Bremme’s radial valve gear uses one eccentric and a pivoted suspension link to guide the eccentric rod. Moving the suspension centre changes the valve motion and reverses its directional component. The animation follows the Bremme/Marshall suspension-link form, calculating the connected rods and valve position as the eccentric turns.
Positioning the suspension support
The eccentric supplies the repeating valve motion. A separate actuator could position the support R as a reversing control, provided its travel, linkage clearance and required holding force are calculated. The support remains fixed during each shaft revolution in this model.
For a separate positioning design, use the FIRGELLI actuator force calculator to compare forces and the linear actuator wiring diagram generator to plan the control circuit. The linear actuator replacement finder compares an existing actuator’s dimensions.
Bremme Valve Gear · Suspension-link Calculator
Guide the eccentric rod with a pivoted link. Adjust the support and compare the valve path, travel, lap allowance and speed.
Equation Used
- Rigid links and one continuous assembly branch.
- Suspension centre fixed during each revolution.
- Length ratios and the support-setting arc are selected model dimensions.
- Valve centring uses the midpoint of extrema.
- Opening ignores port-width limits and steam flow.
The signed sine coefficient describes directional motion, not cutoff percentage.
Follow E–Q–P and the suspension centre R
E is the eccentric centre. E–Q–P is one rigid rod, extended beyond the suspension attachment Q. The link R–Q constrains Q to a circular arc about R. P drives the valve slider through a connecting rod.
Moving R from one side of its central setting to the other changes the guided path and reverses one component of the valve motion. R remains fixed while the shaft makes each revolution. The support arc is a setting guide, not a sliding block moving every cycle.
The main animation uses the clearly labelled suspension-link form in the 1911 Encyclopaedia Britannica, figure 34, identified there as Bremme’s or Marshall’s gear. Hiscox no. 259 and Barber no. 1447 show a compact form using additional links and a bent output rod. The selected dimensions illustrate the motion and do not specify a particular engine.
Explore radial valve-gear motion
Compare eccentric radius, rod size and support setting, then add a selected valve lap and shaft speed. The motion curve shows displacement over one revolution and the positive and negative lap thresholds.
Valve centring is adjusted to the midpoint of the extrema at each design setting. Maximum opening beyond lap is therefore half the total travel minus lap, limited to zero. It is an ideal displacement allowance, without a port-width cap, piston timing reference or steam-flow calculation.
Closed linkage calculation
Take O=(0,0), E=(r cos θ,r sin θ), and nominal Q=(0,L). The selected suspension length is S=0.75L, and its fixed support is R=(−S cos β,L+S sin β). Q is the continuous upper assembly intersection of |Q−E|=L and |Q−R|=S. The extended rod point is P=1.5Q−0.5E.
The valve travels horizontally at y=1.5L. With connecting-rod length C=1.3L, its position is xᵥ=Pₓ−√[C²−(Pᵧ−1.5L)²]. Numerical extrema over a full revolution give travel T=xₘₐₓ−xₘᵢₙ and centring coordinate x₀=(xₘₐₓ+xₘᵢₙ)/2. Maximum opening is max(0,T/2−lap).
Closed-loop derivatives give dxᵥ/dθ; multiplying by 2πn/60 gives velocity. The displayed sine and cosine coefficients come from the first Fourier component of xᵥ(θ). They describe the motion relative to the displayed eccentric angle, not engine lead or cutoff.
Compare opposite support settings
Start with a 15 mm eccentric, 180 mm E–Q rod and +25° support setting. Move the setting to −25° and compare the displacement curve and signed sine component. The support changes the path of Q without introducing a slot or die block.
Doubling shaft speed doubles peak valve speed and halves the cycle time, while travel and maximum opening remain unchanged. Increasing lap reduces the opening allowance without altering the linkage motion.
Geometry assumptions and limits
The historical figure shows the suspension link and extended rod. This model uses selected length ratios, a support-setting arc and a fixed valve guide position. It assumes rigid links and frictionless pins, without clearance or elastic deflection.
The calculated valve path shows how support position changes travel and speed. Determining allowable operating speed or steam distribution also requires loads, piston timing, port dimensions and engine data.
Bremme gear questions
Where is the die block?
This suspension-link form has no slotted expansion link. Q follows a circular arc about R.
Does the support move during a revolution?
No. It is a design or reversing setting, held fixed during the animated cycle.
Why is there motion at the central setting?
The lead-related motion component and finite-link geometry are still present. A central setting does not imply that every point stops.
Is maximum opening a cutoff percentage?
No. It is the centred valve excursion beyond a chosen lap. Piston phase and port geometry are not specified.
Primary references
Encyclopaedia Britannica, 1911, Steam Engine, printed page 834, figure 34: Bremme/Marshall suspension-link form, movable centre R and extended point P.
Thomas Walter Barber, The Engineer’s Sketch-Book, no. 1447, and Gardner D. Hiscox, Mechanical Movements, no. 259: related compact linked form. The numerical model here follows the clearer suspension-link diagram and states its selected dimensions.
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