homemade vacuum pump

[electroshock]

Can anyone help me?

I have just built a hand-operated vacuum pump.

The pump is made from 4" PVC and the resivwar is

the same..17" in length and the pump is 14"

in length. I am able to get 22HGs +-1 my gauge

is scaled 0-30HGs

My question is how can I boost my vacuum by 5HGs (10 would be nice)

is the limit by hand 22HGs or is there a way to increase the HGs?

[RP]

Can you post a picture or diagram of your assembly?  There's no reason why you can't get to 29-30inches or so but things like seal integrity and dead volume under your valves will become increasingly critical as you approach it.

Remember, unlike building pressure with a  compressor, you are working a state of zero pressure.  The closer you get, the more difficult it becomes.

[electroshock]

yah I noticed as I tried...couldnt go past 21HGs

I would like to poast some Picx but i have no way of doing so.

I guess 30 isnt critical im prety happy with my results...just

thought I would tweek it a little

[terry5732]

The "dead" space in a 4 inch barrel is pretty big. Try a similar set-up with 1/2 inch pipe for higher vacuum. Even at a slower rate I would think 29 inches would be hard to do manually.

[maker of toys]

you may have several problems:

1. PVC isn't real good for vacuum service. it off-gasses, it's temperature sensitive, it leaks, it's permeable to gasses, it traps water, it doesn't like solvents, sometimes it implodes.  please wear safety equipment. that said, with good design and hygiene, you can probably get 25" with PVC.
   
2. depending on the temperature and the contents of the chamber you are evacuating, you may be sucking on the "water peak" which is where all the water in the system suddenly tries to boil and creates a huge gas load/virtual leak. That said, with PVC in a room temperature environment, water probably isn't your biggest obsticle.  Other solvents/liquids might be, however; particularly the cleaner and glue that is commonly used to join PVC.
   
3. cleanliness is crucial to a vacuum system. any crap in the seals will create a leak.  Crap loose in the system is a source of off-gassing;  scratches, cracks, seams or crevices in the walls or equipment will also trap gas and liquids.
   
4. your guage may not be calibrated. . . . hardware store guages are usefull enough in a comparitive sense; they'll tell you if you're achieving the same pressure today as you did yesterday, but they provide no reliable information in a absolute sense.  
   
5. your piston is too big.  4" PVC (nominally ~4.25" dia) is going to have more than  12 square inches of area; with 2/3 of an atmosphere sitting on that piston, you're working hard to overcome atmospheric pressure, to the tune of 120 lbs or more. use a 1" or 2" pump, sweat less.
   
6. if you are using spring-loaded check valves, you will be limited by the ability of the air left in the chamber to lift the intake valve.  rubber "flaper" valves might work better, but even these will eventually refuse to lift.  reciprocating pumps will need mechanically operated valves to get a decent vacuum.  (you can do this manually, (eg ball valves) but it's tedious)
   
   

solutions:

patience. the only way around a water/liquid peak is through. . . take a deep breath and keep pumping.  eventually you'll get most/ all of the water/liquid out and the pressure will start to drop again. it takes a lot of pumping to get rid of the vapor.

too, with pvc, you'll have a lot of water trapped in the plastic;  And, of course, the plastic also off-gasses, as does any lube-oil or contamination in the chamber to be evacuated (or its contents).  all of these factors change with temperature;  the water will be easier to pump off at elevated temperature.  so don't give up.

minimize the dead-space in the pump.  this includes the distance between the piston head and the "rings" or whatever you're using.  mechanical vacuum pump systems for high-vacuum service often have a total compression ratio close to  1,000,000 to 1 in 20 or 30 or more stages.  you probably don't need that much; but if you divide absolute atmospheric pressure (nominally 30") by the absolute pressure you want to achieve (say 3" absolute) the bare minumum you can do it with is  (30"/3" =  CR 10).  to get to 2" suddenly you need 15 to 1.  you can see where this winds up. . .

which brings us to:  use a 2 or 3 stage pump.  first stage is the pump you already have.  second stage is a smaller one; rig a some ball valves so that you can start with both stages pulling on the volume to be evacuated, then when you get to 20" or so, you switch so that the gas goes through the big pump, to the little pump, to atmosphere. operate them so that one pump is sucking while the other is exhausing for best results.

hope that spurs some usefull ideas!

-Dan

[BT Humble]

If you're doing this manually just as a $$$-saving measure, I've heard that it's possible to use an old refrigerator compressor "in reverse" as a vacuum pump.

I've never tried it myself, so it's just a suggestion. ;-)

BTH

[electroshock]

Thank god for the Net theres a lot of good information here.

I am going to try to do further experiments and post my results as soon

as I can. One last question that I have would be...would it be possible

to increase the HGs by increasing the size of my tank??

My thought was more volume at 0-PSI to simulate sea level difference

.

[wdyasq]

A question...

Folks here have taken time to TRY and help you.  Now, you ask a question not related to vacuum and want an answer.  What the HELL are you trying to do?

You could also help yourself if you took some time to learn a bit about vacuum before you started trying to improve an unknown (to you).

Suggestions:

         Learn what "HG"s are - it is  actually "Hg"

         Figgure out what is actually happening and why it does.  It "ain't that hard"

         Tell folks what you care to acheive.  They may have an answer that WORKS!

         Use common industry terms and keep the same terms throughout your discussion.  Folks will be able to follow and help in that manor.

Wishing you mercury, millibars and torr,

Ron

[Nando]

Yes refrigerators pumps can be a good vaccum pumps.

I used to go to the city dump with my water bill and select any refrigerator or freezer and get from anything from there, free.

We built at least 20 vaccum pumps for friends -- from small refrigerators or window air conditioning units to large refrig or freezers, even large air conditioning units.

Nando

[electroshock]

"A question... Folks here have taken time to TRY and help you.  Now, you ask a question not related to vacuum and want an answer.  What the HELL are you trying to do?

You could also help yourself if you took some time to learn a bit about vacuum before you started trying to improve an unknown (to you). "

First of all "Ron" or should I call you father...if you actually took

the time and read the whole story, I pretty much covered what I wanted

in the beginning.

-------------------------

Can anyone help me?

I have just built a hand-operated vacuum pump.

The pump is made from 4" PVC and the resivwar is

the same..17" in length and the pump is 14"

in length. I am able to get 22HGs +-1 my gauge

is scaled 0-30HGs

My question is how can I boost my vacuum by 5HGs (10 would be nice)

is the limit by hand 22HGs or is there a way to increase the HGs?

-------------------------

If I were a Mechanical Engineer I would still look for others that

might know what works better or other suggestions. This is partly what this

forum is for among other things.

As for knowing about vacuums, my first attempt building a pump had pretty good results. 20-"HGs" not bad for the first time in the field and what little information on the Web there is. Apparently you're a Genius of a mechanic like myself

or you wouldn't be in this forum. Not one person can think of all the variables on

one sitting at the old drawing board. at least I cant. This is why we have experiments. This forum is a good tool in aiding that process.

As for my research....

-----------------------------

www.hargravesfluidics.com

Standard Atmosphere Table

Altitude Above

Sea Level

Atmospheric

Pressure

Maximum

Vacuum Level

Attainable

Temperature Pressure and

Vacuum Level Density

--------------------------------------

www.scitoys.com/scitoys/scitoys/aero/vacuum/

--------------------------------------

www.sanitationjournal.com/vacuumreliefvalve.html (1 of 2) [4/2/2006 5:37:50 AM]

Small seemingly insignificant components can make a big difference in the performance and longevity of your

pumper truck. Take your vacuum relief valve for example.  Most operators pay little attention to this seemingly

insignificant component but to do so may eventually make you very sorry.  Ignoring relief valve function

actually can rob system performance, waste money and even worse, cause catastrophic system failures.

Vacuum pumps form the heart of every vacuum system.  Left uncontrolled, vacuum pumps will draw down

the vacuum level in a tank to the point where the pump physically can not draw out or evacuate any more air

from the tank. The total amount of vacuum drawn from the tank depends upon the pump condition determined

by rotor and end plates clearances inside the pump. The condition of the vanes and their sealing capability with

the inner bore of the pump, also affect vacuum levels.  In addition, the condition system components such as

hoses and fittings and the amount of leaks present also influence vacuum levels.  Most pumps in good

condition draw at least 25 inches of mercury if no relief valve is present and some will draw close to 27 inches

of mercury.  One common misconception about vacuum pumps is that bigger displacement pumps create

higher vacuum levels.  This is not true. Actually, small displacement pumps, in an equivalent condition, produce

the same vacuum levels as larger pumps, it just takes them longer time to accomplish the job.  

As vacuum levels increase, pumps work harder to evacuate the tank and all components experience increased

forces on their outer surfaces due to atmospheric pressure.  To limit these forces and control vacuum levels,

all properly designed and maintained vacuum systems rely on a well maintained and accurately adjusted vacuum

relief valve.  For servicing portable restrooms, a vacuum level set to maximum of 18 _ 20 inches of mercury

-------------------------------------------

http://www.trident.on.ca/orifice-air-flow.htm (1 of 2) [12/23/2005 10:38:44 PM]

Vacuum Flow Through Orifices

Figures in body of chart are in air flows in SCFM (Standard cubic feet / minute)

Orifice Diameter (In)" Vacuum in inches of mercury

2.     " 4" 6" 8" 10" 12" 14" 18" 24"
   
1.     /64" .018 .026 .032 .037 .041 .045 .048 .055 .063
   
2.     /32" .074 .100 .128 .148 .165 .180 .195 .220 .250
   
3.     /16" .300 .420 .517 .595 .660 .725 .780 .880 1.00
   
4.     /8" 1.20 1.68 2.06 2.37 2.64 2.89 3.12 3.53 4.04
   
5.     /4" 4.78 6.74 8.25 9.52 10.6 11.6 12.4 14.0 16.2
   
3.     /8" 10.8 15.2 18.5 21.4 23.8 26.0 28.0 31.8 36.4
   
4.     /2" 19.1 27.0 33.0 38.5 42.3 46.3 50.0 56.5 64.6
   
5.     /8" 30.0 42.2 51.7 59.5 66.2 72.6 78.0 88.0 101
   
6.     /4" 43.0 60.6 74.0 85.3 95.2 104 112 127 145
   
7.     /8" 58.8 82.6 101 116 130 142 153 173 198
   
8.     " 76.5 108 131 152 169 185 200 225 258
   
   

--------------------------------------------------

I have gathered some good information in my thought process from this forum

and I recently came up with an experiment that might let me double my "HGs"

20-40 with the same pump and design. Regardless of sea level.

"Ignorance can be cured. Stupid is Forever."

As for ignorance, yes it is a lack of knowledge and stupid is the unwillingness or the act to not learn...so my advice to you, read a story before you act.

If you act then make sure it has something to do with the story.

[Chagrin]

Mini-article on using refridgerator compressors for vacuum pumps:

http://www.joewoodworker.com/veneering/visitorspress/refrigerantcompressorvacuumpress.htm

The site has a wealth of information on inexpensive vacuum pressing.

[electroshock]

Thanks for the info this will give me some great ideas

[electroshock]

I found an old Auto-Cad cd and im going to try and post

my design in a tiff format who ever is interested

maybe this will help others who might want to build

their own pump. Thanks for all of the replies to this story.

Been a big help.