Properly check vacuum.

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72gmc4x4
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Joined: Wed May 04, 2016 11:19 pm

Properly check vacuum.

Post by 72gmc4x4 »

How do you properly check vacuum for 30 min?

If the vacuum drops after closing valves on manifold gauges, does that mean vacuum leak? That's what I thought but someone was telling me it always drops when closing valve on gauges.
Dougflas
Posts: 379
Joined: Mon Apr 18, 2016 6:10 pm

Re: Properly check vacuum.

Post by Dougflas »

If you have 29 inches of vacuum while the pump is running, when you close the hand wheels, you should still have 29 inches of vacuum.
72gmc4x4
Posts: 41
Joined: Wed May 04, 2016 11:19 pm

Re: Properly check vacuum.

Post by 72gmc4x4 »

That's exactly what I thought. The gauges will still show 29in of vacuum otherwise you got a big leak..

Thank you.
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wptski
Posts: 82
Joined: Thu May 12, 2016 5:53 am

Re: Properly check vacuum.

Post by wptski »

72gmc4x4 wrote:That's exactly what I thought. The gauges will still show 29in of vacuum otherwise you got a big leak..

Thank you.
That's about all too!
72gmc4x4
Posts: 41
Joined: Wed May 04, 2016 11:19 pm

Re: Properly check vacuum.

Post by 72gmc4x4 »

So....

I pull a vacuum. It gets to 25 inches and then I close the knobs on the gauges and it quickly goes to 10 inches.

I assume leak. I put 125lbs of pressure with nitrogen and it hold for 20 mins...

What am I doing wrong?
Dougflas
Posts: 379
Joined: Mon Apr 18, 2016 6:10 pm

Re: Properly check vacuum.

Post by Dougflas »

Check your gauges and hoses. Take the high side hose and place the ends on the high siide looped tothe low side. Pull a vacuum and test. Do this for all of the hoses.
72gmc4x4
Posts: 41
Joined: Wed May 04, 2016 11:19 pm

Re: Properly check vacuum.

Post by 72gmc4x4 »

They won't loop without an adapter so this is what i did.

Low side hose and quick connect adapter connected to gauge but not AC, pull vacuum and opened low side knob. Came down to 28 or so inches quickly. Closed knob and it held.

Moved high side hose to low side and repeated pulling of vacuum. Also held...

I don't know what is going on.
72gmc4x4
Posts: 41
Joined: Wed May 04, 2016 11:19 pm

Re: Properly check vacuum.

Post by 72gmc4x4 »

Maybe not holding vacuum. I came back after about 10 min and the high side hose had lost some vacuum.

I'm going to retest.
Dougflas
Posts: 379
Joined: Mon Apr 18, 2016 6:10 pm

Re: Properly check vacuum.

Post by Dougflas »

you do not need adapters. Maybe I did not explain it well enough. Take your low side hose off the manifold. Now your manifold has 2 hoses on it (middle and high side) take the end of the high side off and out it on the low side manifold nipple. Draw a vacuum thru the guages. (Place vacuum pump on middle hose. Find which hose is not holding by exchanging the hoses until one does not hold.
72gmc4x4
Posts: 41
Joined: Wed May 04, 2016 11:19 pm

Re: Properly check vacuum.

Post by 72gmc4x4 »

I think I do understand what you are getting at. I attached a crude drawing of how to test. I just returned the gauges because I think they were faulty.

Please don't laugh.

This particular set of gauges has 2 different types of hoses.

The center has two female ends. The low and high side have one male and one female end.

So I can't connect the low to side to the high side on the gauges without an adapter.
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How to test?
How to test?
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