A Customer Case on cartridge sealing, static O-rings, cushioning adjustment and high-temperature applications
Oil leakage from a hydraulic cylinder does not always mean that the rod seal has failed.
In many cases, the visible leakage is only the symptom, while the actual cause is located elsewhere in the sealing system, the installation or the operating conditions.
A Vega Customer Case involving two hydraulic cylinders installed in an injection mold provides a useful example. The cylinders developed a permanent oil leak when extended, together with a problem adjusting the cushioning system. The investigation initially considered several possible causes, including the cartridge static O-ring, the rigid connection between the cylinder and the moving plate, the seals and the high operating temperature.
The subsequent replacement of the complete cartridges revealed an important detail: the green static seals were missing from the old cartridges. The Customer identified these missing seals as the cause of the leakage.
This case illustrates an important engineering principle:
Before changing the sealing material or replacing the entire cylinder, identify exactly where the oil is escaping and which sealing element is involved.
1. The Customer’s Initial Problem
The Customer reported two different problems on the cylinders.
The first was a continuous oil leak when the cylinders were extended.
The second was that the cushioning could not be adjusted correctly.
The Customer requested new sealing elements for the two cylinders and also asked about magnetic sensors with higher temperature resistance.
At this stage, it was not yet clear whether the leakage and the cushioning problem were related.
2. The Operating Conditions Were Important
The cylinders were working in a demanding injection-molding environment.
The information supplied by the Customer included:
- approximately 4,000–5,000 cycles;
- mold temperature of approximately 95 °C;
- HLP 46 zinc-free hydraulic oil;
- working pressures of approximately 120 and 100 bar;
- approximately 85 °C at the cylinder flange;
- approximately 70 °C at the rod;
- approximately 55 °C at the switches.
These conditions immediately made temperature an important factor to consider, particularly for the magnetic switches.
The Customer was already considering sensors capable of operating at temperatures above 130 °C for future trials.
3. The First Step: Locate the Leakage
One of the first questions in any hydraulic-cylinder failure analysis should be:
Where is the oil actually coming from?
The Customer reported that the oil appeared around the cartridge and head rather than along the rod.
The Vega Team nevertheless pointed out that oil can travel along the rod and appear in another location, making visual identification of the origin more difficult.
This is a crucial diagnostic point.
The place where oil becomes visible is not necessarily the place where the leakage originates.
4. The Cartridge Static O-Ring
Once leakage along the rod was considered unlikely, attention turned to the static O-ring of the cartridge.
The Vega Team suggested checking this component because the oil appeared around the cartridge and head.
A static O-ring performs a fundamentally different function from a rod seal.
The rod seal operates dynamically around a moving rod.
The cartridge O-ring provides sealing between stationary components.
Therefore, diagnosing an oil leak requires identifying which sealing interface is actually failing.
5. Why Two Cylinders With the Same Problem Matter
The leakage was present on both cylinders, although it was more pronounced on one of them.
This was significant because simultaneous failures on two cylinders suggest that the investigation should not focus exclusively on an isolated component defect.
When several cylinders in the same application develop the same problem, it is useful to investigate common factors such as:
- installation;
- hydraulic circuit;
- operating temperature;
- pressure;
- alignment;
- maintenance;
- assembly procedure.
The fact that multiple cylinders were affected does not prove that one of these factors caused the failure, but it makes the search for a common factor particularly important.
6. Could the Rigid Connection Have Caused the Problem?
The Customer explained that the connection between the rod and the moving part was rigid.
The Vega Team suggested evaluating a floating joint connection, because a rigid connection can potentially transmit radial forces to the cylinder rod.
This is an important consideration in mold applications.
A hydraulic cylinder is primarily designed to generate axial force.
If the surrounding mechanism imposes lateral forces or misalignment on the rod, the cylinder can experience additional loads that were not part of the original design conditions.
However, the Customer Case does not establish that the rigid connection was the actual cause of the oil leakage.
It was one of the factors considered during the investigation.
7. The Pressure Was Also Considered
The reported working pressure was approximately 100–120 bar.
The Vega Team noted that this was above the minimum pressure of 70 bar required for the standard seals to work correctly.
The Team nevertheless suggested considering special polyurethane seals because they could provide better sealing performance in the application.
This is an important distinction:
A possible improvement is not necessarily the same thing as the confirmed cause of the failure.
At this stage, the investigation was still looking for the root cause.
8. The Cushioning Problem
The second issue concerned the cylinder cushioning.
The Customer reported that the cushioning could not be adjusted.
The Vega Team suggested checking whether the cylinders remained cushioned regardless of the position of the adjustment screws — completely open or completely closed.
This would help determine whether the problem was actually caused by the adjustment system.
The important point is that the leakage and the cushioning problem should not automatically be assumed to have the same cause.
9. Were the Leakage and Cushioning Problems Connected?
Initially, the Vega Team stated that there was not necessarily a relationship between the leakage problem and the difficulty adjusting the cushioning.
This is a useful lesson for troubleshooting.
Two problems occurring at the same time do not automatically mean that one caused the other.
A proper failure analysis should investigate each symptom independently before establishing a causal relationship.
10. Replacing the Complete Cartridges
After the initial investigation, the Customer proposed replacing the complete cartridges.
The Vega Team agreed with this approach and arranged the supply of:
- two complete cartridges RR0400280310A, with standard seals;
- two MSU1 magnetic switches.
Replacing the complete cartridge can be advantageous when several sealing components need to be checked or replaced at the same time.
It can also simplify maintenance and reduce the risk of an incorrect individual seal replacement.
11. The Important Discovery
The most significant finding came after the Customer replaced the cartridges.
The Customer reported that the green seals were missing from the old cartridges and concluded that this was the cause of the leakage.
The Vega Team also noted that it was unusual for the static cartridge O-rings to be missing from both cylinders because the resulting leakage should have been substantial and would normally have been visible during Vega’s hydraulic testing.
This is an important detail because it prevents an overly simplistic conclusion about when or how the seals became missing.
The documented evidence confirms that the seals were missing when the old cartridges were inspected.
It does not establish when they became missing.
12. Why a Missing Static O-Ring Can Cause Significant Leakage
The cartridge static O-ring creates the seal between the cartridge and the surrounding cylinder structure.
If the O-ring is missing, the intended sealing interface is no longer present.
Hydraulic oil can therefore escape through the cartridge/head interface.
This is consistent with the location where the Customer observed the leakage.
The case therefore demonstrates why identifying the actual leakage path is so important.
13. The Copper Paste Found on One Cartridge
The Customer also reported finding copper paste on one of the old cartridges.
The Customer suggested that this could explain why one cylinder had leaked more than the other.
However, the available Case documentation does not contain a technical analysis proving that the copper paste caused or increased the leakage.
Therefore, it should be treated as an observed condition or possible factor, rather than as a confirmed root cause.
This distinction is essential when documenting a technical failure.
14. High Temperature Was Another Challenge
The mold operated at approximately 95 °C, while the temperature measured at the cylinder flange was approximately 85 °C.
The Customer therefore asked about magnetic switches with temperature resistance above 130 °C.
The Vega Team explained that simply using a silicone cable would not solve the temperature problem.
The temperature limitation does not depend only on the cable. It also depends on the electronic components inside the switch.
This is an important principle for high-temperature applications:
A high-temperature cable does not automatically make the complete sensor suitable for high-temperature operation.
15. Temperature Must Be Considered at the Sensor Itself
The temperatures reported by the Customer were different at different locations:
- approximately 85 °C at the cylinder flange;
- approximately 70 °C at the rod;
- approximately 55 °C at the switches.
This illustrates why the temperature of the mold alone is not enough to determine the suitability of a hydraulic-cylinder sensor.
The actual temperature experienced by each component must be considered.
16. The Sealing System Is a Combination of Components
Vega’s technical information confirms that hydraulic-cylinder sealing is not based on a single component.
The sealing system can include:
- rod seals;
- O-rings;
- scraper seals;
- guide bushes;
- other sealing elements depending on the cylinder design.
Vega describes FKM O-rings as part of its standard sealing technology and also offers special sealing options for applications involving water-glycol or unusually high temperatures.
This reinforces the importance of identifying the specific failed sealing element rather than simply referring to “the cylinder seal.”
17. A Static Seal and a Dynamic Seal Are Not the Same
A static O-ring and a rod seal operate under different conditions.
Static O-ring
Its function is to seal between stationary components.
Rod seal
Its function is to maintain hydraulic sealing while the rod moves.
This difference affects:
- friction;
- wear;
- installation;
- lubrication;
- surface requirements;
- failure mechanisms.
Therefore, replacing a rod seal cannot solve a leakage problem that actually originates at a static cartridge interface.
18. Why Replacing the Seal Is Not Always the Complete Solution
This Customer Case illustrates a broader maintenance principle.
If a seal is damaged or missing, replacing it may restore the cylinder.
But if the reason for the seal failure remains unknown, the problem may return.
The correct sequence is:
Leakage
↓
Identify the failed sealing component
↓
Determine the failure mechanism
↓
Identify the root cause
↓
Repair the cylinder
↓
Prevent recurrence
This approach is much more reliable than simply replacing all seals whenever oil appears.
19. A Practical Diagnostic Procedure
When a hydraulic cylinder installed in an injection mold develops an oil leak, a useful diagnostic procedure is:
Step 1 — Identify the exact leakage location
Determine whether the oil is coming from:
- the rod seal;
- the cartridge/head interface;
- a hydraulic connection;
- another static joint.
Step 2 — Inspect the sealing components
Check:
- O-rings;
- rod seals;
- scraper;
- guide elements;
- cartridge.
Step 3 — Inspect the rod
Look for scratches, dents, corrosion or other damage in the sealing area.
Step 4 — Check the installation
Verify alignment and whether the mechanism can impose radial loads on the rod.
Step 5 — Check hydraulic conditions
Verify pressure, temperature and oil type.
Step 6 — Compare other cylinders
If several cylinders show the same problem, look for a common factor.
Step 7 — Inspect the removed components
Do not discard the old seals and cartridges immediately.
They can provide valuable evidence.
20. Why Keeping the Old Components Can Be Valuable
In this Customer Case, the old cartridges could have been returned to Vega for inspection.
Initially, the Customer decided that this was unnecessary because the missing seals had already been identified.
From a diagnostic perspective, however, retaining failed components can be extremely useful.
They can reveal:
- wear patterns;
- deformation;
- contamination;
- assembly marks;
- material damage;
- missing components;
- evidence of excessive loads.
For difficult failures, the old component can sometimes contain more information than the new replacement.
21. Why Multiple Cylinders Should Be Compared
If several cylinders develop the same failure, they should be analyzed together.
For example:
| Component | Cylinder A | Cylinder B | Cylinder C |
|---|---|---|---|
| Cartridge O-ring | Condition | Condition | Condition |
| Rod | Condition | Condition | Condition |
| Rod seal | Condition | Condition | Condition |
| Guide bush | Condition | Condition | Condition |
| Cartridge | Condition | Condition | Condition |
| Contamination | Present/Absent | Present/Absent | Present/Absent |
| Installation | Condition | Condition | Condition |
The purpose is to identify a common pattern.
If the same component fails in the same way on several cylinders, a common operating or installation factor becomes particularly interesting.
22. The Role of Installation
Hydraulic cylinders used inside injection molds often operate in confined spaces.
The cylinder may be mechanically connected to another moving component of the mold.
If the connection is rigid and the external mechanism is not perfectly aligned, the cylinder rod can potentially experience radial forces.
This is why the Vega Team suggested considering a floating connection in the Customer Case.
Again, this was a technical recommendation for investigation, not a confirmed cause of the leakage.
23. The Importance of Correct Troubleshooting
The Customer Case followed an interesting diagnostic progression:
Oil leakage
↓
Check leakage location
↓
Consider cartridge static O-ring
↓
Consider installation and radial forces
↓
Consider sealing material
↓
Replace complete cartridges
↓
Inspect old cartridges
↓
Discover missing static seals
This is a good example of technical troubleshooting based on progressively stronger evidence.
24. What We Can and Cannot Conclude
The available documentation allows us to state that:
- both cylinders developed oil leakage;
- the leakage appeared around the cartridge/head area;
- the cylinders operated in a high-temperature mold environment;
- the cartridge static O-ring was considered as a possible leakage point;
- a rigid connection was considered as a possible source of radial forces;
- special polyurethane seals were considered;
- complete replacement cartridges were supplied;
- the old cartridges were subsequently found to be missing the green static seals;
- the Customer identified the missing seals as the cause of the leakage.
However, the Case does not establish exactly when or why the seals became missing.
That distinction should remain clear in any technical article based on this case.
25. The Broader Engineering Lesson
The most important lesson is not simply that an O-ring can cause an oil leak.
It is that a failure symptom should not automatically be confused with the root cause.
If a hydraulic cylinder leaks, the correct question is not simply:
“Which seal should we replace?”
The better questions are:
“Where exactly is the oil coming from?”
“Which sealing interface has failed?”
“What happened to the sealing element?”
“Why did it happen?”
“Could the same condition affect the other cylinders?”
This approach can significantly reduce unnecessary component replacement.
Conclusion
This Customer Case demonstrates why hydraulic-cylinder leakage should be approached as an engineering diagnosis rather than simply a sealing replacement operation.
Two cylinders installed in an injection mold developed oil leakage around the cartridge area, together with a cushioning-adjustment problem. The application involved approximately 100–120 bar working pressure, a mold temperature of about 95 °C and approximately 85 °C at the cylinder flange.
The Vega Team considered several possible causes, including the cartridge static O-ring, rigid mechanical connection and sealing materials.
Complete cartridges were then supplied.
During the subsequent inspection, the Customer found that the green static seals were missing from the old cartridges and identified this as the cause of the leakage.
The case therefore highlights a simple but important principle:
Do not replace a seal simply because there is a leak. First identify the actual leakage path and inspect the complete sealing system.
For hydraulic cylinders installed in injection molds, reliable troubleshooting should consider the sealing components, cartridge, rod, installation, alignment, hydraulic circuit, pressure, temperature and maintenance history.
The objective is not merely to stop today’s leak.
The objective is to understand why the leak occurred and prevent it from happening again.
Useful and Verified URLs
The following links are on the official vegacylinders.com domain and are in English, matching the article.
- Materials and Components — Official Vega page explaining the sealing technologies used in hydraulic cylinders, including FKM O-rings, PTFE + bronze seals and guide bushes, as well as special sealing options for high-temperature and water-glycol applications.
Materials and Components - Hydraulic Cylinders for Molds — Official Vega overview of hydraulic cylinders designed for plastic injection molds and aluminum die-casting molds, organized by application.
Hydraulic Cylinders for Molds - Cart and Plug Movement — Official Vega application page covering hydraulic cylinders used to move carts, pins and plugs that create undercuts in plastic injection molds, including V215CR, V250CE and other cylinder families.
Cart and Plug Movement - V215CR Tie-Rod Hydraulic Cylinders — Official Vega product page describing the cartridge sealing system, O-rings, guide bushes and magnetic sensors for the V215CR series.
V215CR Tie-Rod Hydraulic Cylinders - Hydraulic Cylinders Catalog — Official Vega catalog page listing the hydraulic-cylinder families and their main mold applications.
Hydraulic Cylinders Catalog
