Has anyone designed/built a positive pressure ...

[Tony]

The first flow bench I came in contact with was in the physics department of a nationally accredited standards laboratory. They had several different types of airflow bench, but one in particular really intrigued me.

This worked on the gasometer principle, in that a large weighted gas bell was floated in a tank of water. The weight of the thing maintained a constant internal positive air pressure. As air was added or removed, the thing rose or fell in it's water tank. The height of the gas bell could be very accurately measured, so the volume of air entering or leaving was precisely known. By suitably weighting the bell, a precise operating air pressure could be calibrated.

This monster produced a constant accurate air pressure source for flowing through things for testing. What we had was much smaller than the gasometer in this picture, but the principle was the same. It occupied it's own large building, and really impressed visitors, it was quite a sight.

[Farrell Vaughan]

gte, thanks for starting this thread. I to, want to test at positive preasure. I'm involved with turbo diesel performance. I have a srew type blower to use as an air source and a preasure gauge that goes to eighty PSI and is graduated in tenths of a pound for test peasure. It will be an orifice type bench and move air in both directions. Kind of like Tony's. What I need to know is how to calculate the size of the flow orifices for both preasure and vacuum testing. Would there be a difference in flow value at the orifice depending whether the signal was positive or negative? After that how would I calibrate the inclined manometer to give a percentage of a flow range. I hear the rise on this manometer affects the flow range. Well guys what do you think?

[Farrell Vaughan]

Sorry but I forgot say that I'd like to test around the twenty to thirty PSI range for safety reasons. Boost can be three to four times this in a working engine.

[Tony]

A fairly average flow bench might require 5Hp to 10Hp of power to generate 1psi of test pressure (28 inches).

Driving that screw blower of yours to 3psi will probably require more like 15Hp to 30Hp of drive power. I hope you have plenty of electrical power available to do that.

[86rocco1]

[SWR]

[bruce]

Another thought to put out there is the quality and life expectancy of your orifice plate.

I have one flowbench client that I have been working with who is testing at +100" H20 and plate quality plays a major factor in accuracy at this high of testing pressure. The design of the plate will also need to be addressed.

[thomasvaught-1]

When Ford tested in the 60s for the 427 High Riser program, we tested at 67" of water. A point of reference, the orifice drum was made out of 3/8" thick welded steel plate, (for SAFETY REASONS). 67" H20 is slightly less than 2.5 psi. You are talking about 30 psi for Safety reasons??? As was said, you are talking about a LOT of pressure here, sir.

JMO

Tom V.

[larrycavan]

[thomasvaught-1]

Larry, That is an interesting question:

We tested at 67" H20 (5" Hg) in the Muscle Car years (60s-70s) as we had the ability to test at that pressure with our equipment.

We also flowed at 20.4" H20 (1.5 Hg) as that was the 4 bbl Carburetor standard test point and at 40.8" H20 (3" Hg) as that was the 2 bbl Carburetor standard test point.

Then we added a 5" H20 test point as Bob Mullins (of Hemi Head fame) was testing at some really low test pressures with his hemi head development stuff for MOPAR.

Then when Super Flow came out with their SF-110 bench we had to get a number at 10" of water (.75" Hg) and later we added a 25" H20 point as that was Super Flow's Bench calibration point.

Now the Hot Rodders want to Test at 28" of H20 as that was the point Smokey Yunick mentioned in his book so we added another point.

With the "High Dollar" bench we now just program in all of the test pressures mentioned above and it runs a sweep of all of them for each valve lift point. LOL!

Tom V.

[maxracesoftware]

[106-1194218389]

I think I have a way to strenghten our flow benches to take more pressure. Build just like we are off of Bruce's plans and then put metal banding around the outside. That would not be too difficult to do.

[larrycavan]

[larrycavan]

[Tony]

30psi = 4,320 Lbs per square foot.

3 foot x 3 foot panel = 38,880 Lbs (almost 20 tons)

Best of luck.