Min Size of Diff Pump

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Luke Harrill
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Min Size of Diff Pump

Post by Luke Harrill » Thu Nov 02, 2017 3:01 am

I've happened upon a tiny oil diffusion pump on ebay. The FAQ said that the amount of oil needed is never less than 35ml, but this pump only requires 15ml and it has a 1" throat.

The only information I've found is from an old add:

Water-Cooled Oil Diff Pump
-All steel construction
-Ultimate vacuum 5×10^(?) mm
-Two-stage
-Requires only 15ml of pump fluid
-Easy to clean
-Light, portable
-Speed 15 liters per second at 10^(4?) mm

https://m.ebay.com/itm/ASCO-Smith-co-Oi ... SwAaJZ6VPE

I'll attach the bad quality screen shot I have of the add...

So, basically I just want to make sure that this isn't too small before I try to buy it. Any opinions?
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Screenshot_2017-10-31-21-21-17-1.png

ian_krase
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Re: Min Size of Diff Pump

Post by ian_krase » Thu Nov 02, 2017 4:13 am

Seems like that should be fine though you might need a smaller gas inlet rate than is common.

John Futter
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Re: Min Size of Diff Pump

Post by John Futter » Thu Nov 02, 2017 6:38 am

By golly
this pump must be about forty years old
can you get a spare heater for it???
are all the internal parts in place with none lost???
Is it jam packed with carbonised muck deep down inside
does it leak ( I have seen two diff pumps now with a leaky weld at the bottom)


these are all questions that need to be answered before buying an interesting steam punk item for the mantlepiece

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Dennis P Brown
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Re: Min Size of Diff Pump

Post by Dennis P Brown » Thu Nov 02, 2017 11:07 am

What ever you do, don't buy that pump for anything more than what that 1950's era ad says - under $80 (and that better include shipping!) That price is an utter joke ($200.) I got a far larger pump (4 inch intake), with a small coupling chamber (that accepted 4 KF coupling ports) and a manual gate valve/all gaskets/coupling hardware for under $150 - with shipping! There are far better deals than that small toy of a pump and as John points out, that pump can have issues being so ancient.

Luke Harrill
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Re: Min Size of Diff Pump

Post by Luke Harrill » Thu Nov 02, 2017 2:30 pm

Thank you all for your advice. My plan was to TIG a 2.75" CF flange directly onto the intake, thus avoiding all of those pesky adapters.

I asked the seller for a photo looking down into the top, but I haven't received one yet. And as far as the heater goes, I would probably have to adapt a different one or custom build it.

This will all depend on how cheap I can get it, as I certainly don't want to waste too much money it.

ian_krase
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Re: Min Size of Diff Pump

Post by ian_krase » Thu Nov 02, 2017 7:57 pm

Are replacement heaters for pumps not something you can hack together or diy?

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Richard Hull
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Re: Min Size of Diff Pump

Post by Richard Hull » Fri Nov 03, 2017 3:59 am

Luke, All the best on finding a 2.75 conflat on a diff pump.....They just do not exist. Manufacturers love to sell their own totally non-standard throat couplings. The best you might hope for is an ISO flange or ASA flange on top.

Ian, You could try and kludge something up for a replacement diff pump heater, but the manufacture's replacement or its equal is a better bet as they have calculated the wattage and heating rate to match the mass of the boiler and fluid.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

ian_krase
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Re: Min Size of Diff Pump

Post by ian_krase » Fri Nov 03, 2017 5:56 am

I don't think I've ever seen any Conflat on a diffpump ever.

Even on turbos they are not as common as LF flanges.

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Dennis P Brown
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Re: Min Size of Diff Pump

Post by Dennis P Brown » Fri Nov 03, 2017 9:01 am

Again, not really sure that even if they sold it for $50 (shipping included; unless it is for a collection display as noted previously) it would be a good idea - that thing is water cooled so no advantage there, tiny and with questionable performance; worse, it is very likely impossible to get parts for; and trying to mate that to a vacuum system will not be easy - you might be able to tig weld to that throat but the metal on that thing might well burn right through and ruin that DP - all this besides that it may not work or could leak! I see zero up side to this DP and there are others for less than that absurd asking price of $200. One can find DP's that are likely to work because they were not mfg 40 or 50 years ago. If you can tig weld I'd think other pumps would be better choices to adapt a flange.

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Richard Hull
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Re: Min Size of Diff Pump

Post by Richard Hull » Fri Nov 03, 2017 7:58 pm

Gee, I have a flawlessly cleaned, good boiler heater, and ready for sale, water cooled, Diff pump with about a 3-4 inch throat and will ship anywhere in the U.S. for $200.00 + postage. If you are outside of the U.S., sorry. As with most all diff pumps, adaptation is a must at the flange. I will be updating my store in trading post soon and include it.

Note to all diff pump aspirants......... As 95% of all diff pumps have oddball flanges, if you can't machine metal or find someone who can or are not willing to have a machine shop make an adapter at $50.00/hr + parts, you need not bother with a diff pump or most any secondary pump....Even turbos sometimes have non-standard flanges. If for some stroke of luck you find a diff pump or turbo with a common, standard flange, you are still looking at big bucks for a "no machining needed" adapter.

Yes Virginia, it is tough to get a suitable vacuum system needed to do fusion in spite of the relaxed "bottom-end" vacuum requirement.

I was fortunate enough, 2 years ago, to purchase a fully functional, air cooled turbo with controller and all cables at HEAS 2015 for $75.00 and it had a rather rare 4.25 or 4.5 conflat on it. Luckily, I found a flange for it at HEAS 2016 for $25.00, rather than go to Lesker or Duniway and pay the big bucks.

Rchard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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