Floating D Valve

[DetroiTug]

I agree with everything in this thread, even my own statements.

I understand the misalignment/wearing issues associated with not allowing the valve to float (run loose). However, the wear being discussed here should not be so anticipated, accepted nor experienced. If the slide valve is lubricated, it's not going to wear considerably with normal usage. They are iron valves, not electric motor brushes. Refer to high speed CNC machine tools and their flat surface way systems. The wear over time is virtually non-existent because they ride on a cushion of oil - every business day for decades. Machine tools that do wear out suffered insufficient lubrication.

I've been in the machining/toolmaking industry since 1977. And the majority of the latter portion has been in the tooling design arena. At no time has it ever been acceptable to mate two non-self lubricating metallic surfaces together in a motive sliding configuration without some sort of lubrication or friction relief. And water is not an industry accepted lubricant for ferrous and non-ferrous metals.

The valves have been running for three years with no issues and no noise.

-Ron

[gondolier88]

SY Gondola's engine has SG cylinders and D-valves, and are now 34 years old. There is a tiny amount of wear on the port face, <2thou. Interestingly, though, is that both D-valves had wear on the top slide-face only, around 1/32". These have 'z' oil grooves milled in, and are well lubricated with 600 grade steam cylinder oil. However, they have perfect contact with the port face, so I just re-milled the oil grooves and they are giving no trouble in service.

The D-valves sit in a box that allows float off the face, however, there are three grub screws around the periphery- in a very tight thread to negate loosening in service- these grub screws allow setting of the exact amount of float that the engineer wishes. Quite important as when backing off steam and the prop is still turning, the compression/re-evaporation in the cylinder can lift the valve over the small amount of pressure left in the steam supply pipe, leading to slapping onto the port face- nothing major, but it sounds like a ticking-clock on speed, and won't do the faces any good- it could in fact be the reason why the faces have wear on them, as the valves hadn't been touched for years until last year when I serviced them, and this year when I re-milled the oil-grooves.

Greg