steamboats

Equinox: for more about this exquisite craft. See Steam Happens, Appendices 25 and 26 below

Will Weidner, Equinox's creator, has graciously contributed a simple to use dynamic spreadsheet for designing D or piston valves. Feel free to download and use the attached file. Simply click here to download the file. It can then be viewed in MS-Excel, OpenOffice or any software that can handle an .xls file. Once the file is opened just change the input values to determine how the changes you've made influence the valve's performance. It's great for new engine designs or tweaking your current engine for peak performance. Here's Will's description of its use:

“The Spreadsheet “VALVGR2.xls” is a useful tool for designing a slide valve for eccentrically driven valve gears. A lot of engine plans may have a slide or piston valve designed by the seat of the pants, but when the analysis is done, it can be seen that a lot of improvement can be made. A huge increase in economy can be the result. When the valve on an existing engine is optimized, it seems like the engine driven feed pump suddenly has an increase in output. Of course lower steam consumption is the reason for this. It will also seem like the boilers’ appetite for wood is greatly diminished.

Using this spreadsheet allows you to make changes to valve parameters (valve travel, advance angle, admission and exhaust lap) and immediately see the effect on valve events. It allows you to do is adjust the admission lap and exhaust lap separately for both the forward stroke (top of piston) and return stroke (underside of piston). This allows you to compensate for the non-uniform motion of the valve vs. piston position due to the connecting rod angularity error. Uniform valve events for forward and return strokes are the result. That’s why there are pairs of input numbers for admission and exhaust lap. Try putting the same numbers in for each to see the angularity effect.

This spreadsheet has limited use for linked-in Stephenson motion because it requires you to know the eccentric throw and advance angle. It is very useful for Stephenson in full gear, or slip eccentric valves. Stephenson gear that is linked-in has a “virtual” throw and advance angle, but they are hard to determine analytically or graphically. They can be determined on the engine by linking in the gear to the desired position. Then measure the valve travel with indicator or calipers while turning the engine over. Note the crank pin angular position from TDC or BDC when the valve is at its extreme position. Subtracting this angle from 90° will give the advance angle.”