Well-type Manometers. - How to build?

[SWB]

How do I figure the ratio between the well and the vertical column? How do I figure out the scale? I need to make sure the column height I want to use will be sufficient.

Thanks,

SWB

[98-1074649673]

When I was working with inclined manometers I was under the theory that u wanted the well surface area to be as large a ratio as possible ie: 1000:1 The less drop you have in the well fluid the less mathmatical error you have in the incline. So if you have the incline rise 1" you would want the well to drop .001. I never did get my incline to work perfectly before I swapped over to the Casio PV/flowsensor setup.

I'll take some pics of my inclined meter today sometime and post them, unfortunatly I do not have pics of the well. If u want the math involved do a search on the net for inclined manometers. Sorry, I don't have a link handy.

[84-1074663779]

If you are going to build a manometer well, it is also good idea to fit a second well at the top of the manometer. If you have an overpressure accident, and blow some water out of the top of the manometer into the upper well, it then just drains back all by itself.

As far as scale length goes, make it any convenient length, and just tilt the whole thing to give the required rise above zero at the 100% flow calibration point. The scale will always be the same inverse square law, and all the individual points can be worked out on a calculator and simply marked off.

flow = 1.0 (100%) then 1.0 x 1.0 = 1.0 full scale length
flow = 0.99 (99%) then 0.99 x 0.99 = 0.9801 of scale length
flow = 0.98 (98%) then 0.98 x 0.98 = 0.9604 of scale length
flow = 0.90 (90%) then 0.90 x 0.90 = 0.81 of scale length
flow = 0.50 (50%) then 0.50 x 0.50 = 0.25 of scale length

If you decide to make your scale 30" long, the 100% flow calibration line will be at 30", and the 50% flow calibration line will be at 7.5"

If all your flow orifices are sized to give rated flow at say 11.25 inches of water, or something, tilt your 30" long manometer so the 100% flow end is exactly 11.25" higher than zero.

If your orifices are all made to work at 15" pressure, you can tilt the same scale up to 15". The angle of tilt does not need to be known or measured, it is only the length of the scale, and vertical rise that are important.

Hope that helps.

[SWB]

I actually want to build a vertical manometer for the test depression. I'd like to have a scale that is really 1:1, or in other words, when the water rises 28" it represents 28" of water. If that makes sense. I'm just not sure how to go about that. If that isn't possible (and I'm pretty sure it's not), then my other choice is to build it and calibrate my scale with a U-tube manometer due to it's inherent accuracy. I.E. I'd pull one inch of water on the U-tube and mark a line on my well manometer at whatever height it rose, pull two inches and mark a new line, etc.

I haven't decided on whether to use a well or U-tube for my inclined yet..

[84-1074663779]

Actually it is very easy to make a very nice direct reading vertical manometer. I only wish I had a digital camera, it would save an awful lot of clumsy words..........

The basic idea is that you have a water reservoir with a large surface area, and a vertical column with a very small surface area.

It is easy to see that if the base of the vertical column is submerged, water can be forced up the vertical column to any desired height without the water level in the reservoir changing (much). So your zero reference height/pressure point does not move. You can read inches directly off a steel ruler mounted behind your column.

A better way to do it is to have a water tank fixed to your manometer half full of water, with a submerged rubber tube coming out from underneath, and curving up in a U shape to the bottom of your straight vertical clear glass (or acrylic) manometer tube.

You can vary the water level in the tank so zero pressure corresponds to zero inches. You can apply positive air pressure to the top of the tank, or negative pressure to the top of the manometer tube in the usual way.

Another way of thinking of this, is as a conventional U tube manometer with one very fat leg and one skinny leg. Fluid movement in each leg will be proportional to surface area. It is not difficult to get a surface area ratio of 1000:1 or more.

A 28 inch pressure rise would only drop the water in the reservoir 28 thou, an error which can easily be ignored.

This also works extremely well with sloping manometers.

The quarter inch clear acrylic tube I use has an internal diameter of 2.8mm, and a surface area of about 6 square mm.

My tank is two inch thin gauge copper pipe (50mm) about four inches long (100mm). When mounted on its side, and half full, the surface area will be 50mm x 100mm. The area ratio of 5000/6 is about 830:1 and it works fine.

A decent sized filler in the top of the tank made from a 1/2 inch pipe plug allows water level to be adjusted very precisely with a syringe to zero level. Or you can slot the screw holes in the steel ruler and move that up and down a bit to set the zero.

[SWB]

I got all that.

I'll have to play with it and see how it goes!

Thanks guys.

Sean

[jsmith]

I'm not sure it's necessary to have a huge surface area. All that is necessary is to calculate the ratio: eg, if you had a surface ratio of 20 to 1, you could simply divide the height you require (say 1") by 21. This gives you 0.048".

Basically for every inch of test pressure the well height will drop by 0.048".

Now you simply create a measurement scale in inches , say 0 to 28. But when you mark your inches you mark them off 0.952" apart rather than the full measurement.
Your 28" will in fact only be 26.656" above 0 and the well will have dropped by 1.344 in order to give you your 28".

It is very easy to do this and create a nice scale using any CAD package.

I am interested to know how people change the pressure direction on the vertical manometer.

See image attached:

Basically the picture attached shows the Well type manometer, the manometer has a hose coming from each end. When the flowbench is sucking I need hose 'A' to be connected to hose '1' (hose 2 to atmosphere). When my machine is blowing I need hose 'A' to be connected to hose '2' (hose 1 to atmosphere).

Has anyone found a way of doing this which doesnt involve pulluing hoses off and swapping them over?

A nice manual valve would be the best answer - does anyone know of one?

[THOMAS AUGUSTOVICH]

Easiest way to switch the pressure / vacuum signals around
without pulling lines is to use TWO three way valves.

The way a three way valve works:

There are three ports: "A", "B", and "C".

We will always call the center port or bottom of the "Three way valve" port the "C" port.

You must use TWO "Three way valves" to do what you want to do.

"Three way valve" number one line hook-up

"C" port goes to the TOP of the vertical manometer
"A" port goes to the "signal source" for your testing
"B" port goes to the atmosphere (Not hooked up to anything)

"Three way valve" number two line hook-up

"C" port goes to the "well" of the vertical manometer
"A" port goes to the atmosphere (Not hooked up to anything)
"B" port goes to the "signal source" for your testing

This will allow you to have both control levers face the same way for "Intake" testing and have both face the opposite way
for "exhaust" testing. easy to remember that way. both levers
must face the same way.

If you want to have only one line going to the plenum you can plastic "tee" the two "signal" lines into one before they go to the plenum.

Hope this helps.

TA