Bulkheads
What Is A Bulkhead?
A bulkhead fitting is used in hydraulic (and other fluid) systems to allow a hose, tube, or pipe connection to pass securely through a panel, wall, or enclosure while keeping the joint strong and leak-free. It has threads on both sides with a locking nut, so it can be fixed tightly in place.
You would typically use a bulkhead when:
- Routing hydraulic lines through panels, tanks, or machine walls.
- Creating a secure connection point where hoses need to connect on either side of a partition.
- Maintaining a leak-free seal when fluid needs to pass from one section of equipment to another.
- Organising hose layouts, keeping systems neat and accessible.
- Protecting hoses and fittings from rubbing or strain at entry points.
A bulkhead fitting is used to provide a strong, sealed connection through a wall or panel, making it ideal for equipment housings, hydraulic tanks, and machinery where hoses need to pass between compartments.
How To Install A Bulkhead
Choose the location:
- Identify where the bulkhead will pass through (e.g., tank wall, panel, or enclosure).
- Ensure there is enough clearance on both sides for hoses/fittings to be attached.
Drill the hole:
- Drill a clean hole to match the external diameter of the bulkhead body.
- Deburr the edges to prevent damage to the fitting or seals.
Insert the bulkhead:
- Slide the bulkhead body through the hole from the correct side (depending on flow direction or layout).
- Make sure any O-rings or seals are seated correctly against the wall or panel.
Fit the locknut:
- Thread the locknut onto the bulkhead from the opposite side of the wall/panel.
- Hand-tighten first, then use a spanner to secure firmly (do not overtighten, as this can damage seals).
Attach hoses or pipes:
- Connect your hydraulic hose, pipe, or adaptor to each end of the bulkhead.
- Use the correct sealing method for the thread type (washer, O-ring, or PTFE tape for tapered threads).
Test the connection:
- Once installed, pressurise the system gradually and check for leaks.
- Re-tighten slightly if necessary.
Connecting Threads Guide
Threads That Match Directly:
- BSPP to BSPP → Seals with a bonded washer or O-ring.
- BSPT to BSPT → Seals on the threads with PTFE tape or sealant.
- NPT to NPT → Seals on the threads with PTFE tape or sealant.
- JIC to JIC → Seals metal-to-metal on the 37° cone seat.
- ORFS to ORFS → Seals on the O-ring face for a leak-free joint.
- SAE O-Ring Boss to SAE O-Ring Boss → Seals with an O-ring at the port face.
- Metric to Metric → Seals with an O-ring or bonded washer.
Sometimes Compatible (with care):
- BSPT male into BSPP female → Will screw in, but must be sealed with a washer or sealant.
- JIC and SAE 37° → Often compatible, both use a 37° flare, but check standards before use.
- JIS BSPP to BSPP → Same thread, but JIS often seals on a 30° cone rather than a washer.
Not Compatible:
- BSP ↔ NPT → Different angles (55° vs 60°), will not seal reliably.
- Metric ↔ BSP/NPT → Different thread form, not interchangeable.
- UNF ↔ BSP/NPT/Metric → Won’t seal unless part of a designed fitting.
- NPSM ↔ anything else → Only seals with a gasket, not designed for high pressure.
Rule of thumb:
- Tapered threads (BSPT, NPT) seal on the thread + tape/sealant.
- Parallel threads (BSPP, Metric, SAE, UNF) need a washer or O-ring.
- JIC and ORFS seal on the face or cone, not the thread.
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BSPP (British Standard Pipe Parallel) |
BSPT (British Standard Pipe Tapered) |
NPT (National Pipe Taper) |
JIC (Joint Industry Council) |
JIS (Japanese Industrial Standard) |
Metric (mm) |
Imperial (") (UN/UNF/UNC) |
SAE (Society Of Automotive Engineers) |
ORFS (O-Ring Face Seal) |
UNF (Unified Fine Thread) |
NPSM (National Pipe Straight Mechanical) |
| Thread Form | Parallel | Tapered | Tapered | Parallel with 37° Cone | BSPP/Metric (Parallel) | Parallel | Parallel | Parallel (UN/UNF) | Parallel (UNF) | Parallel | Parallel |
| Flank Angle | 55° | 55° | 60° | 60° | 55°(BSPP) / 60° (Metric) | 60° | 60° | 60° | 60° | 60° | 60° |
| Sealing Method | Washer / O-Ring | Thread Interference + PTFE Tape | Thread Interference + PTFE Tape | 37° Cone Seat (Metal To Metal) | Gasket Or 30°/60° Cone Seat | Washer / O-Ring | Gasket / O-Ring | O-Ring Boss | O-Ring On The Face | Angled Cone Seat / O-Ring | Gasket |
| Standard | ISO 228 / BS 2779 | ISO 7 / BS 21 | ANSI B1.20.1 (USA) | SAE J514 (USA) | JIS B 0203 / B 2351 | ISO 261 / ISO 724 | ANSI B1.1 (USA) | SAE J1926 | SAE J1453 | ANSI B1.1 (USA) | ANSI B1.20.1 (USA) |
| Applications | Medium-high pressure hydraulics, pneumatics, water systems; common in UK/European machinery | High-pressure pipework (hydraulic, steam, gas, water); widely used in construction | High-pressure hydraulics; common in North American equipment | High-pressure hydraulics (up to ~420 bar); mobile plant, aerospace & automotive | Medium pressure hydraulics & pneumatics; Japanese/Asian machinery & vehicles | Medium-high pressure hydraulics; European industrial, agricultural & mobile equipment |
Low Pressure, for fastening & mechanical joints, not fluid sealing; general engineering & hydraulic systems |
High-pressure hydraulics; common in hydraulic blocks, automotive & aerospace | Very high pressure, leak-free hydraulics; common in agriculture, construction, heavy plant | Medium pressure hydraulics; also used in automotive, aerospace & precision machinery | Low-pressure mechanical joints; used in piping, fire protection & water systems |
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