Steam engine slide valve

[ThomasJ]

Working with castings from "burnzoil" foundry in No. CA. eBay seller. Great casting kits and additional cylinders for my Donkey Engine. Customer service also excellent. Several build pix. but no plans included. I need help with slide valve pocket dimensions. Some advice has been 9% width reduction of area over two adjacent ports. My cylinder ports are .280+.200+.300=.780X.09=.702. Sound reasonable ? Thanks, Thomas

 

[Charles Lamont]

I am not entirely clear about the question, but I'll have a go. Most slide valves have no, or very little, exhaust lap, so the exhaust cavity would normally match the distance between the inner edges of the steam ports.