In modern cone crushers the hydraulic system has two vital tasks: protecting the crusher against uncrushable material (tramp release) and changing the closed side setting (CSS). Depending on the crusher design, these tasks are performed by tramp release cylinders, clearing cylinders, a hydroset cylinder that raises and lowers the main shaft, and the related accumulators, valve blocks and hydraulic power unit. In older spring-protected designs, spring packs perform the same protective function.
In this guide we cover in detail the function of the hydraulic cylinders, their location in different designs, the importance of accumulator precharge pressure, failure signs, maintenance and seal replacement steps, and spare part selection. For general cone crusher operation, see our cone crusher guide.
Functions of the Hydraulic System
1. Tramp release (overload protection)
When an uncrushable object such as a bucket tooth, drill bit or piece of steel enters the crushing chamber, the crushing force rises suddenly. The tramp release cylinders connecting the bowl to the frame open when this load exceeds a certain level, allowing the bowl to lift and the object to pass; the gas pressure in the accumulator then returns the system to its original position. The frame, main shaft and bearings are thus protected.
2. Clearing
After a power failure or sudden stop, the crushing chamber can remain full. Clearing cylinders lift the bowl so that the chamber empties and the crusher can be restarted.
3. Setting (hydroset)
In crushers with a moving main shaft (hydroset type), the hydroset cylinder under the main shaft adjusts the CSS by raising and lowering the shaft, and protects the crusher by sending oil to the accumulator under overload. In types with a rotating bowl, the setting is made by turning the bowl with a hydraulic motor.
System Components
| Component | Function | Typical failure |
|---|---|---|
| Tramp release cylinders | Allow the bowl to lift under overload | Seal leaks, scored rod, corrosion |
| Hydroset cylinder | Main shaft position and protection | Piston seal leakage, step wear |
| Accumulator | Absorbs shock and returns the system | Loss of nitrogen precharge, membrane/bladder rupture |
| Hydraulic power unit (pump, tank, filter) | Supplies pressure and oil | Pump wear, dirty oil |
| Valve blocks and hoses | Control the flow | Sticking valves, hose fatigue |
| Pressure sensors | Protection and automation signal | Calibration drift |
Why Is Accumulator Precharge Pressure Critical?
An accumulator is a pressure vessel containing nitrogen gas. Because the gas is compressible, it absorbs shock and pushes the system back to its original position. Precharge pressure falls over time. With low precharge pressure:
- The tramp release system responds late or insufficiently,
- Ring bounce increases,
- Cylinder seals and hoses are exposed to greater pressure fluctuations,
- In hydroset types, the CSS becomes unstable.
Precharge pressure must be checked at the interval and value specified by the manufacturer, with a suitable charging kit and using nitrogen only. Never fill an accumulator with oxygen or air.
Signs of Failure
- Oil leakage at the cylinder rod or connections,
- The CSS changing by itself (hydroset),
- Frequent overload alarms and ring bounce,
- The bowl not reseating after an overload,
- The hydraulic pump starting frequently,
- Scoring and rust on the cylinder rod,
- Darkened hydraulic oil, water or particles in the oil.
Inspection and Maintenance Schedule
| Check | Interval | Method |
|---|---|---|
| System pressure | Every shift | Pressure gauge / control panel |
| Leak check | Daily | Cylinders, hoses, fittings |
| Hydraulic oil level | Daily | Tank gauge |
| Accumulator precharge pressure | Every 3–6 months | Nitrogen charging kit |
| Oil analysis and filter | Manufacturer’s interval | Cleanliness code, water, particles |
| Cylinder rod surface | At liner changes | Visual check for scoring and rust |
| Hose condition | Monthly | Cracks, swelling, chafing |
Cylinder Seal Replacement Step by Step
- Safe shutdown: The crusher is locked out; hydraulic pressure is fully released and the hydraulic side of the accumulators is drained.
- Supporting the bowl: Before removing a cylinder, uncontrolled movement of the bowl or main shaft is prevented.
- Removing the cylinder: Pins and hoses are removed and the fitting ports are capped.
- Workshop disassembly: The cylinder is dismantled in a clean environment; the rod, barrel and piston are inspected.
- Seal replacement: All seals, the wiper and O-rings are replaced as a set; a suitable lubricant is used during assembly.
- Testing: If possible, the cylinder is pressure and leak tested on a test bench.
- Installation and bleeding: The cylinder is refitted, the system is bled and the precharge pressure is checked.
- Function test: Clearing and setting functions are tested and leaks are checked.
Common Mistakes
- Never checking accumulator pressure.
- Replacing seals piecemeal: Replacing them as a set reduces the risk of repeat failure.
- Opening cylinders in a dirty environment: Particles quickly damage new seals.
- Wrong hydraulic oil: Oil incompatible with the seal material causes swelling or hardening.
- Fitting new seals without replacing a scored rod: The seal soon leaks again.
- Not looking for the root cause of frequent tramp events: A missing or faulty metal separator.
Troubleshooting Table
| Symptom | Possible cause | Solution |
|---|---|---|
| Frequent ring bounce | Low precharge pressure, small CSS, fine/wet feed | Check the accumulators, open the CSS, screen out fines beforehand |
| CSS drifting (hydroset) | Piston seal leakage, valve leakage | Check the seal kit and valves |
| Oil leaking from a cylinder | Worn seal, scored rod | Seal kit; replace or re-chrome the rod if necessary |
| Pump runs frequently | Internal leakage, accumulator failure | System leak test, accumulator inspection |
| Bowl does not reseat after tramp | Low accumulator pressure, valve failure | Check precharge and valves |
An Example from the Field
At a granite plant, ring bounce alarms on a cone crusher were increasing day by day. The team temporarily eased the problem by opening the CSS, but the product became coarser. When the hydraulic system was examined, the precharge pressure of two accumulators had fallen far below the manufacturer’s value and the membrane in one had ruptured. The accumulators were renewed and charged to the correct pressure; it was also found that the magnetic separator on the feed belt was not working, and it was repaired. The alarms fell to a normal level and the CSS could be returned to its original value.
Spare Part Selection
- Seal kits: The material (NBR, polyurethane, PTFE, etc.) must suit the working pressure and temperature.
- Cylinder and rod: Dimensions, chrome plating quality and pressure rating.
- Accumulator: Volume, working pressure and a certified pressure vessel.
- Hoses and fittings: Correct pressure rating and length.
CSP Mühendislik supplies tramp release cylinders, hydroset cylinders, seal kits, accumulators and hydraulic connection elements as part of its cone crusher spare parts range.
Pre-Purchase Checklist
- Have the crusher model and cylinder part numbers been identified?
- Is a seal kit or a complete cylinder needed?
- Are the number, volume and pressure rating of the accumulators known?
- Have the hydraulic oil type and seal compatibility been checked?
Safety
- Before working on the hydraulic system, pressure must be brought to zero and the accumulators drained.
- Do not check hoses under pressure by hand; high-pressure oil can penetrate the skin.
- Accumulator charging must only be done by trained personnel and with nitrogen.
Frequently Asked Questions
When should an accumulator be replaced?
When it cannot hold its precharge pressure, when the membrane or bladder is ruptured, or when a periodic pressure vessel inspection finds a non-conformity.
Can a spring-protected crusher be converted to hydraulics?
It is generally not economical; the crusher frame design is different. For spring-protected crushers, regular inspection of the spring packs is recommended.
What do frequent tramp events indicate?
That there is metal or uncrushable material in the feed; the metal separation system should be checked. A very small CSS and fine/wet feed can also cause similar alarms.
How often should hydraulic oil be changed?
According to the manufacturer’s interval and oil analysis results. A deteriorating cleanliness code or the presence of water requires an early change.
Spare Parts and Service for Hydraulic Cylinders
CSP Mühendislik supplies cylinders, seal kits and accumulators for cone crusher hydraulic systems as part of its cone crusher spare parts range, and supports cylinder overhauls, accumulator checks and system testing with our service team. Send your crusher model on WhatsApp for a quick quote.
