What diameter tube for manometers?

[UKDoug]

I've been out shopping for parts for my PTS bench build.

One thing I wasn't sure on was the best diameter clear plastic tube to get for my manometers? It seems to be available in a real variety.

What have you guys used in the past?

[200cfm]

I use 1/8" diameter.

[2seater]

I use 1/4" Teflon tubing.

[UKDoug]

Is that internal bore or external diameter?

Teflon sounds expensive? What is that used for in real life and where would I be likely to find it?

[MrHijet]

Aquarium tubes should be available everywhere

[UKDoug]

Aquirium tubes are teflon lined?

[bruce]

Might have been Tygon?

[86rocco1]

I'm using 1/8" I.D. rigid acrylic tubing from an aquarium supply store. Personally, I think the tubing should be a small as possible so that the ratio of the surface area of the reservoir to tubing is as big as you can reasonably make it but if the tubing's too small, say for argument's sake 1/16" I.D. and you'll have problems with surface tension in the tube.

[bruce]

I used Clear Cellulose (Acetate and Butyrate) 5/16" OD x 3/16" ID tube from Mcmaster Carr to build this manometer.

[jfholm]

Ed,
The one thing that I have been pondering is what diameter of tubing would be best also.

Here is an example that we have found when racing, whether it applies here or not is what I am going to throw out now. On our oil pressure gauges when running a small inside diameter line to the gauge from the engine the gauge would repond slowly. We increase the tubing from 1/16" id to 1/4" id and the oil pressure gauge would act like almost like a tach, it would move that much faster. That way if the engine gave a whisper of losing oil pressure it would show instantly.

On my present inclined manometer I have 1/8" id tubing and it responds a little slowly. My verticle manometer on the other hand is 1/4" id and reponse seems to be much faster and also more sensitive so it is easier to adjust to the desired reading. For that reason I am going to 1/4" id on my new inclined manometer. For the reasons you have listed though I do not think I will go any larger.

John

[86rocco1]

John, I suppose that's one more thing to consider when sizing the tubing. I'm really not sure if increased sensitivity it all that important or even desirable in this case. Smaller tubing would act as a bit of a natural oscillation damper perhaps making it easier to get good consistent readings, I guess it depends on the flowbench you're using and the type of testing you're doing, I really don't know, I'd be interested to hear other people's thoughts on the matter.

[bruce]

I know that my velocity probes are faster responding with a smaller inside diameter tube on the manometer.

Not relevant to the direct discussion though . . .

[2seater]

The Teflon tubing I used is 1/4" o.d., i.d. is about 3/16". It is semi-transparent and I used it to get as slippery a surface as possible. I like the larger diameter to help my old eyes, and I do believe larger diameter is more responsive. I purchased Teflon at a hydraulic supply store. I am not really sure if it works any better than plain old clear vinyl tubing, which is dirt cheap. It is pressed into a slot routered into a straight board. I would try the cheapest tubing first and see if you want to upgrade to something else later.

[2seater]

I almost forgot. I do use small diameter tubing for the dry parts, like the velocity probes, but I like the larger tubing for the liquid. The reservoir does need to be larger as the wetted area increases, so that is a valid point.

[jfholm]

Ed has jogged my memory one more time. With the larger id on the tubing for our oil pressure gauge it did react faster etc, but also was so sensitive the needle would be a little jumpy from the gears in the pump causing a rapid pulsation from the pumping effect.

John