When selecting industrial valves, many engineers mistakenly treat pilot pressure and working pressure as the same parameter. In practice, a valve body may be correctly rated for the process pressure, yet actuator failure occurs because the pilot pressure exceeds the actuator’s design limit. The root cause is that these two pressures serve completely different functions:one controls the actuator, while the other relates to the process medium. Understanding this distinction is essential for safe and reliable valve operation.

Pilot pressure controls the actuator, working pressure relates to the medium

The fundamental difference between pilot pressure and working pressure lies in which component they act on and what function they perform—one drives valve movement, the other relates to process flow.

Pilot pressure: the driving force for valve actuation

Pilot pressure, also known as control pressure, refers to the pressure used to operate the valve actuator. In pneumatic systems, compressed air is supplied through the pilot circuit into the actuator chamber (cylinder or diaphragm), generating force that moves the valve stem or disc to open or close the valve.

Its sole function is to provide mechanical energy for actuation, independent of the fluid passing through the valve body.

For example, in a pneumatic angle seat valve, pilot pressure is supplied by the air compressor system. If the pressure is below the required range (typically 0.4–0.6 MPa), the actuator force will be insufficient, causing incomplete closing or unstable operation. Conversely, if the pilot pressure exceeds the actuator’s maximum rating, it may lead to actuator housing deformation, seal failure, or even structural rupture.

Working pressure: the operating pressure of the process medium

Working pressure, sometimes referred to as operating pressure, is the pressure of the medium flowing through the valve, such as water pressure in pipelines, steam pressure in thermal systems, or chemical fluid pressure in process lines. This pressure acts directly on the valve body, seat, and sealing components.

The working pressure must remain within the valve’s rated pressure range. Exceeding this limit can result in body deformation, seal leakage, or even catastrophic failure. For instance, a DN50 stainless steel ball valve rated at 1.6 MPa may develop cracks or leakage if subjected to continuous pressure above 2.0 MPa, significantly increasing the risk of system failure.

Actuator pressure rating: material and diameter make the difference

The maximum allowable pilot pressure is determined by the actuator’s design strength. Two factors primarily define its pressure capacity: material type and actuator size.

Different materials, different pressure limits

PA66 (Nylon 66) actuators

PA66 is a lightweight and cost-effective engineering plastic commonly used in medium- and low-pressure applications. Typical PA66 actuators tolerate pilot pressures up to approximately 8 bar (0.8 MPa). These actuators are suitable for light industrial and general-purpose applications. However, long-term exposure to elevated temperatures (above 80°C) reduces mechanical strength, making PA66 unsuitable for high-temperature pneumatic systems.

Stainless steel actuators

Actuators manufactured from stainless steel (such as 304 or 316) offer significantly higher mechanical strength and superior corrosion resistance. They generally withstand pilot pressures above 10 bar (1.0 MPa), with reinforced models reaching 16 bar (1.6 MPa). Stainless steel actuators are ideal for demanding environments, including chemical processing and high-temperature steam applications, where stability under pressure is critical.

Larger diameter usually means lower allowable pressure

Even within the same material category, actuator size affects pressure capacity.A PA66 actuator with a 50 mm diameter may be rated for 8 bar, whereas a 100 mm diameter unit might only be rated for 6 bar. The increased surface area leads to higher internal force under the same pressure, which stresses the housing.The same rule applies to stainless steel actuators. A 304 stainless steel actuator with an 80 mm diameter may safely operate at 10 bar, while a 150 mm model should remain below 8 bar to maintain structural integrity.

This relationship can be explained using the formula: Force on actuator = Pilot pressure × Effective area. As the diameter increases, the effective area expands, resulting in higher total force at the same pressure. Therefore, pilot pressure limits must be reduced for larger actuators to prevent mechanical overload.

Correct selection ensures reliable operation

Pilot pressure and working pressure serve two entirely different functions—control versus conveyance—and should never be confused during valve selection.

Best practice is to:

First confirm the material and diameter of the actuator to determine allowable pilot pressure.

Then match the valve body rating to the process working pressure.

Finally, verify both values in the product datasheet before installation.

Only when both pressure parameters are correctly matched can the valve operate safely, reliably, and with long-term durability. Proper pressure selection prevents premature actuator failure, reduces maintenance costs, and ensures overall system stability.

If you also need to use any type of pneumatic valves in your system, you can contact us directly.

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