Hiscox’s disc valve for large gas pipes uses a pinion to rotate a toothed sector on a ported disc. The source drawing shows a flat circular plate with four openings. The illustration pairs the rotating plate with assumed matching stationary openings, so passages appear as the ports align.
Disc Valve for Large Gas Pipes Interactive Calculator
Explore Hiscox’s pinion-driven ported disc valve with an illustrative four-port layout. The disc rotates in its own plane against a fixed port plate. The stated example uses four 35° annular openings. Calculate their overlap and the ideal axial pressure load on the covered parts.
Equation Used
- Four equally spaced annular ports, each 35° wide.
- Inner port radius is 0.20 of bore radius; outer radius is 0.85.
- At θ = 0 the moving ports are offset by 45° from the fixed ports; at θ = 45° they align.
- Flat parallel plates, ideal sealing of covered ports and no leakage.
- Uniform specified differential pressure acts on covered port regions.
- The shown 80:20 sector-to-pinion ratio is illustrative, not a dimension supplied by the historical source.
This is a ported rotary disc, not a butterfly valve. Port proportions, tooth count and pressure distribution are assumptions for this example. The pressure input is a differential in psi, not a gauge-pressure rating.
Opening by port alignment
The moving plate stays in one plane as it rotates. Its circular outline therefore stays circular in the end view. This differs from a butterfly disc, which tilts through the pipe bore.
The pinion engages the peripheral toothed sector. The illustration uses the equivalent of an 80-tooth sector wheel and a 20-tooth pinion, making the pinion turn four times as far in the opposite direction. A marked point on the plate makes its smaller angular motion visible.
Dashed outlines show the fixed ports behind the moving plate. Blue regions are openings through both plates; tan regions visible through a moving port are still covered by the stationary plate. The animation opens to the selected limit and returns.
A historical large-pipe control
Hiscox identifies mechanism 1615 as a disc valve for large gas pipes and describes its pinion-and-sector drive. The sketch does not give production dimensions, port angles, leakage characteristics or pressure ratings.
The calculator therefore labels its four-port dimensions and gear ratio as illustrative assumptions. It explains the geometry without representing a modern certified gas valve or specifying a suitable installation.
Overlap of matching annular sectors
Each assumed port has outer radius rₒ = 0.85R, inner radius rᵢ = 0.20R and angular width w = 35°. One annular-sector area is ½(rₒ²−rᵢ²)w, with w in radians. Four ports give A_ports = 2(rₒ²−rᵢ²)w.
For the selected opening angle θ between 0° and 45°, relative port offset is δ = 45°−θ. The angular overlap is max(0,w−δ). Multiplying that angle by 2(rₒ²−rᵢ²) gives the open area through both plates. The remaining 10° between adjacent ports creates an initial interval with no opening.
The percentage is relative to maximum port area, not to the whole circular bore and not to flow capacity. The simple pressure-force estimate is Δp times covered port area. It is an axial force, not gear torque.
A 600 mm bore with the stated port pattern
The circular bore area is about 0.28274 m². Its four assumed ports total about 0.07505 m². At θ = 0° the fixed openings are covered; at θ = 10° overlap is just beginning; at θ = 45° they are aligned.
At θ = 27.5°, the angular overlap is 17.5°, half the 35° port width. The open area is consequently half the maximum port area. This is a consequence of the specified port geometry, not a general valve-flow characteristic.
Doubling diameter multiplies bore area, port area and the uniform-pressure force estimate by four. Doubling pressure difference doubles that force without changing geometric opening.
Limits of the geometric comparison
The source sketch is not a sectional manufacturing drawing. The paired-port layout and proportions are stated assumptions used to make a calculable example. A real valve can have different openings, seating and pressure distribution.
Predicting gas flow requires fluid conditions and a validated flow characteristic. Operating torque also depends on sealing, friction, pressure distribution and gearing efficiency. None can be obtained by treating this axial pressure force as a motor torque.
Ported disc valve questions
Why is the opening range 45° rather than 90°?
The illustrated four-port pattern repeats every 90°. Its alternating covered and aligned positions are 45° apart.
Why can the plate move without opening a passage?
The assumed 35° ports leave a 10° closed interval before their edges overlap.
Does 50% open mean half the gas flow?
No. It means half the maximum geometric port overlap.
Why does pressure not change the drawn opening?
Opening is imposed by the gear position. Pressure changes the ideal load estimate, not the prescribed angle.
Is zero covered-port force at alignment a zero-load valve?
No. Only the modeled load on covered port regions becomes zero. Other pressure, seal, bearing and flow forces are outside this model.
Reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, mechanism 1615, printed page 389 (PDF page 399). The image and description establish the ported disc with a pinion-and-sector drive; the numerical dimensions and assumptions for this example are listed separately.
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