first run of bench +orifice disk leakage revisited - lots of leakage with MSD style disk...

[bseibenick]

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[bseibenick]

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[bseibenick]

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[bseibenick]

I made a little progress tonight. I took part of the bench apart and checked a few things and made a solid cover over the exhaust valve to ensure that it was not leaking. I tried the candle idea and found one small leakage where the top chamber connects to the bench. A little silicone and that leak was fixed. I did not find any other leaks with the candle. All total I got the leakage down to 54cfm at 10"wc.

With the exhaust valve sealed and doing an intake leakage test, I am guessing that my leakage has to be coming from the outside into the upper chamber? Assuming no leakage, the differential pressure between the upper and lower chamber should be '0'. Since it is not, something is causing a pressure difference across the orifice.

Hmmm...I guess more investigation.

Any ideas?

[Mouse]

Brian,

It looks like that is about a 2.5" orifice. Kind of big to be trying a leak test. I would drill a 1/4" hole in a small piece of sheet metal and duct tape it to your orifice and try your leak test with that.

John

[Mousehouse1]

Like Mouse suggested. Do your leak test with a small orifice hole. Most use something around 1" hole or a little smaller. How did you seal the orifice plate to the bench? Like you started doing track down each leak or problem one at a time. Don't make more then one change and see how it effects the bench. Then make another change and so on.

[Mouse]

The bolts that go through your orifice locating bracket... are those lag bolts or do they go through the panel into nuts or something?

If they go through the panel, I would try just duct taping the orifice plate in place for a test run.

Don't forget to make use of the FP1 manometer mode (mode 3) to see what the actual differential pressures are, and if there is considerable turblence (bouncing numbers). The manometer mode of the FP1 is a wonderfull troubleshooting tool.

I also noticed your cal orifice is bolted in place. This can warp it. There should be a gasket on your test port too. Try just duct taping it in place for now, or better yet, just smush it down into a thin bead of plumbers putty.

And if you can see inside your chamber through the cal orifice, tape some pieces of threads in there in various places, paticularily near your measuring orifice, so that you can see what they are doing. Long threads hanging from the ceiling just over the orifice are best.

Trust me, when I do design work, it involves a lot of thread, duct tape, hot glue, tie wraps and plumbers putty.



Edited By Mouse on 1141310814

[bseibenick]

I will make up a small orifice plate between 0.75 and 1" when I get home and duct tape it in place. Currently I have t-nuts to catch the bolts that hold down the orifice disk. I will also use some duct tape to cover the intake hole on the top.

Another quick question...with this style bench, what is the best location for the differential pickup tubes and the test pressure pickup tube? I have the test pressure tube mounted to the baffle just to the left of the hole in the top of the bench. I have the differential tubes mounted on either side of the orifice plate, about an 1nch above the the opening to keep them out of the air stream. Could these locations be causing me troube? The interesting thing is that I do not think I am getting much turbulance and the pressure and cfm are not bouncing around.

[bseibenick]

Ok...more progress tonight. When I got home from work I machined up a small square edged orifice with a diameter 0.8750. I taped it to the bench and fired everything up. At 10"wc I have 10cfm leakage...FINALLY. Not perfect, but good progress. I have heard that anything 5cfm or less leakage is considered good?

Some other results...I could not get enough cfm through my 0.8750 orifice to calibrate it using the 118.8cfm plate Mouse sent with the FP1. I put in my 1.7500 orifice in the bench and got it calibrated with a cd of 0.2152. From what I understand, that is a low cd? I also tried to calibrate my 2.4980 orifice and with a cd of 0.0001 in the FP1 could only get 131cfm @28"wc...I am guessing I do nont have enough motors in my bench for that size orifice.

I am kind of curious why I get a different leakage number with different size orifice plates in the bench? To me that does't make sense...

[larrycavan]

I would consider painting the top of the top plenum where you mount your calibration plate and head adapter....

Also, make up a small probe out of some small id tubing and connect it to the fp1....probe around the seams with it and see if you pick up any leaks...

maybe mix up some soap and water...look for bubbles like the gas man does.....

Larry C

[larrycavan]

[Mouse]

The problem with using an orifice that is too big is that you are measuring differential pressures that are just too low to be reliable. If you are only getting .013" dif pressure across your orifice, the accuracy falls way off.

I believe that you can also get bidirectional air currents through an orifice that is too big measuring flow that is too low.

[bseibenick]

The top of the plenum/box is painted on both top and bottom...the sides are only painted on the inside. That is what you are seeing in the pictures. Would it help to paint both sides?

[larrycavan]