Sensor fittings for detection of pressure drop
Signal Fittings for Detecting Pressure Drop
Signal fittings from Parker Legris enable automated detection of pressure drop in pneumatic systems through reliable end-position sensing of the cylinder piston. These functional fittings combine mechanical connections with electrical or pneumatic signal outputs and are available with connection threads 1/8", 1/4", 3/8", 1/2", and M5x0.8. Their use reduces downtime, facilitates maintenance planning, and increases operational safety in manufacturing plants, positioning systems, and automated transport devices.
Product Structure and Materials
Signal fittings consist of a housing, a sealing element, a switching element, and connections for pneumatics and electrics. Typical housing materials include nickel-plated brass alloys for corrosion resistance, technical plastic (e.g., PBT, PA) for weight reduction, and stainless steel variants for increased resistance to aggressive environments and cleaning agents. Seals are usually made of NBR (nitrile butadiene rubber) or FKM (fluorocarbon rubber); NBR offers good resistance to oils and general hydraulic fluids, while FKM is advantageous at higher temperatures and with more aggressive media. The contact parts and switching elements are gold-plated or tin-plated to ensure service life and contact quality. For housings exposed to high chemical stress, the stainless steel or high-performance plastic variant is recommended.
Connections, Threads, and Interfaces
The choice of connection threads influences sealing surfaces, assembly effort, and compatibility with existing lines. Parker Legris offers signal fittings in the following standard threads:
- 1/8", 1/4", 3/8", 1/2" BSP/NPT variants and metric M5x0.8
These thread variants allow direct integration with cylinders, valves, and distributors. In addition to screw connections, quick-connect fittings for polyurethane or polyamide tubes are often available, reducing assembly time and sealing requirements. Electrical connections follow industry standards such as M8/M12 connectors, cable outlets with protective tubing, or screw-on connectors for easy field wiring. When selecting, pay attention to the compatibility between pneumatic threads (BSP vs. NPT) and electrical protection classes (IP65 to IP67) to avoid leaks and malfunctions in the production environment.
Sealing and Protection Concepts
Tightness is central to the function of signal fittings. In addition to O-rings, combined sealing systems are often used: a primary metal or plastic seating surface, as well as secondary elastomer seals to absorb vibrations and thermal loads. In applications with higher dirt or moisture ingress, screw-on protective caps and IP-certified housing surfaces are recommended. For high-temperature processes, manufacturers offer special sealing materials and heat-resistant plastic options.
Electrical and Pneumatic Operating Principles
Signal fittings function either electrically, pneumatically, or as hybrids. Electrical variants switch via Hall, Reed, or switching contacts upon contact with the piston and send a digital signal to PLCs or control units. Pneumatic variants transmit or block compressed air, thereby generating a pressure signal that is processed in downstream pressure gauges or valves. Hybrid types combine both: a pneumatic output signal for simple local logic operations and an electrical signal for central controls. Choose the design according to the required reaction time, interference immunity, and integration requirements into the control technology.
Application Areas and Performance Requirements
Signal fittings are used wherever reliable detection of piston end positions, positions, or pressure drop is necessary: automated assembly cells, injection molding removal positions, packaging machines, conveyor technology, and test benches. In the food and pharmaceutical industries, stainless steel and FDA-compliant sealants are required. In harsh manufacturing environments, increased IP protection classes and vibration-resistant fastening elements are crucial. For high switching frequencies, choosing a low-wear switching element (e.g., Hall sensor instead of mechanical contacts) is advisable.
Assembly, Commissioning, and Maintenance
Before assembly, threads and sealing surfaces must be cleaned and provided with suitable sealants (for NPT threads) or thread lockers. For BSP threads, O-ring seals, mechanically clean contact surfaces, and correct tightening torque according to manufacturer specifications are usually sufficient. The electrical connection cable must be routed according to protection requirements, grounding shields must be used, and plug connections must be secured with locking tabs. Maintenance intervals depend on the load: visual inspection of seals, functional testing of the switching threshold, and replacement of elastomers every 12–24 months are common practice. Documented test protocols and spare parts lists increase availability.
Practical Example 1: End Position Monitoring on Pneumatic Cylinders
In an assembly cell for PCB assembly, pneumatic cylinders are equipped with signal fittings that report the piston's end position. The electrical variant with an M8 connector provides a digital signal to the PLC as soon as the piston reaches the target position. This signal controls the locking of a gripper and allows synchronized cycle sequences. Thanks to gold-plated contacts, switching thresholds remain stable even with high humidity and conductive particles.
Practical Example 2: Pressure Drop Detection in Conveyor Technology
In a pneumatically operated conveyor system with multiple swivel units, signal fittings are used pneumatically to quickly detect pressure drops in sub-lines and stop the supply before product displacement occurs. The fittings are equipped with FKM seals and a screw-on metal housing to resist cleaning agents and oil mist. Integrated pressure switches allow local diagnosis without interfering with the central control system.
Practical Example 3: Hygienic Application in Food Production
In a filling plant, stainless steel signal fittings monitor the piston position of valve actuators. The housings are smoothly polished, seals are FKM-compliant, and all electrical connections are IP67-protected. The measuring unit is integrated into the process control to precisely regulate filling volumes and cycle times and to automatically trigger cleaning cycles.
Integration and Spare Parts Management
For trouble-free operation, it is recommended to select signal fittings with standardized connectors and exchangeable modules. Document manufacturer and article numbers, stock O-rings and electronic switching modules as spare parts, and check compatibility with existing cylinders or valve islands. Further technical information and application examples can be found at maku-industrie.de/technik and specific practical cases at maku-industrie.de/anwendungsbeispiele.
Selection Criteria Summarized
Select signal fittings based on the following criteria:
- Thread and connection size, sealing material, protection class, switching principle, housing material
FAQs
Which thread sizes are available and what should I consider when choosing?
Available sizes are 1/8", 1/4", 3/8", 1/2", and M5x0.8. Choose the thread according to the existing pneumatic connections; for NPT threads, additional Teflon tape or sealing paste is required, while BSP variants often work with an O-ring seat. Pay attention to compatibility with your cylinder and material compatibility with media and environment.
How do electrical and pneumatic signal fittings differ in practice?
Electrical types provide digital signals directly to PLCs/control units and are often more robust for long cable runs and susceptibility to interference. Pneumatic variants provide local pressure signals without wiring, are suitable for simple logic operations, and are insensitive to electromagnetic interference. Hybrid models combine the advantages of both systems.
What maintenance measures are necessary to prevent failures?
Regular visual inspection of seals, functional testing of switching thresholds, and replacement of elastomeric components every 12–24 months. Pay attention to correct assembly, clean threads, and appropriate protection classes for environmental influences. Documentation and stocking of critical spare parts reduce downtime.