Difference between revisions of "Equipment/High Vacuum Station"

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{{EquipmentInfobox
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|name=High vacuum station <!-- Name of the item. -->
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|image=20150513 214222.jpg‎ <!-- Image of the item. Leave with placeholder image if none exists. -->
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|model=Unknown <!-- Model -->
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|category=Equipment <!-- Main category. Please leave alone to keep item in this category -->
 +
|subcat=Defunct
 +
|status=Removed
 +
|consumables=Pump oil<!-- Any items used up in normal operation, such as; ink, paper, saw-blades, cutting disks, oil, etc.. -->
 +
|accessories=Unknown <!-- Any items associated with the equipment but not consumable, such as; drill bits, safety gloves, goggles, etc.. -->
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|reqtraining=Yes<!-- Is training required to use this equipment? Yes or no. -->
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|trainlink=Unknown <!-- If training is required, provide a link to training signup or contact page. Otherwise leave blank. -->
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|acnode=<!-- Is the equipment ACnode locked? -->
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|owner=LHS<!-- Provide a link to owners members page if other than LHS -->
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|origin=Unknown <!-- If via pledge, please link to the completed pledge page on the wiki -->
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|location=Basement, ante-room beside lift<!-- Floor, room/zone and location within that area -->
 +
|maintainers=Sci<!-- NO LINKS PLEASE; it currently breaks the template. If someone is nominated as managing the upkeep of this item, please list them here. -->
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|template_ver=1.1 <!-- Please do not change. Used for tracking out-of-date templates -->
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}}
 
==Summary==
 
==Summary==
  
Line 5: Line 23:
 
==Proposed Uses==
 
==Proposed Uses==
  
Resin degassing (backing pump ONLY - separate degassing chamber)
+
* Creating x-ray sources, CRTs & other electron-beam experiments
Creating x-ray sources, CRTs & other electron-beam experiments
+
* Vacuum glasswork (EG; thermionic valve making/repair)
Vacuum glasswork (EG; thermionic valve making/repair)
+
* Surface coatings (optical coatings, photocathodes, metalic finishes, titanium oxide coatings)
Surface coatings (optical coatings, photocathodes, metalic finishes, titanium oxide coatings)
+
* Electron microscopy
Electron microscopy
+
* Outer-space environment test chamber
  
 
==Design concept==
 
==Design concept==
  
To enable all the uses people are interested in, the system needs to have vacuum access at a number of stages in the pumping system.
+
 
 +
To create an ultra-high vacuum source capable of being purposed to a wide range of high-vacuum related tasks.
 +
 
 +
* Combining a resin degassing chamber/line into the design has now been abandoned as there are enough lower-spec rotary pumps available now to build a dedicated station for that purpose.
  
 
===Backing/roughing pump===
 
===Backing/roughing pump===
  
The backing pump is a rotary pump that should be capable of reaching near 0mbar. On a double valve setup one pump should be able to act as backing pump to the diffusion pump or to directly pump a separate degassing chamber. This should allow the degassing to be used without the worry of contaminating the ultraclean conditions of the High-Vacuum chamber or diffusion pump.
+
The backing pump is a rotary pump that should be capable of meeting or exceeding the backing pressure and maximum output of the diffusion pump.
 +
 
 +
<del>There is a pledge for a suitable pump, as none offered so far have sufficient ultimate pressure and/or pumping speed.
 +
http://wiki.london.hackspace.org.uk/view/Pledges/Vacuum_Pump</del> The pledge was successful and a backing pump has been aquired.
 +
 
 +
 
 +
===Diffusion pump===
 +
 
 +
The diffusion pump donated by James Collings is an Edwards E04. It's ultimate vacuum capacity is 5x10^-7 mbar (0.0000005mbar) with a pumping speed of air of ISO 600l/s^-1 (hydrogen: ISO 800l/s^-1). It has a maximum starting pressure of 300 mbar and requires a backing pump capable of keeping the backing pressure at about 1mbar (assuming DC704EU pump fluid).
 +
Recommended backing pumps are the Edwards RV8 or RV12. The RV8 has a displacement of 9.7m^3h^-1 and an ultimate pressure of 2x10^-3. The RV12 is advised for fast roughing, has a displacement of 14.2m^3/h^-1 and an ultimate pressure of 2x10^-3 mbar.
 +
 
 +
The diff pump operates by boiling a special silicone oil to vapour and forcing it out through special baffles onto a water-cooled jacket. There the oil re-condenses and trickles down along with any air molecules it grabbed on the way. It sets up a pressure differential across the pump, where at its exist it should be at a high enough pressure the backing pump will be able to pump it away.
 +
 
 +
Current prices for the compatible fluids (as of October 6th, 2011, direct from Edwards Vacuum) are;
 +
 
 +
* DC702 fluid - £117, 500ml (critical backing pressure 1.3 mbar, ultimate pressure 5x10^-6 mbar)
 +
* DC704EU fluid - £134.10, 500ml (critical backing pressure 1.0 mbar, ultimate pressure 5x10^-7 mbar)
 +
* DC705 fluid - £211.50, 500ml (critical backing pressure 0.9 mbar, ultimate pressure 5x10^-7 mbar)
 +
* Santovac 5 fluid - £852.30, 500ml (critical backing pressure 0.8 mbar, ultimate pressure 5x10^-7 mbar)
 +
* Edwards L9 fluid - Unknown price, possibly discontinued (critical backing pressure 0.9 mbar, ultimate pressure 5x10^-7 mbar)
 +
 
 +
On this I would recommend DC704EU fluid. For £17 extra you can achieve a magnitude better vacuum than the absolute cheapest. The spec sheet also describes it as a good durable and general-purpose fluid.
 +
 
 +
====Cold baffle====
 +
 
 +
The cold baffle is a small plate in the pump stack with water-cooled plates. These cold plates minimise any pump fluid vapour that might otherwise deflect upward and contaminate the vacuum processes above.
 +
 
 +
===Pump stack===
 +
 
 +
Above the diffusion pump are a series of manifolds for various purposes, including the cold baffle mentioned as part of the diffusion pump above.
 +
 
 +
To fulfil all the uses proposed, placing an extension piece with a branch next with the main plate valve above it will allow the full power of the diffusion pump to be accessed by a side-valve without having to pump down the main chamber. This high-vacuum access valve could then be used for attaching vacuum tubes, glass-forming manifolds, electron microscopes, fusors or any other number of parts.
 +
A foreline vacuum pressure sensor will be necessary here.
 +
 
 +
The valve currently need a slightly wider packing piece to be used in the stack at this location. The current one is only 3/4" thick, and in this position fouls the valve control gearbox.
 +
 
 +
===Vacuum chamber===
 +
 
 +
The vacuum chamber is a recessed base, likely for a glass bell-jar. However once fitted with a new O-ring gasket it will likely be fine for initial use with a simple flat cover. 25mm polycarbonate will probably do.
 +
 
 +
The chamber has three ports for vacuum feedthrus, though one is modified and may limit use. There are a number of threaded mounting points and, most notably, a large angled port at the circumference. This large port will require a special blanking plate making, but after that can probably be used for any custom or special-use interfaces required.
 +
 
 +
==Support equipment==
 +
 
 +
Both diffusion pump and cold baffle require a self-contained cooling loop. Possibly even separate radiators if one effects the critical temperature of the other.
 +
 
 +
The parts from James contained four Pirani Gauge heads and two Penning Gauge heads. These will need gauge controllers/readouts finding or making for them.
 +
 
 +
Some surface-coating processes work best if a glow-discharge plasma is used to remove surface oxidisation before coating. Sci has a 5.5Kv mains transformer that should be capable of producing this in vacuum.
 +
 
 +
Surface coatings also require a tungsten crucible or wire to be heated to vaporise metals. A high-current variable PSU or Variac would be used here.
 +
 
 +
To keep all the component parts secure and in-line, as well as keeping dangerous parts from being exposed, building a steel framed trolley to house it all seems like a sound idea.
 +
 
 +
==Servicing and care==
 +
 
 +
A wire mesh over the pumping hole of the vacuum chamber should help a lot to prevent any debris reaching the pump.
 +
After any use of the chamber for deposition purposes, it should be cleaned with fibre-less cloth and isopropyl alcohol.
 +
 
 +
===(proposed) usage rules===
 +
 
 +
*Do not use without being trained.
 +
*No mercury or mercury-containing products should be allowed in the chamber, due to potential vaporisation in backing-pump exhaust, pump oil/fluids contamination and use of aluminium manifolds which mercury will rot.
 +
*No marshmallows. Or any other foodstuffs. Use the degasser.
 +
 
 +
==Parts needed==
 +
 
 +
Some [https://groups.google.com/forum/#!topic/london-hack-space/lqF1zd3baAY additional parts] will be needed.
 +
 
 +
*Water pump (for cooling loop).
 +
*1.5-2" thick, ~4" wide sturdy plastic (delrin?) to turn an large threaded fitting for the chamber.
 +
**I have a 100m dia, 45mm thick lump of nylon and a fair bit of 50mm delrin if it's any use. artag.
 +
*20mm+ thick polycarbonate sheet (will probably order cut to size).
 +
 
 +
 
 +
===Cooling system===
 +
 
 +
The E04 diffusion pump uses an 850Watt heater. The typical surface temperature will reach upwards of 200c (maximum 250c for pump body, max 400c for pump base).
  
[[User:Andrewgodwin:Adrian]] has offered the use of his rotary pump for this componant. It should be fine for the degassing section, but unless we find detailed specifications for the diffusion pump we'll just have to wait and see if it's powerful enough to back the diff-pump. If not, cost of a 2nd hand one should be about £130.
+
The pump technical data specifies the maximum water pressure should be 5bar/72.5psi. Minimum water supply temperature should be 10c, and maximum return temperature should be 35c. (presuming return in this case means "water coming back out of the pump cooling jacket")
 +
The minimum flow-rate should 75l/h^-1.
  
===Degassing chamber===
+
As the baffle and valve assembly as also have cooling-loops, some additional capacity should be factored in. No numbers exist for these parts however. As they are indirectly heated however and part of reflux prevention, they perhaps should have a secondary cooling loop or auxiliary radiator between them.
  
The initial chamber is a home-made one made by Sci from an old fire extinguisher and water fittings.
+
Estimating any radiator capable of handing about 1Kw should be fine. Several PC water-cooling pumps are within capacity, and variable-speed.
  
Degassing resins allows small air bubbles to expand under low pressure and burst, removing the gas from the liquid. In plain resins this leads to stronger smoother castings, and with filler powders it creates a stronger bond between filler and resin.
+
Due to likely enclosed location, heat exhaust should be ducted away.
  
As resins can bubble quite a lot in degassing, the vacuum line on the chamber should have a catch-pot fitted for safety. This is an empty vacuum-sealed container with two connections at the top. Any spilt resin or spray that makes its way down the initial vacuum line will be caught in this "dog-leg" and prevented from contaminating or damaging the rotary pump.
+
==Progress reports==
  
If you want to watch marshmallows expand, this is the portion of the system you'll be using.
+
'''''21-09-2011'''''
  
===Diffusion pump===
+
All components are currently being stored in the Out Of Order workshop toilet on Jontys suggestion. This should keep them away from being damaged or contaminated by workshop dust.
 +
All manifolds seem in good order and have been in use until recently.
 +
Diffusion pump heater and thermal cut-out both test as good with a meter. Wiring should be replaced however. Pump should be drained & cleaned as a precaution. Fluid should be measured and filtered/inspected. A temperature sensor could be installed on the drain port.
 +
~ Sci
 +
 
 +
'''''04-02-2012'''''
 +
 
 +
Post-xmas checkup on stored parts. Took some measurements of pump stack parts.
 +
Short video here: http://www.youtube.com/watch?v=3U_D1sNpXWc
 +
~ Sci
 +
 
 +
'''''11-02-2012'''''
 +
 
 +
Finished taking measurements of pump-stack parts. Inventoried vacuum pipe fittings. Have added scrap industrial control panel to parts pile (sounder works at 5v) as well as pressure-switch and 3 castors (4th currently errant).
 +
All parts so far are in imperial dimensions, large manifolds are all SpeediVac and smaller ones are GeneVac.
 +
Several of the parts have been modified by the previous owner, so I'm inclined to look for additional parts. Though [http://imajeenyus.com/vacuum/20060729_diff_pump_system/index.shtml others] have made do with copper pipe, I'd be concerned about trace-gas leakage through such thin material. Also we may need an additional bellows pipe section to get complete vibration-isolation from the backing pump (maybe. And only crucial for electron-microscope purposes). Will see if I have any compatible parts spare, and keep my eye on ebay.
 +
Also took dimensions of the storage-toilet as I presume, being the closest thing to a "clean room" available, it'll be where the pump system will live. So will constrain station dimensions to ensure it'll fit.
 +
 
 +
Considering use of a large steel pipe-T (water main size, ~10" ID) to serve as a bell-jar/chamber with port for a large observation window.
 +
 
 +
Chamber has some very simple adaptive manifold connectors it should be fairly easy to replicate/customise, as well as add more custom ports as need be.
 +
 
 +
'''''19-03-2012'''''
 +
 
 +
Have collected a Pirani/Penning gauge controller. Purchased from ebay for £5, plus packet of chips for ride to collection. Edwards Model 4, approximate age of existing gauge heads. Should be compatible. Supports two pirani and one penning head. Not rack/panel-mount, but should do the job very nicely. Will need compatible mains plug.
 +
 
 +
Likewise purchased some mixed Speedivac fittings (£11 including postage) that should make building up the vacuum pipework a lot nicer (avoiding using the home-made joints is a bonus).
 +
 
 +
Also donated a water-flow meter. Currently runs on 24v relay, but has fitting for hall-sensor control, so suggest gutting of stock electronics and wiring directly into control systems.
 +
 
 +
'''''23-09-2012'''''
 +
 
 +
Most of the welding is done, but we ran out of welding gas. Need more before transformer mounts can be done.
 +
Dry-fitting has begun, though will need short 5/16ths 24tpi Whitworth bolts to connect to chamber base.
 +
 
 +
Backing pump has been mounted on anti-vibration feet.
 +
 
 +
Welds will need grinding flat and re-doing in places once dry-fit of all parts is done and setup proved.
 +
 
 +
'''''19-02-2014'''''
 +
 
 +
Long-overdue update to the wiki page.
 +
 
 +
The diffusion pump has been serviced and cleaned. The cooling jacket is leak-free. It appears to have previously gone UTA catastrophically while at operating temperature, as it contained glass debris and burnt-on pump oil residue. It has been temporarily sealed for dust protection and returned to the equipment trolley.
 +
The next step is to complete the radiator & fan enclosure to get the pump cooling-loop operational.
 +
 
 +
To go to a bell-jar based design, circles of billet aluminium 13" dia are available from Alauminium warehouse, but will need facing on a large lathe. A used gas cylinder has been donated to serve as bell-jar. Suitable seals are approximatly £30.
 +
The trolley will likely need re-designing eventually.
 +
 
 +
Inline temperature sensor, flow-sensor, pumps, etc.. all available from PC water-cooling suppliers.
 +
 
 +
'''''13-05-2015'''''
 +
 
 +
The implosion-sheild is done. This is both to protect users in the case of catastrophic failure of the glass bell-jar, and protect the bell-jar from users and passers-by in the mixed usage workshop.
  
The diffusion pump, as well as the majority of the vacuum manifolds and high-vacuum parts are from James Collings. A diffusion pump operates from approximately 10-30mbar down to as low as 10^-10mbar, though we are unlikely to be able to reach that extreme. 10^-6mbar (0.000001mbar) seems likely though.
+
The bell-jar will be padlocked down as an access-control measure.
  
The diff pump operates by boiling a special silicone oil to vapour and forcing it out through special baffles onto a cooled jacket. There the oil re-condenses and trickles down along with any air molecules it grabbed on the way. It sets up a pressure differential across the pump, where at its exist it should be at a high enough pressure the backing pump will be able to pump it away.
+
We're still in need of vacuum gauges, feedthrus and vacuum hose to connect the backing pump. Getting close now!
  
Currently the recommended pump oil for the Edwards E04 is Santovac 5. This is currently priced at £220 per 100ml.
+
[[Category:Projects]]

Latest revision as of 01:00, 2 May 2016

High vacuum station
20150513 214222.jpg
Model Unknown
Sub-category Defunct
Status Removed
Last updated 2 May 2016 01:00:10
Consumables Pump oil
Accessories Unknown
Training requirement Yes
Training link Unknown
Owner LHS
Origin Unknown
Location Basement, ante-room beside lift
Maintainers Sci

Summary

The HVS is an in-progress equipment project to provide LondonHackspace members with access to a multi-purpose high vacuum system.

Proposed Uses

  • Creating x-ray sources, CRTs & other electron-beam experiments
  • Vacuum glasswork (EG; thermionic valve making/repair)
  • Surface coatings (optical coatings, photocathodes, metalic finishes, titanium oxide coatings)
  • Electron microscopy
  • Outer-space environment test chamber

Design concept

To create an ultra-high vacuum source capable of being purposed to a wide range of high-vacuum related tasks.

  • Combining a resin degassing chamber/line into the design has now been abandoned as there are enough lower-spec rotary pumps available now to build a dedicated station for that purpose.

Backing/roughing pump

The backing pump is a rotary pump that should be capable of meeting or exceeding the backing pressure and maximum output of the diffusion pump.

There is a pledge for a suitable pump, as none offered so far have sufficient ultimate pressure and/or pumping speed. http://wiki.london.hackspace.org.uk/view/Pledges/Vacuum_Pump The pledge was successful and a backing pump has been aquired.


Diffusion pump

The diffusion pump donated by James Collings is an Edwards E04. It's ultimate vacuum capacity is 5x10^-7 mbar (0.0000005mbar) with a pumping speed of air of ISO 600l/s^-1 (hydrogen: ISO 800l/s^-1). It has a maximum starting pressure of 300 mbar and requires a backing pump capable of keeping the backing pressure at about 1mbar (assuming DC704EU pump fluid). Recommended backing pumps are the Edwards RV8 or RV12. The RV8 has a displacement of 9.7m^3h^-1 and an ultimate pressure of 2x10^-3. The RV12 is advised for fast roughing, has a displacement of 14.2m^3/h^-1 and an ultimate pressure of 2x10^-3 mbar.

The diff pump operates by boiling a special silicone oil to vapour and forcing it out through special baffles onto a water-cooled jacket. There the oil re-condenses and trickles down along with any air molecules it grabbed on the way. It sets up a pressure differential across the pump, where at its exist it should be at a high enough pressure the backing pump will be able to pump it away.

Current prices for the compatible fluids (as of October 6th, 2011, direct from Edwards Vacuum) are;

  • DC702 fluid - £117, 500ml (critical backing pressure 1.3 mbar, ultimate pressure 5x10^-6 mbar)
  • DC704EU fluid - £134.10, 500ml (critical backing pressure 1.0 mbar, ultimate pressure 5x10^-7 mbar)
  • DC705 fluid - £211.50, 500ml (critical backing pressure 0.9 mbar, ultimate pressure 5x10^-7 mbar)
  • Santovac 5 fluid - £852.30, 500ml (critical backing pressure 0.8 mbar, ultimate pressure 5x10^-7 mbar)
  • Edwards L9 fluid - Unknown price, possibly discontinued (critical backing pressure 0.9 mbar, ultimate pressure 5x10^-7 mbar)

On this I would recommend DC704EU fluid. For £17 extra you can achieve a magnitude better vacuum than the absolute cheapest. The spec sheet also describes it as a good durable and general-purpose fluid.

Cold baffle

The cold baffle is a small plate in the pump stack with water-cooled plates. These cold plates minimise any pump fluid vapour that might otherwise deflect upward and contaminate the vacuum processes above.

Pump stack

Above the diffusion pump are a series of manifolds for various purposes, including the cold baffle mentioned as part of the diffusion pump above.

To fulfil all the uses proposed, placing an extension piece with a branch next with the main plate valve above it will allow the full power of the diffusion pump to be accessed by a side-valve without having to pump down the main chamber. This high-vacuum access valve could then be used for attaching vacuum tubes, glass-forming manifolds, electron microscopes, fusors or any other number of parts. A foreline vacuum pressure sensor will be necessary here.

The valve currently need a slightly wider packing piece to be used in the stack at this location. The current one is only 3/4" thick, and in this position fouls the valve control gearbox.

Vacuum chamber

The vacuum chamber is a recessed base, likely for a glass bell-jar. However once fitted with a new O-ring gasket it will likely be fine for initial use with a simple flat cover. 25mm polycarbonate will probably do.

The chamber has three ports for vacuum feedthrus, though one is modified and may limit use. There are a number of threaded mounting points and, most notably, a large angled port at the circumference. This large port will require a special blanking plate making, but after that can probably be used for any custom or special-use interfaces required.

Support equipment

Both diffusion pump and cold baffle require a self-contained cooling loop. Possibly even separate radiators if one effects the critical temperature of the other.

The parts from James contained four Pirani Gauge heads and two Penning Gauge heads. These will need gauge controllers/readouts finding or making for them.

Some surface-coating processes work best if a glow-discharge plasma is used to remove surface oxidisation before coating. Sci has a 5.5Kv mains transformer that should be capable of producing this in vacuum.

Surface coatings also require a tungsten crucible or wire to be heated to vaporise metals. A high-current variable PSU or Variac would be used here.

To keep all the component parts secure and in-line, as well as keeping dangerous parts from being exposed, building a steel framed trolley to house it all seems like a sound idea.

Servicing and care

A wire mesh over the pumping hole of the vacuum chamber should help a lot to prevent any debris reaching the pump. After any use of the chamber for deposition purposes, it should be cleaned with fibre-less cloth and isopropyl alcohol.

(proposed) usage rules

  • Do not use without being trained.
  • No mercury or mercury-containing products should be allowed in the chamber, due to potential vaporisation in backing-pump exhaust, pump oil/fluids contamination and use of aluminium manifolds which mercury will rot.
  • No marshmallows. Or any other foodstuffs. Use the degasser.

Parts needed

Some additional parts will be needed.

  • Water pump (for cooling loop).
  • 1.5-2" thick, ~4" wide sturdy plastic (delrin?) to turn an large threaded fitting for the chamber.
    • I have a 100m dia, 45mm thick lump of nylon and a fair bit of 50mm delrin if it's any use. artag.
  • 20mm+ thick polycarbonate sheet (will probably order cut to size).


Cooling system

The E04 diffusion pump uses an 850Watt heater. The typical surface temperature will reach upwards of 200c (maximum 250c for pump body, max 400c for pump base).

The pump technical data specifies the maximum water pressure should be 5bar/72.5psi. Minimum water supply temperature should be 10c, and maximum return temperature should be 35c. (presuming return in this case means "water coming back out of the pump cooling jacket") The minimum flow-rate should 75l/h^-1.

As the baffle and valve assembly as also have cooling-loops, some additional capacity should be factored in. No numbers exist for these parts however. As they are indirectly heated however and part of reflux prevention, they perhaps should have a secondary cooling loop or auxiliary radiator between them.

Estimating any radiator capable of handing about 1Kw should be fine. Several PC water-cooling pumps are within capacity, and variable-speed.

Due to likely enclosed location, heat exhaust should be ducted away.

Progress reports

21-09-2011

All components are currently being stored in the Out Of Order workshop toilet on Jontys suggestion. This should keep them away from being damaged or contaminated by workshop dust. All manifolds seem in good order and have been in use until recently. Diffusion pump heater and thermal cut-out both test as good with a meter. Wiring should be replaced however. Pump should be drained & cleaned as a precaution. Fluid should be measured and filtered/inspected. A temperature sensor could be installed on the drain port. ~ Sci

04-02-2012

Post-xmas checkup on stored parts. Took some measurements of pump stack parts. Short video here: http://www.youtube.com/watch?v=3U_D1sNpXWc ~ Sci

11-02-2012

Finished taking measurements of pump-stack parts. Inventoried vacuum pipe fittings. Have added scrap industrial control panel to parts pile (sounder works at 5v) as well as pressure-switch and 3 castors (4th currently errant). All parts so far are in imperial dimensions, large manifolds are all SpeediVac and smaller ones are GeneVac. Several of the parts have been modified by the previous owner, so I'm inclined to look for additional parts. Though others have made do with copper pipe, I'd be concerned about trace-gas leakage through such thin material. Also we may need an additional bellows pipe section to get complete vibration-isolation from the backing pump (maybe. And only crucial for electron-microscope purposes). Will see if I have any compatible parts spare, and keep my eye on ebay. Also took dimensions of the storage-toilet as I presume, being the closest thing to a "clean room" available, it'll be where the pump system will live. So will constrain station dimensions to ensure it'll fit.

Considering use of a large steel pipe-T (water main size, ~10" ID) to serve as a bell-jar/chamber with port for a large observation window.

Chamber has some very simple adaptive manifold connectors it should be fairly easy to replicate/customise, as well as add more custom ports as need be.

19-03-2012

Have collected a Pirani/Penning gauge controller. Purchased from ebay for £5, plus packet of chips for ride to collection. Edwards Model 4, approximate age of existing gauge heads. Should be compatible. Supports two pirani and one penning head. Not rack/panel-mount, but should do the job very nicely. Will need compatible mains plug.

Likewise purchased some mixed Speedivac fittings (£11 including postage) that should make building up the vacuum pipework a lot nicer (avoiding using the home-made joints is a bonus).

Also donated a water-flow meter. Currently runs on 24v relay, but has fitting for hall-sensor control, so suggest gutting of stock electronics and wiring directly into control systems.

23-09-2012

Most of the welding is done, but we ran out of welding gas. Need more before transformer mounts can be done. Dry-fitting has begun, though will need short 5/16ths 24tpi Whitworth bolts to connect to chamber base.

Backing pump has been mounted on anti-vibration feet.

Welds will need grinding flat and re-doing in places once dry-fit of all parts is done and setup proved.

19-02-2014

Long-overdue update to the wiki page.

The diffusion pump has been serviced and cleaned. The cooling jacket is leak-free. It appears to have previously gone UTA catastrophically while at operating temperature, as it contained glass debris and burnt-on pump oil residue. It has been temporarily sealed for dust protection and returned to the equipment trolley. The next step is to complete the radiator & fan enclosure to get the pump cooling-loop operational.

To go to a bell-jar based design, circles of billet aluminium 13" dia are available from Alauminium warehouse, but will need facing on a large lathe. A used gas cylinder has been donated to serve as bell-jar. Suitable seals are approximatly £30. The trolley will likely need re-designing eventually.

Inline temperature sensor, flow-sensor, pumps, etc.. all available from PC water-cooling suppliers.

13-05-2015

The implosion-sheild is done. This is both to protect users in the case of catastrophic failure of the glass bell-jar, and protect the bell-jar from users and passers-by in the mixed usage workshop.

The bell-jar will be padlocked down as an access-control measure.

We're still in need of vacuum gauges, feedthrus and vacuum hose to connect the backing pump. Getting close now!