A jaw crusher is usually used as the primary crusher in a crushing plant, so its output has a direct effect on the capacity of the entire production line. When the machine produces less than expected, the problem may come from the feed material, discharge setting, jaw plates, electrical supply, feeding system, or operating conditions.
In many cases, low capacity is not caused by the crusher itself. Incorrect feeding, oversized material, an unsuitable discharge opening, or worn components can all reduce throughput.
This guide explains the common causes of low jaw crusher capacity and practical ways to improve output.
Quick Answer: Why Is a Jaw Crusher Producing Less Than Expected?
The most common reasons for low jaw crusher capacity include:
- Feed material is harder or tougher than the crusher is designed to handle
- The motor is rotating in the wrong direction or is incorrectly wired
- The discharge opening is set too small
- Jaw plates have shifted or become excessively worn
- The working-site voltage is too low
- Excessive clearance has developed between the moving jaw and its bearing
- Feed size is too large
- The crusher is being overfed or underfed
- The vibrating feeder is not working at the right angle or amplitude
- The jaw crusher’s discharge opening or nip angle is not properly adjusted
Before changing the machine, check the feeding conditions, CSS (closed-side setting), jaw plate condition and electrical system first.
Common Causes of Low Jaw Crusher Capacity
1. The Feed Material Is Too Hard or Tough
Jaw crushers are designed to process materials within a certain range of hardness, toughness and feed size.
If the material is significantly harder or tougher than the crusher’s intended operating range, the crushing process becomes less efficient. The motor may also operate under a heavier load while throughput falls.
If the material properties are outside the machine’s recommended range, possible solutions include selecting a crusher better suited to the material or using additional crushing equipment in the process.
The material itself should therefore be checked before making changes to the crusher.
2. The Motor Is Rotating in the Wrong Direction
Incorrect motor wiring can cause the crusher to rotate in the wrong direction.
For some jaw crusher designs, this can happen when the motor connections are reversed. An incorrect electrical connection, such as using a star connection where a delta connection is required, can also affect motor performance.
If the motor rotation is found to be incorrect, the wiring should be checked and corrected by a qualified technician according to the crusher manufacturer’s electrical specifications.
The crusher should not be operated continuously until the rotation direction has been confirmed.
3. The Discharge Opening Is Set Too Small
The discharge opening has a direct influence on jaw crusher throughput.
If the opening is set below the recommended operating range, material may take longer to pass through the crushing chamber. This can reduce overall capacity and increase the risk of blockage.
The discharge opening should be adjusted according to the crusher’s operating requirements and the feed requirements of the next crushing stage.
A smaller discharge opening is not always better. If finer material is required, it is often more practical to use a secondary crusher rather than forcing the primary jaw crusher to produce an unnecessarily small product.
4. The Jaw Plates Have Shifted or Are Incorrectly Positioned
Jaw plate position also affects crushing performance.
If a jaw plate moves from its intended position, the tooth profiles may become improperly aligned. In severe cases, the tooth tips of the fixed and movable jaw plates can face each other rather than working with the intended tooth-to-gap relationship.
Check the jaw plate profile, tooth spacing and mounting position. If the dimensions no longer meet the manufacturer’s requirements, the worn or damaged plates should be replaced.
After installation, the fixed and movable jaw plates should be correctly aligned and securely tightened to prevent movement during operation.
5. The Working-Site Voltage Is Too Low
A jaw crusher requires sufficient electrical power to handle heavy crushing loads.
If the voltage at the installation site is too low, the motor may not be able to operate normally under load. The result can be reduced crushing capacity and unstable operation.
If low voltage is suspected, measure the voltage under operating conditions rather than checking it only when the machine is idle. The electrical supply should meet the motor and crusher manufacturer’s requirements.
6. Excessive Clearance Between the Moving Jaw and Bearing
The moving jaw is supported by bearings, and excessive wear can create additional clearance.
When the bearing or moving jaw is significantly worn, the outer bearing ring may begin to move relative to its intended position. This can affect the movement of the jaw and reduce crushing efficiency.
Inspect the bearing, moving jaw and related components if abnormal movement or excessive clearance is found. Depending on the actual condition, the worn bearing or moving jaw may need to be replaced.
How to Increase Jaw Crusher Capacity
Improving jaw crusher output is not simply a matter of increasing the feed rate. The feed size, feed distribution, feeder settings, discharge opening and crusher operating conditions all need to work together.
1. Control Feed Size to Prevent Blockages
The feed opening must be matched to the maximum size of the material entering the crusher.
A commonly used design relationship is:
Feed opening size ≈ 1.1–1.25 × maximum feed particle size
The exact value should always be checked against the specifications of the particular crusher.
One common operating mistake is to treat the measured physical size of the feed opening as the maximum allowable feed size. This can result in oversized rocks entering the crushing chamber.
Even if a blockage does not happen frequently, each blockage can stop the production line for a significant period while operators clear the chamber.
For this reason, controlling the maximum feed size is one of the basic requirements for maintaining stable jaw crusher production.
2. Control the Feed Rate and Avoid Overfeeding
Both insufficient feeding and excessive feeding can reduce jaw crusher capacity.
When the feed rate is too low, the crusher is not being used efficiently and the production line cannot reach its intended throughput.
On the other hand, feeding too much material can fill the crushing chamber faster than the crusher can process it. Material may accumulate in the chamber and prevent crushed material from leaving efficiently.
The result can be bridging, blockage and unstable production.
The goal is therefore not to feed as much material as possible, but to maintain a steady feed rate that matches the crusher’s processing capacity.
3. Maintain a Consistent Feeding Rhythm
The feeding system has a major influence on jaw crusher performance.
In some crushing plants, the vibrating feeder is installed with a long exposed section outside the feed hopper. If the feeding point is poorly positioned, the feeder may operate more like a vibrating chute than an efficient feeding and screening system.
The position and angle of the feed hopper should allow material to enter the feeder smoothly without placing excessive pressure on it.
The feed should not simply fall vertically onto the feeder, particularly when a dump truck is used to discharge material directly into the hopper. Excessive impact and material pressure can affect the feeder’s ability to vibrate and control the feed.
The objective is to make the feeder’s output consistent with the jaw crusher’s processing rhythm.
4. Adjust the Vibrating Feeder to Use Its Screening Function
Many vibrating feeders are equipped with grizzly bars that can remove smaller material before it reaches the jaw crusher.
This pre-screening function can reduce the amount of material that needs to pass through the crusher and improve the overall throughput of the crushing circuit.
However, if the feeder amplitude or installation angle is incorrect, large pieces of material can become trapped between the grizzly bars. When this happens repeatedly, some operators may block the grizzly section with steel plates and use the equipment only as a conventional feeder.
A better approach is to first check the feeder settings.
Adjusting the vibration amplitude and feeder angle can improve material separation and make better use of the grizzly section. Removing suitable fines before primary crushing can reduce unnecessary load on the jaw crusher and increase the effective capacity of the plant.
5. Adjust the Discharge Opening and Nip Angle Correctly
The jaw crusher discharge opening determines the size of material leaving the primary crushing stage and has a direct effect on throughput.
Because jaw crushers are commonly used for primary crushing, the discharge opening should be selected according to the feed requirements of the next crushing stage.
Simply opening or closing the discharge setting without considering the complete crushing circuit can create other problems.
The nip angle—the angle formed between the fixed jaw plate and moving jaw plate—is another operating parameter that affects crushing performance. A typical range may be around 17–26°, but the appropriate value depends on the crusher design and operating conditions.
The horizontal stroke of the moving jaw, rotational speed, discharge-zone crushing conditions and material moisture can also influence capacity.
These parameters should therefore be adjusted as part of the complete crushing system rather than individually.
Jaw Crusher Capacity Troubleshooting Checklist
If a jaw crusher is producing less than expected, check the following items in order:
| Check | What to Look For | Possible Action |
|---|---|---|
| Feed size | Oversized rocks entering the chamber | Control maximum feed size |
| Feed rate | Too little or too much material | Adjust feeder output |
| Feed distribution | Uneven material entering the chamber | Improve feeder and hopper arrangement |
| Discharge opening | Setting is too small | Adjust according to the required product size |
| Kjeveplater | Excessive wear or incorrect alignment | Inspect, reposition or replace |
| Motor rotation | Incorrect rotation direction | Check electrical connection |
| Voltage | Voltage drops under load | Check the power supply |
| Bearing clearance | Excessive movement or wear | Inspect bearing and moving jaw |
| Feeder | Incorrect angle, amplitude or blocked grizzly | Adjust feeder settings |
| Material condition | Excessive hardness, toughness or moisture | Check material properties |
Why Feed Control Matters So Much
The jaw crusher and feeding system should be treated as one operating system.
Increasing the feeder output without checking the crusher’s actual capacity can cause blockage. Reducing the feed too much wastes available crushing capacity. Similarly, changing the discharge opening without considering the secondary crusher can create an imbalance further down the production line.
A stable crushing plant normally depends on three things working together:
Controlled feed size → steady feeding → correctly adjusted crusher
When these conditions are maintained, the jaw crusher can operate closer to its intended capacity without unnecessary stoppages.
Frequently Asked Questions
What is the most common cause of low jaw crusher capacity?
Feed problems are among the first things to check. Oversized material, uneven feeding, excessive feeding and insufficient feeding can all reduce effective throughput. The discharge setting and jaw plate condition should also be inspected.
Does a smaller discharge opening increase jaw crusher capacity?
Not necessarily. A smaller opening produces a finer product but can reduce throughput and increase the load on the crusher. The setting should be selected according to the required product size and the capacity of the downstream equipment.
Can worn jaw plates reduce crusher capacity?
Yes. As jaw plates wear, the crushing profile changes and the crusher may become less effective at gripping and breaking material. Excessive wear can therefore contribute to lower throughput.
How can I prevent jaw crusher blockage?
Start by controlling the maximum feed size and maintaining a steady feed rate. The hopper and feeder should also be arranged so that material enters the crushing chamber smoothly and continuously.
Does the vibrating feeder affect jaw crusher output?
Yes. The feeder determines how much material enters the crusher and how consistently it is supplied. Its angle, vibration amplitude, feed position and grizzly condition can all affect the overall crushing rate.
Can material hardness affect jaw crusher capacity?
Yes. Material that is harder or tougher than the crusher’s intended operating range can reduce crushing efficiency and increase the load on the machine.
Final Takeaway
Low jaw crusher capacity is often the result of several operating factors rather than a single mechanical problem.
Before replacing the crusher, check the feed size, feeding rate, discharge opening, jaw plate condition, motor rotation, electrical supply, bearing clearance and feeder settings. In many cases, correcting these conditions can restore production without major changes to the equipment.
For a new crushing plant, these factors should be considered when selecting the jaw crusher, feeder and downstream crushing equipment so that the entire production line works at a balanced capacity.