Getting New Bench Working

[bubba2400]

Ok, my friend and I have been working on putting a homemade bench together. We made some water manometers together just to get the thing working and to make sure we were capable of building one.

I bought a 250cfm @16" orifice plate from Bruce and also a 250cfm @28" calibration plate to verify our readings are correct.

We used 8 Surplus Center 240 volt motors. I used Rocco's spreadsheet to make the inclined manometers scale with a 16" pressure differential.

Now on to our issues: With the 28" plate on the top of the bench and the 16" plate on the inside I can crank up all 8 motors and set the U-manometer to 28" depression. When this is accomplished I am only showing around 50% flow?????

From what I take of this is that there is a ton of air leaks. We did not build it to be able to reverse the flow so it's tuff to look for leaks. But I have caulked every place that I could think of that may be leaking air. Also painted the inside of the of the flowbench before the front panel was put on.

So, after all the rambling, any suggestions of what is going on?

I plan on buying Bruce's plans and rebuilding this thing in the spring, but would like to see it kind of work if possible in the current state.

Thank you

James

[Brucepts]

Test the 250@28" plate the following and see if you can get any of these to match up:

133@8" 149@10" 189@16"

Might give you an idea of a leak and how bad it is at various differential pressures?

Setup another U-tube laid over to give better resolution, attach a tube to it and run it around the joints looking for a leak.

[bubba2400]

8" - 75cfm
10" - 87.5
16" - 106.25

This is what I came up with. That seems really bad, it's just over half the flow it should be. Do I have something else wrong somewhere?

I would think with that much leakage I could feel and hear it pretty easy but I can not hear or feel any air movement. Even tried spraying water to see if I could see a spot where it sucked in and didn't find anything.

I also hooked up a vacuum gauge in the chamber below the orifice plate and it was reading 2" of vacuum.

[1960FL]

Bubba,

Your incline does not look to have 16" of Rise i did a quick scale on the picutre and it looks mor like 10" or 11". The 4 blocks you see are sections of your 2 x 4 band on the front so each is aprox 3.5 inches or 14" total and as you can see they are higher than the scale you are using. it does not matter the angle of the incline but the rise must be the same as the DP of the plate.

Rick

[bubba2400]

I was playing around with the inclined when I took this picture. It is not mounted on the bottom so I can swing it slightly so it wasn't quite 16", and the bottle is not mounted perfect just yet, just taped in place so it was not up where it should be in this picture. But that also shows that it does not work correctly. At a lesser drop the water should move farther than it does. Right now it only shows around a 6" pressure differential.

Now, if the motors could not pull enough vacuum for some reason would I be able to pull the 28" on the test piece, or in this case the calibration plate?

The way I am seeing this if I can pull the 28" and more on the test piece then below the internal orifice plate should have the correct pressure differential unless it was leaking air from above the internal orifice. Does that sound correct?

Thanks again

[Brucepts]

Where are your pressure pickups located?

Is one of them clogged?

Setup your incline and u-tube so they are both measuring static pressure from the same pickup and compare the two by running your flowbench up to 16", test all the way up the scale and verify they both follow each other.

[bubba2400]

Attached is the picture with how the bench is built. The pressure pickups are located in the rear wall of the bench. The pickups are just barbed fittings that are screwed in to the back wall with .250" clear tubing connected. So basically a .250" hole or so in them.

The motors are located in a divider wall just to the right of the ball valves that bleed air in.

The well for the inclined manometer is about 2" ID. One question on this, how does the inclined tubing and well diameters affect the inclined manometer?

I will test the two manometers tonight to verify they both read the same.

[Brucepts]

Move your upper inclined pickup down to the same distance above the orifice plate board as the lower one is below the plate board. May or may not make a difference but it works that way in my PTS design

The well diameter and incline tube diameter are in the spreadsheet calculations and need to be taken into account

[bubba2400]

Ok, so I may need a little explanation of the Delta P column in the spreadsheet. What do I use that for? I used the spreadsheet to make the percent scale for the inclined manometer but that was about it. Which I though I just used the delta S column for that????

Thanks again for answering all the newb questions!!

[bubba2400]

Got the bench to work tonight. Was doing some reading and found where we needed to put a baffle between the entrance to the bench and the orifice plate. Did that and everything reads right on.

Now we need to fine tune everything. Going to router some grooves in a board for the u-manometer so that it is perfectly straight, which it is not right now. And get a more accurate scale printed up for it.

Also router a groove in for the inclined manometer to make sure it is straight.

Right now we are right about perfect on the readings but I don't want to make anything too permanent until I get the things above taken care of.

I also ordered the plans from Bruce today so will be making a few changes this spring to this bench.

Thanks for all the help everyone.