A tappet can contact a lever so that limited follower travel moves a valve. Hiscox illustrates this compact arrangement and identifies pumps, rock drills and percussion tools as uses.
Tappet Lever Valve Motion Interactive Calculator
Vary position within an assumed opening flank, rise interval, nominal valve travel, constant motion ratio and entered clearance. Outputs show ideal displacement arithmetic only.
Equation Used
- θ is measured from the start of the assumed opening flank and clamped at β.
- Follower rise is an assumed simple-harmonic displacement law.
- Entered clearance is removed at the follower before constant-ratio multiplication.
- Link geometry, pressure, spring or gravity return, force, acceleration, contact stress, flow and wear are omitted.
What the Historical Drawing Shows
Gardner D. Hiscox labels movement 266 as tappet lever valve motion and states that it was used on pumps, rock drills and percussion tools. The compact drawing establishes a tappet-to-lever-to-valve topology, but it does not provide dimensions, a cam profile, clearances or operating data.
The animation uses a generic cam to illustrate the assumed displacement law. Its cam shape and motion are not dimensions supplied by the historical drawing.
What This Explanatory Model Is Useful For
Use it to see how one assumed opening-flank displacement is reduced by an entered follower clearance and multiplied by a constant entered motion ratio.
Do not use it to set a real valve, recommission equipment, design a cam, establish timing or clearance, or predict flow, shock, wear or safe speed.
Assumed Opening-Flank Kinematics
Here h is ideal follower rise, R is constant entered motion ratio and c is entered follower clearance. θ is clamped to the entered rise interval β. This is one assumed monotonic flank, not a complete rise-dwell-return cam.
Worked Assumed Scenario
At θ = 30 degrees of a 120-degree rise, nominal valve travel 25 mm, ratio 2:1 and clearance 0.15 mm, ideal follower rise is about 1.83 mm and ideal valve travel is about 3.36 mm. The clearance-equivalent valve travel is 0.30 mm once the gap is taken up.
These are ideal entered-value results, not measurements or operating recommendations.
Model Boundary
- Historical arrangement: movement 266 is a tappet lever valve motion used on pumps, rock drills and percussion tools.
- Calculated: one assumed simple-harmonic opening displacement, constant-ratio travel after entered clearance and normalized available travel.
- Not calculated: actual cam shape, dwell, return, timing relative to a machine cycle, lever geometry, backlash, compliance, acceleration, force, spring or pressure return, impact, contact stress, flow, leakage, wear or safety.
Frequently Asked Questions
Is this the exact motion of Hiscox movement 266?
No. The source gives no dimensions or cam law.
Why use simple harmonic motion?
It provides a smooth illustrative rise from zero to the entered maximum. The cited NASA reference discusses simple-harmonic follower motion as one possible cam law.
Does the calculator include a closing flank?
No. It stops at the end of the assumed opening interval.
Does motion ratio remain constant in a real lever?
Not necessarily. Finite link geometry can make instantaneous ratio vary.
Is entered clearance a recommended setting?
No. It is only an input to the ideal arithmetic.
Can ideal valve travel predict flow?
No. Port and seat geometry, pressure, fluid properties and discharge behavior are absent.
References
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