first run of the bench - first run

[cboggs]

Well gang, .. got the bench running today, ..

had it going with all the flow ranges open since the rubber stoppers
hadn't showed up yet, ..with my SF calib plate from my 110 on it, ..
pulling 36" with no problem ,, .. manometers steady as a rock, ..

then, .. BLAM !, .. .. the dividing wall in the lower chamber that
has all the motors on it broke in 1/2, .. .. guess I needed
some form of support :p

We're going to perform the repairs tomorrow and get back to it.

The good new is it looks like it'll pull 600 cfm @ 36" with no problem
at all, .. and likely much more, .. and the manometers where very
steady, .. my manometer only goes to 36", .. so I can't wait to hook
up the digital stuff and see what this thing can really do!

this is going to be a killer bench I think!!

Curtis

[Thomas Vaught]

Curtis, If you look at the old MSD bench pics you will see threaded rod where they had to patch up their dividing wall after an issue.

Wish I had a nickel for everytime someone has told me that story in the last 20 years.

I talked to a couple on the board by phone so far and both have revised the plenums to make them more robust.

My latest bench is designed to have a double wall of 3/4" thick (1.5") in the upper and lower plenum
chambers and the motor wall and other walls supporting each other.

Amazing the amount for force that a little depression of 36 inches of water can have on wood.

Very rough calculation:

20.4" of water = 1.5" of Mercury.
30" of water is about 2.2" of mercury.
2.05" inches of mercury = 1 psi.

So if you figure the square inches of your dividing wall it saw a pretty good force for being unsupported except at the edges. Every square foot has basically 144 lbs on it. A 24"x24" plenum wall would have 576 lbs for force trying to cave it in.

JMO

Tom V.

[86rocco]

Thanks for sharing. I'll consider this a cautionary tale, I was wondering how much bracing and extra support I'll need to put in my bench, after reading this, I think I'll err on the side of overkill.

[Mousehouse1]

What kind of wood did you use & how thick? Did you use screws on all sides around the perimeter of the board?

Mine is screwed from the bottom, front, top & back. I didn't put any side supports in but might if need be.

[larrycavan]

[Nick]

I used a lot of 2x2 with liquid nails. The is no more than 8in of board without a 2x2 support. I had a similar result the first time I put the hurt to mine, then came the braces. Now there is no deflection in the panels. It's amazing what a little vacuum can do!!!!



Nick

[Tony]

Not trying to scare anyone, but if the test hole becomes accidentally blocked, some vacuum motors can pull as much as 4psi at zero flow. That is 576 Lbs per square foot.

Fitting some sort of pressure relief valve may be a good idea. At least you will then know pressure can never go higher than what the safety valve is set to.

[cboggs]

Larry,

We made a second board to double up the divider today, .. gotta go
get some liquid nails tomorrow and install along with the few braces.

I've got three 2"x2" braces to put in each side, ..

I like the idea of a pressure valve incase it gets plugged, ..

Tomorrow night, .. I'll try to fire it again, .. but gotta tie down everything in
the shop first, .. and remember not to wear any loose fitting clothes!

Curtis

[cboggs]

Oh almost forgot, heres a photo of the split divider board.

Curtis

[larrycavan]

[cboggs]

OK gang,

Got the divider fixed, chambers sealed & painted, .. and ran some basic tests.

This is where I'm going to need some help.

First, .. I spent 2 hours today moving the pressure pick ups for the inclined
manometer all over the place and can not get rid of the "bounce" in the
manometer. It'll jump about a 1/4" on the scale, .. not a slow "wander"
but a fairly violent bounce.

I'm assuming I have a turbulence issue in the lower chamber. Moving the
lower pick up is the only thing that seemed to have any effect.

Anyone have any ideas about this????????????

Now one thing that may be effecting it is the flow rate valves.
I just used the standard old stainless salad bowls in a hole cut in the
bottom of the chamber, .. .. and upon farther inspection they DO leak.
Would this make the inclined manometer jump around??

Any ideas for a better way to do this or a way to fix this????????

The side doors, .. we all know that story. they work fine when running an intake test
but on an exhaust test it just tries to blow the door open.
I'd like to find a large gate valve, .. or I'll close them off and use Tom's port holes.

The good news is I ran Bruce's calibration plates, . I have a 90cfm, 160 & 400.
My 100 cfm range seems to be very close, .. 400 cfm seems to be +15 cfm, ..
and the 200 cfm range seems to be closer to 250.

I just ran the plates and haven't gone though a calibration as I want to fix the
turbulence or bounce in the inclined manometer first.

I've got a TON of work backing up in the shop, .. I have another flow bench but I have some
rather large heads to work on and would really like to flow them at a faster speed.
I need to get this thing working so I can go back to making money.:p

help???

Curtis

[larrycavan]

[Mousehouse1]

Another cure for the leaking exhaust and intake doors is to use deck plates. Buy the beckson ones. I haven't had any trouble out of the ones that I bought.

I like the silicone idea Larry. I was going to use rubber material under my bowls to help them seal but I might try the silicone method first.

Curtis I like Bruce's plates as well. I had him make me 5 total and they range from 150-700cfm. They were all within a few cfm and cd of his numbers. The cd's weren't more then 1-2 off of what he had written on them.

[larrycavan]

Yep...that Bruce guy makes some nice calibration plates...it's almost like he's done two or three of them at some point in his career....

Larry C

[Rick360]

Curtis,
In the pic of the broken board it looks like that is made of particle board. Is that right?? If so, that is much weaker than plywood and isn't made for the same type of loads as plywood. I would not use particle board in this application.

Rick