Reservoir For Inclined Manometer - Products that can be used as reservoir?

[Dom G]

I am getting back on track trying to finish my MSD based flowbench. To get started, I'm making my own manometers and wonder if anyone can suggest a ready-made or store bought product that can be easily modified to serve as the reservoir in my inclined manometer?

Since I'm using tubing with a 1/8" ID, the inlet and outlet would have to easily match up. There's probably something obvious available, I just haven't turned it up yet with the search function or a quick stroll thru the hardware store.

My 8 vacuum motors showed up today so I hope to make more progress this weekend on the bench.

Thanks.

Dom

[Unkl Ian]

Someone suggested using a large syringe.

[Rick360]

I used a short air cylinder. It has nicely machined inside surface and pipe threads on each end for connections. Won't distort with any pressure/vacuum a bench will see.

You can remove the shaft and piston and plug the hole or make an adjustable zero plunger thru the rod opening. Here are some on ebay that are similar and I'm sure there are more, these were the first ones I found. They can probably be found at an industrial or military surplus store also.



Rick

[84-1074663779]

I made my own manometer tanks out of 1.5" copper pipe with flat copper end plates silver soldered on.

PVC pipe with a pair of end caps works well too. Clear acrylic pipe with some end plugs ? Lots of ways....

[larrycavan]

Before switching to the FP1 manometers, I purchased several lengths of 5/8" clear acrylic tubing. Caps were made from common plastic pipe caps that I drilled and installed barb fittings for the 1/8" tubing to connect to.

I mounted it to the backboard of the bench with pinch clamps bought at the local hardware store. To zero the scale you simply slid the well up or down in the pinch clams.

Keep in mind, the size of the reservoir and tubing impacts the calculations for the scale.

If you need a length of clear acrylic, I'll be happy to mail you one. I have a few left and no real use for it now.

Larry


Larry

[Dom G]

Thanks for everyone's suggestions. I was just hoping someone found a slick off the shelf item that could be quickly modified into production.

Larry, thanks for offering to send me some clear acrylic. I think I'll just use fairly large ID (2.5") PVC pipe with end caps that have fittings with 1/8" hose barbs.

Though I do have a question regarding your comment Larry about the size of the reservoir and tubing affecting the calculations for the scale. I was planning to simply use the scale length, inches of rise, and the square law rule to determine the scale markings. Will this not work? Do I need to factor other variables into the calculation?

Thanks.

Dom

[84-1074663779]

What happens is that as the fluid rises in the sloping manometer tube, the fluid level falls in the reservoir.

Suppose your design manometer rise is fifteen inches, and the fluid level drops one quarter inch in the reservoir. The REAL manometer rise will therefore be fifteen and a quarter inches. Only a small error, but still an error.

The exact rate of fluid rise and fall is proportional to the surface areas of tube and reservoir. You don't need a lot of fluid volume in the reservoir, just as large a surface area as possible, that is the trick.

For a cylindrical reservoir, make it reasonably long and mount it horizontal, and half fill it so it has the maximum possible exposed surface area. Setting the fluid level to zero can be frustrating unless an easy method of adjustment has been provided for. I have used a reasonably large screw in plug (brass 1/2 BSP pipe plug) as a fill port in the top of the reservoir. I then use a small syringe to add/remove fluid to get the zero exact.

A further advantage of having a very large surface area reservoir is that it is much less sensitive to slight fluid loss, the zero point is very stable and easy to set.

Another simple way might be to raise or lower the whole reservoir mechanically to adjust the zero point. Some sort of hinge and set screw maybe ?

Getting a ratio of 1000:1 fluid relative surface areas between reservoir and manometer tube is fairly easy. An 0.1% error can probably be ignored.

Use a similar volume dry reservoir at the top so an over pressure accident will allow all the fluid to just drain back by itself. Both reservoirs can be mounted behind the manometer board out of sight for a neat appearance.

[86rocco]

[larrycavan]

Dom,

If you use .125" id tubing for the scale leg and something quite large like 2" for the reservoir, the error is so small that it can be virtually ignored. There's a great spreadsheet on here that Rocco or Tony or someone posted. Search for [post 1-30525-inclined_manometer.xls]You can use it to calculate the effects of the reservoir and it also provides scale correction. It's really a very nice piece of work. With the ratio of .125 / 2
with 13" of vertical rise and a 28" scale, 100% is 13.11".

Here are some pics I finaly got around to taking of my bench in it's current state. It's 12 years old and just been through some modifications including:

1. Elimination of the water guages in favor of digital [FP1]
2. Added top chamber with baffel plate to eliminate direct blast on the orifice disk.
3. New flow disk installed with one range and fixed in place. No more multi range flowing [ Only difference I've seen in tests with a SF110 are my bench reads a couple of CFM higher at .050 and .100 lifts. After that, it's so close it absolutely amazes me.

Larry

[larrycavan]

More pics

[larrycavan]

One more

[84-1074663779]

Yes, quite obviously the error can be compensated fairly simply with a bit of thought, I just wanted to keep everyone aware of the problem.

A reservoir works well on the vertical test pressure manometer too. That way a standard steel ruler vertical scale can be used referenced to zero. That is much nicer than having to make a custom 28 inch pressure scale that is really only perhaps (?) 27.75 inches long.