[domito (OP)]

Hi,

What's the cheapest way to create a barometric pressure drop in a sealed container say 2by2 feet made of out plastic ( a rubbermaid bin with lid)?

I was thinking a p#nis pump would do it?

Also, what cheap instrument should I look for to measure this decrease?

ALSO, Does anyone know how much the average air pressure drop is preceding an incoming storm? Would the percentage of drop need to be smaller seeing as I'm creating this drop within a small container?

I'm trying to create a simulation of incoming rainy season to stimulate breeding behaviors in animals.

Thanks.

- Mike

[another_someone]

What about a wine vacuum saver/sealer?

Are you sure you can get away with a drop in pressure, without a commensurate increase in humidity (or have you already taken account of that)?

[techmind]

ALSO, Does anyone know how much the average air pressure drop is preceding an incoming storm? Would the percentage of drop need to be smaller seeing as I'm creating this drop within a small container?

Well... thinking of the weather charts (see eg the BBC Weather site, and look for "Atlantic pressure charts"), I recall typical "low" pressures in Europe may be typically 960millibar, compared to a typical pressure nearer to 1000millibar. That sounds like a 4% drop to me. Not sure about tropical storms, but I doubt you'd ever need more than 6%-7%.

If you're using a sealed container then you need to consider that temperature changes will also affect the pressure (3 Celcius change will change the pressure by 1%). Also care that your animals don't axphixiate (I misspelled that!) as they convert all the available oxygen to CO2.

[domito (OP)]

Hi,

Yes, I'm trying to work this out with not killing the animals as my main concern.

4% drop. Ok got it, thanks for finding that info. I wouldn't know where to even start looking for this information.

Which way does the pressure change go with an increase or decrease in temperatures?

Also, please excuse my ignorance, but does a change in air pressure affect temperatures as well?

Also, if some animal was "sensitive" to drops in air pressure and used them for breeding cues could I get away with simulating small frequent changes in pressure rather than a long drawn out lower air pressure situation? Just guess, i'll have to test this all slowly and safely regardless.

It would greatly reduce the chance of causing harm to just lower the air pressure for minutes and then let everything normalize. Repeat a few times a day.

I have taken into account an increase in humidity. Thanks for looking out.

Also, in your opinions, is a large container suited to this task because it allows greater accuracy and lowers the risk of depleting the oxygen? I mean, the pressure change is what i'm after, but if I increase the container size from 2x2x2 to 3x3x3 and cause the same % drop in air pressure am I not left with much much more oxygen left in the large container due to volume of the box?

[Bored chemist]

You might want to calculate the force that a few percent of an atmosphere pressure would exert on a 3 foot square wall of a box. 5% gives you about half a ton.
The simplest and cheapest form of pressure gauge is a u shaped tube with water in it.
Since you don't want to asphyxiate the animals I suggest that you build a box, fit it with a u tube, drill 2 holes in it and connect one of them to, for example, a vacuum cleaner then throttle the air going into the other hole to reduce the pressure. That way there's always a flow of fresh air for the animals.

[techmind]

Which way does the pressure change go with an increase or decrease in temperatures?

The pressure will increase with increasing temperature, if the volume of gas is kept constant. See Ideal Gas law - http://en.wikipedia.org/wiki/Ideal_gas_law

Also, please excuse my ignorance, but does a change in air pressure affect temperatures as well?

If you abruptly reduce the air pressure, then the temperature will fall.
Given that the air was at around 300Kelvin to start with, a 1% change in pressure will cause about a 3 degree Kelvin (or Celcius) change in temperature.

Bored Chemist's vacuum clear idea is a good one, although you have to wonder whether your animals will be upset by the draught and noise. Also running a vacuum cleaner all day will use an awful lot of electricity (about 1kW, so will cost around 12p/hour, and make the room rather warm!).

[Bored chemist]

The ideal gas laws require that the box doesn't leak and that it maintains the same shape and size (strictly, the same volume) Given the forces involved I doubt that somehow.
A smaller pump, even the sort used for aqaria would probabaly work (you might need to put it inside the box). The advantage to using a cleaner is that they are easy to get hold of.

[domito (OP)]

Well,

I have to say that you've all been a great help!

Thanks!

[domito (OP)]

Oh and by the way... Bored,

The aquarium pump idea was BRILLIANT...

It has to take the air from somewhere, so I put it in the tank. It's cheap, I have one. It is "loud" but lots of people run pumps and all sorts of noise producing things inside their cages/tanks.

Also, tubing is widely available, so are shut off valves.. WHICH I already have. So, I'm going to place it in the tank, suppress the noise somehow. Run tubing going through the tank wall, out.. connected to a valve. Pump air out, valve it off.

Brilliant, brilliant.