HOHN

It turns out that the materials cost about $20. Not too bad.




Here's a closeup of the water level (uneven because I closed the valve and the atmospheric pressure changed):


Setup this way, with the basal water column balanced at 24", I can measure up to almost 48" of water column, or about 1.7 PSI.

A single inch of water column depression is .036 PSI, so I have a good amount of precision available with this cheap concoction. Most I can read from a distance is about a 1/4", so that means my resolution is .5" WC, or right around .018 PSI.

At the top, I have a shutoff valve vented to atmosphere and a pressure port to which I can connect something to get my readings.

The nice thing about this setup is it can measure both pressures less than and greater than atmospheric. That means I can MEASURE just how restrictive is my intake on my truck.

...OR I can measure the amount of backpressure in the exhaust on my truck. I believe that the stock exhaust with the stock turbo isn't that restrictive, and this will let me put an actual number on the backpressure in the exhaust, to even a a small fraction of a single PSI.


Now, this isn't a perfect manometer. The water is tap water, not distilled-- and I can't guarantee that it will be perfectly vertical in testing and usage.


But it's close enough to make some fairly accurate generalizations.

jh

PistolWhipt

What cha gonna use it for ..... weather predictions ??

PISTOL

HOHN

OK, I was wondering if people really knew how useful something like this can be. In addition to predicting the weather (it acts as a barometer when the valve is closed), it has some other uses.

Ever wonder how restrictive your intake is from the factory? Ever wonder just how much of an improvement in flow is that hi-dollar cold air intake?

This will tell you-- scientifically.

Ever wonder just how restrictive your stock exhaust might be? Ever wonder if a larger exhaust is worthwhile on a stock turbo? I have, and this will give me the answer.

This thing is so sensitive that the weather change overnight produced a change of more than an inch of water column-- and the weather hasn't changed much at all! One inch of water is about 2.5 millibars-- not much.


So, if there's any appreciable restriction in airflow to something I want to measure, this little (ok, 4ft long) device will detect and quantify it.

Next step is building a flowbench with multiple manometers, but it's hard to do that under my present circumstances.

Høhn

HOHN

Here's a little FYI piece for those who aren't up on a manometer's function:

A manometer measures pressure by comparing column height differential in a working fluid of known density.

As pressure increases or decreases on one side of the manometer, the fluid displaces by a certain amount. This amount is not arbitrary-- it is a balance of forces. On one hand, you have the force exerted by the measured pressure (typically atmospheric, or whatever you are measuring). On the other, you have the force of gravity on the column differential.

When the pressure on both side of the manometer are equal, the column height are identical. But as pressure is increased on one side, the columns "offset" this increased pressure by increasing the force of gravity acting in the opposite direction.

When the column heights are equal, the gravitational forces on both sides are equal. But when one side is higher, gravity acts more on that side.

Let's say I put 100 lbs of water in a tall thin cylinder that has a cross-sectional area of 1 sq inch. At the bottom of that cylinder, I will have 100psi of water pressure (if I plugged a hose into the bottom), because gravity is acting on the mass of the water to create pressure. Remember, Pressure= Force/area. So when I have a force (gravity) acting on a known area, I have pressure.

This is why there's a limit to how high you can suck something up through a straw. That limit is where the weight of the fluid in the straw is equal to the force exerted by the atmosphere on the fluid.

Say you have a straw that's 30ft long and you're standing on a ladder sucking up water as high as you can. You're at sea level on a standard day with atmospheric pressure of 14.7 PSI.

The amount of water (in volume) that you can suck up into the straw will depend on the diameter of the straw-- but the HEIGHT of the water will not change. If you have a small straw of .1 sq inch area, then you can suck up a maximum of 1.47 pounds of water into the straw. If water is around 8.3 lb/gallon, then you have less than a quart in the straw before you can't suck it up and higher.

But if your straw is one sq inch in sectional area (10 times larger), you can suck up 14.7 pounds of water (weight of water= atmospheric pressure). This is almost two gallons.

How high would the water go before you (or even a vacuum pump) couldn't suck it up any higher? Given the tube of 1 sq inch area, and atmospheric pressure of 14.7 psi, you can get 14.7 pounds of water in the tube. This is about 1.76 Gallons. In cubic inches, this is 407 cubic inches in round numbers.

Since your straw is 1 sq inch in area, this means you can draw up a column of water 407 linear inches, or almost 34 feet.


So no matter how hard you suck on the straw, or how big it is, you'll never be able to drink through a straw longer than 34 feet.

All that to say that my manometer measures pressure differentials above and below atmospheric with pretty good precision and very low cost.


Hºhn

AlpineRAM

I use a contraption like ths to sync carbs on bikes. You just need a snubber on each end to keep the fluid from pulsating.

Hohn- On the intake side I think that this contraption will be a primitive water injection if you start to rev with a stock air filter.
(At least that's my opinion from reading several inches hg from the filter mfgs websites using the cfm from your turbo calcs)

AlpineRAM

BC847

That particular design is called a "Slack-Tube" manometer.

I use one regularly in my HVAC work.

- To set the running manifold pressure on LP and natural gas burners. 10" for LP, and 3.5" on natural.

- To check/adjust static pressures in air handling ductwork.

- Used with "Pitot Tubes", to check/adjust/regulate air flow.

While one can use a manufactured mechanical gauge to do the same, ultimately the question of calibration comes up. With the liquid based manometer, it's just a matter of setting the scale pointer or topping the fluid as needed.

It's a VERY useful tool.

HOHN

I'm hoping to avoid a siphon-injection setup! Keep in mind that I have the huge Donaldson unit on my truck, rated 1000cfm @ 8", so it's not much of an issue. That said, I'd like to see for myself the pressure drop of the filter.

I'll have to be very careful that I don't exceed 48" depression or I'll have a big red food coloring mess

cincydiesel

This post exceeds my IQ level. I'm going back to my cave now. Thanks Hohn

Howy

Nice looking setup. I may just have a new little project. I use these at school when we're doing flow testing in our water tanks. I like that you add some food dye to the water. We never did and at times it can be hard to read the measurements. Manometers are pretty simple handy tools. Thanks for posting this up. Its good general science a lot of people should know about.

Have a good one.

1-2-3

We used to use them on paint booths to monitor filters. If your tube was long enough, you can use it as a water level. You can set things perfectly level hundreds of feet away from the source point.

grantx5

In college we used a thing like that to suck beer out of a keg. There was very little pressure involved, well, until about an hour later then we all had to run to the head.

AkitaSumo

We use a much more expensive one to measure and validate the back pressures in our air cooled boxes...

AlpineRAM

You will see that the design of the connection does play a big role- if you don't take care the venturi effect across the open end of your connector will create a vacuum that is not relevant for your turbo but still wreaks havoc with your meter. I think it would be nice to know the pressure distribution right before the turbo- one could estimate the velocities there.
I have been wondering about the intake hose setup on these trucks- and whether it might be beneficial to supply air with just the compressor intake diameter and maybe 2-4 guiding fins instead of the setup with the big difference in diameter that is used. (I don't claim that my idea would be better, just that I do not understand the logic behind the way it is done at the moment.

AlpineRAM

Dieseldude4x4

We have to use one very similar to that to test the drop across the after coolers on the EMD's here at work. Nice job.