The double-beat disc valve shown here is a ring-shaped moving disc with an inner and an outer seating edge. Lifting the ring opens two concentric passages. The fixed centre seat is carried on a crossbar, with a central pin guiding the moving assembly. The illustration follows Hiscox’s mechanism 593.
Double-beat Disc Valve Interactive Calculator
Explore the annular disc form in Hiscox 593: one ring lifts from inner and outer seating edges. Enter the two diameter proportions, differential pressure and lift to compare pressure loads and geometric opening area.
Equation Used
- 0 < d < D. The diameter-ratio slider keeps the concentric annulus valid.
- Uniform differential pressure acts across the annular projected area when seated.
- Force is reported as a magnitude; its direction depends on which side has higher pressure.
- Both circular seating edges have the same prescribed axial lift.
- Curtain area is a geometric sum, not a discharge coefficient or volumetric flow prediction.
- The illustrative opening cycle is prescribed independently of pressure and does not predict self-opening.
The pressure load follows the projected annular area set by the two seating diameters. Increasing the inner-to-outer diameter ratio reduces this area, while lift changes the separate opening-area result.
One annular disc, two seating edges
The plan view identifies the shaded moving annulus between diameters D and d. In section, that annulus appears as two separate pieces, but they are opposite cuts through the same circular ring. A light spider connects the ring to a sliding guide sleeve.
The outer seating edge is carried by the body. The inner seat is supported from the stationary crossbar. Both seats remain fixed while the ring and its spider rise together. Both circular edges separate from their seats by the same lift.
The animation prescribes an opening and closing cycle to explain the geometry. It does not claim that a selected pressure alone produces that displacement. Fluid arrows identify available routes through the open edges; their speed does not represent a calculated flow.
What the calculator compares
Use the outer diameter and inner-to-outer diameter ratio to define the projected annular area. Enter the pressure difference across the closed valve, rather than assuming line pressure is always the pressure difference. The calculator compares the annular pressure load with a full disc of the same outer diameter.
Maximum lift supplies a separate geometric opening-area calculation. It is useful for understanding why two circular edges provide more opening perimeter, but it does not determine delivery rate or whether the valve will open under its own pressure loading.
Projected load and curtain area
The full circular area is πD²/4. Subtracting the inner circular area gives the annular projected area π(D²−d²)/4. Multiply either area by differential pressure to obtain its ideal static pressure load.
One bar equals 0.1 N/mm². Thus F=0.1ΔPπ(D²−d²)/4 gives newtons when pressure is in bar and diameters are in millimetres. Alternatively, use pascals and metres directly, without an additional conversion factor.
The two opening circumferences are πD and πd. At axial lift h their combined ideal curtain area is π(D+d)h. This is not necessarily the smallest flow passage in the complete valve. Supports, seat thickness and flow contraction can reduce the effective opening.
300 mm outer and 180 mm inner diameter
With D=300 mm, d/D=60% and differential pressure 4 bar, the full-disc comparison load is approximately 28,274 N. The annular-disc load is approximately 18,096 N, or 64% of the full-disc load.
At 10 mm lift, the sum of the two geometric curtain areas is approximately 150.8 cm². Changing lift changes this area but does not change the seated pressure-load calculation. Doubling pressure doubles both loads; it does not change the geometry.
Interpret the results within the model
A narrow annulus reduces the projected pressure area, while its two edge circumferences remain substantial. This is a geometry comparison, not a strength or durability conclusion. A usable ring still needs adequate stiffness, guidance and seating accuracy.
The separate Cornish bell-type double-beat valve uses vertically separated seats. The Cruquius museum describes that construction and its pressure-area balance. The present illustration instead follows the ring-disc arrangement in Hiscox 593; the two forms should not be treated as identical drawings.
Opening and closing forces also depend on weight, springs, friction, acceleration and the pressure distribution during flow. The calculator evaluates seated pressure-area load only; these additional forces require separate data.
Double-beat disc valve questions
Are the two blocks in section separate moving discs?
No. They are opposite sections through one annular disc.
What does the percentage input mean?
It is inner seating diameter divided by outer seating diameter. It is not a directly assumed force reduction.
Why does lift not change the pressure-load tiles?
Those tiles describe the seated projected-area load. Lift changes the curtain-area result and the animation.
Why can the animation move at zero pressure?
It is a prescribed geometry demonstration, not a prediction of a free valve’s dynamic response.
Is the reported area a flow rate?
No. Flow requires additional information about the fluid, pressure distribution and losses.
References
Hiscox, Mechanical Movements, Powers, Devices and Appliances, mechanism 593, printed page 158 (PDF page 168): double-beat disc valve with supported centre seat and guide pin.
Cruquius Museum: valves, a reference for the distinct Cornish bell-type construction and differential-area pressure balance.
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