So, what kind of casting machine is it? Vac + Cast? Vacbell only?
Rotary pump or vane? (Big huge thing, or something that looks like a
little airbrush compressor?) (Did it hurt to lift when you installed
it? If so, then Rotary.)
Step one: check your vent valve. (yeah, I know, but I’ve left it open
myself on occasion.)
step two: If it’s the bell you’re having trouble with, check both
sides of the rubber for crud that’s impeding a seal.
step 2A: get both sides of the rubber wet, and see if you get a good
seal that way.
Step 3: start pulling the lines apart. Pull the upstream connection
out of the vacuum gage. Stick your finger over it to seal it, and
see what you get.
There shouldn’t be much in the way of connections or hoses between
the gage and the pump. If it’s not pulling decently with nothing but
the gage connected, it’s either the pump, or one of the two or three
connections (or hoses) in between. Be suspicious of the hoses. I’ve
seen even new ones split. They generally do it in the deepest,
darkest corners of the machine, and always on the side that faces
away from where you’d be looking from.
If you’re still having trouble with nothing but the gage connected,
try listening for the leak. Seal the upstream end of the gage, and
listen for the hissing. (You may have better luck in the half second
after you shut off the pump.)
Best of luck,
PS–> if it’s a casting table you’re having trouble with, you do
have a metal trap set up under your table orifice, right? (And you
didn’t just suddenly start having trouble after a pour, right? ) If
you had trouble starting right after a pour, the odds are good you
had a blowout that dropped molten metal into your lines and burned a
hole in them. For some reason, all of the tabletop vac casting rigs
I’ve seen lately have omitted the metal trap that’s needed to
prevent blowouts from trashing the machine. Not much of a problem to
add one, just a couple of bits of hardware store plumbing to add and