Fluid power (hydraulic and pneumatic) components are "difficult customer" parts for a CNC shop: a sealing face loses its function with a tiny scratch, a burr at intersecting bores circulates through the system and jams a valve, residual chips end the life of a servo valve. On the other hand, these part families are very well suited to subcontracting: high quantities, repetitive geometry, predominantly turning and milling. In this sector, Turkey's general advantages are backed by a strong supply chain built around the construction machinery, agricultural machinery and automation clusters.
Hydraulic and Pneumatic Part Families Suited to Subcontracting
| Part | Typical material | Critical features | Manufacturing method |
|---|---|---|---|
| Manifold / block | S355J2 / C45, EN-GJS-400, EN AW-6082, 1.4404 | Network of intersecting bores, port threads (ISO 1179 / ISO 6149 / SAE J1926), surface flatness, freedom from burrs | 3/4/5-axis milling, deep-hole drilling |
| Valve body (cartridge cavity) | C45, 16MnCr5, EN-GJS, aluminium | Cartridge cavity profile (ISO 7789 / SAE J1926 / manufacturer standard), Ra 0.4–0.8, position tolerances | Turning + milling, cavity with form tool |
| Piston, rod, shaft | 42CrMo4, 20MnV6, C45E + chrome plating, 1.4057 | h7/h8 diameter, cylindricity 5–10 µm, Ra 0.2–0.4, hard chrome, straightness | Turning + grinding + plating + honing/lapping |
| Cylinder barrel, cap, gland | Drawn steel tube (E355 H8), casting, aluminium | Bore H8–H9, Ra 0.2–0.4 (honed), O-ring groove, thread | Turning, honing, milling |
| Fitting, adapter, nipple | C22/11SMnPb30 (zinc-nickel), CW614N, 1.4571 | Thread (BSPP, metric, ORFS, JIC), 24° cone (DIN 3861), surface, freedom from burrs | Swiss-type turning, multi-spindle automatic |
| Pneumatic valve and cylinder parts | Aluminium 6082/6026, brass, POM, stainless steel | Moderate tolerances, anodising, cleanliness, high quantities | Swiss-type turning, milling |
| Pump and motor parts | Case-hardening steels, castings | Gear profile, micron tolerances, grinding after heat treatment | Turning, milling, grinding; specialist supplier domain |
Material Selection and Machinability
- Steel (C45, S355, 42CrMo4): High-pressure manifolds and pistons; 42CrMo4+QT is standard for pistons. From hot forgings or drawn bar; internal burr control is difficult, intersecting bores need special deburring.
- Cast iron (EN-GJS-400/500, EN-GJL-250): Valve bodies and blocks; good machinability, vibration damping, porosity risk (pressure testing essential). Unplated surfaces need corrosion protection.
- Aluminium (6082, 6026, 7075): Pneumatic and low-to-medium pressure hydraulic (≤ 210 bar) manifolds; light, fast to machine, protected by anodising. Steel thread inserts (Helicoil) may be needed for thread strength.
- Brass (CW614N, CW617N; lead-free CW511L/CW724R): Fittings, pneumatic valves; lead-free is mandatory in drinking-water-contact applications.
- Stainless steel (1.4404, 1.4571, 1.4057, 1.4462): Food, chemical, marine and offshore hydraulics; machining time and cost are high.
Critical Manufacturing Topics
Intersecting bores and burrs
In manifolds, a burr is the most dangerous contaminant in the system. Expected: a defined deburring method at intersections (back-cutting tool, brush, thermal deburring (TEM), electrochemical deburring (ECM), high-pressure water jet), 100% or sampled inspection with a borescope, and a measurable criterion instead of "burr-free" (e.g. "edge break 0.1–0.3, no loose burrs"). Brushing is economical for aluminium and brass, TEM or ECM for steel.
Port threads and sealing faces
The thread standard (ISO 1179-1 BSPP, ISO 6149-1 metric, SAE J1926 UN/UNF, ISO 8434) and sealing type (O-ring groove, flat face, cone) must be stated clearly on the drawing; port face perpendicularity and Ra 0.8–1.6 (elastomer seal) or 0.4 (metal-to-metal) are inspected. 100% inspection with thread gauges is a common expectation.
Cartridge valve cavities
Cartridge cavities are machined in a single pass with a form tool; the tool must conform to the manufacturer's standard (e.g. Sun, HydraForce, Bosch Rexroth). The cavity's concentricity, bottom perpendicularity and surface determine cartridge sealing; they are inspected with gauges (go/no-go) and profile projection.
Pistons and rods
Hardening + grinding + hard chrome (20–30 µm) + polishing chain; diameter h7/h8, cylindricity 5–10 µm, Ra 0.2–0.4. On long rods, straightness (0.1 mm/m) and uniform chrome thickness. The sub-supplier chain (heat treatment, chrome) is the subcontractor's responsibility and must be certified.
Honed cylinder bores
Drawn tube (E355 H8/H9 pre-honed) or honing after machining; Ra 0.2–0.4 and the cross-hatch angle (plateau honing) determine seal life.
Technical Cleanliness
A significant share of hydraulic system failures is caused by contamination; part cleanliness is therefore a measurable requirement:
- ISO 4406: Cleanliness class of the system oil (e.g. 18/16/13); part cleanliness must not degrade it.
- VDA 19 / ISO 16232: Residual particle weight per part and maximum particle size (e.g. "≤ 1 mg, ≤ 400 µm, metallic shiny particles ≤ 200 µm"). Measurement: wash-extraction + filter analysis.
- Washing process: Water-based or solvent washing, ultrasonic, high-pressure bore flushing, drying; sealed bags and clean packaging after washing. Details are in our packaging article.
- Plugs and caps: Ports are closed with plastic plugs; internal surfaces are protected during transport.
Testing and Documentation
- Pressure test: Hydrostatic test of manifolds and bodies at 1.5 times the working pressure (e.g. 470 bar for a 315 bar system), duration and leak criterion on the drawing; 100% testing is common for castings because of porosity.
- Leak test: Air leak test (pressure decay) on pneumatic parts; measurable criterion (e.g. ≤ 5 cm³/min at 6 bar).
- Inspection report: FAI and series sampling; gauge records for cartridge cavities; Ra measurement on sealing faces. Our CMM report article explains how to read it.
- Material and process certificates: EN 10204 3.1, heat treatment hardness, chrome thickness, anodising thickness.
- Cleanliness report: Batch-based VDA 19 analysis on request.
Turkey's Position
Turkey has a notable sector in construction machinery (Hidromek, Çukurova, suppliers to JCB and Caterpillar), agricultural machinery (tractor production), automation and hydraulic cylinder manufacturing; hydraulic cylinder, valve and fitting manufacturers and their subcontracting chains are located in Istanbul, Bursa, Konya, Ankara and Izmir. The practical consequences: deburring of intersecting bores, honing, hard chrome, cartridge cavity tooling and cleanliness infrastructure are available locally; E355 drawn tube and 42CrMo4 chrome-plated bar are supplied from stock. Duty-free entry under A.TR, 3–7 days by road and a 30–45% cost advantage make Turkey a natural nearshore source for hydraulic system manufacturers in Europe.
What a Hydraulic Part RFQ Should Contain
- Working and test pressure, fluid type (mineral oil, HFC, water-glycol, air).
- Port thread standard and sealing type; cartridge cavity standard.
- Ra and geometric tolerances on sealing faces.
- Burr criterion and inspection method (borescope, sampling).
- Cleanliness requirement (VDA 19 class or mg/part).
- Testing requirement (100% or sampling; duration, criterion).
- Coating and corrosion protection; plugs and packaging.
- Quantity, batch size, documentation expectations. Our RFQ guide contains a general template.
Frequently Asked Questions
Is it possible to make manifolds from aluminium?
6082/6026 is common in pneumatics and hydraulics up to 210 bar; where higher pressure, fatigue loading and steel thread strength are required, steel or castings are chosen.
How is burr control documented?
Borescope photos (intersection points), a defined deburring method and sampling records; 100% borescope inspection is possible on critical parts.
Who performs the pressure test?
If the subcontractor has a test bench, it tests and records per batch; otherwise it is done at a sub-supplier or at the customer. This should be clarified in the RFQ.
How much does the cleanliness class affect the price?
Standard washing is included in the price; VDA 19 class cleanliness + analysis + clean packaging typically adds 3–8% to the part price.
Conclusion
Hydraulic and pneumatic components are parts that require tolerance, burr, cleanliness and testing discipline together, and they are produced economically in subcontract shops that apply this discipline. Tornelle works in steel, cast iron, aluminium, brass and stainless steel for manifolds and valve bodies, fittings and adapters, pneumatic parts and the piston–rod chain; deburring of intersecting bores, clean packaging and the documentation package are applied as standard. Send your technical drawings and pressure and cleanliness requirements for your hydraulic parts via our quote form; you will receive a line-by-line quote including the scope of testing and documentation.
