Valves and pumps are everywhere in industrial equipment, and they all need deep holes drilled in them. From the valve body or pump housing to the spool bores and piston bores inside, the quality of the deep hole drilling determines whether the component seals properly or leaks.
I have worked on valve and pump components for oil and gas, hydraulic systems, chemical processing, and water treatment. The requirements vary by industry, but the drilling principles are similar across all of them.
Valve Body Drilling
A valve body is a casting or forging that houses the internal components – the gate, ball, plug, or spool. The main bore through the valve body carries the fluid. In a gate valve, this bore is straight through from flange to flange. In a ball valve, it goes through the ball cavity.
The challenge is that valve bodies are not symmetrical. The wall thickness varies around the bore, which means the cutting forces are unbalanced. The drill wants to push away from the thick wall and into the thin wall.
Valve Body Parameters
| Valve Type | Bore Diameter | Material | Cutting Speed | Feed Rate |
|---|---|---|---|---|
| Gate valve | 50-300mm | WCB steel | 60-80 m/min | 0.10-0.18 mm/rev |
| Ball valve | 50-600mm | 316 stainless | 50-70 m/min | 0.08-0.14 mm/rev |
| Globe valve | 25-200mm | Cast iron | 80-120 m/min | 0.10-0.20 mm/rev |
| Check valve | 40-400mm | Duplex SS | 40-60 m/min | 0.06-0.10 mm/rev |
I use BTA drilling for large valve bores over 80mm. The BTA head is self-piloting, which helps keep the bore straight even when the wall thickness is uneven. For smaller bores, I use gun drilling with a guide bushing close to the entry.
Spool Bore Drilling
Hydraulic valve spools slide inside a precision bore. The clearance between the spool and the bore is typically 0.005-0.020mm. That means the bore has to be round, straight, and smooth.
The spool bore is usually 10-50mm in diameter and 100-500mm deep. The material is often steel or cast iron with a surface hardness of 45-60 HRC.
Spool Bore Parameters
| Parameter | Cast Iron | Steel (45 HRC) |
|---|---|---|
| Cutting speed | 80-100 m/min | 50-70 m/min |
| Feed rate | 0.04-0.08 mm/rev | 0.03-0.06 mm/rev |
| Coolant pressure | 400-600 psi | 800-1200 psi |
| Surface finish target | 0.4-0.8 Ra | 0.2-0.4 Ra |
I rough-drill the spool bore with a gun drill, then finish with a single-pass reamer or a skive-and-roller burnish tool. The burnishing creates a work-hardened surface that resists wear from the spool sliding.
Pump Housing Bores
Pump housings have multiple bores for the impeller shaft, wear rings, and bearing housings. These bores need to be concentric to each other within tight tolerances – typically 0.03-0.05mm total indicated runout.
I approach pump housing bores in stages:
- Core-drill the shaft bore – through the entire housing
- Bore the wear ring pockets – to concentricity with the shaft bore
- Line-bore the bearing housings – from both ends, meeting in the middle
For the shaft bore, which is the reference for all other bores, I use BTA drilling. The bore is typically 30-80mm in diameter and 200-600mm long.
Pump Shaft Bore Parameters
| Parameter | Value |
|---|---|
| Cutting speed | 70-90 m/min |
| Feed rate | 0.08-0.14 mm/rev |
| Coolant pressure | 400-600 psi |
| Bore diameter tolerance | H7 (0.025mm for 50mm bore) |
| Surface finish | 0.8 Ra maximum |
Cartridge Valve Cavities
Cartridge valves screw into machined cavities in a manifold block. The cavity has a pilot bore, a sealing bore, and a threaded section. All three sections need to be concentric and the sealing bore needs a surface finish of 0.4 Ra or better.
I use a combination tool for cartridge valve cavities – a gun drill for the pilot bore, then a step tool that machines the sealing bore and threads in one pass. This approach maintains concentricity between all three sections.
Key Takeaways
- Valve body bores are often in asymmetric castings – BTA drilling is self-piloting and handles this well
- Spool bores need sub-micron finishes – plan for a secondary finishing operation like burnishing
- Pump housings use the shaft bore as the reference for all other bores
- Keep the shaft bore within H7 tolerance to ensure concentricity
- Cartridge valve cavities benefit from combination tooling that machines all sections in one pass
For related topics, see my articles on casting and forging and brake and coupling components.