Mixer Discharge Gate Problems
This guide covers 15 faults on the hydraulic discharge gate of the concrete mixer, with the symptoms, possible causes and checks and fixes for each. Always release the pressure in the circuit before working on the hydraulic system.
Safety warning: The checks and interventions in this guide must only be carried out by trained maintenance personnel. Before entering the mixer or working on the hydraulic, pneumatic or electrical system, stop the plant, isolate the power and apply the LOTO (lockout/tagout) procedure; release the pressure in the hydraulic and pneumatic lines. If in doubt, contact MEKA technical service.
Gate opening valve coil keeps burning out
Symptom: The coil of the hydraulic valve that opens the mixer discharge gate keeps burning out.
The solenoid valve coil supply voltage (24 VDC / 220 VAC) may be fluctuating, or the valve body may be mechanically sticking. To fix the problem:
- Check the coil supply voltage and ensure a stable operating voltage
- Carry out the electrical checks needed to eliminate voltage fluctuations
- Clean the solenoid valve plunger and moving mechanical parts
- Check that the valve moves freely and works correctly
Hydraulic pump cavitation (foaming) and loud noise
Symptom: The hydraulic pump cavitates (foams) heavily and makes a loud noise while running.
Checks and fixes:
- Check the hydraulic oil level and the condition of the oil
- Inspect the pump suction line for air ingress, leaks or blockage
- Check the suction and hydraulic filters and clean or replace them as needed
- Check for air entrainment or unsuitable oil that could make the hydraulic oil foam
- Measure the pump inlet pressure and operating values
- Check for internal pump wear caused by cavitation
- If necessary, consider overhauling or replacing the hydraulic pump
Hydraulic pressure fluctuates and does not hold the target value
Symptom: The hydraulic system pressure fluctuates on the pressure gauge and does not settle at the target value.
Checks and fixes:
- Check the hydraulic pump flow and pressure output
- Inspect the pressure control valve, relief valve and proportional valves
- Check the hydraulic system for air
- Check the oil level, oil quality and filters and carry out the necessary maintenance
- Check the circuit for components that could cause external or internal leakage
- Verify the calibration of the pressure sensor and pressure gauge
- After the adjustments, test that the system pressure holds steady at the target value
Oil leaking from the hydraulic cylinder rod seals
Symptom: Industrial oil leaks out of the hydraulic cylinder (piston) rod seals.
Checks and fixes:
- Check the cylinder rod surface for scratches, wear or deformation
- Inspect the rod seals and sealing elements for wear
- Replace damaged or hardened seals with suitable new ones
- Check the cylinder for pressure-related overload or internal leakage
- Check the contamination level of the hydraulic oil and the condition of the filters
- After fitting, test the cylinder for sealing and performance
Closed gate drifts down on its own
Symptom: With the gate in the closed position, it drifts down by a few millimetres on its own.
Checks and fixes:
- Check the hydraulic cylinder for internal leakage
- Inspect the cylinder seals and sealing elements for wear
- Check the hydraulic lock valve, check valve and directional control valves
- Check the valve block for contamination, leakage or incomplete closing
- Measure whether the system pressure stays stable with the gate closed
- If necessary, replace faulty valves or sealing elements
- After maintenance, test the gate's holding in the closed position and under load
Gate binds on one side and sticks at the hinge when opening
Symptom: The mixer discharge gate binds on one side and sticks on the hinge shaft while opening.
Checks and fixes:
- Check the discharge gate hinge shaft and bearing points
- Inspect the hinge shaft for bending, wear or misalignment
- Check the gate connection points for mechanical binding or deformation
- Clean and properly lubricate the hinge bearings
- Check the hydraulic cylinder connections for parallelism and alignment
- Replace worn bushings, bearings or connecting parts
- After maintenance, test that the gate opens and closes smoothly and evenly
Emergency manual lever does not move the piston
Symptom: The hydraulic piston does not move even though the emergency manual lever is operated.
Checks and fixes:
- Check the mechanical movement and linkages of the emergency manual lever
- Inspect the manual/pilot valve block for sticking, contamination or faults
- Check the hydraulic system pressure and oil level
- Check the hydraulic hoses and lines for blockages or leaks
- Check the hydraulic cylinder for mechanical binding or a load-related obstruction
- Test that the valve coils and control elements work correctly in manual bypass
- Repair or replace faulty valves, connecting parts or seals
- After maintenance, test the emergency manual function
Gate opens slowly and discharge takes longer
Symptom: The mixer gate has become very slow to open and the mixer discharge time has increased.
Checks and fixes:
- Check the hydraulic system pressure and flow
- Inspect the hydraulic pump, valve block and flow control elements
- Check the gate cylinder and connection points for binding or mechanical resistance
- Check the hydraulic oil level, oil quality and filters
- Check the flow control valve settings and set a suitable opening speed
- Check the cylinder seals and sealing elements for internal leakage
- After maintenance and adjustment, test the gate opening/closing speed and the discharge time
Limit switch arm breaks or gets covered in mortar
Symptom: The mechanical arm of the gate limit switch keeps breaking or getting covered in mortar.
Checks and fixes:
- Check whether the limit switch arm is overstressed during gate movement
- Inspect the gate mechanism, its bearings and pivot points for binding or misalignment
- Check the limit switch mounting position and actuation distance
- Fit a suitable guard or cover to prevent mortar build-up
- Replace the damaged limit switch arm and consider a more robust type
- Test that the gate movement and the limit switch signal work correctly
Gate support bars are flexing
Symptom: The mechanical bars (arms) carrying the gate body show visible flexing.
Checks and fixes:
- Check the gate support bars and connection points for deformation
- Inspect the bars for cracks, permanent bending or material fatigue
- Check for conditions causing overload or uneven load distribution on the gate mechanism
- Check the hinges, connecting pins and bearings for play
- Replace deformed or weakened support bars
- Check the alignment and operation of the gate opening/closing mechanism
- After maintenance, test the gate system for safe operation under load
Hydraulic hoses whip
Symptom: The hydraulic hoses whip violently during operation because of high pressure.
Checks and fixes:
- Check the hydraulic hose connections, fittings and clamps
- Secure the hoses safely with suitable clamps and supports
- Check the system pressure and pressure spikes
- Inspect the hoses for deformation, cracks, bulging or wear
- Replace damaged hoses or hoses not rated for the pressure
- Check whether sudden valve opening/closing is causing pressure spikes
Automation shows a "Gate Open" error while the gate is closed
Symptom: Even when the gate is fully closed, the automation computer shows a "Gate Open" error.
Checks and fixes:
- Check the closed-position limit switch
- Check that the limit switch arm and actuation point are in the correct position
- Check the sensor connections, cables and terminals
- Check the gate mechanism for misalignment or mechanical play that prevents full closing
- If a proximity sensor is used, check the sensing distance and detection settings
- Test whether the automation input signal (PLC digital input) is read correctly
- Replace faulty sensors or connecting parts
- After maintenance, verify the gate open/closed feedback signal in the automation system
Hydraulic motor runs but the pump shaft does not turn
Symptom: The hydraulic motor is running and making noise, but the hydraulic pump shaft does not turn.
Checks and fixes:
- Check the mechanical connection between the hydraulic motor and the pump
- Inspect the coupling, clutch and shaft connections for breakage, stripping or play
- Check the hydraulic system pressure and flow
- Assess the hydraulic motor for binding, wear or mechanical damage
- Check that the pump shaft turns freely
- Check the hydraulic oil level, filters and suction line
- Repair or replace faulty connections or equipment
- After maintenance, test the system under load
Oil foaming out of the hydraulic tank breather
Symptom: Oil foams out of the breather filter on the hydraulic tank cover.
Checks and fixes:
- Check the hydraulic oil level and whether the tank has been overfilled
- Check the suction line for leaks that could let air into the system
- Check the oil for foaming, viscosity and suitability
- Inspect the breather filter for blockage or contamination and replace it if necessary
- Check the pump suction line and connections for looseness or air ingress
Discharge gate jammed with concrete in the mixer
Symptom: The discharge gate is jammed and there is concrete inside the mixer.
Before entering the mixer or working on the gate mechanism, follow the safety warning at the top of this page. To fix the problem:
- Safely remove the concrete from inside the mixer
- Check the discharge gate mechanism and clear the cause of the jam
- Check the gate hinges, lock and moving parts
- After cleaning and maintenance, test that the gate opens and closes properly
Still not solved? If the fault persists after these checks, you can reach the MEKA technical service team 24/7. For the genuine parts you need, see Concrete Batching Plant Spare Parts.
Other concrete batching plant troubleshooting guides:
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