In regards what the TS asked, can an automotive tire pump be used to pull a vacuum. That's been answered. Here's the reason why: The drawing below shows the piston inside the cylinder. As the motor turns the pump crank the piston glides back and forth, drawing air in through the Air Inlet Filter. Air flow is controlled by the Reed Valves. The inlet valve allows air to be drawn into the cylinder. When the piston reverses direction the inlet reed valve closes and air is pushed out the Outlet. When the piston draws back again the outlet reed valve closes allowing air to only be drawn in through the filter. No matter which direction you run the pump motor the end result is going to be the same.

Perhaps a new thread should be created asking how to build a vacuum pump. To which I would agree that the best idea I've seen so far was to use an old refrigerator compressor. That pump also has reed valves but it also has an inlet port where the freon was drawn into the pump, similar to what is drawn. I think. Fridge pumps likely have changed over the years and it's been a very very long time since I pulled one apart.

 

That pump also has reed valves but it also has an inlet port where the freon was drawn into the pump, similar to what is drawn. I think. Fridge pumps likely have changed over the years and it's been a very very long time since I pulled one apart.

That drawing is the same way an old style refrigeration compressor works, sorry Tony. The only difference is the refrigeration has a pipe from the cooling circuit. The modern refrigerator(last ~20 years?) is usually a multi piston swash-plate type of pump, just like they have used in car air conditioner pumps for quite a long time.

 

And again, the construction of an automotive tire pump compressor prevents it from being converted to a vacuum pump. Most of them have no inlet check valve.

You better look at TonyR's drawing. Piston or even diaphragm air compressors HAVE to have a check valve for both directions of the piston or diaphragm. They are after all 2 stroke devices, and pump through the head of the cylinder. Being they have no camshaft or other valves without the reed or more usual disc check valve they would never compress air, just move it in and out of the cylinder.

 

NONE of the TS anticipated applications would benefit from suddenly being flooded with water. Thus a water powered aspirator SEEMS A POOR CHOICE.

Ah, I understand now. You were using an water jet aspirator but nobody gave you basic instructions of how to use one if you only remember flooding your project. You were supposed to use a large Erlenmeyer flask as a vacuum trap and a three-way valve to break the vacuum before turning off the water.

I would put that mistake on the same level as connecting an ammeter in parallel with a load - a rookie mistake. Little check-valves are also available to protect you from if you cannot remember to open the vent valve before turning off the water.

 

I see the same gentlemen argue in many different topics. It would be nice to see mathematical proofs and diagrams instead of bickering. I know you guys have a ton of experience though when I read these comments I really can't tell who knows what they are talking about when opinions vary so much. Food for thought..

 

I see the same gentlemen argue in many different topics. It would be nice to see mathematical proofs and diagrams instead of bickering. I know you guys have a ton of experience though when I read these comments I really can't tell who knows what they are talking about when opinions vary so much. Food for thought..

I don't see a vacuum trap or a vent needing any equations.

 

Right now it will be for vacuum filtrations. It would be nice to be able to use it for desiccating chambers and vacuum distillations in the future though. Both those applications are not so intermittent as filtrations.

I will definitely get a real vacuum pump when I find one for a good price, but for now all I have is the tire inflator.

I found an old car battery and am able to run the machine with this. All I need now is a charger for it

So with that in mind and only that in mind you choose and buy a vacuum pump for an intended application. Regardless of how you power it or modify it an automotive tire pressure pump or similar is not suited for your applications. That being a given if a vacuum pump is suited for what you want you can either buy one new or used or do without. Those are the options. There is little to no sense in dragging this out. Question asked and question answered is all there is.

Ron

 

I don't see a vacuum trap or a vent needing any equations.

How then are the uninitiated such as myself and TS able to learn anything valuable? If I type up a paragraph of baloney about vacuum pumps, how would you show others my reasoning is false??

 

If I type up a paragraph of baloney about vacuum pumps, how would you show others my reasoning is false??

Well as for me I would likely start with the basics of how vacuum pumps work and the different types of vacuum pumps. Pulling a vacuum really depends on application. Do you want to evacuate an automotive air conditioning system or pull a vacuum for example a helium leak test. Do you just need a vacuum roughing pump or do you need a turbine pump to get down to milli torr of pressure? As to your reasoning? I just point out how things work backed up by industry standards. Unless a thread starter can well define their objective at the onset it becomes real difficult to give accurate and concessive information to assist with their goals. The goal needs well defined. It should not take a multiple post to get there. There has been absolutely no mention of how much vacuum the thread starter wants? Not defined as units of pressure and vacuum albeit below atmospheric pressure is still pressure.

So what is your point?

Ron

 

You better look at TonyR's drawing. Piston or even diaphragm air compressors HAVE to have a check valve for both directions of the piston or diaphragm. They are after all 2 stroke devices, and pump through the head of the cylinder. Being they have no camshaft or other valves without the reed or more usual disc check valve they would never compress air, just move it in and out of the cylinder.

The last two automotive tire inflaters that I disassembled were different from the drawing in that the piston was solid, and the crank was offset from the cylinder axis, so that the cylinder was only sealing on the compression stroke, on the intake stroke the flat piston was angled to allow air in. The discharge valve was part of the casting and not reversable. so without a fair bit of changing and running the motor the other direction it could not pull a vacuum. The pump in Tony's drawing costs quite a bit more.

 

Well as for me I would likely start with the basics of how vacuum pumps work and the different types of vacuum pumps. Pulling a vacuum really depends on application. Do you want to evacuate an automotive air conditioning system or pull a vacuum for example a helium leak test. Do you just need a vacuum roughing pump or do you need a turbine pump to get down to milli torr of pressure? As to your reasoning? I just point out how things work backed up by industry standards. Unless a thread starter can well define their objective at the onset it becomes real difficult to give accurate and concessive information to assist with their goals. The goal needs well defined. It should not take a multiple post to get there. There has been absolutely no mention of how much vacuum the thread starter wants? Not defined as units of pressure and vacuum albeit below atmospheric pressure is still pressure.

So what is your point?

Ron

Well first off I would consult the books before asking a community. My point is this: I read many different topics on different forums (of which I do not participate in the conversation) and the majority of folks present an opinion without feeling the need to augment with fact or reference. In contrast, there are some users who present a proof with every comment they make. In the case of not having a well defined goal as this topic appears to be, how does arguing without fact help anyone? It just maddens the unhelpful. Saying that you have a doctorate or years of experience, or "industry standard" is a poor substitute for a proof. Both MrSalts and MisterBill have made reasonable claims from experience on something I know little about, how would you proceed to form an opinion of your own? The obvious answer to me is to discard the opinions of both until reinforced with fact. Furthermore, I'll see a TS post once then 5 guys jump in and before you know it, there are 5 pages of opinions one has to filter through.

 

How then are the uninitiated such as myself and TS able to learn anything valuable? If I type up a paragraph of baloney about vacuum pumps, how would you show others my reasoning is false??

Because you either need one or you don't. Not everything needs an equation. Did you write out an equation before you made your last sandwich?

 

Ah, I understand now. You were using an water jet aspirator but nobody gave you basic instructions of how to use one if you only remember flooding your project. You were supposed to use a large Erlenmeyer flask as a vacuum trap and a three-way valve to break the vacuum before turning off the water.

I would put that mistake on the same level as connecting an ammeter in parallel with a load - a rookie mistake. Little check-valves are also available to protect you from if you cannot remember to open the vent valve before turning off the water.

This was a second semester college chemistry course lab class, and of course at that time none of us were familiar with that sort of apparatus. AND, the need for a trap indicates that such a mishap is frequent. In al three of the serious chemistry abs that I have since visited there were vacuum taps at every work station. And at every shop that did casting of resins of any kind there were vacuum pumps being used. Aso at the E-Beam welding installations.

 

Well first off I would consult the books before asking a community. My point is this: I read many different topics on different forums (of which I do not participate in the conversation) and the majority of folks present an opinion without feeling the need to augment with fact or reference. In contrast, there are some users who present a proof with every comment they make. In the case of not having a well defined goal as this topic appears to be, how does arguing without fact help anyone? It just maddens the unhelpful. Saying that you have a doctorate or years of experience, or "industry standard" is a poor substitute for a proof. Both MrSalts and MisterBill have made reasonable claims from experience on something I know little about, how would you proceed to form an opinion of your own? The obvious answer to me is to discard the opinions of both until reinforced with fact. Furthermore, I'll see a TS post once then 5 guys jump in and before you know it, there are 5 pages of opinions one has to filter through.

The fact is that I for one made a guess that the vacuum requirements were moderate level and low flow. For that sort a re-purposed compressor can be adequate.

 

Because you either need one or you don't. Not everything needs an equation. Did you write out an equation before you made your last sandwich?

Don't patronize me. A sandwich equation could easily aid in a diet plan and grocery shopping if I eat 1000 sandwiches a year. Necessary? No. Helpful? Likely to those who seek an additional means of discovery. There is a difference to debating and being argumentative and now I'm bordering on the latter as I have nothing useful to contribute to TS. Good day..

 

I wasn't patronizing you - I have enough kids of my own. If you feel patronized you need to bring up the level of your questions.

 

Hi Guys,
Recall the TS's Topic, please keep on the Topic query.
Mod.

I got this 12V car compressor:

which I want to convert into a vacuum pump. The issue is, its meant for connecting to a car battery, it has one of these car lighter plugs:

 

Then he clarified that he wants to do vacuum filtrations and possibly (eventually) pull a vacuum in a desiccator.

 

Well alrighty then. Just do this. There done. With what is available this is about as good as it gets.

Ron

 

Then he clarified that he wants to do vacuum filtrations and possibly (eventually) pull a vacuum in a desiccator.

BOTH of those applications require only a moderate vacuum at a moderate flow rate. Thus a compressor can be re-purposed to do the task. Yes, a rotary vane pump would be better but cost a whole lot more. And I still suggest getting a used medical appliance compressor as a good source. In my area there are even free distribution places to recycle that sort of stuff. If you can find one with a damaged case it is even cheaper.