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U Tube Manometer

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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U Tube Manometer

Unread postAuthor: CS » Fri Nov 30, 2012 6:25 pm

Spud Wiki wrote:Needle Valve plus Pressure Gauge

Bernzomatic Torch
Another type of fuel meter is simply a needle valve and a low range pressure gauge. The needle valve can be the valve and very small outlet hole in a typical Bernzomatic torch head.

The needle valve is plumbed to the chamber as is the low pressure gauge. To protect the torch and gauge it is a good idea to plumb both through a single small ball valve. To use, the ball valve is opened. Then the needle valve is opened a small amount. When the pressure in the chamber has risen 4% the two valves are closed. Assuming an atmospheric pressure of 14.7 PSI, adding 4% propane will raise the pressure in the chamber by 0.59 PSIG. Since the pressure rise is small, standard 120 or 250 PSIG gauges won't work for this type of meter.

A possible replacement for a low pressure range gauge is a "U-tube manometer". In this type of pressure gauge the pressure is related to the difference in height of the two columns of liquid. If the U-tube is filled with water, then a 1" difference in height represents a 0.0361 PSI difference in pressure. So, 0.59 PSI would be a 16.3" height difference for the two water columns.

Image

link (scroll to bottom)

Measuring propane seems easy enough, as the article says you need 16.3" height difference.

Has any one used a U tube manometer to fuel a hybrid? I haven't found anything searching Google images, using the parameter site:spudfiles.com, or using the search here on spudfiles.

And the wild idear...

If you wanted to measure 45 psi in a 1:1 ratio manometer it would need to be very tall. So I was thinking what if the side exposed to the atomsphere was a 4" pipe, and compressed air side was 1/8" ID tubing. With that big difference in ratio will that destroy the accuracy? Basically should I just use a pressure gauge like a regular person? Would it even work as I intend?
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Unread postAuthor: D_Hall » Fri Nov 30, 2012 8:53 pm

Yes, you should just use a pressure gauge like a regular person.

No, it won't work as you intend.
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Unread postAuthor: saefroch » Fri Nov 30, 2012 10:21 pm

You could try to pull this off just for kicks, but a normal pressure gauge will have higher accuracy, occupy less space, be more durable (not subject to orientation), and probably also cost less.
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 01, 2012 4:30 am

youtube manometer, here you go:

[youtube]http://www.youtube.com/watch?v=BofZuzBIQdw[/youtube]

Presented in glorious comic sans :roll:
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Unread postAuthor: POLAND_SPUD » Sat Dec 01, 2012 6:58 am

Isn't a blood pressure gauge more convenient ?
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Unread postAuthor: CS » Sat Dec 01, 2012 7:44 am

My misconception, still interesting though: 5 ignorant f###ing hours later...

Variations on the U-Tube Manometer

The differential pressure is always the difference in column heights, regardless of the size or shape of the tubes. As shown in Figure 6A, the legs of both manometers are open to the atmosphere and the indicating fluids are at the same level. Connecting the same pressure to the left leg of each manometer causes its level to lower. Because of the variation in volume in the manometer legs, the fluid in each column moves a different distance. However, the difference between the fluid levels in both manometers is identical (see Figure 6B).

Image


Well the plan is a liquid column (manometer) for propane, and air regulator for air. Got a hybrid burst disk cartridge I need to test out. Thinking of chaining several together with air hose and pinching off in between each one so they can be fueled all at once, then later sealed off from each other for firing.

Poland, issue of cost. I don't have anything like the stuff your talking about lying around. I do have all the junk handy for a manometer lying around and portability isn't and issue.
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Unread postAuthor: POLAND_SPUD » Sat Dec 01, 2012 10:18 am

Poland, issue of cost. I don't have anything like the stuff your talking about lying around.
lol one day you'll have to leave your home and buy something

ohh and trust me every f#### household has/had one - they are really easy to come by

Plus they are really inexpensive on ebay (unless you htink 5$ is a lot)>>
http://www.ebay.com/itm/Vintage-Lumisph ... 2ec3525212
http://www.ebay.com/itm/Clayton-Sphygmo ... 2c6a4c6865
http://www.ebay.com/itm/Sphygmomanomete ... 5aeb0ea23b


...and they go up to 300mmhg which is ~5.8 psi... so they should be accurate enough for manometric metering
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Unread postAuthor: Technician1002 » Sat Dec 01, 2012 10:53 am

Remember that blood pressure is measured in MM Hg. Don't mix the units. Mg is considerably heavier than water. This is not mixing apples and oranges, it it mixing water and Mercury.

Conversion factor;
1mm Hg = 13.16 mm H2O
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Unread postAuthor: POLAND_SPUD » Sat Dec 01, 2012 11:11 am

uhmm dude I know that - the reason I posted it here is not because I found something about 'mms of water' somewhere in the text but because he is looking for a a cheap and accurate gauge to measure pressure

Accurate gauges in this range (0-10psi or so) are usually very expensive but blood pressure gauges are dirt cheap
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