Help setting up inline pressure gauges

[jen0leb]

Hi guys,new poster here
I'm trying to set up an inline gauge pressure for my experiments. I attached an analog one between my peristaltic pump and the filter, but i can't see any readings. Should i buy a more sensitive gauge?

http://imgur.com/a/yuHZR

I also wanted to set up a gauge on the outlet of the filter because i want to measure my pressure drop. Is it as straight forward as just installing another analogue on the outlet and subtracting the 2 values?
I would love to hear all your comments!

 

[LittleInch]

"Should I buy a more sensitive gauge?" - Dunno - give us a bit of a clue as to the operating pressure you're expecting out of the system. It's a PD pump so the pressure is a function of the system resistance downstream.

That tubing looks like very low pressure stuff to me so yes, it would appear that your guage is far too high range, but no data to back this up.


you can do it that way for the filter or buy a distinct differential pressure guage which has tow orts for U/s and d/s connections

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jen0leb]

Thank you for your reply!
I expect a pressure of about 5 psi in my system - I knew going in that the range of the pressure gauge was far larger than what was needed but i expected to see at least something register. I've not worked with analogue pressure gauges before and i wasn't sure if that observation was due to the large range or something else i'm missing.
I've ordered a new analogue gauge with a 15psi range and hopefully will get to test it this week.

You are right about the differential gauge - ultimately we will have to go with that for a good prototype but i'm still in the quick and dirty stage.
Have you had any experience setting up pressure controls on packed bed systems? This is not my forte and i was hoping to get some insight on here from people who have done it before.

 

[LittleInch]

If you look closely at the guage you can see that from 20, 40 up there are 4 marks indicating 5 psi marks, but from 20 to 0 only 3 indicating to me that 0-5 doesn't register to take up the linkages.

At £10 a unit or less I'm not surprised it doesn't register at the bottom 2% of range....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jen0leb]

You are right! Thanks for your help.

 

[SwinnyGG]

My typical practice that for sizing of gauges, I pick a gauge where the expected operating pressure (or range of pressures) will center the needle on the scale- so for 5 psi operating pressure, I'd want a 0-10 psi gauge.

 

[danw2]

Having air in the impulse line will buffer the pressure, particularly low pressures.

The 200psi range is way, way too high for your app.

Invert the 15psi gauge so air is displaced from the gauge and impulse line by the medium fluid, then flip it upright.

10 psi is an oddball range, 15psi is a standard range.

 

[jen0leb]

great point @danw2 - thanks for the tip!

 

[MikeHalloran]

YOU ARE DOING IT WRONG.

The gage in the photo is filled with liquid, for damping.

It gives an erroneously low reading unless you

PUNCTURE OR REMOVE THE RUBBER SHIPPING PLUG

from the top of the gage.



Mike Halloran
Pembroke Pines, FL, USA

 

[jen0leb]

I did vent the gauge by removing the rubber plug before i started. Should that plug be removed throughout?

 

[MikeHalloran]

YES.

Nobody makes a liquid filled gage that won't make a mess in portable service.
I guess they assume all will be mounted rigidly, stem down.

Some have a plug with a tiny nipple that you can cut off to leave a small vent hole.
If not, remove the plug, puncture it with a needle, heat the needle to red heat and then withdraw it slowly to burn/melt a hole, and reinstall the plug, or just remove the plug and throw it away.

If you rely on techs to remove and replace the plug after use, they will return with readings that are consistent only in being way too low.

There is a similar risk with Dwyer Magnehelics, which don't have liquid fills to leak, but do have two chambers, one of which must be left open because it's a differential gage. Actually, there are four ports; two high, two low, so the gage must have one port connected to pressure or vacuum as applicable, the other port on the same side plugged, and one of the other pair of ports open. They are excellent gages, available in quite a range of pressures, sturdy, not expensive, etc., but you have to pay attention, or read the directions, which are not permanently affixed.



Mike Halloran
Pembroke Pines, FL, USA

 

[jen0leb]

Thank you will do that!

 

[SwinnyGG]

For such low pressures, if you're buying another gauge, just buy one that isn't liquid filled.

Dan is right that 10psi is not a standard range, which means fewer options, but unless you're producing a large quantity of this test rig that doesn't matter too much.

https://www.mcmaster.com/#4026k3/=17o25dr

 

[jen0leb]

Update:
The 1-15 psi worked great. I still have a problem with the pulsing flow due to the peristaltic pump. I will be looking at replacing it with a positive displacement to insure uniform flow and repeat the experiment.

Thank you all for your help!