A practical case showing why oil-flow requirements must be checked for each cylinder configuration
When selecting a hydraulic cylinder for an injection mold, designers often focus on the main mechanical parameters:
- bore diameter;
- stroke;
- working pressure;
- available force;
- installation dimensions.
However, another parameter can be equally important when the application requires high movement speed:
the maximum oil flow rate.
The amount of oil that can be supplied to a cylinder directly influences how quickly the piston can move. But the maximum permissible flow is not necessarily the same for every cylinder configuration.
A technical exchange between the Client and the Vega Team provides a useful example involving two different cylinder configurations and very different maximum flow rates. The Client asked how much oil was required for four compact cylinders and for four modified cylinders with integral piston rods.
The Vega Team provided specific flow-rate limits for both configurations.
1. Why Oil Flow Matters
The hydraulic flow supplied to a cylinder determines how quickly the piston can move.
In simplified terms:
Cylinder speed = Oil flow ÷ Effective piston area
Therefore, increasing the oil flow can increase the piston speed, provided that the cylinder and the complete hydraulic system are designed to operate at that flow rate.
However, the maximum flow cannot be determined simply from the cylinder bore.
The actual limit may depend on:
- cylinder design;
- internal hydraulic passages;
- seals;
- piston and rod configuration;
- cushioning system;
- oil ports;
- operating conditions.
For this reason, the maximum flow rate should always be verified for the specific cylinder configuration being used.
2. The Client’s Question
In the technical case, the Client asked how much oil was required for:
- four compact cylinders;
- four cylinders modified with integral piston rods.
This is an important type of question because the number of cylinders must be considered together with the maximum flow allowed for each individual cylinder.
The answer from the Vega Team clearly distinguished between the two configurations.
3. Compact CM040 Cylinders: 7 l/min Each
For the compact:
CM040EOEG#050
the Vega Team specified a maximum flow rate of:
7 l/min per cylinder.
For four cylinders, the corresponding total flow would therefore be:
4 × 7 = 28 l/min
This is the total flow if all four cylinders are supplied simultaneously at their specified maximum individual flow.
This distinction is important.
The value of 7 l/min is the limit for each cylinder, while 28 l/min is the corresponding total when four identical cylinders operate simultaneously at that flow.
4. Modified Cylinders With Integral Rod: 90 l/min Each
The second configuration was significantly different.
For the:
CR050022C3GESN125S073
with integral cushioned rod, the Vega Team specified a maximum flow rate of:
90 l/min per cylinder.
With four cylinders operating simultaneously, this corresponds to:
4 × 90 = 360 l/min
This is a very substantial difference compared with the 28 l/min total associated with the four compact CM040 cylinders.
The case therefore demonstrates that different cylinder configurations can have radically different flow-rate capabilities, even when they are being considered for a similar application.
5. The Important Qualification: Cushioning
There is a particularly important detail in the technical response.
The 90 l/min value applies to the CR050 configuration with the integral cushioning system.
The Vega Team specified that if the cushioning system is:
- not used, or
- only partially used,
the maximum flow is reduced to:
10 l/min per cylinder.
This means that the same cylinder configuration can have a dramatically different permitted flow depending on how the cushioning system is actually used.
For four cylinders, that would correspond to:
4 × 10 = 40 l/min
if the cushioning condition described by the Vega Team applies.
6. The Three Flow Conditions in This Case
The technical information can therefore be summarized as follows:
| Cylinder configuration | Maximum flow per cylinder | Four cylinders simultaneously |
|---|---|---|
| CM040EOEG#050 compact | 7 l/min | 28 l/min |
| CR050022C3GESN125S073 with integral cushioning | 90 l/min | 360 l/min |
| CR050022C3GESN125S073 with cushioning not used or only partially used | 10 l/min | 40 l/min |
The values above are derived directly from the per-cylinder limits communicated by the Vega Team.
7. Why the Difference Is So Important
The difference between:
28 l/min
and
360 l/min
is enormous.
If the hydraulic system were designed on the assumption that four cylinders could always receive 90 l/min each, but the actual configuration allowed only 7 l/min per cylinder, the hydraulic system would be substantially oversized relative to the cylinder’s permitted flow.
Conversely, if a high-flow configuration is selected specifically because a fast movement is required, the hydraulic circuit must be capable of supplying the required flow.
This is why cylinder selection and hydraulic-system design should be considered together.
8. Maximum Flow Is Not the Same as Required Flow
Another important distinction is between:
maximum permissible flow
and
flow actually required by the application.
A cylinder may be capable of accepting a certain maximum flow, but the application may require considerably less.
For example, if a cylinder requires only 3 l/min to achieve the desired speed, there is no reason to supply its maximum permissible flow.
The designer should determine the required piston speed first and then calculate the necessary flow.
The maximum flow should then be used as a design limit, not necessarily as a target.
9. Calculating the Required Flow
The basic relationship is:
Q = A × v
where:
- Q = hydraulic flow;
- A = effective piston area;
- v = piston speed.
This relationship allows the designer to determine the flow required to achieve a specific cylinder speed.
For example, if the required speed increases, the required flow increases proportionally, assuming the effective piston area remains unchanged.
However, the calculated flow must then be compared with the maximum permitted flow for the specific cylinder configuration.
10. Four Cylinders Change the Hydraulic Requirement
When several cylinders operate simultaneously, the hydraulic circuit must be evaluated for the combined flow.
If four identical cylinders each require the same flow:
Total flow = flow per cylinder × number of cylinders
In the case documented here:
CM040
7 l/min × 4 = 28 l/min
CR050 with the specified cushioning condition
90 l/min × 4 = 360 l/min
CR050 when cushioning is not used or only partially used
10 l/min × 4 = 40 l/min
The difference demonstrates why the number of cylinders must be included in hydraulic-system calculations.
11. Simultaneous Versus Sequential Operation
The total flow requirement depends on whether the cylinders move simultaneously.
If four cylinders move at the same time, their flows must be added.
If they move sequentially, the hydraulic requirement may be significantly lower.
For example, if only one cylinder moves at a time, the pump does not necessarily need to provide the sum of all four individual maximum flows.
Therefore, before sizing the hydraulic supply, the designer should determine:
- how many cylinders move simultaneously;
- the required speed of each cylinder;
- whether movement is synchronized;
- whether the cylinders operate continuously or intermittently.
The technical case confirms the per-cylinder flow limits but does not specify the actual synchronization strategy of the mold. That part must therefore be evaluated according to the application.
12. The Role of Cushioning
The most interesting aspect of this case is the relationship between cushioning and maximum flow.
The CR050 configuration with integral cushioning was specified at:
90 l/min per cylinder.
However, the Vega Team explicitly stated that if the cushioning is not used, or is only partially used, the maximum flow falls to:
10 l/min per cylinder.
This means that the designer cannot simply look at the cylinder model and assume a single universal maximum flow.
The actual configuration and operating conditions must be considered.
13. Why the Hydraulic Circuit Must Match the Cylinder
A hydraulic circuit consists of more than a pump and a cylinder.
It also includes:
- valves;
- hoses;
- pipes;
- fittings;
- manifolds;
- oil ports;
- filters;
- flow-control components.
Every element can influence the actual flow available at the cylinder.
Therefore, selecting a cylinder with a high permitted flow does not automatically mean that the machine will achieve the desired speed.
The complete hydraulic circuit must be capable of delivering the required flow with acceptable pressure losses.
14. Compact Cylinders and Flow Limitations
Compact hydraulic cylinders offer important advantages in injection molds because installation space is often extremely limited.
Vega’s product catalog specifically categorizes compact cylinders for applications such as ejection-plate movement and cart and plug movement.
However, compactness can also mean that the internal hydraulic passages and connections must be carefully considered when defining the permitted flow.
This is why the maximum flow should always be taken from the technical specification of the exact cylinder configuration, rather than estimated from the cylinder diameter alone.
15. Choosing a Cylinder for High-Speed Movement
When the application requires high piston speed, the designer should proceed in the following order.
Step 1 – Define the required piston speed
Determine how quickly the cylinder must complete its stroke.
Step 2 – Determine the effective piston area
The bore and rod configuration determine the effective area.
Step 3 – Calculate the required flow
Use the relationship between area and piston speed.
Step 4 – Compare the required flow with the cylinder limit
The required flow must remain within the maximum flow specified for the actual configuration.
Step 5 – Consider cushioning
If the cylinder has a cushioning system, verify the flow limit under the actual cushioning condition.
Step 6 – Consider the number of cylinders
Determine how many cylinders operate simultaneously.
Step 7 – Check the hydraulic circuit
Verify that the pump, valves, hoses and connections can provide the required combined flow.
16. Do Not Size the Pump Only From the Cylinder Bore
A common simplification is to select the hydraulic pump based only on:
- cylinder bore;
- operating pressure.
This is incomplete when speed is important.
The pump must also provide sufficient flow.
For multiple cylinders, the designer should consider the maximum simultaneous demand.
In the case documented here, the difference between the two configurations illustrates the importance of this calculation:
28 l/min total
versus
360 l/min total.
The hydraulic system would obviously have very different requirements depending on which configuration is used.
17. What Information Should Be Requested From the Client?
For a request concerning cylinder flow rate, the following information is particularly useful:
- number of cylinders;
- cylinder model;
- bore;
- stroke;
- required movement speed;
- simultaneous or sequential operation;
- hydraulic pressure;
- oil type;
- cushioning configuration;
- pump capacity;
- valve configuration;
- hose and manifold dimensions.
The original Client request was specifically based on four compact cylinders and four modified cylinders with integral piston rods, making the number of cylinders an important part of the calculation.
18. A Practical Lesson for Injection-Mold Designers
When a Client asks:
“How much oil do these cylinders need?”
the answer should not simply be a single flow value.
The correct answer depends on:
- the cylinder model;
- the exact configuration;
- the number of cylinders;
- the required speed;
- whether the cylinders operate simultaneously;
- the cushioning configuration.
The technical case demonstrates this very clearly.
The compact CM040 was specified at 7 l/min per cylinder, while the CR050 configuration with integral cushioning was specified at 90 l/min per cylinder. If the cushioning was not used or only partially used, the latter was limited to 10 l/min per cylinder.
19. Conclusion
Hydraulic flow rate is an important parameter when selecting cylinders for injection molds, particularly when fast movements are required.
The technical case analyzed here involved a Client requesting the oil requirement for four compact cylinders and four modified cylinders with integral piston rods.
The Vega Team specified a maximum flow of 7 l/min per CM040EOEG#050 compact cylinder. For four cylinders, this corresponds to a combined maximum of 28 l/min when operating simultaneously at that limit.
For the CR050022C3GESN125S073 configuration with integral cushioning, the specified maximum was 90 l/min per cylinder, corresponding to 360 l/min for four cylinders. However, if the cushioning was not used or was only partially used, the maximum flow was reduced to 10 l/min per cylinder, or 40 l/min for four cylinders.
The key lesson is therefore:
The maximum hydraulic flow of a cylinder must always be evaluated according to its exact configuration and operating conditions. It cannot be determined simply from the cylinder bore or model name. Cushioning, the number of cylinders and simultaneous operation can significantly affect the flow requirement of the complete hydraulic system.
For injection-mold applications, the correct approach is to first determine the required cylinder speed, calculate the necessary flow, verify the maximum permitted flow for the exact cylinder configuration, and finally check that the hydraulic circuit can supply the combined demand.
Useful and Verified Vega URLs
For the English article, I would use these official Vega pages on the Italian domains requested:
1. Hydraulic Cylinders for Molds
Vega – Hydraulic Cylinders for Molds
This is the best general internal link. It presents Vega’s hydraulic-cylinder range and categorizes the products by application, including ejection-plate movement and cart/plug movement.
2. Ejection Plate Movement
Vega – Ejection Plate Movement
This is particularly relevant because the page specifically identifies hydraulic cylinders for ejection-plate movement and includes V220CC, V400CL, V450CM and V500CZ.
3. Hydraulic Cylinder Catalog
Vega – Hydraulic Cylinder Catalog
Useful as a broader technical reference because the catalog organizes the cylinders according to their applications.
4. Hydraulic Cylinder Shop / Configurator
Vega – Hydraulic Cylinders and Configurator
Useful when discussing the selection of the exact cylinder configuration rather than simply the cylinder family.
