Hi John, In the many years that I have helped people in the
casting field,I have seen almost without fail that casting/
investing problems are related to the machinery as well as the
person doing the casting.The difference in Vac is certainly worth
worrying about. At 26 " merc, investment and water will not
"boil" at the investment manufacturers suggested water temp of
70- 72 oF … but raise the temp to 100+ oF(investment mfg co’s
do not recommend doing this) and the mix will boil fine , however
you will see different work times and a shortening of the life of
the pump unless meticulously maintained. All of the small
vac/cast systems i am familiar with will all pull better than 29"
merc when new.Mine is 27 years old and still pulls at that level
… it has had continuous oil changes ,custom built filters and
watertraps, testing and replacing of hoses,tubing etc.which is
why it works as well as it does.
As far as casting is concerned, the amount of vac also has an
effect and believe me when i say the closer you can be to 30"
merc, the better off you are.Vac gauges are notorious for not
telling the truth and must also be checked for accuracy when
problems occur. Those of us who do limited volume production
have seen the differences in vacuum casting when pumps are weak .
So, to answer your question, … yes, the difference is worth
Vive La Diference!!!