Robinair Pump KNF Inlet Fitting

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ggombert
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Robinair Pump KNF Inlet Fitting

Post by ggombert »

Hi,
I have a Robinair 15600 air-conditioning service pump that I use as a roughing pump on the fore line of my diffusion pump setup. I would like to replace the kludge of for line connection(s) that I currently use with a real KNF fitting of some sort.
Has anyone else done with a purchased adapter from Lesker(s) etc that would mate with the pump above to do this?

Thanks in advance!
Glenn
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Rich Feldman
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Re: Robinair Pump KNF Inlet Fitting

Post by Rich Feldman »

Hi Glenn.

I haven't used a purchased adapter like you asked about.
But I have used my JB-brand A/C service pump with tubes much fatter than A/C service hoses, and don't think the connection is a kluge.

To the pump's 3/8 inch flare nipple, I mate a 3/8 flare nut with an o-ring to seal the joint. The nut has minimum ID of 3/8 inch, and is soldered directly to a fat-hose connector.
An early stage is shown in the last last picture here:
viewtopic.php?f=10&t=3977#p25527

A conventional flared-copper-tube connection would have poorer vacuum conductance, but then the attached parts would not have to rotate when you screw the nut onto the pump.
Rotation would not be a problem for a KF half-nipple, silver-soldered to the flare nut.

Rich
All models are wrong; some models are useful. -- George Box
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Richard Hull
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Re: Robinair Pump KNF Inlet Fitting

Post by Richard Hull »

On all of my refrigeration direct drive pumps I go to the pump body and remove the manufacturers original fitting into the actual pump body casting! These are usually standard NPT threaded affairs.

I then go and buy a new brass body NPT plug attachment or saw into the old fitting, if brass, and bore out and modifiy as needed to get the biggest hole into the pump I can that can be adapted to a KF 25 brass flange half nipple that I have bought or machined. (Yes, I can machine my own KF fittings) I then silver solder or even soft solder the two together to get maximum conductance at the pump head.

Until you have waited and waited for tiny little 3/8-inch lines to pump to a decent technical grade vacuum, you will never appreciate or attain the large conductance speed of your pump.

One hates to resort to these high winding noise makers over a real, quiet, low winding scientific pump, but their low used or even new cost can get you going fast. The least you can do is to remove and modifiy the imposed stranglehold on conductance at the inlet and adapt them to real scientific vacuum connections. After all, you aren't in the HVAC biz.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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