Inclined Manometer Not Steady

[kiwibuilder]

I have built a flow bench based on the msd bench, but a small problem is stopping me from being 100% happy, my inclined manometer under testing tends to flaot, it can move as much as 2 to 3 markings on the scale, i have come to the conclusion that it is possible turbulance within the bench, has anyone had the same problem, if so what did you do. Has anyone fitted a flow straightner to the top chamber.

[larrycavan]

[kiwibuilder]

My problem happens with most parts venturis, carbs, exhaust ports (2 stroke) yes it is the inclined scale i was reffering to that is unsteady. When testing i always stay above 60% flow on the inclined scale with test pessures 20 - 28 in h2o on the vertical manometer. Inclined manometer will not hold steady with a constant test pressure the fluid moves up & down about 2 - 3 marking on the inclined scale kinda hard to describe.

[larrycavan]

Without any details or sketches of your bench to work with, it's difficult to pinpoint the exact cause of the problem. However, I suspect it's the location of your inclined manometer probe [probably the top plenum probe but the lower probe could cause it as well].

If you can reach into the bench and install a length of plastic tubing over the end of the top plenum probe, you can then relocate the other end of the tubing to a quiet section of the bench and see if it helps the situation.

What's a little unusual is your vertical manometer holds steady. That indicates to me that the location of that probe is a good area for you to test the inclined manometer probe location, unless you have located that probe directly in the test cylinder.

A sketch or photos of your bench would help to resolve the problem if the above fix doesn't work for you.

[RRBD]

I noticed the same thing on my bench when I get close to 100% on the inclined using the biggest flow tube. Could it be the motors fluctuating? I use a dampener in the manometer lines to slow it down.

[bruce]

Install a peice of cotton ball in the lines leading to your incline manometer and see if the problem goes away. The cotton ball acts as a filter/dampener and takes away the pulsations. This worked for me on my bench when I was using water manometers.

[kiwibuilder]

Thanks for the reply all i have moved the manometer pickup pipes around before this i think did help a little tried both top & bottom chambers & yes the my vertical manometer does also jump about it also drops but only about 1 in h20 or so. I have the vertical test pressure pickup within a fixture i have made to mount parts into with 5 small holes around the pickup to equalize airflow. I have not tryed vertical manometer pickup from the same pipe as the inclined scale.