Eliminating pump pressure fluctuations 1

[htsmech]

I am trying to eliminate pump pressure fluctuations in an analytical instrument. We have a few unique constraints.

1. The sensor itself is sensitive to ~.1psi fluctuations, and is at about .5psig

2. We are very sensitive to mixing of the sample fluid with the preceding buffer, so tees or wyes will cause some dead spots and increase mixing. For this reason we are using a peristaltic pump, which has relatively high pressure fluctuations. (Any suggestions on alternatives?)

I am looking at a fluidics analogy of an RC filter (more questions about that in another post), but if you have any suggestions, please let me know.

Thanks,

Steve

 

[hacksaw]

you made need to use a bypass loop arrangement to a back pressure controller. This can be as simple as a manometer or an over flow weir device. This will stabilize flow and press, with an up stream tap to your analyzer.

your pressure controls can be in the main flow loop down stream of the analyzer sample point you should be able to stablize the pressure to mm of w.c.

 

[peglor]

You could try a gear pump. These have positive displacement and give more stable flow than a peristaltic pump. They still produce slight pressure fluctuations, but the frequency at which the fluctuation occurs is much higher (Fluctuations/revolution = No. of teeth on driven pump gear) and the amplitude of the fluctuation is lower.

It is possible to set up peristaltic pumps to produce much steadier flow by using more rollers on the pump tube as well as having a second set of rollers out of phase with the first set, so that the drop in flow caused by a roller lifting off one tube will be offset by the roller on the second tube being in the middle of pumping.

Hope this helps.

 

[Scipio]

You could also look at using an in-line pulsation dampener to reduce pulsation and avoid dead spots. I've looked into them before but never used one (never required in-line flow), but I did a quick search on the web, first one I found was Pulseguard's "PumpGuard PuG". They've got links to catalog cutsheets of that and a number of other models on this link;

http://www.pulseguard.com/pulsation_dampening/catalog_index.htm

Might take awhile to figure out which links go where, I found the site miserable to navigate, but there is some useful info buried in there.