Pneumatic Fittings & Manifolds for Leak-Tight Connections
Precision connections hold pneumatic systems together. In body shops, EV battery lines, washdown food plants and offshore skids, fittings and manifolds face temperature swings, shock, vibration and corrosive media — and leaks cost pressure, uptime and safety margins.
SPAC Engineering
Technical Team · September 2026
September 2026
9 minutes
Technical Guide
SPAC Engineering
This guide lays out how to specify fittings and manifolds that stay tight, how to read threads and tube sizes correctly, what alloys to select, and how to install for zero drama. It closes with inspection steps, leak detection tips and a brief FAQ that answers the questions procurement and engineering teams ask most.
Air fittings are the connectors that join tubing, valves, FRL units and actuators into a sealed pneumatic circuit. They convert threads to tube connections, route air through tees and manifolds, add flow control and isolation, and allow fast maintenance swaps. Typical locations include valve islands feeding ISO-15552 cylinders, panel manifolds supplying tooling, and drops to point-of-use regulators and instruments.
4–16 mm
Typical tube outer diameters
M5 · BSP 1"
Thread size range in plant use
BSPP · BSPT
Common thread standards
304 · 316 · 2507
Alloy options for harsh duty
The right fitting choice reduces leak paths, speeds service and resists vibration — keep to one plant thread standard wherever possible.
Common Airline Fitting Types & When to Use Them
Most plants standardise on three families, then add specialists as needed. Push-in fittings give fast, tool-free tube connection — ideal for modular automation, valve islands and frequent maintenance. Specify with a matched tube outer diameter and a rated pressure margin.
Compression fittings use metal ferrules that bite the tube for high integrity on vibration-prone or higher-temperature areas, or where tube materials demand a mechanical grip. Threaded adaptors and flow devices — male or female connectors, elbows, tees, banjos, reducers, plugs, checks and needle-style flow controls — handle routing and metering.
Within push-in, choose straight, elbow, tee, Y and banjo bodies to suit routing. Use in-line flow controls at cylinder ports to tune extend or retract speed cleanly. For a quick overview of available forms, see SPAC’s pneumatic fittings range covering airline fittings, compression-style options and push-in connectors.
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THE THREE-FAMILY RULE
In most plants, push-in, compression and threaded adaptors cover the majority of needs. Pick push-in where speed and modularity matter, compression where vibration and heat are high, and face-sealed threads for repeatable maintenance.
Threads, Sealing & Identifying Sizes
You will meet BSPP (ISO 228, parallel), BSPT (ISO 7, tapered) and metric straight threads; in legacy imports, NPT appears occasionally. BSPT seals on the thread flanks with a compatible male-female taper and a suitable thread sealant. BSPP and metric straight typically seal via an O-ring or bonded washer at the face — do not rely on parallel threads alone for sealing.
To identify size, measure the tube outer diameter for push-in. For threads, use a pitch gauge and callipers on the major diameter, then match the reading to a thread chart. Do not assume a “1/4” marking equals 6 mm tube — tube OD and thread size are independent. Typical tube ODs in modern automation are 4, 6, 8, 10, 12, 14 and 16 mm; match the tube OD exactly to the fitting spec.
If you are replacing parts and unsure of the interface, remove one fitting, photograph the thread end and tube end, measure OD and pitch, then request a like-for-like cross from the factory.
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TUBE OD ≠ THREAD SIZE
These are two independent measurements. A 1/4 in thread does not imply 6 mm tube. Verify both — pitch gauge on the thread, callipers on the tube OD — before you cross-reference a replacement.
Choosing Alloys for Harsh Environments
Alloy choice is application-led. Match the material to the media, temperature and H2S partial pressure of the full system — and request a material review rather than assuming equivalence.
Brass & Stainless (General → Corrosive)
Brass / nickel-plated brass — general automation
304 & 316 stainless — food, pharma, chemical, offshore
Superior corrosion resistance & cleanability
Higher temperature capability than brass
304 · 316 for wetted duty
Duplex & Super-Austenitic (Aggressive)
Duplex 2507 & 6Mo classes for chlorides
Offshore splash zones & sour service
NACE MR0175 / ISO 15156 & MR0103
NORSOK notes for offshore manifolds
2507 · 6Mo for offshore
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TRACEABILITY IS PART OF THE SPEC
SPAC supplies stainless and alloy fittings with full material traceability — heat numbers, material certificates and a QMS pack aligned to audit requirements. In sour or offshore duty, demand the paperwork, not just the datasheet rating.
Leak-Tight Under Vibration: Design & Assembly
Design out leaks before you reach the line. Shorten unsupported tube runs and add clamps at regular intervals to remove mass-driven whip. Move bends closer to ports to reduce lever arms, and use elbow bodies to keep tubing neutral. Keep manifolds rigidly mounted on plates or rails — not free-hanging from hoses — and use compression or stainless push-in bodies where continuous vibration or thermal cycling is present.
During assembly, deburr tube cuts square, then push to the positive stop and mark insertion depth to confirm full engagement. On compression fittings, follow torque charts and avoid dry galling on stainless threads with a suitable approved assembly lubricant. Do not overwrap threads with PTFE: for BSPT, use minimal approved sealant on the male thread only; for BSPP with bonded seals, no tape is required.
For banjo elbows on cylinders and valves, set orientation first, then lock the collar to the specified torque to avoid side-load. After assembly, pressure test and soap-solution check every joint; where safety or access is constrained, use ultrasonic leak detection.
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MANIFOLDS SIMPLIFY SERVICE
Panel manifolds reduce leak points and speed maintenance. Specify port count, main header size, drop-port threads, isolation options and drain provision — and mount them upstream of a compressed air filter regulator so downstream circuits see clean, stable pressure.
SPAC Engineering Details That Matter
Back-ferrule geometry
SPAC's advanced back-ferrule design bites consistently without excessive make-up torque, promoting repeatable, vibration-resistant seals.
Carburised bodies on select series
Controlled surface hardening improves thread wear and galling resistance — important on stainless-to-stainless assemblies and frequent maintenance loops.
Portfolio breadth
Stainless, duplex and special-alloy fittings and manifolds to suit food, pharma, automotive, EV battery and offshore duty.
Bespoke manifolds
Custom hole patterns, valve subplates, isolation features and instrument tees, supplied with drawings and test records.
Full traceability
Heat numbers, material certificates and a QMS pack supplied for audits and project files.
Send your P&ID and service list for a specification review and a matched fittings plus manifold package.
Fitting Family Selection Guide
| PROPERTY | Push-In | Compression | Threaded |
|---|---|---|---|
| Assembly Speed | Excellent | Moderate | Moderate |
| Vibration Resistance | Good | Excellent | Good |
| High-Temperature Duty | Moderate | Excellent | Good |
| Tool-Free Maintenance | Excellent | Moderate | Moderate |
| Routing Flexibility | Excellent | Good | Excellent |
| Modular Automation | Excellent | Good | Good |
Checks That Prevent Leaks
Weekly visual
Look for tube creep from collets, witness-mark movement and bracket loosening.
Pressure stability
Compare regulator setpoints to actual downstream gauges at steady load.
Leak sweep
Soap solution at joints during planned stops, plus ultrasonic checks on noisy lines.
Re-torque window
On compression joints in hot-cold cycling zones, re-check lightly after initial heat soak, per manufacturer guidance.
Quick Answers
What are air fittings?
Connectors that join tubing and threaded ports in a pneumatic circuit, providing sealed, serviceable connections and routing between tubing, valves, FRL units and actuators.
What are the different airline fittings?
Push-in connectors, compression fittings, and threaded adaptors including elbows, tees, banjos, reducers and plugs. Flow controls and checks are common add-ons.
What size are airline fittings?
Tube sizes are typically 4 to 16 mm OD. Thread sizes follow BSPP, BSPT or metric designations from M5 and BSP 1/8 up to BSP 1 inch in typical plant use.
How do I tell what air fitting I have?
Measure tube OD, identify the thread type with a pitch gauge, and check the major diameter. Photograph the part and port if you need a like-for-like cross-reference.
What are the three types of fittings?
In most plants, push-in, compression and threaded adaptors cover the majority of needs.
How do you detect an air leak?
Pressurise, listen, apply soap solution to suspect joints, and use ultrasonic detectors to find micro-leaks or inaccessible points.
Where should a check valve be installed?
Close to the component you want to protect or hold pressure on, oriented with the flow arrow. Common spots are after regulators feeding cylinders or tool drops, and on branch lines to prevent backflow between circuits.
What are the disadvantages of check valves?
Added pressure drop, potential chatter at low flows, blocked exhaust in fault cases, and maintenance if contamination prevents full sealing.
Leak-tight, vibration-proof connections start with the right fitting type, verified threads, the correct alloy and disciplined assembly. Use push-in where speed and modularity matter, compression where vibration and heat are high, and face-sealed threads for repeatable maintenance. For sour or offshore duty, align materials with NACE and NORSOK notes and demand full traceability.
Need a fast, audit-ready fittings & manifold package?
SPAC Pneumatic UK supplies stainless and alloy fittings, bespoke manifolds, complete documentation and direct engineering support. Explore the full range of pneumatic fittings or send your specification for a 24-hour response.
Send Your Specification →↳ Stainless push-in fittings for corrosive or high-temp service
↳ Compression fittings for vibration-prone and thermal-cycling zones
↳ Bespoke manifolds with custom hole patterns and valve subplates
↳ Duplex 2507 and 6Mo fittings for offshore and sour service
↳ Full traceability — heat numbers, certs and QMS pack for audits
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