Equipment Gloat

[James Combs]

I was in my small town a couple days ago and walked into our one and only pawn shop to ask directions to a small newspaper office and look what they had on the shelf.

This Dremel Scroll saw was tagged at $100 but the sales clerk said $85 would by it.
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This vacuum pump was tagged at $125 and appeared new.
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I left and did my business at the news paper, came back and offered $200 for the two and bought them $212 after tax.

I haven't done anything with the vacuum pump yet but there is definitely a vacuum lathe chuck in the future plus I have a large pressure cooker that is going to become a vacuum chamber for casting pen blanks.

I plugged the vacuum pump in and held my finger over the inlet and it definitely has suction, not sure how much but it does work and is very quite.

I cleaned up the saw and polished the table. The light spot in the first photo was the location of a warning label that did not have any wear spots or scratches so I know the saw has not been used.
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I had turned it on at the pawn shop but it was very noisy with out a blade but it seem to run all right. Stuck a blade in it at my shop and powered it up at my shop and it ran smooth as silk...well as smooth as a scroll saw will run.:rolleyes:

I also checked the motor brushes, they appeared to be almost new.
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After I got it back together I cut a small circle in a piece of clipboard material and it worked like a charm so now all I need is someplace to put it.:eek:

[Carroll Courtney]

That vac sells for over 250 by itself,dang you did good---Carroll

[Dave Beauchesne]

James:

The Vacuum pump is a refrigeration duty style pump and will pull 35 microns ( as it is noted ) if it has new oil and is looked after.

If used for vacuum chucking, you will definitely have to have a bypass, as 35 microns is around 29.92 inches [I]mercury [I] vacuum - near a perfect vacuum. Make sure you have some sort of air filter for the bypass, and use only good quality '' refrigeration vacuum pump oil '' in it. It is likely a rotary vane style with very tight tolerances and is not made for what you want to use it for, specifically. It is not made to have large volumes of potentially dirty air flowing through it. The price was cheap, to be sure.

This advice from a 30 + year HVAC kinda guy.

Dave Beauchesne

[Jeff Monson]

James:

The Vacuum pump is a refrigeration duty style pump and will pull 35 microns ( as it is noted ) if it has new oil and is looked after.

If used for vacuum chucking, you will definitely have to have a bypass, as 35 microns is around 29.92 inches [I]mercury [I] vacuum - near a perfect vacuum. Make sure you have some sort of air filter for the bypass, and use only good quality '' refrigeration vacuum pump oil '' in it. It is likely a rotary vane style with very tight tolerances and is not made for what you want to use it for, specifically. It is not made to have large volumes of potentially dirty air flowing through it. The price was cheap, to be sure.

This advice from a 30 + year HVAC kinda guy.

Dave Beauchesne

1st off thats a smoking deal on the vacuum pump, I have the same Robinair pump and it works great.

Dave, could you explain the bypass system? I use a vacuum line directly to my vacuum bag when I use the pump, is this incorrect? The reason I ask is there is always alot of oil fog coming out of the breather. The level doesnt drop much, but the air in my shop is sure foggy when I use the system.

[Dave Beauchesne]

Jeff:

James stated he would use it for a vacuum chuck as well as a pen blank ' cooker '.

I don't have a vacuum chuck on my little midi-lathe, but some of our Guild members do on their larger lathe setups, and they have a bypass setup so there is not too much vacuum on the chuck - at those really deep vacuum values, you could definitely collapse a vacuum chuck collar or the material being chucked up itself. You don't need 29 inches of mercury vacuum to accomplish either vacuum chucking or veneer bag veneering.

One inch of mercury is equivalent to 13 inches of water ( if I remember correctly ) - so 29 inches of mercury x 13 is about 377 inches of water. Guys use ' inches of vacuum ' when talking about vacuum, but often it is ' water ' inches, so there is a considerable difference. The bypass system consists of a valve on a tee open to atmosphere that allows a portion of ambient air into the line with the vacuum on it so you don't pull such a deep vacuum on the end product. So, if you have a cloud of sawdust in the air and that is allowed to get into the vacuum pump - - - - not so good. They are made to suck air and contaminants out of refrigeration systems, but the contaminants are not ' chunky ' !!

A badly smoking vacuum pump could be a couple of things - 1) it needs an oil change, or 2) it is on its way out. Like my previous post noted, these pumps are a precision piece of equipment, and, for example, at work, I change the vacuum pump oil after every second job or so; say after 5 - 10 hours running. The vacuum pump usually off gasses water vapor, but oil mist as you describe is not a real good sign. Like I said, get some proper vacuum pump oil - Robinair, Yellow Jacket, Ritchie are common brands - all interchangeable as long as the bottle is sealed. Most pumps take a quart or so to recharge them - usually to half a sight glass on the front of the pump itself.

Dave Beauchesne

[Steve Ryan]

Quick rule of thumb. Every 2" of mercury is apx one pound per sq inch. 29" mercury is about 14.5 pounds sq inch. 10" round vacuum chuck will have close to 1100 pounds of pull holding the workpiece in place, assuming no leaks in the system.

[James Combs]

James:

The Vacuum pump is a refrigeration duty style pump and will pull 35 microns ( as it is noted ) if it has new oil and is looked after.

If used for vacuum chucking, you will definitely have to have a bypass, as 35 microns is around 29.92 inches [I]mercury [I] vacuum - near a perfect vacuum. Make sure you have some sort of air filter for the bypass, and use only good quality '' refrigeration vacuum pump oil '' in it. It is likely a rotary vane style with very tight tolerances and is not made for what you want to use it for, specifically. It is not made to have large volumes of potentially dirty air flowing through it. The price was cheap, to be sure.

This advice from a 30 + year HVAC kinda guy.

Dave Beauchesne

Thanks Dave, I have and engineering background my self but had not done much in HVAC and had not heard of the "micron" ratings before but completely understand it now that I found a comparison table.


Jeff:

James stated he would use it for a vacuum chuck as well as a pen blank ' cooker '.

I don't have a vacuum chuck on my little midi-lathe, but some of our Guild members do on their larger lathe setups, and they have a bypass setup so there is not too much vacuum on the chuck - at those really deep vacuum values, you could definitely collapse a vacuum chuck collar or the material being chucked up itself. You don't need 29 inches of mercury vacuum to accomplish either vacuum chucking or veneer bag veneering.

One inch of mercury is equivalent to 13 inches of water ( if I remember correctly ) - so 29 inches of mercury x 13 is about 377 inches of water. Guys use ' inches of vacuum ' when talking about vacuum, but often it is ' water ' inches, so there is a considerable difference. The bypass system consists of a valve on a tee open to atmosphere that allows a portion of ambient air into the line with the vacuum on it so you don't pull such a deep vacuum on the end product. So, if you have a cloud of sawdust in the air and that is allowed to get into the vacuum pump - - - - not so good. They are made to suck air and contaminants out of refrigeration systems, but the contaminants are not ' chunky ' !!

A badly smoking vacuum pump could be a couple of things - 1) it needs an oil change, or 2) it is on its way out. Like my previous post noted, these pumps are a precision piece of equipment, and, for example, at work, I change the vacuum pump oil after every second job or so; say after 5 - 10 hours running. The vacuum pump usually off gasses water vapor, but oil mist as you describe is not a real good sign. Like I said, get some proper vacuum pump oil - Robinair, Yellow Jacket, Ritchie are common brands - all interchangeable as long as the bottle is sealed. Most pumps take a quart or so to recharge them - usually to half a sight glass on the front of the pump itself.

Dave Beauchesne

Dave thanks again, was definitely planning on a bypass once I figured out the equivalent inches of mercury rating. I will be adding significant filtering to both the vacuum line from the chuck and/or the vacuum chamber and the bypass. I will probably use the same type filter on both then bypass and the device. This thing could probably boil casting materials if I dead ended it in the vacuum chamber:eek: and that wouldn't be good.


Quick rule of thumb. Every 2" of mercury is apx one pound per sq inch. 29" mercury is about 14.5 pounds sq inch. 10" round vacuum chuck will have close to 1100 pounds of pull holding the workpiece in place, assuming no leaks in the system.

Steve, thanks for the numbers, was going to do some quick calcs myself no need to now.


1st off thats a smoking deal on the vacuum pump, I have the same Robinair pump and it works great.

Dave, could you explain the bypass system? I use a vacuum line directly to my vacuum bag when I use the pump, is this incorrect? The reason I ask is there is always a lot of oil fog coming out of the breather. The level doesnt drop much, but the air in my shop is sure foggy when I use the system.

Jeff, actually I did feel the heat and saw a puff or two of smoke come off it when I saw it in the pawn shop.:D:rolleyes:;)

BTW and one of you other guys correct me if I am wrong but I believe these things (oil bath type vacs) will also blow smoke if you have too much bypass or a hole someplace in the system on the inlet side. I was the maintenance manager at a forklift manufacture for several years and I recall may HVAC tech complain about getting smoke when checking a roof top unit.

[Dave Beauchesne]

James:

As for the oil ' smoke ' it could be if there is too much bypass I suppose. When I am using one of the three I have in my stable, it is on refrigeration systems that are leak free integrity wise, and the pumps are kept in top notch shape. BTW, make sure you seal up the inlet when storing the pump; the oil has a hygroscopic nature and will get saturated with moisture to some degree.

For the intended purpose, this type of vacuum pump is not really being applied appropriately. Best of luck with it.

Regards;

Dave Beauchesne

[James Combs]

James:

As for the oil ' smoke ' it could be if there is too much bypass I suppose. When I am using one of the three I have in my stable, it is on refrigeration systems that are leak free integrity wise, and the pumps are kept in top notch shape. BTW, make sure you seal up the inlet when storing the pump; the oil has a hygroscopic nature and will get saturated with moisture to some degree.

For the intended purpose, this type of vacuum pump is not really being applied appropriately. Best of luck with it.

Regards;

Dave Beauchesne

Dave thanks, I do understand that my application is not exactly the original intent of the pump but the price was right. I really appreciate the info and will use it to keep the pump serviced accordingly. As you pointed out, no contaminants (ie good filtration) and frequent oil changes are a necessity.