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    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 today’s 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 service.

    *No special tools are required to remove and clean the pump body.


    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 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 power source.



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    Copyright 2006
    Silica Vacuum Products