Material leakage is the most intuitive fault of piston pumps, mostly occurring at three locations: the "connection between plunger and pump cylinder", "flange interface", and "check valve sealing surface". The core causes revolve around "seal failure" and "structural wear", requiring targeted troubleshooting by location.
- When the plunger reciprocates, materials continuously leak from the gap between the pump cylinder and the plunger; in severe cases, dripping or jetting leakage occurs.
- Leakage is accompanied by a slight pressure drop and a gradual reduction in conveying capacity.
After shutting down the pump, observe the leakage location:
- If leakage is concentrated between the plunger and the gland, prioritize checking the sealing assembly.
- If leakage is accompanied by metal debris, check the wear of the plunger and pump cylinder.
- Remove the packing seal: Check if the packing has cracks, carbonization (for graphite packing), or fiber breakage (for asbestos packing); replace it if any of these issues exist.
- Disassemble the mechanical seal: Inspect if the contact surfaces of the rotating ring and stationary ring have scratches or pits, and check if the sealing ring is deformed or aged (it is ineffective if it feels hard when pinched by hand).
Measure the inner diameter of the pump cylinder with an inside micrometer and the diameter of the plunger with an outside micrometer, then calculate the fitting gap. If the gap exceeds 0.1mm, the worn parts need to be repaired or replaced.
- Packing seal: Replace with new packing (matching the pump model specifications). When installing, cut the packing into 45° bevels, fill it into the stuffing box in layers, stagger each layer by 90°, and tighten the gland bolts properly (it is advisable to "tighten 1-2 more turns after it can no longer be twisted by hand" to avoid plunger jamming due to over-tightening).
- Mechanical seal: Replace the entire mechanical seal (rotating ring + stationary ring + sealing ring). During installation, ensure the contact surfaces are clean, apply a small amount of grease (matching the material properties, e.g., food-grade grease for food-grade pumps), and ensure the rotating ring can rotate flexibly.
- Minor wear (scratch depth < 0.1mm): For the plunger surface, adopt "nitriding repair" (re-spraying the nitrided layer); for the inner wall of the pump cylinder, perform "honing" to restore the fitting gap.
- Severe wear (gap > 0.1mm): Directly replace the plunger (the material must be consistent with the original pump, e.g., 38CrMoAlA nitrided steel) and the pump cylinder. After replacement, run the pump for a break-in period (operate at low speed and low pressure for 30 minutes).
- Material leaks at the flange connection between the inlet/outlet pipeline and the pump body; the leakage amount increases as the pressure rises.
- The interface is accompanied by material residue and corrosion marks (if corrosive materials are conveyed).
- Aging of flange gasket: Rubber/asbestos gaskets harden and crack due to long-term corrosion by materials and temperature effects.
- Loose flange bolts: Long-term vibration causes bolts to loosen, resulting in poor fitting of the sealing surface.
- Deformation of flange sealing surface: Uneven bolt force during installation or long-term high temperature causes the flange surface to warp.
After shutting down the pump, loosen the bolts, remove the gasket to check for aging or damage; attach a straightedge to the flange surface to check for gaps (a gap > 0.1mm indicates deformation).
- Aging gasket: Replace with a gasket of the same specification (use PTFE gaskets for corrosive materials and metal-clad gaskets for high-temperature materials).
- Loose bolts: Tighten the bolts in "diagonal order" in batches (to avoid one-sided force); refer to the pump manual for the tightening torque (e.g., the torque for M16 bolts is 50-60N・m).
- Deformed flange: Minor deformation can be repaired by "grinding the sealing surface" (polishing with fine sandpaper in the circumferential direction); severe deformation requires flange replacement.
- Materials in the inlet/outlet pipeline flow back after the pump is shut down, or the pump chamber pressure fluctuates frequently during operation.
- A "hissing" leakage sound is heard at the check valve.
- Wear of valve core/valve seat: Particles in the material scratch the valve core (spherical/conical) or the valve seat sealing surface, resulting in poor sealing.
- Spring failure: The check valve spring loses elasticity due to long-term compression fatigue, preventing the valve core from fitting closely to the valve seat.
- Material residue: Viscous materials form lumps between the valve core and valve seat, hindering the valve core from resetting.
Disassemble the check valve, observe if the valve core/valve seat has scratches or pits; press the spring by hand to check its elasticity (the spring is ineffective if it cannot reset quickly after being released); clean the residual materials on the sealing surface.
- Minor wear: Manually grind the sealing surfaces of the valve core and valve seat with abrasive paste (400-800 mesh) until they fit without gaps.
- Severe wear/spring failure: Replace the valve core, valve seat, or spring (must match the original check valve model).
- Material residue: Rinse the sealing surface with a high-pressure water gun (or a suitable solvent, e.g., clean water for mortar residue, alcohol for resin residue) to ensure no lumps remain.
- Regularly inspect the sealing assembly: Check the packing seal of low-pressure pumps every 100 hours and the mechanical seal of high-pressure pumps every 200 hours.
- Control material cleanliness: Install a filter at the feed inlet (the filter pore size ≤ 1/2 of the maximum applicable particle size; e.g., use a 15mm filter for particles up to 30mm) to prevent hard particles from entering the pump chamber.
- Standardize installation: Tighten flange bolts in diagonal order, and ensure the contact surfaces are clean and free of impurities before installing the sealing assembly.
Insufficient pressure is a core fault affecting the conveying capacity of piston pumps, manifested as "output pressure failing to reach the rated value" and "pressure dropping rapidly as the conveying distance increases". The causes fall into three categories: "flow loss", "insufficient power", and "structural failure", which need to be troubleshot in order of priority.
- Type 1: After startup, the pressure is consistently lower than the rated value (e.g., rated 20MPa, actual only 10MPa), and the conveying capacity decreases by more than 30%.
- Type 2: Frequent pressure fluctuations (e.g., fluctuating repeatedly between 15-20MPa), accompanied by pipeline vibration.
- Type 3: Pressure gradually decreases over the operating time, dropping from the rated value to a low level within 1-2 hours.
Flow loss is the main cause of insufficient pressure, essentially resulting from "material leakage or backflow in the pump or pipeline". Specific troubleshooting steps are as follows:
- Troubleshooting: Refer to the check valve inspection method in "Material Leakage Faults". If the sealing surface of the valve core is worn, it will cause material backflow during the pressure feeding stage, making it impossible to build up pressure.
- Verification: After shutting down the pump, close the feed valve and observe whether the pump chamber pressure is maintained. If the pressure drops by more than 2MPa within 10 minutes, it indicates a check valve leak.
- Troubleshooting:
- Check if the pipeline is kinked or deformed (especially flexible hoses). A reduction in pipeline diameter (e.g., from the original 100mm to 80mm) will increase flow resistance.
- Disassemble the end of the pipeline (e.g., grouting port) and check for material caking and blockage (viscous materials tend to accumulate at pipeline elbows).
- Verification: Use clean water instead of materials for conveyance. If the pressure returns to normal, it indicates that the original material had excessive resistance or caused blockage in the pipeline.
- Troubleshooting: An excessively large fitting gap between the plunger and pump cylinder (refer to the gap measurement in "Material Leakage Faults") or scratches on the inner wall of the pump chamber will cause material leakage from the gap during the pressure feeding stage, reducing volumetric efficiency (normal volumetric efficiency ≥ 85%, which may drop to below 60% after leakage).
- Verification: Measure the actual conveying capacity (e.g., hourly conveying volume) and compare it with the rated conveying capacity. If the deviation exceeds 20%, it indicates a decrease in volumetric efficiency.
If no abnormalities are found in the flow loss troubleshooting, check whether the power system fails to provide sufficient driving force:
- Troubleshooting:
- Verify the rated motor power (e.g., a pump with a rated pressure of 20MPa requires a 15kW motor; using an 11kW motor instead will result in insufficient power).
- Use a tachometer to measure the motor output speed. If the speed is lower than the rated value (e.g., rated 1450r/min, actual only 1200r/min), it may be due to incorrect motor wiring (e.g., star connection mistakenly connected as delta connection) or improper inverter parameter settings.
- Verification: Operate the motor under no-load conditions. If the speed is normal but drops by more than 10% under load, it indicates insufficient motor power.
- Troubleshooting:
- Check if the gearbox has oil leakage. Insufficient lubricating oil will reduce gear transmission efficiency.
- Disassemble the gearbox and inspect for gear wear, tooth breakage (accompanied by abnormal noise and speed fluctuations), or bearing damage (jamming during rotation).
- Verification: Manually rotate the crankshaft. If there is excessive resistance or jamming, it indicates a gearbox fault.
Failure of pressure control components (such as relief valves and pressure sensors) will prevent stable pressure maintenance:
- Troubleshooting:
- The relief valve is a pressure protection component. If the valve core is stuck in the "normally open" position, material will leak from the relief port, making it impossible to increase pressure.
- Check the relief valve set pressure (e.g., for a pump with a rated pressure of 20MPa, the relief valve should be set to 22MPa; an incorrect setting of 15MPa will limit the maximum pressure).
- Verification: Close the relief valve outlet. If the pressure returns to normal, it indicates a relief valve fault.
- Troubleshooting: If the displayed value of the pressure sensor deviates by more than 10% from the actual pressure gauge (external standard pressure gauge), it indicates that the sensor calibration has failed or the sensor is damaged.
- Verification: Replace the pressure sensor with a new one. If the displayed pressure matches the actual pressure, the original sensor is faulty.
- Regularly clean pipelines: After every 50 hours of operation, flush pipelines with clean water or a suitable solvent to prevent material accumulation.
- Calibrate pressure components: Calibrate the relief valve set pressure and pressure sensor monthly to ensure an error of ≤ 5%.
- Match the power system: During selection, ensure that the motor power and gearbox transmission ratio match the pump’s rated pressure and speed to avoid "a small horse pulling a large cart" (insufficient power for the load).
Abnormal noise is a signal of "hidden faults" in piston pumps, often accompanied by vibration. Ignoring it may lead to severe component damage (such as crankshaft breakage or bearing scrapping). Based on the "sound-generating parts", abnormal noise can be divided into three categories: "abnormal noise from the power transmission system", "abnormal noise from the volume change system", and "abnormal noise from material impact". Troubleshooting must be conducted by combining sound characteristics and vibration conditions.
- Sound Types: Low-frequency vibrating sound like "hum" (bearing wear), metal impact sound like "clatter" (gear/crankshaft faults), friction sound like "squeak" (insufficient lubrication);
- Accompanying Phenomena: Vibration is concentrated in the gearbox and crankcase areas; there is a noticeable vibration sensation when touching the pump housing by hand; abnormal noise intensifies as the rotational speed increases.
- Check the crankcase oil level gauge: If the oil level is below the minimum scale (or the lubricating oil is black and contains impurities), it indicates insufficient lubrication;
- Inspect the gearbox lubricating oil: If the oil is turbid and contains metal debris, further disassembly and inspection are required.
- After shutting down the pump, manually rotate the crankshaft: If there is a "jamming" or "loose" feeling, it indicates bearing wear;
- Place a stethoscope close to the bearing areas (e.g., both ends of the crankshaft): If a "regular humming sound" is heard after starting the pump, a bearing fault can be confirmed.
- Disassemble the crankcase and use a dial indicator to measure the crankshaft deflection (standard deflection ≤ 0.05mm/m): If it exceeds the standard, the crankshaft is deformed;
- Check if the connecting rod bolts are loose (retighten with a torque wrench, referring to the rated torque), and observe the fitting gap between the connecting rod big end and the crankshaft (standard gap: 0.1-0.15mm).
- Disassemble the gearbox and check if the gear tooth surfaces are worn or have broken teeth; use a feeler gauge to measure the gear meshing gap (standard gap: 0.1-0.2mm): If the gap is too large, the gears are worn.
- Insufficient Lubrication: Replace with new lubricating oil (use 40# mechanical oil for the crankcase and CKC220 extreme pressure gear oil for the gearbox), and fill to the standard oil level according to the manual;
- Bearing Damage: Replace with a bearing of the same model (e.g., deep groove ball bearing 6208), apply bearing grease during installation, and ensure tight fitting between the bearing and the journal;
- Crankshaft/Connecting Rod Deformation:
- Minor bending (deflection: 0.05-0.1mm/m): Can be repaired by "pressure straightening", and re-nitriding treatment is required after straightening;
- Severe deformation or loose bolts: Replace the crankshaft/connecting rod; after reassembly, check the parallelism of the connecting rod (deviation ≤ 0.1mm);
- Gear Faults: Replace worn gears (must be replaced in pairs to ensure meshing accuracy), adjust the gear center distance, and ensure smooth meshing.
- Sound Types: Impact sound like "tap-tap" (check valve faults), metal friction sound like "scrape" (plunger/pump cylinder wear);
- Accompanying Phenomena: The frequency of abnormal noise is consistent with the plunger reciprocation frequency (e.g., 50 reciprocations per minute, with synchronized abnormal noise frequency); some cases are accompanied by material leakage or pressure fluctuations.
