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Help with Vacuum Pump Fittings

wrenwright on Fri June 20, 2008 10:13 PM User is offlineView users profile

I'm trying to hook up a Vacuum pump that I have for evacuating my system. It's a Sargent Welch pump. The problem I have is that I'm not sure how to go from the large fitting in the photo below to something that will work on my gauge set for R12. The fitting is held on with a surround clamp and a wing nut. The output is a 1/2 pipe thread.

I noticed when I ran the pump, I had some mist coming out of the outlet. Is this normal?

Also, what type of oil does this pump use?

Here is a photo:


iceman2555 on Sat June 21, 2008 12:18 PM User is offlineView users profile has been a long time since I last saw one of these units. SW pumps were mainly used in high vac manufacturing, educational and scientific endeavors. Yours looks like one of the older 8900 series pumps.
A good quality vacuum pump lubricant (prefer petroleum based) should work well with this pump.
If not mistaken the 'attachment' on your pump can be removed and replaced with a automotive type adapter. A adapter that employees both flare and acme fittings should be attached. If an adapter plate can not be obtained....why not simply purchase the necessary fittings from a HVAC supplier and fabricate an adapter. Seems as if the gauge of the metal in the photo is sufficient to allow for drill/tapping for installation of the correct fittings. The other ports (small and large) could be capped or removed. Removal would solve a problem with possible future leakage.

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bearing01 on Sat June 21, 2008 12:26 PM User is offline

when I turn on my vac pump I too get a brief shot of vapor mist come out the exhaust sometimes. I'm sure this is just water boil off due to drop in pressure.

wrenwright on Sat June 21, 2008 12:40 PM User is offlineView users profile


Actually, it's an 8821 model. Where do I buy these fittings you mention?


Edited: Sat June 21, 2008 at 12:42 PM by wrenwright

mk378 on Sat June 21, 2008 12:49 PM User is offline

Just solder something up starting at end of the copper elbow, such as a 1/4" male flare fitting, this is R-12 standard. Then you can buy a little adapter to R-134a "acme" threads. If you want to ditch the elbow and start from the clamp, that fitting is called a "KF25" and is common in scientific work. You can buy a KF25 to NPT adapter flange from a place like Kurt Lesker (

Oil mist is normal, it will lessen once a full vacuum is reached. Oil traps can be purchased which fit on the exhaust, or fit a long (but unobstructed!) hose to the outlet and lead it out of the garage.

Edit: It's KF25, not KF15. Pretty sure it's not a 40, the next standard size.

Edited: Sat June 21, 2008 at 12:59 PM by mk378

wrenwright on Sat June 21, 2008 12:53 PM User is offlineView users profile

Thanks, mk378. That's what I needed to know.


Went to the hardware and bought a ball valve, adapter from 3/4" to 1/4" and a short piece of copper tubing to connect it all together. Looks like I'm in business.

Edited: Sat June 21, 2008 at 7:43 PM by wrenwright

wrenwright on Sun June 22, 2008 5:02 AM User is offlineView users profile

Here's what I ended up with. Thanks for the help again.

Dougflas on Sun June 22, 2008 9:37 AM User is offline

If it were me doing this, I'd have purchased a packless refrigeration valve from a HVAC supplier instead of that ball valve. Those hardware items don't hold the vacuum as well. Johnstone supply # B12-022

wrenwright on Sun June 22, 2008 12:32 PM User is offlineView users profile


One thing I had a question about is how long my gauge set should maintain vacuum.

Last night I hooked up my gauge set to my pump, turned it on and closed the valve on the manifold and the ball valve I installed inline on the pump. I was getting a vacuum reading (I had attached an r134a fitting to the end of the second hose to block incoming air) of about 29" on the gauge set.

It held vacuum for about ten minutes and then I noticed that it started creeping downwards. Also, I noticed that when I opened the ball valve on the pump, the vacuum reading increased.

Is this normal? Are r134a fitting designed to seal completely when they are not attached to a fitting or do need to get some sort of cap to go over the end of the rubber tube?

The reason for this test was to make sure that I don't have any leaks in my pump/manifold set before I try to evaluate a system in a car. I've read that the system should "hold vacuum", but is there some timeframe we're looking for, i.e. should a system hold vacuum indefinitely?

If I do have to change over to a packless valve, is this something that can be bought at Home Depot or the like or do I have to go to a specialty vendor? There is a Grainger here in town, but I didn't have much luck finding a packless valve on their website.


Edited: Sun June 22, 2008 at 1:01 PM by wrenwright

mk378 on Sun June 22, 2008 1:16 PM User is offline

Connect just the blue hose from your manifold to the pump, and close the low-side valve wheel. This will isolate the vacuum to just the blue hose and low side gauge.

Matt L on Sun June 22, 2008 1:43 PM User is offline

My gauge set has blank fittings on the sides, which look just like the 134a fittings on the car, but they have no holes for refrigerant passage. Hooking the quick-connect attachments to these allow the gauge to hold a vacuum for days.

With the gauge set connected to my car, the vacuum holds overnight with no trouble. However, both of these vacuum readings are looking at the secondary scale on the low-pressure gauge. I should get a micron gauge.

wrenwright on Sun June 22, 2008 1:49 PM User is offlineView users profile

It sounds as if I should be holding vacuum as long as everything is hooked up. I'll hook up the end of the blue hose to the holder on the manifold and see how that affects things.

By the way, should the r134a fitting hold vacuum even when it isn't hooked up to a fitting? I have the manual type connector.

I'm basically trying at this point to ensure that the ball valve I bought will work or if it is going to cause a leak down.

wrenwright on Mon June 23, 2008 4:23 PM User is offlineView users profile


I followed the advice above and looped the service hose up to the hanger and then applied vacuum to the gauge set. It was pulling 28" last night and 12 hours later, was still holding 20". This was with the ball valve to the pump in the closed position.

Does this sound acceptable? I'm getting some leakage, but don't the hoses leak slightly over time?


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