Part of the reason that a factory condition Accucraft Ruby will go better in reverse than in forward is due to the fluid mechanics in the direction control block. With the direction control in the forward direction, the steam path is very different dimensionally than when in the reverse direction.
Physical Structure: The valve body is a rectangular machined brass with an approximately 5 mm hole down the middle opening to the rear for the valve plug mechanism. Steam from the boiler enters the valve through a top rear opening, and exhausts through a top forward opening. On each side there are two pipes going to the cylinder valves. When the direction control is in the forward position, the front tube(s) supplies steam to the cylinder valves, and the rear side tube(s) is the exhaust. In reverse, this is reversed. The round valve shuttle (plug) is a machined metal plug with tight sliding fit to the body. There is a threaded rear hole for attachment to the mechanisms. This hole is not through into the steam space. This threaded attachment is used to adjust the depth of the valve plug into the valve body. The valve shuttle has two grooves machined into the circumference. The rear one is relatively narrow and approximately 1.7 mm in width and .4 mm in depth. The forward one is about 7.3 mm in width and 0.5 mm in depth. From the rear groove bottom to the front of the shuttle there is a 1.7 mm round passage that makes a sharp bend and then through the front. This passage is +12 mm long. Steam Flow: When in the forward direction, the steam enters the rear groove. From there enters a sharp edged 1.7 mm hole that is perpendicular to the bottom of the grove. This entry hole can be in any radial position in relation the point where steam enters. The steam then goes through a 90 degree sharp angle and proceeds through the rest of the passage down the center of the valve plug to the front of the valve plug. From there it flows into the full center space of the 5 mm diameter valve body, and then into the pipes leading to the cylinder valves. When entering this forward space, it must fill this space, and transfer at right angles into the cylinder pipes. The exhaust from the cylinders utilizes the longer valve shuttle groove in its path to the stack. When in the reverse direction, the small groove and its restricted steam passage are not used. The valve shuttle is pulled back leaving the smaller groove behind the steam supply port, and the though passage is blocked. The longer groove then provides the steam passage from the supply to the cylinders. The exhaust utilizes the full 5 mm of the valve body to go from the cylinders to the stack. Executive Summary: The valve is asymmetrical, with a more efficient fluid path when placed in the reverse direction mode. Mike Eorgoff
