A reciprocating slide valve alternately covers and uncovers steam ports as its edge moves across the valve face. This calculator performs a static maximum-travel comparison from entered dimensions; it does not solve a Walschaerts linkage, valve events, flow, pressure or engine performance.
Considering an actuator-driven slide valve
An actuator-driven slide valve requires force, stroke and timing calculations in addition to the port dimensions. The static opening calculation below does not establish actuator suitability or reproduce the timing of a mechanical valve gear.
With leverage, force is traded against travel. A bracket change that improves force can also increase required stroke, slow the output motion, or move the actuator into a poor mounting angle.
A crank or cam may tolerate continuous rotation through a difficult part of the cycle, while a linear actuator has defined end positions and internal limits. That difference matters when the mechanism needs repeatability or must not drive into a hard stop.
- Map actuator stroke to the actual output travel before choosing a model.
- Check for binding, changing leverage, and peak load near the ends of travel.
- Decide whether timed motion is acceptable or position feedback is required.
For a FIRGELLI design review, calculate the load case with the FIRGELLI actuator force calculator and plan the switching or controller arrangement with the linear actuator wiring diagram generator. If an actuator or cylinder is already installed, the linear actuator replacement finder helps keep the comparison tied to real dimensions.
Valve Gear Interactive Calculator
Enter valve half-travel, steam lap, outside lead and port width. Results are a static dimensional comparison—not a valve diagram, cut-off calculation, flow area, linkage solve or engine recommendation.
Equation Used
- Valve half-travel, lap, lead and port width are independent entered dimensions.
- The static comparison uses one valve edge and one port width along the direction of valve travel.
- Opening is capped at entered port width.
- Entered outside lead is reported separately and is not used to infer phase or maximum displacement.
- Port length normal to valve travel is not entered, so flow area is not calculated.
- Cut-off, release, compression, linkage closure, flow coefficient, pressure, mass flow, forces, wear, clearances, power, efficiency, operating limits and safety are omitted.
Documented Slide-Valve Topology
U.S. Patent 479,401 documents a reciprocating slide valve whose ports alternately coincide with steam ports in a seat plate. U.S. Patent 360,594 likewise describes working surfaces that open and close ports during valve motion. These sources support the generic moving-edge and port topology shown here.
What This Calculator Represents
The tool compares entered maximum half-travel with entered steam lap to obtain a one-dimensional valve-edge exposure, caps that exposure at entered port width and reports the fraction of that width uncovered. It separately repeats entered outside lead.
Static Edge-exposure Calculation
capped opening = min(port width, raw exposure)
port opening fraction = capped opening / port width
travel shortfall = max(0, steam lap - half-travel)
U.S. Patent 539,920 distinguishes the motion that overcomes lap and lead from the valve's throw. With no phase law or dead-center position in the inputs, lead cannot be folded into a maximum-opening formula.
Worked Dimensional Example
For 32 mm entered half-travel, 24 mm steam lap and 120 mm port width, raw exposure is 8 mm. The capped opening remains 8 mm, which is 6.7% of entered port width. Entered outside lead is reported separately as 3 mm.
Model Boundary
- Calculated: static one-edge exposure, port-width cap, fraction of entered port width and shortfall to lap.
- Reported directly: entered outside lead.
- Illustrated: generic slide valve and steam port.
- Not calculated: Walschaerts or other linkage motion, phase, lead at dead center, valve events, cut-off, flow area, mass flow, pressure, forces, power, wear, clearances, settings or safety.
Frequently Asked Questions
Why is lead not added to maximum opening?
Lead is a port opening at a specified dead-center condition; this tool has no phase or valve-displacement law.
Is capped opening a flow area?
No. A second port dimension and a flow model are absent.
Does this calculate cut-off?
No.
Does the animation close a Walschaerts linkage?
No; it is a generic motion cue.
Can it set real valve gear?
No.
Can it predict power or steam economy?
No.
References
- U.S. Patent 479,401, Steam-engine valve: reciprocating slide valve and steam-port coincidence.
- U.S. Patent 360,594, Steam-engine valve: working surfaces opening and closing steam ports during valve motion.
- U.S. Patent 539,920, Valve-gear: separate contributions associated with lap/lead and valve throw.
- U.S. Patent 1,798,816, Steam engine: documented lead position, full-open position and valve-event sequence.
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