DIY accumulator

[JScoob]

I posted this on nasioc, but was referred to this site.

I have an idea for an DIY accumulator for cheap and could use some feedback.

I plan to use PVC pipe to create my accumulator housing and use ordinary bicycle inner tubing as the pressure bladder. I would tap the PVC pipe so that the inner tube valve can push through so that I can pump or deflate as I need. I plan to pump the inner tube to about 100 PSI and set my pump switch to provide 110 PSI of water pressure. The inner tube will ideally be the same diameter as the inner diameter of my pipe, and the same length as the pipe - filling as much of the inner cavity of the pipe as possible.

When water pressurizes to 110 psi, this should compress the 100 psi inner tube completely. As the accumulator drains, the inner tube pushes out with 100psi force, thus maintaining 100psi of water constantly, until the bladder is completely expanded.

What do you think?

[-=TWITCH=-]

Nice post some pics when you get it done!

Chris

[Brad]

There will not be much volume change in this system. Calculate the volume of air on the inner tube at 100psi and then see how much you have to reduce the volume to get to 110psi. I have not done the math but it would be worth the effort.

[JScoob]

Yes - I realized later(with a red flag from Ed) that my logic is flawed. 110 PSI water will only compress a 100PSI bladder 10%. P = nRT/V ... as you can see as volume decreases, pressure increases directly. So a 1/2 decrease in volume will increase the air pressure in the bladder by factor of 2...200psi.

I want the bladder to be about 1/4 its original inflated size. The maximum water PSI that I can get is 10bar = 140 PSI. So 140/4 = 35PSI in the inner tube. When I apply 140 PSI on a 35 PSI air bladder, the bladder will compress to 1/4 its original size.

However, that being said, that means I would have 140 psi in the accumulator for a brief period of time - which means I'll be spraying too much water at first. Perhaps I will adjust to 110PSI/4 = 27.5PSI in the bladder. Yes, that sounds more reasonable.

I will post pics in the next few days, with parts and such. I'm pretty sure the whole thing can be done for $15, including the epoxy/adhesive misc stuff. If this works, the cool thing is that you can make your accumulator almost any shape you want to fit your engine bay or trunk - you just need to find the right plastic shape that can withstand 100 psi and a couple of inner tubes.

[Brad]

We use a small diaphram type of accumulator, its rest pressure is 60psi for a 100psi system. It works well.