Vacuum Pump and Chamber

Details

Located under Mini-CNC.

Pump: Edwards Speedivac 2

  • Single stage 180W fore vacuum pump, direct drive rotary vane
  • 45 litre/minute
  • Max vacuum 13Pa (0.098 mmHg) residual
  • 0.5 liters of oil full load

Chamber (20 litres - 29cm diameter 30cm height cylinder)

  • Solid steel + 10mm thick acrylic glass cover
  • Festo vacuum meter gauge
  • Pump and release valves

Primary use is degassing silicone for moulds, removing bubbles in polyurethane and epoxy castings, removing air from liquids and soaking porous substances (eg. wood) with liquids.

Condition Notes

Working order, reasonably dirty, rubber seal deterioration - hardening
1/2 oil left, oil looks clean

Induction and Training

No induction required (assumed)

Owners

?

Risk Assessment

Document TBD

Acrylic lid destruction under pressure (low)

  • wear protective clothing. eye protection?
  • inspect lid for cracks

Chemical spill (low)

  • do not overfill

Before Use

Preparation is key. After the pump is on, air will be removed in under two minutes, and you will not be able to access insides without releasing pressure.

  • Check the acrylic cover for cracks. Do not use it if it is damaged.
    Keep in mind that when in use, the vacuum chamber is at 1 atm = 101kPa = 10332 kg/m2, so the lid with a diameter of 30cm = 0.07m3 must withstand around 700kg of force.
  • Motor oil level should be between min and max marks. Motor oil should be clean (transparent).
    Do not it use without oil or when oil is dirty, it will quickly wear out motor ability to create vacuum.
    Oil lubricates the rotor cavity and creates an air seal between the cavity wall and vanes.
    Vacuum motors use special mineral vacuum oil with reduced evaporation under low pressure. Do not refill oil unless you know which one is needed. Do not mix in any other random mineral oil, most probably it will evaporate immediately on first use and fill the chamber with oil mist.

  • Rubber seal should be clean. It may be a good idea to wipe it and make it wet with water for it to seal properly.
  • Use an oversized container for your liquids. When degassing viscous substances such as silicone or epoxy, keep in mind they will increase about three times up initial volume and would be somewhat unpleasant to wipe from the chamber floor.
  • Boiling point temperature of liquids decreases under low pressure. Lighter liquids can boil. As an example, ethanol boiling point would be around 34°C and methanol around 15°C. Solvent vapour can compromise the lid.

During Use

  • Tell others what you’re doing.
  • Close the lid, open pump valve, close release valve
  • Plug the pump into wall socket, it will turn on
  • If the gauge arrow doesn’t move there’s a leak, gently press on the acrylic lid until it seals and arrow starts moving
  • Higher stages of vacuum will take some time to reach, if you see your substance is degassing actively you may consider switching off the pump and closing the pump valve. Chamber can hold low pressure with valves closed for several hours.
  • Tell others what to do when you’re away. In case of any suspicious noise or cracks, unplug the pump, use eye protection, release the pressure gently using the release valve.
  • If your container seems to be overflowing, release some pressure using the release valve, and the liquid will drop back in.
  • Pump exhaust releases some oil vapour, this is normal

Degassing process will look differently for different substances. Under low pressure air bubbles trapped in liquid will expand in size, combine, and float to the top. When the pressure is back to normal, leftover bubbles will collapse. Liquids may expand and will look like boiling, but air bubbles will go away eventually while pressure stays the same .

Here are some examples how it may look like:

Think about setting time when dealing with silicone, polyurethane and epoxy. Plan ahead and do things quickly. Initially, to increase the quality of most fills you may want to degas twice, first after mixing the components - you introduce air when mixing, then the form you cast it in - you introduce more air when pouring. It is easy to run out of time and have your compounds solidify.

After Use

  • Switch off the pump, close or keep closed pump valve
  • Release the pressure gently using the release valve
  • Clean inside of the chamber from spills

Maintenance

  • Rubber gasket will eventually fail. Can be replaced with silicone sealant.
  • Needs special vacuum oil. Vacuum oil must be replaced with the same type (which?) when it is dirty or level is low.
  • It is now covered by oil mixed with sawdust, keep it some distance from wood shop

References

https://en.wikipedia.org/wiki/Rotary_vane_pump
https://www.youtube.com/watch?v=Zz95_VvTxZM