The disc valve and guard shown by Hiscox uses an elastic disc and a perforated spherical guard. The disc is retained near its center; its outer portion can flex away from the ported seat, while the curved guard limits that movement. The revised animation follows this arrangement rather than the unrelated spring-loaded tapered-poppet construction previously described.
Disc Valve and Guard Interactive Calculator
Inspect a centrally retained elastic disc beneath a perforated curved guard. Adjust its diameter, requested edge lift, guard slope and sheet thickness.
Equation Used
- Central clamp radius20percent of disc radius.
- Circular-arc guard section and illustrative perforations.
- Prescribed flexing shape, not a material simulation.
- Outer curtain area approximate; no effective-flow rating.
Geometric opening and illustrative flexing only. No fluid-flow, pressure, material or timing prediction.
A flexible disc beneath a perforated guard
The closed disc covers the openings in a flat supporting seat. In the illustrative opening stroke its outer part bends upward while the central clamped region remains fixed. The perforated guard is also fixed. At maximum allowed travel the disc reaches the underside of that guard. Flow-direction markers appear only when there is an open path around the disc edge.
The guard section is a circular arc starting tangent to the flat central clamp region. The clamp radius is defined as 20% of disc radius for this model. Guard edge slope, disc diameter and sheet thickness determine the drawn geometry. The historical plate does not supply these dimensions.
The flexing shape is an illustrative interpolation between the flat disc and guard contour. No pressure, elastic modulus or material model is entered, so this is not a prediction of deformation under load. The motion sequence is for inspection, not valve timing.
What the calculator compares
Explore the opening around the outer edge of a centrally retained flexible disc and the available travel beneath a curved guard. Diameter and guard slope change the limiting height; sheet thickness changes the visible disc and its nominal material volume.
This comparison does not select a pump valve, establish a pressure rating or predict the flow through the seat ports and guard holes.
Explicit guard and opening geometry
Let disc radius be R=D/2, central clamp radius a=0.2R, and flexible radial span w=R−a. For guard edge slope α measured from horizontal, circular-arc radius is ρ=w/sinα and guard rise is H=ρ(1−cosα)=w tan(α/2).
The modeled maximum edge lift is the smaller of requested lift and H. If the request exceeds H, the page states that the guard stops the motion. The approximate outer curtain area is πD times that available lift, divided by 100 for square centimeters. It is a geometric edge-area estimate, not a discharge area corrected for losses.
Nominal unperforated sheet volume is πD²t/4 in cubic millimeters, divided by 1000 for cubic centimeters. This is blank-sheet volume before a center hole or other machining; it is not mass.
Example: 76.2 mm elastic disc
For D=76.2 mm, guard slope 45°, requested lift 6 mm and sheet thickness 2 mm, the flexible span is 30.48 mm. Guard rise is about 12.63 mm, so the requested 6 mm lift fits. The curtain-area estimate is 14.36 cm² and nominal sheet volume 9.12 cm³.
If the same requested lift is increased to 20 mm, the guard still limits the edge to about 12.63 mm. The animation reaches the guard and stops; it does not pass through the guard or silently depict the requested height as feasible.
Geometric opening is not flow capacity
Seat-port area, guard perforations, fluid properties, pressure, disc stiffness and transient motion affect a real valve. This model does not solve those effects. The displayed edge-area estimate can exceed another restriction in the assembly and must not be interpreted as a flow rating.
The earlier page’s tapered seat, axial guide clearance, closing spring, mud-pump specifications, service-life claims and universal tolerances did not describe the cited elastic-disc construction and have been removed. Guard edge slope is now measured explicitly from horizontal; it is not a poppet seat angle.
Disc-valve questions
Does the entire disc translate upward?
No. The modeled center remains clamped while the outer portion flexes.
Why does increasing requested lift stop changing the opening?
The fixed guard limits the movement. The calculator reports that limit and shows the disc meeting the guard.
Does thickness change calculated deflection?
Not in this geometry-only study. It changes the drawing and nominal sheet volume; a pressure and material model would be needed to predict flexure.
Are the perforations sized by this calculator?
No. Their drawing illustrates the historical guard construction, not an engineered hole pattern.
Historical construction reference
Gardner D. Hiscox, Mechanical Movements, Powers and Devices, printed page 158, figure 592 (PDF page 168). The original section was inspected: elastic disc and perforated spherical guard. The guard geometry and flexing interpolation used here are stated model assumptions.
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