Why Using Only Part of a Hydraulic Cylinder Stroke Can Create Sensor Problems

Why an 8 mm Working Stroke Is More Difficult Than a 20 mm Stroke

Selecting the correct hydraulic cylinder for an injection mould or die casting die is often considered a matter of choosing the right bore, stroke and mounting dimensions.

In reality, many application problems are not caused by the cylinder itself.

They arise because the cylinder is used differently from the way it was originally designed.

One of the most common examples is the use of only a small portion of the available stroke.

At first glance, there appears to be nothing wrong with this approach.

If a hydraulic cylinder offers a nominal stroke of 20 mm and the mould only requires 8 mm, it may seem perfectly acceptable to use only part of the available movement.

Mechanically, the cylinder will still operate correctly.

However, the situation changes when the cylinder is equipped with magnetic position sensors.

The shorter the effective movement becomes, the more demanding the adjustment of the switches can be.

A real engineering enquiry submitted to the Vega Technical Department demonstrates why reducing the working stroke without considering the sensing system may create unexpected problems during mould commissioning.

The Customer’s Question

The customer had recently purchased an injection mould that incorporated an older hydraulic cylinder design.

Although the installed cylinder had a 20 mm nominal stroke, the mould actually used only 8 mm of that movement.

From a mechanical standpoint the application worked correctly.

The concern involved the magnetic switches.

The customer wanted to know whether the existing MSU1 switches could be positioned accurately enough to detect such a short effective stroke, or whether Vega could recommend a better solution.

This is an excellent engineering question because it shifts the focus away from hydraulic force and toward position detection accuracy.

The Hidden Problem of Partial Stroke Operation

Many designers assume that a hydraulic cylinder behaves identically regardless of how much of its available stroke is actually used.

Mechanically, this assumption is often correct.

From the perspective of the sensing system, however, the situation is completely different.

Magnetic switches are designed to detect the magnetic field generated by the piston as it moves inside the cylinder.

When the piston travels over most of the available stroke, the switches have a relatively wide adjustment range.

The installer can easily position the sensors to detect the desired extension and retraction points.

When only a very small portion of the stroke is used, this adjustment window becomes much narrower.

As a result:

  • switch positioning becomes more critical;
  • installation tolerances become smaller;
  • fine adjustment requires greater precision;
  • commissioning time may increase.

The hydraulic cylinder itself has not changed.

Only the way it is being used has changed.

Vega’s Engineering Assessment

After reviewing the application, Stefano Rogora from the Vega Technical Department highlighted an important design consideration.

He explained that using a V215 cylinder for such a small working stroke was not the most appropriate solution.

In fact, he pointed out that the V215 was more expensive than the V250, while the customer’s use of only 8 mm of the available stroke increased the likelihood of switch adjustment difficulties.

He also proposed testing a prototype of the new MSRD three-wire electronic PNP switch, although he cautioned that even this solution might not completely eliminate the problem because of the extremely short effective stroke.

This response illustrates an important engineering principle.

Sometimes the challenge is not selecting a better sensor.

It is recognising that the original cylinder configuration may not be the most suitable for the application.

Why Switch Adjustment Becomes More Difficult

To understand the problem, imagine two different cylinders.

The first uses almost its entire stroke.

The second moves only a few millimetres.

In the first case, the piston travels through a relatively large distance, making it easier to identify stable switching positions.

In the second case, extension and retraction occur within a much smaller movement.

Consequently:

  • the available adjustment range becomes limited;
  • small positioning errors have a greater effect;
  • installation tolerances become increasingly important;
  • repeatability becomes more dependent on precise sensor alignment.

This does not necessarily mean that the sensing system cannot work.

It simply means that achieving reliable adjustment becomes more demanding.

Looking Beyond the Cylinder

One of the most valuable lessons from this case is that hydraulic cylinder selection should never be based solely on force and dimensions.

The sensing system must also be considered.

When designers evaluate a hydraulic cylinder, they normally compare:

  • bore diameter;
  • rod diameter;
  • stroke;
  • mounting dimensions;
  • hydraulic pressure.

Yet the reliability of the complete system may depend just as much on:

  • switch technology;
  • adjustment range;
  • effective piston travel;
  • installation tolerances;
  • ease of maintenance.

Ignoring these factors may result in a cylinder that performs perfectly from a hydraulic standpoint while creating unnecessary commissioning difficulties.

The Customer’s Final Solution

Following the technical discussion, Vega proposed a more appropriate solution.

Instead of relying on the original switch configuration, the customer was advised to use the MSU3 switch.

According to the Technical Department, the MSU3 allows adjustment for a minimum stroke of 5 mm, making it considerably better suited to an application requiring only 8 mm of effective movement.

This recommendation demonstrates an important engineering principle.

The best solution is not always replacing the hydraulic cylinder.

Sometimes selecting the correct sensing technology is sufficient to achieve reliable operation.

Choosing the Right Sensor Instead of Changing the Cylinder

In Part 1, we examined a common situation in mould design: a hydraulic cylinder with a 20 mm nominal stroke being used for only 8 mm of effective movement.

Mechanically, there is nothing inherently wrong with this configuration.

The cylinder can still generate the required force, withstand the operating pressure and complete the required movement.

The challenge lies elsewhere.

When magnetic position sensors are used, a very short effective stroke dramatically reduces the available adjustment range, making switch positioning considerably more sensitive.

This is exactly the issue presented by the customer, who asked whether the existing MSU1 switches could reliably detect an effective movement of only 8 mm, or whether another solution would be preferable.

The Engineering Approach

One of the most interesting aspects of this case is the response provided by the Vega Technical Department.

Rather than recommending immediate replacement of the hydraulic cylinder, Stefano Rogora first analysed the application itself.

He explained that using a V215 cylinder for such a limited working stroke was not the ideal solution because:

  • the cylinder was more expensive than a V250;
  • using only 8 mm of its available stroke increased the difficulty of adjusting the magnetic switches correctly.

He also proposed testing a prototype of the new MSRD three-wire electronic PNP switch, while honestly pointing out that even this sensor might not completely eliminate the problem because the effective stroke remained extremely short.

This is a good example of practical engineering.

Rather than promising that a different sensor would solve every issue, the Technical Department explained the limitations created by the application itself.

Why Sensor Selection Matters

When engineers select a hydraulic cylinder, they often focus on mechanical characteristics such as:

  • bore diameter;
  • rod diameter;
  • operating pressure;
  • mounting dimensions;
  • maximum stroke.

However, once the cylinder becomes part of an automated mould, another component becomes equally important:

the position sensing system.

Without reliable position detection, the machine cannot accurately determine whether the cylinder has reached its intended position.

This can lead to:

  • interrupted production cycles;
  • positioning errors;
  • incorrect machine sequences;
  • unnecessary troubleshooting during commissioning.

In many applications, the sensing system becomes just as important as the hydraulic cylinder itself.

Why the MSU3 Was a Better Solution

After evaluating the customer’s application, Vega proposed a different switch.

The recommended solution was the MSU3.

According to the Technical Department, the MSU3 allows adjustment for a minimum stroke of approximately 5 mm, making it considerably more suitable for applications requiring only 8 mm of effective movement.

Although the cylinder itself remained unchanged, selecting a switch specifically designed for shorter adjustment distances significantly improved the likelihood of reliable operation.

This illustrates an important engineering principle.

Sometimes the best solution is not replacing the hydraulic cylinder.

Sometimes it is simply choosing a sensing technology better suited to the actual movement.

Should a Shorter Stroke Cylinder Be Used Instead?

Cases like this naturally raise another question.

Would it be better to replace the existing cylinder with one having a shorter nominal stroke?

The answer depends on several engineering considerations.

If the mould is already built, replacing the cylinder may require:

  • machining modifications;
  • different mounting dimensions;
  • changes to hydraulic connections;
  • additional downtime;
  • higher overall costs.

If reliable sensing can instead be achieved by selecting a more suitable switch, this often represents the most economical and practical solution.

On the other hand, when designing a completely new mould, engineers should avoid specifying significantly longer strokes than the application actually requires whenever possible.

Matching the cylinder stroke more closely to the real movement generally simplifies both hydraulic operation and sensor adjustment.

Designing the Entire System

Perhaps the most valuable lesson from this customer enquiry is that hydraulic cylinders should never be considered as isolated components.

The final performance depends on the interaction between:

  • the hydraulic cylinder;
  • the magnetic piston;
  • the position sensors;
  • the machine controller;
  • the mould mechanics;
  • the installation tolerances.

Optimising only one of these elements rarely produces the best overall result.

Reliable machine operation is achieved when every component is selected with the complete system in mind.

Engineering Is About Solving the Real Problem

One of the strengths of this case is that the customer’s original concern was not related to force, pressure or cylinder durability.

It was a commissioning problem.

The cylinder itself worked correctly.

The uncertainty involved the ability of the switches to detect a very small portion of the available stroke.

Instead of recommending unnecessary mechanical modifications, the Vega Technical Department evaluated the sensing requirements and proposed a solution specifically adapted to the application’s effective movement.

This reflects a broader engineering philosophy.

The objective is not to replace components unnecessarily.

It is to understand the real source of the problem and solve it in the simplest, most reliable and most economical way.

Conclusion

This engineering case demonstrates that selecting a hydraulic cylinder involves much more than calculating force and choosing mounting dimensions.

When only a small portion of the available stroke is used, the reliability of the position sensing system becomes a critical design consideration.

A cylinder that is mechanically perfect may still present commissioning challenges if the switches cannot be adjusted accurately within the limited effective movement.

By analysing the complete application rather than focusing solely on the cylinder, the Vega Technical Department identified that the most appropriate solution was not a different actuator, but a more suitable magnetic switch capable of reliable operation over a minimum stroke of 5 mm.

The case highlights an important lesson for mould designers and machine builders alike:

Successful hydraulic engineering is achieved by optimising the entire system—not just the cylinder.

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