Hydraulics Is a Sealing Business
Nobody calls us about a manifold body that machined beautifully. They call when a fitting leaks at 250 bar. After machining thousands of hydraulic parts — nipples, check valve bodies, manifolds, flange fittings — the lesson is always the same: the sealing surface is the part. Everything else is just material around it. So when we review a hydraulic drawing, we look at sealing geometry first.
Thread Standards: Get This Wrong and Nothing Fits
Hydraulic threads are a standards minefield. NPT (taper, US), BSPP (parallel, metric-friendly Europe), BSPT (taper British), metric parallel, SAE straight thread with O-ring — they all look similar on a drawing and none of them interchange. We machine a lot for European buyers where BSPP and metric are the norm, and for US buyers where NPT dominates. On the RFQ, write the thread standard explicitly. A 1/2 inch BSP vs NPT confusion is a scrapped batch every time.
| Standard | Region | Sealing Method | Common Use |
|---|---|---|---|
| NPT | North America | Tapered thread, sealant | General hydraulic, air |
| BSPP (G) | Europe | Parallel + bonded washer / O-ring | General hydraulic |
| BSPT | UK, Commonwealth | Tapered thread, sealant | Older systems |
| SAE O-ring boss | North America | Straight thread + O-ring | High-pressure hydraulic |
| Metric parallel | Europe/Asia | O-ring or washer | ISO systems |
The Cross-Hole Burr: Small Defect, Expensive Leak
The classic hydraulic failure: a drilled cross port intersecting a bore leaves a burr on the inside edge. That burr breaks off in service, wedges in the valve seat, and the system loses pressure. Deburring intersecting holes is not optional on hydraulic parts — it is a defined process step, often with specialty tools or EDM for tight internal intersections, followed by inspection. Ask your supplier how they deburr cross holes. If they look confused, walk away.
Materials That Hold Pressure
Aluminum 6061-T6 is the default for manifolds and valve bodies — light, machines fast, plenty strong for most systems. For corrosive or high-temperature circuits, 316 stainless or duplex grades are the norm. Brass shows up in fittings where corrosion resistance and machinability matter. The important spec on the drawing is the pressure rating and the test requirement — 100 bar, 250 bar, proof tested? That drives material choice and wall thickness review.
Surface Finish and Cleanliness
Sealing faces get machined, not anodized over — anodizing adds thickness and changes the seal geometry. Typical finish on a sealing face is Ra 0.8 or better, and every port gets deburred and chamfered. After machining, hydraulic parts are cleaned and often plugged to keep chips out of the cavities. If your part ships with blind cavities, expect a cleanliness step in the process and say so on the RFQ if it matters to you.
Send us your hydraulic drawing with the thread standards and pressure rating marked, and we will quote it with the deburring and testing steps included — no surprises at the first pressure test.
The Parts We Actually Machine
A typical week brings the same hydraulic family again and again: nipples and adapters, check valve bodies, manifold gaskets, flange fittings, and the occasional complete valve block. Most of them are family parts — the same body with different port sizes, which is exactly where machining shines. Variants share the program and fixtures, so quoting the whole family together cuts setup cost per part and shortens delivery. If your drawing is one of several variants, send them all in one RFQ. The quote comes back lower and the lead time shorter than ordering each variant separately.
Frequently Asked Questions
Which thread standard should I use for hydraulic fittings?
Match your regional system: NPT for North America, BSPP or metric for Europe, SAE O-ring boss for high-pressure US designs. Never mix standards in one assembly.
How do you deburr intersecting cross holes?
With specialty deburring tools for accessible intersections and EDM or advanced tooling for tight internal ones, followed by inspection. Cross-hole burrs are the #1 cause of hydraulic leaks.
Is aluminum strong enough for hydraulic manifolds?
6061-T6 is standard for most manifolds and valve bodies up to hundreds of bar. Higher pressures or corrosive media call for stainless or duplex — state the pressure rating on the drawing.
What surface finish is needed on a sealing face?
Typically Ra 0.8 or better, machined after any anodizing — never anodize over a sealing surface because the coating changes the geometry.
Do you pressure test machined hydraulic parts?
On request. If the drawing specifies proof or leak testing, we build it into the process and quote. State the test pressure and medium.