>Has anyone ever used a high pressure compressed gas tank, like used for
>welding gasses, for the air doors? on a separate is it possible to bend
>the door hinges or roof with too much pressure in the system? if so what
>is the max pressure that can safely be used. My hoses are rated to
>150psi and I used up to 140psi but never held the button with the door
>fully up. Is it possible to damage the car like that?
I believe what limits this is the throw of the cylinder, not the pressure
used. The issue that plagued original hydraulic cars was the high pressure
coupled with the failure of the door latch solenoid opening, causing, as I
understand, the piston to bow the door. Usually the pressure on the
cylinder is determined by the regulator -- it should be high enough to open
the door in about 2 seconds, not much quicker than that -- no reason for it
to be real high, mine is around 80 psi.
As to the high pressure solution, I didn't go through the math so can't
comment on that (except that 1 atm is 14.7 psi so you might want to round
up), but regardless, I think that air (not o2) would be cheaper and more
available. When I used to dive, it was about $2-3.00 for 80 cubic ft.
There will be DOT issues with the tank and its location. High pressure
tanks are a bit dangerous in a wreck so placement is critical. I will never
forget my SCUBA class in 1974 where they showed the explosive potential of a
2,500 psi 74 cubic ft. tank. On last thing, of course, is that when adding
pressure from the larger tank to the smaller, each time it gets more and
more inefficient (transfers less and less volume) with the lower available
pressure in the large tank. Have you tried Tanner's expensive compressor?
Although it is a bit of an overkill for me, for you it might be a better
alternative. Kim
>
>Anyway back to my original reasoning.
>I'm sick of my cheesy electric air compressor! I'm planning on adding a
>high pressure tank to the system to give it a quick charge when needed.
>I did some calculations and I figure I would get about 200 door openings
>per charge. it works out to be about about $.01 per door opening given
>the right equipment. and an air leak free system.
>
>I know there are some engineers on this list. could one of you check
>over my calculations. I don't want to put this thing together and find
>it costs me $10 to open my doors twice! I'm an electrical and computer
>engineer mot a mechanical one. Even though this stuff is basic It cant
>hurt to be sure.
>
>1 ft^3 = 1728 in^3
>1 atm = 14 psi
>
>I was planning on using a 20 ft^3 air tank readily available from
>welding supply stores. Regulated to about 110psi. And adding another
>solenoid to switch the high pressure compressed tank to charge the
>standard low pressure ones, as a back up for the electric compressor.
>This is what I came up with
>
>20 ft^3 = 34560 in^3
>
>The volume of the pneumatic cyl: Vcyl = pi * r^2 * h
>
>diameter of cylinder = 1.5"
>height of cylinder is approx 13"
>
>Vcyl = 3.14 * .75"^2 * 13" = approx 23 in^3
>
>I plan to run the system at 110 psi. That seems to be a good measure
>for the drivers door. the passenger door works fine at 100, but the
>drivers side needs higher pressure I guess its wearing out.
>
>110 psi = 7.85 atm
>
>Neglecting error from temperature change.
>Patomoshpere * Vatmoshpere = Psystem * Vsystem
>
> 1 atm * 23 in^3 = 7.85 atm * Vsystem
> Vsystem = approx 3 in^3 : this is the volume of air the cylinder
>volume
> would be at 110 psi
> Vcyl / Vsystem = 7.66 : The # of Vcyl at 1 atm which compress to 1
>Vcyl at 110psi
> Vcyl * 7.66 = 176in^3 : the volume of air at 1 atm which occupies
>Vcyl at 110 psi
> 20 ft^3 / 176 in^3 = 196 : door openings
>
> $36 for 300ft^3 of compressed nitrogen. I plan to transfer the gas from
>a large 300 cubic foot tank to the smaller 20 cubic foot tank
>personally.
> 300 ft^3 = 518400 in^3
> 518400in^3 / 176 in^3 = 2945 door openings per refill of large tank
> approx 1.2 cents per door open.
>
>I might have been able do it simpler, but that's from memory. Any input
>or ideas on the subject would be greatly appreciated. thanks
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