How to Inflate a plastic bag?

Hello everyone,

I am trying to build a project that involves "inflating".
It's same as blood pressure monitors.
I have an inflatable plastic bag and i need to inflate it like blood pressure monitors do.

Whole process goes like this:

Inflate
Stay inflated for a while
Release air slowly (deflate)

And it has to be operate very quiet.

I can't decide on mechinal parts rather then Arduino side.
I think relays, motor drivers and other parts can be integrated with an air pump or something.

And i dont need "faster" inflating, inflatable bag is sized around a pc keyboard :slight_smile:
What kind of air pump can be used?
Are there any other things to consider?

Thanks in advance!

The air pump will be the noisy part, so that is where you need to start looking.

jremington, do you recommend any product? what kind of specs i should look into?

How much pressure is required?

Weedpharma

Normally this blower is run in a single direction but might work okay in reverse. IIRC the blower isn't very noisy (I have a couple).

I was thinking you could run it in reverse to pull the air back out of the bag. If you want the fan to turn in two directions, you'll probably want a h-bridge. The cheap $3 L298N boards would work.

Here's a link to my L298N tutorial.

This sort of fan wouldn't be good if you need much pressure.

If you want the same sort of pressure as in a blood pressure cuff then you could hack an automatic blood pressure monitor.

martyr:

Release air slowly (deflate)

I believe the release value of a blood pressure monitor would be controlled to release small amounts of air at a time.

A blood pressure monitor doesn't suck the air back out of the cuff. One has to squeeze the cuff to force the air out.

I'd decompose a (cheap) blood pressure monitoring device, to get all the required hardware. Check the required signal levels (voltages) for the pump and valve(s), before disassembling the working device.

On websites like Ebay.com and Banggood.com are 12V air pumps, which are used for blood pressure meters.
Like these : http://www.ebay.com/itm/400945049244
Some are for lower voltages like 6V.
They are noisy, and don't work in reverse.
They can supply enough pressure to support someone's arm or so.

On those websites, you will also find 12V valves. Like these : http://www.ebay.com/itm/401022827790

You could deflate the bag by just opening a valve and let the air out, or you could use a pump to deflate it.
When you use a single pump (a pump as used for blood pressure meters) then you might need 4 valves to reverse the flow.

If you buy 12V pumps and valves, you need a simple driver chip or a few mosfets.

What about a pressure sensor ?
Once I blew a bag with such a small pump (because of an error in my sketch). The 'bang' was very loud.

Koepel:
On websites like Ebay.com and Banggood.com are 12V air pumps, which are used for blood pressure meters.

That pump looks a lot like the one inside the blood pressure monitor I hacked. Purchasing just the motor and valve sure seems like a good idea.

A pressure release value can be made from a syringe and a rubber band.

The rubber band presses the plunger down. As pressure builds the plunger is pushed against the rubber band. A series of holes are drilled through the side of the syringe to allow the air to escape once the maximum pressure is reached. You probably need to test the syringe before drilling the holes to figure out where these holes should be drilled.

This pressure release valve works great for carbonating root beer. Holding the carbon dioxide under pressure while making root beer greatly increases the final carbonation level.

Big fat syringes work best for this application since the static friction of the syringe plays less of a role.