pumps, the “pressure buildup” method is commonly used: While the pump is in operation, close the shut-off valve at the end of the delivery pipe, or operate the directional control valve to move the piston to the end of its stroke and hold it there. At this point, observe the connected pressure gauge and record the current maximum pressure value of the system.
4. Carefully adjust the overflow valve:
Identifying the Adjustment Mechanism: The adjustment mechanism of most relief valves consists of a locknut and an internal hexagonal adjusting screw. Rotating the screw clockwise generally increases the pressure, while rotating it counterclockwise reduces the pressure.
Perform the adjustment as follows: First, use a wrench to loosen the lock nut. Then, using an Allen wrench, rotate the adjusting screw extremely slowly. Each adjustment should not exceed one-quarter of a turn, and you should pause briefly after each adjustment to allow the pressure gauge reading to stabilize before making the next fine adjustment. The target pressure must strictly adhere to the specified value given in the equipment’s technical manual; never exceed the system’s maximum allowable pressure.
5. Locking and Verification: Once the pressure stabilizes at the target value, and while keeping the adjusting screw completely stationary, securely tighten the lock nut using a wrench. During the locking process, closely monitor the pressure gauge to ensure that the reading does not change due to the locking operation. After locking, perform another loading-unloading cycle to verify that the set pressure remains stable and reliable.
III. Key Considerations and Follow-up Tasks
Safety first—overpressure is strictly prohibited: Absolutely no adjustments should be made to exceed the rated values specified on the nameplate in an attempt to achieve higher output. This is the primary cause of premature failure of hydraulic components and safety incidents.
Synchronized Inspection and Maintenance: When adjusting the pressure, check whether the hydraulic oil is clean and free of foam. If the oil is contaminated or contains excessive air, the pressure will fail to remain stable. If the pressure fluctuates significantly or shows no response during adjustment, it could indicate that the relief valve itself is damaged—for example, the valve spool is stuck or the spring has become fatigued—requiring either cleaning or replacement.
Record archiving: After adjustment is complete, record the final set pressure value, date, and operator’s name for future maintenance and troubleshooting purposes.
In short, adjusting the working pressure of an in-vehicle pump’s hydraulic system is a highly technical operation. It requires operators not only to have a solid grasp of the underlying principles but also to adopt a meticulous attitude and cultivate standardized operational habits. By adhering to the principles of “thorough preparation, accurate monitoring, careful fine-tuning, and reliable locking,” we can ensure that the equipment consistently operates stably under efficient and safe pressure conditions, thereby guaranteeing the smooth execution of construction tasks.
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