O-RING LUBRICANT / GREASE
There are two areas where
O-rings are generally used on Pyrex neon manifold systems: The
connections between various components and the stopcocks. There are
also different types of O-ring connections as well as stopcocks.
However they all have the same function: To make a high vacuum seal.
SVP utilizes a precision cut Threaded Glass Compression O-Ring
Connector to obtain our modular designs and a standard Teflon plug,
high vacuum O-ring sealed stopcock.
THREADED GLASS COMPRESSION O-RING CONNECTORS:
The O-ring of this type of connection should not be lubricated or
greased. These connectors rely on the friction of the compressed
O-ring to hold components in place and to function properly. If the
O-ring were slippery from lubrication it would not work correctly.
“GREASELESS” O-RING STOPCOCKS:
The O-ring seal Pyrex stopcocks that are used on virtually all new
Pyrex manifolds throughout today’s neon industry are often referred to
as “greaseless”. Although they can be used as such, with no
lubrication at all they can be difficult to use. Therefore, a small
amount of lubrication is used, which allows the O-rings to slide more
easily inside the glass barrel. However, the type of lubricant used is
important to long-term performance and ease of maintenance.
SVP Neon Equipment strongly recommends not
using silicone based stopcock grease, such as Dow Corning silicone
stopcock grease, or fluorinated grease such as Krytox® or similar
products. For reference Dow Corning silicone grease is typically
supplied in a blue and white tube, while Krytox® is usually supplied
in a small white tube.
Silicone based grease, when used in glass vacuum apparatus, will
polymerize to the glass as a non-conducting film that can allow static
charge build-up. This invisible film will migrate through the vacuum
system, trapping contaminants as it does so and preventing efficient
pump-downs. This polymerization also makes it extremely
difficult to clean the silicone film off the glass when the system is
dismantled for cleaning or repair, even though the contamination is
not visible to the eye.
When a glassware repair is necessary the silicone film must be
completely removed by chemical means if a long-term successful repair
is to be expected. The often used method of attempting to burn off the
silicone film in an annealing oven prior to repair only worsens the
situation as many times the oven temperature is too high and will
literally burn the film into the structure of the glass, thereby
making any future repair questionable. If not removed by chemical
means prior to repair and annealing, the silicone film will be sealed
into the glass where the repair is made. This is sometimes evident by
a “cloudy” area adjacent to the repaired section. An example of this
can be seen
Here. Glass that is repaired in this
manner and fused together with a silicone film present will always be
a potential leak in the area of the repair. The repaired area may or
may not leak. If it does, the leakage and subsequent “pin hole” may
not be evident for months, or even years after the repair is
Fluorinated grease such as Krytox®, is extremely resistant to almost
all solvents and chemicals, which is exactly what it was designed to
be. This makes it very difficult to remove from glassware as well and,
therefore, poses many of the same problems encountered with silicone
when attempting to repair glassware that has been exposed to it.
SVP highly recommends using a hydrocarbon based high
vacuum grease, such as the various Apiezon® blends or Lubriseal®.
These products are available from SVP Neon Equipment as well as other
Hydrocarbon based grease or lubricant, such as the various Apiezon®
blends, Lubriseal® and similar products, is easily removed from the
glass surface with a number of different solvents when manifold
components need to be cleaned. When a repair is required it is not
necessary to chemically pre-clean the glassware prior to repair as it
is with silicone or fluorinated based greases. Annealing the glassware
prior to repair will completely remove all grease and residue without
fear of compromising the surface of the glass, as in the case with
silicone or fluorinated grease.