Edwards Pirani Gauge/Display Troubles

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Tom McCarthy
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Re: Edwards Pirani Gauge/Display Troubles

Post by Tom McCarthy » Thu Dec 15, 2016 7:56 pm

I haven't used the gas ballast yet - have been operating cold with high vacuum mode and gas ballast closed. The oil is a little cloudy, so I'm going to have a go at decontaminating it and if that doesn't work I'll change it. I'll run the pump with GB II as you've advised for a couple hours tomorrow evening.

The gauge is behaving itself quite well now, just need to set the vacuum pot after running the pump.

You're right, I don't really need the gauge to be all that accurate. I'm using it with a Turbovac 151 too, so fore-vacuum only needs to be about 1mbar anyways.

I'm not quite happy with the pressure rise. The RV manual says it's probably something up with the inlet valve (not the gas ballast as I've had it closed), should I open it up and see if I can spot anything?

Thanks again for all the help.

Tom

John Futter
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Re: Edwards Pirani Gauge/Display Troubles

Post by John Futter » Thu Dec 15, 2016 10:09 pm

Cloudy oil
rise in pressure after switch off = water vapour

You need to run the pump for an hour dead headed ie blanked off with the gas ballast wide open

No longer than this otherwise it will throw out all its oil

The gas ballast introduces a bit of air to help shift the water from the pump to outside the pump.
Never run the pump with the inlet open you will quickly fill the pump oil with water out of the atmosphere

fizz
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Re: Edwards Pirani Gauge/Display Troubles

Post by fizz » Fri Dec 16, 2016 4:39 pm

I have said SV10, but it should be SP10 give me a call.

fizz
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Re: Edwards Pirani Gauge/Display Troubles

Post by fizz » Sat Dec 17, 2016 4:02 pm

Hi Tom

I have said the model # of the valve is SV10 this is incorrect and should be SP10 , Email me about this item.

Robin

Tom McCarthy
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Re: Edwards Pirani Gauge/Display Troubles

Post by Tom McCarthy » Sat Dec 17, 2016 5:23 pm

Ran the pump with Gas Ballast open for an hour yesterday evening - that helped a little bit. Followed it up with 2 3 hour long runs. Oil is now 100% clear and as long as Gas ballast is closed when pump turned off, it holds the vacuum. Opening the gas ballast introduces a little leak, but I think this is to be expected.

Looks like it's all good then, will try a couple more runs to confirm it's ok.

Thanks for all the help.

Tom

Tom McCarthy
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Re: Edwards Pirani Gauge/Display Troubles

Post by Tom McCarthy » Sun Dec 18, 2016 10:39 pm

Have continued playing with the pump and gauge.

The pumping is perfect now, goes straight down to 10ish microns with gas ballast closed, oil is clear. However, turn the pump off and we're in quite a gradual return to atmosphere. Actually, sometimes it goes to about 500 microns and other times the whole system levels at about 200 microns. I'm suspecting a leak rather than pump issues now - I make sure to keep the inlet closed off as best I can so as not to get any more water vapour in it and oil is totally clear. (One thing that's odd is when the gas ballast is open and pump is running, the oil stays clear, but fills with little bubbles moving through it). Unless there's still some dodgy vapours or leftovers hanging around in the pump, I think the pump is running fine. Leak is on the order of 3-5 microns a second, or thereabouts.

The system is just pump inlet <> KF attach to a Lesker valve <> KF25 - KF15 Adapter <> KF10 o-ring to gauge. From reading past posts, there's been mention that valves are 'notorious' for leaks, outgassing is the other suspect. Looks like it's time to
a) get out the industrial cleaning wipes and wipe down insides of connections
b) get my hands on some cans of Dust-Off for checking leaks

If this isn't the way to go, please let me know! Or, if there's any quick fixes for checking out what's up, do let me know. I'm a bit suspicious that the setup is leaking as it seems so minimal. Vacuum is hard though - http://fusor.net/board/viewtopic.php?f= ... eck#p68662

Tom
IMG_1203.JPG
Current setup

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