My experience on these systems was good if the old style control valves had the original graphite stem packing still in them. However, if they were rebuilt with the new style U-CUP packing, we had a problem pulling a vacuum. The U-CUP packing needs pressure from the inside to prevent leaking. You might like to check this out further from other sources to see if this is so. Vivian (Toots) Smith tootsm@charter.net
Analysis of the building’s gas-fired hot water system revealed the energy expended to keep the water hot at the fixtures by circulating it or using electric tracing was so high that the life cycle cost exceeded that for instantaneous electric hot water heaters located in the several bathrooms. Being an old steam engineer it hurt to do it, but I recommended they eliminate the central gas-fired hot water system and install local, instantaneous electric hot water heaters. Ken Heselton, P.E., C.E.M. KEH Energy Engineering Joppa, MD