SVP DIFFUSION PUMP FEATURES:
SVP Pyrex Diffusion Pumps are high
performance, high vacuum secondary vacuum pumps specifically designed
for luminous tube production. As with all secondary vacuum pumps, they
work in unison with a mechanical vacuum pump* to produce higher
pumping speeds and better ultimate vacuums than the mechanical pump
alone can obtain. They have no moving parts, so they are not prone to
mechanical failure. SVP Diffusion Pumps are well suited for use with
any luminous tube manifold system, regardless of manufacturer.
Manifold adaptors are available to allow easy connection to any
manifold system. Whether this type of pump is referred to as a
secondary pump, aspirator, finishing pump, or any other generalized
name, with the exceptional reputation and track record that SVP
Diffusion Pumps have they by far offer the most performance for the
money in todays market.
* A mechanical vacuum pump
(sometimes called a fore-pump, or roughing pump) is required for a
diffusion pump to function. For luminous tube work a two-stage oil
sealed rotary vane vacuum pump with a minimum of 100 L/min. (3.5 cfm)
free air displacement and capable of producing at least 8 to 10
microns of vacuum in a stand-alone test is suitable.
PUMPING SPEED Pumping speed is an important
consideration when processing criteria for high quality tubes demands
that a vacuum of <5 microns (<5 x 10-3 Torr) is obtained before the
unit cools to 150ºC, with a final vacuum of <1 micron (<1 x 10-3 Torr).
SVP Diffusion Pumps are rated at a maximum pumping speed of 10 Liters
per second for the Standard Flow model, and 18 Liters per second for
the High Flow model in the 10-4 Torr range. This means an overall
pumping speed of 600 liters and 1,080 liters per minute (at reduced
pressure) respectively; far more than what is normally needed for
luminous tube production.
ULTIMATE VACUUM The ultimate vacuum in the tube before
back filling is also an important factor in producing top quality
luminous tubing. A better ultimate vacuum means less contaminant
gasses remaining in the unit. Less contamination means a longer tube
life with less discoloration. SVP Pyrex Diffusion Pumps can obtain a
no load ultimate vacuum of 5 x 10-6 Torr (0.005 micron) in a clean,
outgassed, well designed Pyrex manifold at an ambient air temperature
standard of 70ºF.
HIGH VACUUM IN SECONDS It is important to obtain a
good ultimate vacuum as quickly as possible following the bombarding
process, before the unit cools to the re-absorption temperature of
175ºC. When used with the designated SVP Pyrex High Vacuum Manifold
and mechanical vacuum pump, high vacuum (1 micron, or 1 x 10-3 Torr)
can be obtained within a few seconds with no load on the system.
During actual working conditions the length of time needed to reach
high vacuum will vary with load, but will typically be less than 30
seconds with 15 to 20 seconds not uncommon.
IMPROVED PROCESSING The greatly improved pumping speed
and better ultimate vacuums provided by SVP Diffusion Pumps mean
cleaner, brighter tubes that age-in more quickly, operate more
efficiently and have a longer service life. This is especially
important when processing mercury units as mercury vapor will combine
chemically with any contaminants left in the tube. If the
contamination is significant, the result is premature discoloration.
More specifically, mercury units should literally be able to burn for
years before the first signs of discoloration are evident.
NO VAPOR BACKSTREAMING It is important to produce the
cleanest vacuum possible in the manifold and unit being processed.
Therefore, it is essential to choose a secondary pump that does not
exhibit oil vapor backstreaming. Although we can not speak for other
manufacturers of Pyrex diffusion pumps, we can say that design
features of SVP Diffusion Pumps eliminate vapor backstreaming into the
manifold when used with the recommended motive fluid and mechanical
pump and operating at the correct temperature*.
*Independent test results available on request
NO MOVING PARTS By design, diffusion pumps have no
moving parts. This is an important feature when considering equipment
longevity. Apparatus with delicate moving parts, such as the high
speed rotating blades of a turbomolecular pump, not only are
susceptible to mechanical failure, but also are severely damaged by an
inrush of debris. Glass fragments, mercury and even phosphor powder
from a broken unit while processing can cause catastrophic damage to a
turbo pump. Although a diffusion pump may need cleaning after such an
event, it is not damaged and can quickly be returned to service.
SAFE OPERATION Metal diffusion pumps, which use an
integral metal heating element that provides an electrical ground path
to the entire pump body, can be severely damaged in the event of a
bombarder flashback. Some glass diffusion pumps use an immersion
heater, which goes through the pump body and into the boiler and also
exposes the diffusion pump to a ground path. In the case of
turbomolecular pumps, the drive motor, which is connected to an
electrically operated frequency controller, is an integral part of the
metal pump housing and internal components. In these cases, the ground
path potential will actually induce a bombarder flashback to the pump
instead of preventing it. SVP Diffusion Pumps utilize an external
porcelain insulated heating element. The glass pump body further
insulates the pump from ground potential and the heating element.
EASILY MAINTAINED Other than an occasional oil change
and cleaning, SVP Pyrex Diffusion Pumps are virtually maintenance free
and can be serviced in-house* by the neon technician. With reasonable
care an SVP Pyrex Diffusion Pump will provide years of trouble free
*No special tools are required to
remove and clean the pump body.
MANIFOLD ADAPTOR* The
Manifold Adaptor, which is also
constructed of Pyrex glass, provides the connection between the
diffusion pump intake and main stopcock on the manifold. The adaptor
is an optically dense baffle to prevent stray vapor molecules from
entering the main stopcock. This configuration also aids in
installation by allowing more adjustability of the pump body position.
* A standard manifold adaptor is
included with the purchase of a diffusion pump. Adaptors to retrofit a
diffusion pump to any manifold system may be purchased separately.
ISOLATION/VENT VALVE The
Isolation/Vent Valve allows
the diffusion pump and manifold to remain under vacuum and still be
able to vent air into the mechanical vacuum pump when the system is
turned off. Venting air into the mechanical pump when it is turned off
prevents mechanical pump oil from backing out of the mechanical pump
and into the diffusion pump.
COOLING FAN** The continuous duty
Cooling Fan provides
maximum cooling for the air-cooled diffusion pump. This increases pump
efficiency and allows the pump to operate at a higher boiler
temperature, thereby increasing vaporization and velocity. The cooling
fan easily mounts to the support rod and includes chrome plated metal
grill, power cord* and mounting hardware.
**Power cord must be hard wired to