Special actuators • High-temperature designs • Selection • Commissioning • Service
Special actuators are drives designed to work in conditions where standard catalogue solutions stop being predictable. In the power and heating sectors, the success of an investment is determined above all by elevated temperatures, heavy dust loads, aggressive condensates and variable loads. These are factors that accelerate the wear of seals and guides, increase motion hysteresis and make stable positioning more difficult.
In this article we show a pragmatic, engineering-based approach to the design, selection and operation of special actuators – particularly in high-temperature designs – referring to maintenance and automation practice, as well as to specific configurations: D63×150 (No. 18.4846) and D125×150 (No. 18.4873).
If you’d like to see a step-by-step guide to creating custom actuators, check out this guide: Custom Pneumatic and Hydraulic Actuators – How Specialty Actuators Are Made
When special actuators are indispensable
In standard systems, catalogue actuators work correctly. In power and heating plants, however, things are often different. The temperature of flue gases and secondary air can locally exceed 150 °C, while thermal radiation and dust erosion heavily load working surfaces. Add to this sudden mechanical and thermal load changes.
In such conditions, special actuators ensure stable operating times and reliable positioning of dampers, gates, butterfly valves and ignition lances – regardless of temperature fluctuations and pressure differences. This means fewer unplanned downtimes for maintenance teams and predictable TTR, while automation gains stable control and a better oxygen balance in the process.
Working environment: temperature, dust and corrosion
Temperature and thermal radiation
Elevated temperatures and local heat sources require materials with stable friction properties. That is why high-temperature actuators use FKM or FFKM seals and PTFE or PEEK bearing elements. As a result, friction remains predictable and tightness is maintained throughout the operating range.
Dust and erosion
Dust from ash and coal acts like an abrasive. Solid particles may also penetrate the sealing zones. To counter this, designs include double scrapers, extended guides and appropriately chosen piston rod roughness. These solutions reduce wear and stabilise motion hysteresis.
Process chemistry in FGD
In flue gas desulphurisation installations, aerosols and acidic condensates appear. Protective coatings and stainless steel elements secure the cylinder body and mountings. As a result, position sensors maintain signal stability and stroke times remain repeatable.
From brief to SAT: the project workflow
Technical brief
A well-prepared brief is half the battle. It includes the geometry and kinematics of the driven element, required force or torque on the linkage, and the target operating time. It also defines the number of cycles, ambient temperature, dust level, position sensor requirements and DCS/PLC interfaces. The more complete the data, the fewer design iterations are needed.
Concept and prototype
Based on the brief, the concept is developed: bore size, stroke with controlled reserve, type of guides and seals, and thermal shielding. A 3D model and bill of materials are prepared. The prototype undergoes functional tests, leak tests and temperature trials to confirm the assumptions.
FAT i SAT
FAT verifies parameters in near-operating conditions. SAT checks installation, direction of operation, stroke times and signals in the control system on site. This makes implementation predictable and provides maintenance teams with a drive tested for real operation.
High-temperature designs: materials, seals and shielding
Cylinder body and piston rod
Bodies are made of structural steel with protective coatings or stainless steel. Piston rods are produced from hardened and chrome-plated steels or appropriate stainless grades. This selection reduces wear and corrosion over the long term.
Guides and friction
FKM/FFKM seals and PTFE/PEEK bearings stabilise the friction coefficient under varying temperatures. Extended guides improve resistance to side loads and buckling, which in lever systems translates into real durability.
Shielding and spacers
Thermal shields and covers, as well as mounting spacers, reduce heat transfer to the cylinder body. In extreme conditions, an air barrier helps to “cut off” hot particles from sealing nodes. As a result, maintenance intervals lengthen and cycle times remain stable.
Applications: secondary air dampers, OFA/S-OFA, FGD and lances
Secondary air dampers – repeatability of position and consistent stroke times are key.
OFA and S-OFA – precision control is critical as it affects NOx emissions and oxygen balance above the furnace.
FGD – sealing and resistance to corrosive aerosols are top priorities.
Ignition lances – smooth extension in hot, dusty zones is essential.
In each case, reliable position feedback and predictable actuator response times remain critical.
Example configurations: D63×150 (18.4846) and D125×150 (18.4873)
D63×150 18.4846 – designed for high-temperature zones. Equipped with FKM seals, low-friction bearings and scrapers adapted to mineral dusts, it ensures stable closing and predictable operating times in secondary air and OFA systems.
D125×150 18.4873 – for higher loads and torques. Extended guides improve buckling resistance, while the set of seals and shields stabilises parameters in erosive and corrosive environments of flue gas ducts and FGD. In practice, this means maintaining required force on the linkage and longer service life of wearing parts.
Integration with automation: positioning, diagnostics, safety
Special actuators can be equipped with linear position transducers for continuous regulation and limit sensors for signalling. Interfaces are adapted to DCS/PLC so that commissioning runs smoothly. Cycle time and pressure monitoring enable early detection of sticking or leaks.
Where the actuator is part of a safety function, the design includes trip valves and position locks, harmonised with SIL/PL requirements. This ensures quick diagnostics and reduced risk of downtime.
Selection and calculations: force, stroke, kinematics and media
The process starts with a reliable estimate of the required force or torque, taking into account lever ratios and friction losses. A 20–30% margin above nominal conditions is applied to stabilise operation under fluctuating temperature and pressure. Stroke must cover the full damper movement with a small adjustment reserve.
Cycle time depends on flow rates, pipe diameters and valve characteristics. In pneumatics, compressed air quality according to ISO 8573 is critical. In hydraulics, oil cleanliness in ISO classes, correctly selected safety valves and lock blocks determine durability and stability.
Additional selection criteria: CPP PREMA practice
Vibrations, shocks and thermal gradients
Reinforced mountings, longer guide sleeves and anti-vibration elements extend service life. Thermal gradients during start-up and shutdown are addressed with shields, spacers or relocation of the cylinder outside the hot zone.
Supply quality and low-temperature operation
Stable pressure and dew point are decisive in pneumatics. In hydraulics, oil viscosity during cold starts and cavitation risk require appropriate oil grades, pre-heating or valve characteristic adjustments. Outdoor installations must consider icing and freeze–thaw cycles.
Fail-safe strategy, ATEX and EMC
The safe position (open, closed, hold) defines equipment and control solutions. Pneumatics use trip valves and locks, hydraulics use check valves, accumulators and hydraulic locks. ATEX dust requirements, IP tightness and EMC resistance determine enclosures, connectors and cabling.
Installation, access and standardisation
Co-axiality of linkages, access to connectors and sensors, bending radii and condensate-free routing are important. Standardised parts across sites (seal profiles, sensor types, connectors) shorten response times and simplify inventory. Drop-in retrofits maintain spacing and axis heights, enabling quick installation during short shutdowns.
Documentation and acceptance
Well-prepared I/O lists, cycle time measurement sheets, leak test reports and installation photos facilitate future diagnostics. CPP PREMA delivers an implementation package and service guidelines with each actuator. For safety-related systems, SIL/PL audit records are included. This ensures a quick and clear return to baseline during later inspections.
Maintenance: inspections, parts and retrofit
Effective maintenance relies on regular inspections. Clearances in guides, scraper condition and tightness at operating temperature are checked. Position sensors are calibrated, and cycle time trends are monitored.
Spare part kits – seals, scrapers, guides – make quick overhauls easier. Standardisation across sites streamlines logistics. Drop-in retrofits preserve spacing and axis heights, reducing mechanical work and downtime.
FAQ – quick answers
Are special actuators always more expensive? At purchase, often yes – but in total cost of ownership they usually win thanks to longer life and fewer downtimes.
What temperature range do high-temperature designs withstand? Defined by the application project; determined by seals (FKM/FFKM), bearings (PTFE/PEEK) and shielding/spacers.
Is DCS/PLC integration difficult? No. I/O lists, FAT/SAT acceptance and reference cycle times simplify commissioning and later diagnostics.
Can existing mountings be reproduced? Yes. Drop-in retrofits preserve spacing and axis heights, limiting mechanical work and downtime.
Summary
Special actuators – especially in high-temperature designs – maintain stable motion in zones where standard drives quickly wear out. Success depends not only on “temperature, dust and chemistry” but also on vibrations, thermal gradients, medium quality, fail-safe strategy, ATEX, EMC, installation conditions, service access and part standardisation. Addressed already at the design stage, these factors translate into real reliability, shorter TTR and better process controllability.
If you are planning to modernise secondary air dampers, OFA/S-OFA systems, FGD installations or ignition lance drives, consider actuators designed precisely for your plant’s conditions – with appropriate materials, seals, guides, shielding and integration strategy.
tel.: +48 502 829 200
e-mail: sebastian.kania@cpp-prema.pl
Do you need support in selecting a special actuator, modernising a damper/OFA/S-OFA/FGD drive, diagnosing an existing installation, or preparing FAT/SAT? Our specialist supports maintenance and automation teams from the very first brief through to commissioning and service: telephone consultations, rapid analysis of photos/drawings, remote assistance and – when necessary – an on-site visit.