Under the selected construction used here, eccentric radius is h + L + l, eccentric throw is twice that radius, and full port-opening span is 2h. These identities do not determine complete D-slide-valve events or engine performance.
D-Slide Valve Selected Dimension Construction
Explore selected D-slide-valve dimension identities with a closed eccentric, rod and guided valve chain.
Equation Used
- The selected construction defines eccentric radius as h+L+l.
- Throw is twice eccentric radius.
- The animation uses a finite constant-length connecting rod, but its angularity is not part of the dimension formulas.
- Valve events, flow, pressure, loads, wear and tolerances are excluded.
Throw is defined here as twice eccentric radius; h is one-half of the selected full port-opening span.
Eccentric, constant rod and translating D valve
An eccentric and its strap move the D valve through a constant-length rod. Steam surrounds the outside of the valve in the chest. The two outer passages connect to the cylinder ends, while the central passage carries exhaust. The hollow underside links one cylinder passage to exhaust as the opposite outer edge uncovers admission. The fixed illustrative geometry includes outside lap; its port colors follow edge overlap, not a flow or engine-timing calculation. The selected dimension inputs below do not set this example geometry.
What the calculator determines
Select half port-opening span h, outside lap L and lead l. The calculator reports selected eccentric radius, diameter-like throw, full opening span and lead as a percentage of the selected radius.
Selected dimensional construction
r = h + L + l; throw = 2r; full opening span = 2h; lead share = 100l/r.
Selected-input arithmetic
For h = 1 in, lap = 0.25 in and lead = 0.03125 in, selected eccentric radius is 1.28125 in and throw is 2.5625 in.
Dimensions only
The construction excludes crank datum, connecting-rod angularity in the formulas, port width distribution, inside lap, exhaust clearance, cutoff, release, compression, admission, pressure, flow, forces, wear and manufacturing tolerances.
Questions
Does this calculate valve events?
No.
Why is throw twice radius?
This page uses throw as the eccentric diameter or full peak-to-peak displacement reference.
Mechanical reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances (1901), page 71, figure 238: single D slide valve with lap. The valve extends beyond the outside edges of the steam ports by one lap at each end.
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