Troubleshooting Hydraulic Pressure Loss in Injection Molding Machines

Hydraulic pressure loss is one of the most common — and most disruptive — problems in injection molding. It can cause slow clamping, weak injection, incomplete filling, and inconsistent cycle times. This guide walks you through systematic diagnosis and repair.

Symptoms of Hydraulic Pressure Loss

• Clamping force is lower than setpoint
• Injection speed or pressure is below target
• Cycle time has increased
• Machine movements are slow or sluggish
• Hydraulic pump is louder than normal
• Oil temperature is higher than usual

Step-by-Step Troubleshooting

Step 1: Check the Basics

Before diving into complex diagnostics:

1. Oil level — Low oil starves the pump. Top up if below minimum
2. Oil condition — Dark, milky, or smelly oil is degraded. Check for water contamination
3. Oil temperature — Above 65°C reduces viscosity and pump efficiency. Check cooler function
4. Oil filter — Clogged filters restrict flow. Check filter indicator or replace

Step 2: Inspect the Hydraulic Pump

The pump is the primary pressure source. Vane pumps and piston pumps have different failure modes:

Vane Pump Issues:

• Worn vanes — Low pressure at low speed, normal at high speed
• Worn cam ring — Gradual pressure loss over time
• Internal leakage — Oil temperature rises faster than normal
• Shaft seal leak — Visible oil at the pump shaft

Piston Pump Issues:

• Worn pistons/barrel — Reduced volumetric efficiency
• Swashplate wear — Erratic pressure control
• Valve plate damage — Noisy pump, pulsating pressure
• Control system failure — Pump doesn't respond to demand signal

Step 3: Test the Control Valves

Directional control valves can cause pressure loss through internal leakage:

1. Solenoid check — Verify solenoids are energizing (listen for click, check LED indicators)
2. Spool movement — A stuck spool prevents full flow. Check for contamination
3. Internal leakage — Worn spool-to-bore clearance allows bypass flow. Measure case drain flow
4. Proportional valve — Check amplifier card output and valve response curve

Step 4: Check the Hydraulic Cylinders

• Piston seal wear — Oil bypasses the piston internally
• Rod seal leak — Visible oil on cylinder rod
• Cushion valve — Stuck cushion valve restricts cylinder speed

Step 5: Inspect Hoses and Fittings

• Look for external leaks at hose connections
• Check hose condition — Cracked, swollen, or hardened hoses should be replaced
• Verify fitting tightness (but don't over-tighten)

Pressure Test Procedure

1. Install a calibrated pressure gauge at the pump outlet
2. Set the machine to manual mode
3. Activate clamping at full pressure
4. Compare gauge reading to the controller setpoint
5. If gauge reads low, the problem is upstream (pump or relief valve)
6. If gauge reads correct but machine is weak, the problem is downstream (valves, cylinders, or leaks)

Common Causes and Solutions

Prevention

• Change hydraulic oil every 4,000-6,000 operating hours
• Replace oil filters every 3-6 months
• Monitor oil temperature — install alarms for high temperature
• Keep the reservoir clean — prevent contamination during oil changes
• Schedule annual pump efficiency tests

Need Replacement Parts?

We stock all major hydraulic components for injection molding machines:

• Hydraulic Vane Pumps — Taixin, Vickers, YUKEN
• Hydraulic Piston Pumps — YUKEN, Rexroth compatible
• Directional Control Valves — Cetop 3/5/7
• Hydraulic Oil Filters — Suction and return line

Request a quote with your machine model and symptoms, and we'll recommend the right parts.