Vacuum Pumps

This depends on how fast and precise you need to be. A squeeze-bulb air pump (as used for checking blood pressure) can do this. I think you can buy plastic eductors that use a pressure stream of water to entrain air or liquid and thereby draw a vacuum. If you use the technique of sucking with the cheeks (rather than the lungs), you may even be able do this by mouth. More expensive would be a vacuum pump as used in refrigeration service. A U-tube mercury manometer would be suitable for measuring the vacuum, or you could can get various vacuum gauges and switches.

what i suggest you is you can go for a mehanical vacuum pump-which works in the rough vacuum range with a digital or analog gauge with a simple shut off valve......so that u can isolate the vacuum at 33kpa/250 torr

regards

sudhan...

hammy.hari@gmail.com

Kyle,

You can use a vacuum regulator to control the degree of evacuation. Maybe one like this:

http://www.smcpneumatics.com/displayitem.php?keyword=ITV2050-212L4

Mark Bingham
http://fourth-axis.com

thansks. I will look for it

-33kPa is about 77 kPa Absolute. This is a rough vacuum. 7 litres is a small volume. Probably a good aquarium pump can do the job. Otherwise a small diaphragm pump will do.

http://www.google.co.in/search?hl=en&client=firefox-a&rlz=1R1GGGL_en-GB___IN359&hs=Lk&q=diaphragm+pumps+manufacturers&revid=47485489&ei=cpc5S5mNM82GkAXW7MHzCA&sa=X&oi=revisions_inline&resnum=0&ct=broad-revision&cd=3&ved=0CFgQ1QIoAg

-33kPa ≠ 77 kPa

I think you probably misunderstood my meaning. DO the aquarium can handle this job?

10s for sugguestion.

-33 kPa = 67 kPa Absolute (About 0.67 kg/cm2) Sorry for that subtraction error. Aquarium pump should handle the pressure. Since it has to be connected in reverse to generate vacuum one should get a model that has both inlet and outlet connections. Since the flow rate is small it will take a few minutes to pump down. Otherwise a diaphragm pump will be needed. I have been using one of these for years now for vacuum down to -45 to -50 kPa (55 to 50 kPa absolute).

One of the ways of controlling the vacuum at that figure is to introduce a liquid into the container at such a temperature that it boils at that pressure. The pressure will be sustained at that figure until the liquid has all evaporated, after which it will fall further.

Water is a suitable and readily-available fluid.

→ Steam Tables.

Check out the following website, http://www.piab.com They offer a large selection of vacuum pumps that should work for your application. I have used their pumps for many different applications from medical to military applications.

Use a vacuum switch and valve.

Another thought is to remove a measured mass of air. At -33kPa gauge this will be 3.5 litres excess. I suspect near zero cost is a criterion, so how about:-

At least 4 metres of drip-watering 4mm bore tube/beverage tube, 2 valves to fit and screw adaptors.

A 300mm dia baloon.

A 20 litre/4 gal/5galUS oil drum.

Instructions. Drill the drum's screw cap twice 10 to 20mm apart 4mm dia. With a screw adaptor, connect the length of tube to the outside of the cap and the baloon to the inside. Through the second hole fit a second adaptor. Inside the cap connect enough tube to nearly reach the drum's bottom, on its outside connect four or more metres of tube with a 4mm valve at the far end. Feed the baloon into the drum. Totally fill the drum with water, leave no airspace. Screw the cap on tightly.

Connect the baloon tube to the 7 litre container via one valve.

Vertically separate the drum some 3300mm above the 4mm water valve.

Catch and measure, either by weight or volume, 3500ml(g) of water.

Close the valves.

Please note that +/- pressure gauges for manifold vacuum/liquid fuel were widely available. Also under $20 silicon gauge and absolute pressure transducers to use with a DMM. If you want a cheap pump a 12 volt tyre pump should work at $6 up sucking on its inlet.

Good luck happy new year and please tell yopur helpers your final method

Tornado suggests a mercury manometer.

Very good if you have mercury: otherwise tinted water will do the job if you have the height available, some 5 to 10 metres.

Kyle is your lab. a big shed?

Water evaporates and must be monitored and refilled periodically. Unity weight manometer oil, typically red, is a better media. However Dwyer, Omega, Kobold etc. make Delta P Gauges that make it hard to justify a manometer.