Diffusion Vacuum Pump

What is the Diffusion Vacuum Pump?

A diffusion vacuum pump uses a boiling oil jet to reach high vacuum with no moving parts. It is used for coating, metallizing and industrial high-vacuum processes where a simple, robust pump is preferred.

Overview

The diffusion pump contains a boiler that vaporizes a low-vapor-pressure oil. The vapor rises through a chimney and is directed downward through jets at high speed. Gas molecules in the pump body are entrained by the vapor and carried to the lower stages, where a backing pump removes them, while the oil condenses and returns to the boiler. There are no moving parts, so the pump is robust and inexpensive for its pumping speed, which ranges from hundreds to tens of thousands of liters per second. Ultimate pressure can reach 10⁻⁶ to 10⁻⁹ mbar with suitable oil and a cold trap. A backing pump and a cold trap or baffle are mandatory to prevent oil backstreaming and to maintain foreline pressure. Diffusion pumps are used in coating, metallizing, vacuum furnaces and older high-vacuum systems.

How does it work?

Vacuum pumps remove gas molecules to lower pressure in a sealed volume. Positive-displacement types, including rotary vane, diaphragm, scroll and roots pumps, trap a volume of gas and push it out. Momentum-transfer pumps, including turbomolecular and diffusion pumps, accelerate molecules toward an exhaust that a backing pump removes. Water-ring and ejector pumps use a liquid or a jet to entrain and carry gas away. Performance is described by ultimate or base pressure and by pumping speed, which is measured in liters per second or cubic meters per hour. Real performance also depends on the gas load, on outgassing from chamber walls, and on the conductance of the connecting piping. Vapor handling, corrosion resistance and cleanliness determine which pump suits a given process, and pumps are often combined in stages to cover a wide pressure range.

What are the key features?

• No moving parts for robust, low-cost high vacuum
• Pumping speeds of hundreds to tens of thousands of L/s
• Ultimate pressure of 10⁻⁶–10⁻⁹ mbar with suitable oil
• Jet and chimney structure with staged compression
• Requires backing pump and cold trap or baffle
• Oil recirculates after condensing on cooled walls

What are the technical specifications?

A typical diffusion vacuum pump configuration offers ultimate pressure of 10⁻⁶–10⁻⁹ mbar, pumping speed of 100–50,000 L/s, boiler power of 0.3–5 kW, oil charge of 0.1–2 L, backing pressure of Below 0.1 mbar and cooling water of Required, 1–5 L/min. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Diffusion Vacuum Pump is used in vacuum coating and metallizing, vacuum furnaces, optical and reflective coatings, industrial high-vacuum systems and freeze drying at high vacuum. Across the wider Vacuum Pumps class, laboratories also deploy it for chamber evacuation for drying and degassing, rotary evaporation and distillation and freeze drying and centrifugal concentration.

Which standards and certifications apply?

Relevant standards and methods include IEC 61010-1, IEC 61326-1, ISO 21360, ISO 27893, ISO 20485 and GB 4793.1. Certification candidates for this model are CE, ISO 9001 manufacturing and RoHS; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Protect the pump from the process with a cold trap, foreline trap or filter, and vent to atmosphere before switching off a high-vacuum pump. Change oil and check seals on schedule for oil-sealed pumps, and inspect scroll tips and diaphragms for dry pumps. Keep tubing as short and wide as possible to preserve conductance, and use the correct flange type and vacuum grease sparingly. Monitor pressure with gauges appropriate to the range, such as Pirani, capacitance or ion gauges. Follow IEC 61010-1 for electrical safety and local pressure equipment rules. For oil-free or clean processes, confirm that the pump cannot backstream oil or particles. Record base pressure and pump-down curves during commissioning and at each service so that degradation is detected early.

How do I select the right Diffusion Vacuum Pump?

Choose a diffusion pump when high pumping speed at lower cost matters and occasional oil backstreaming can be managed with a trap. For clean, oil-free high vacuum, a turbomolecular pump is preferable. In the RFQ, state target pressure, speed, backing pump, cooling water and trap requirement.

How does it compare with other Vacuum Pumps variants?

Work from the required working pressure, the gas composition and the volume to be evacuated. For rough vacuum in filtration and drying, a diaphragm or single-stage rotary vane pump is sufficient. For medium vacuum in rotary evaporation and coating, a two-stage rotary vane or scroll pump is appropriate. For high and ultra-high vacuum in electron optics, surface analysis and semiconductor work, a turbomolecular pump with a suitable backing pump is needed. Consider whether the gas is condensable, corrosive or particle-laden, and add traps, filters and corrosion-resistant materials as required. Size pumping speed from the chamber volume, the target pressure and the acceptable pump-down time, remembering that conductance limits real speed. Decide between oil-sealed and dry designs based on contamination risk, and specify gauges, valves and controllers as part of the system.