Add a stated diametral clearance to a spool diameter to find the nominal bore diameter. This geometry calculation does not determine suitable clearance, leakage or cylinder drift.
Hydraulic Valve Interactive Calculator
Convert a stated diametral clearance from micrometres to millimetres, then add it to spool diameter.
Equation Used
- Entered clearance is treated as diametral clearance added directly to spool diameter for nominal bore.
- Pressure does not affect this dimensional addition and is not used in the bore result.
- No distinction between diametral and radial clearance is inferred beyond the explicit geometry convention.
- No flow/leakage, viscosity, temperature, land length, eccentricity, pressure balance, spool force, lap, metering, contamination, wear, drift, rating or safety model.
The bore result is nominal geometry, not a manufacturing tolerance recommendation. Use the specified clearance convention for the particular spool and bore; a radial clearance must be doubled before treating it as diametral.
Spool and bore diametral geometry
If C is explicitly defined as diametral clearance, nominal bore diameter is D+C after converting micrometres to millimetres.
The animation exaggerates the gap for visibility. It does not show metering, pressure forces or leakage.
Check the clearance convention
The calculator adds a diametral clearance to spool diameter. Leakage, permitted clearance and cylinder drift are shown as not calculated because the necessary valve and system data are absent.
From micrometres to bore diameter
One thousand micrometres equal one millimetre. Divide the entered diametral clearance by 1000 before adding it to the spool diameter in millimetres. The pressure input does not enter this geometry calculation.
Worked bore-diameter example
For a 20 mm spool and an entered diametral clearance of 25 µm, convert clearance to 0.025 mm and add it to obtain a nominal bore diameter of 20.025 mm. This example does not recommend that clearance for a particular valve.
Scope and limitations
Real valve design requires exact radial/diametral convention, spool and bore roundness/taper, land lengths and lap, port geometry and metering edges, eccentricity, surface finish and materials, fluid viscosity versus temperature, pressure boundaries, flow forces, contamination/filtration, thermal expansion, manufacturing capability, wear, allowable internal leakage and verified manufacturer qualification.
Frequently asked questions
Does this calculate leakage flow?
No. Bore and spool diameters alone do not determine leakage. The flow path, fluid properties, pressure boundaries and other valve details are required.
Is the entered clearance a recommended tolerance?
No. It is a user-supplied dimension. The calculator adds it to the spool diameter using a diametral convention.
Does pressure affect nominal bore diameter here?
No. The pressure input is not used in the dimensional addition. Elastic deformation and thermal expansion are not modeled.
Can this predict cylinder drift?
No. Drift depends on valve and cylinder leakage paths, load, geometry and circuit conditions.
Calculation basis
Diametral clearance is the difference between bore diameter and spool diameter. For concentric circular parts, it is twice the radial gap. The calculator converts the entered clearance from micrometres to millimetres and adds it to spool diameter.
This dimensional identity does not prescribe a tolerance or predict leakage. Leakage and cylinder drift require an identified valve and circuit, fluid properties and operating conditions.
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