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Harkesh Exclusive Tool

Diaphragm Force Calculator

Most seal suppliers don't offer this. Compute the effective diameter, effective area, convolution radius and developed force of a rolling diaphragm from bore, piston and pressure — then quote a custom diaphragm from Harkesh.

Why effective area is constant: in a rolling diaphragm the convolution rolls between the bore and piston as the assembly strokes, so the pressure-bearing effective diameter stays ~constant — force tracks pressure linearly through the full stroke, unlike a flat diaphragm.

Effective Diameter

47 mm

Effective Area

1734.9 mm²

Convolution Radius

1.5 mm

Force

694 N

Force

156 lbf

Harkesh custom diaphragms

Harkesh custom-manufactures rolling, flat and convoluted diaphragms in fabric-reinforced and homogeneous elastomers to your exact bore, stroke and pressure. Run your numbers above, then send us the spec for a tooling and sampling quote.

Guideline only. Values and ratings are representative at ambient conditions and are not a warranty of performance. Actual results vary with temperature, pressure, concentration and exposure time. Validate for your specific application — our engineers can help.

Rolling diaphragm in a cylinder, showing bore diameter, piston diameter, the rolling convolution and the effective diameterCylinder borePistonBore ØPiston ØEffective Ø = (Bore + Piston) / 2
For a rolling diaphragm, the effective diameter is the mean of the bore and piston diameters — which is why force stays a clean, linear function of pressure across the stroke.

Rolling diaphragm force, the right way

A rolling diaphragm is not a flat membrane — it is a top-hat shaped elastomer (usually fabric-reinforced) whose sidewall convolution rolls between a cylinder bore and a piston as the assembly strokes. Because the convolution is always rolling, the pressure-bearing effective diameter stays essentially constant over the entire stroke. That is the single most important property for design: force is a clean, linear function of pressure, with none of the position-dependent area change that plagues flat diaphragms. This Harkesh-exclusive calculator captures that behaviour exactly.

Effective diameter

The effective diameter is the mean of the bore and the piston: deff = (bore + piston) / 2. It sits halfway across the convolution gap, which is where the line of action of the pressure load effectively acts as the sidewall rolls.

Effective area and force

The effective area is simply the circle of that diameter: Aeff = π/4 × deff². The developed force is then F = Aeff × pressure. With area in mm² and pressure in bar (1 bar = 0.1 N/mm²), the calculator returns force in both newtons and pound-force so you can size springs, actuators and load cells directly.

Convolution radius

The radial gap between bore and piston is split symmetrically by the rolling sidewall, so the convolution radius is Rc = (bore − piston) / 4. This radius sets the minimum bend radius the elastomer and reinforcement fabric must tolerate without fatigue — too tight a convolution shortens diaphragm life.

From numbers to a part

Harkesh custom-manufactures rolling, flat and convoluted diaphragms to your bore, stroke and pressure in fabric-reinforced and homogeneous compounds. The competition rarely tools custom diaphragms — we do. Run your spec above and request a tooling and sampling quote.