Hello, I'm Nate, and I'm looking to build a compressed-air engine. I'm using a pneumatic cylinder with a 3" bore and a 12" stroke. That was simple enough to find. What hasn't been simple to find is a manual valve large enough to actuate it. I've found small 5-way valves on ebay and amazon, but they don't allow enough air to pass through them to make them practicable. So I started looking for another way to get what I need... google. Unfortunately, google isn't as helpful as I thought it would be. I've found a few photos of D-slide valves, but nothing for a double-acting cylinder that actually has dimensions written in. I thought about (and tried, unsuccessfully) loading one of these pictures into AutoCAD and extracting the dimensions, but the pictures are either too grainy or too inaccurate, or just plain won't work with the program. So, does anyone know where I can find actual dimension drawings of a piston type valve? Like I said, I'm using a cylinder with a 3" bore and a 12" stroke, so my piston valve has to be able to handle a large quantity of air passing through. I've done a lot of research on this, so please don't go about trying to convince me of a better design. Also I have access to a machine shop that includes CNC mills, engine lathes, and manual mills, so I can make the parts myself if I have the dimensions. I don't want to mess around with D-slide valves, because they're more difficult to machine manually, and I have to have this done by the middle of May.