Variable Volume Surge Tanks?

[Brent1414]

I have never used one of these forums before, so be nice! Also, is this the right secton to post this?

I am designing a pneumatic system which requires 3 surge vessels, I have sized them to be approximately 2L, but the system is for an experiment would we like the ability to change it to collect as much data as possible, say +/- 1L(or more if possible). I will be using nitrogen, helium, and eventually into methane with CO2 and other contaminants. It needs to beable to hold 250 psi and have the ability to be vertically mounted with in/out ports at the top and bottom, regardless of the volume. I was thinking of something like a cylinder with external rods, but none have a port that changes with the position of the piston.

Does anyone know about this or have any ideas on how to solve my problem?

Thanks,

Brent

 

[zdas04]

I'm not going to ask why three surge vessels or why they need to be variable volume, as much as I'd like to know I'm just going to assume that they are important to your experiment.

The easiest way I can think of to do this would be to make the vessel 1L and add pairs of nozzles that you could put block valves on with external pipes between the block valves. You could put four of these nozzle pairs and size the pipe between them at 1/4L each. Then with all four external pipes open you would have 2L of surge volume (or you could make the pipes 1/2L each and be able to vary your surge volume between 1L and 3L).

If you just have to have a continuously variable surge volume in a vertical vessel, you would almost have to put a boot on the side of the vessel with a piston in it. This would almost certainly have to be designed for purpose and would not be an off-the-shelf item.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[BigInch]

I'd suggest that you try to find a bladder tank with that 250 psig pressure rating.
Pistons, etc. will complicate the problem ...immensely.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[btrueblood]

Not sure what I'm missing - this is a pneumatic surge tank? Like, normally that is just a vessel with a single inlet, connected to the pneumatic line, not like a surge tank or accumulator on a hydraulic system where a piston and gas charge act as a spring... ?

Take any pneumatic rated cylinder. Fill the rod side of a cylinder with water (or other "incompressible" fluid) and cap that port, use the piston side as your surge volume. To change volume, drain or add fluid as needed. Plumb as many of these as needed (I'd think you'd only need one, and isolation valves to add/subtract other, fixed-volume tanks, from the circuit).

Ok, you might have a little bit of gas seeping past the piston seal and dissolving into the fluid on the other side, and then forming bubbles when the pressure is relieved...but you can vent, drain, and refill the fluid periodically to eliminate any accumulated gas, and it happens pretty slowly, even with helium.

 

[Brent1414]

Thanks guys! zdas, I also don't know why there are 3, I am just going with my boss's vision. I think your solution should probably work, It would be nice to have more variability in the sizes, but it is looking more and more like this is the only option. The problem with the bladder tanks and incompressible fluid in a cylinder is that I cant have all that dead volume at any point. If there was a a cylinder which has a port going through the rod, allowing the gas to pass through then it would be an ideal option. Unfortunately I haven't been able to find one with that. 1 option I have been debating is trying to modify a cylinder to have a port through the rod, But I feel that will end horribly.

 

[Brent1414]

Also on the bladder issue I need the volumes to stay constant during each test, and only change as I need them too.

 

[BigInch]

If your fluid is incompressible, it should be easy enough to keep a constant volume, just keep pressure in the bladder constant and you have it. A regulator would do that.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Brent1414]

I just spoke to my boss, we have given up on this idea. The plan has changed to a cylinder with an incompressible fluid on the other side, which is clearly the easiest way around this.

Thanks for the help guys!

 

[btrueblood]

"The plan has changed to a cylinder with an incompressible fluid on the other side, which is clearly the easiest way around this."

Yup.

 

[dcasto]

This might help

http://www.welkereng.com/engineering/products/index.htm