Baby Bench, - How small is TOO small?

[rusty105]

Ok, I have to change my plans a little. I was working on a design about the size of a SF600, or the size of the PTS bench, BUT I don't currently have the room for it. I do think I have the room for a SF110 size table top bench, but I am worried about capacity. The heads I am working on stop around 225, so large capacity is not needed, for now. What I am thinking about doing is something table top sized, I can mount the manometers on a wall, or get the PTS DIY digital manometer setup when it is ready. I am thinking about mounting the fans outside the box, OR using 2 shop vacs in parallel. I do realize that 300FCM @ 28" is not likely to happen. But this is also a learning experience. Will a 3'L x 2'D x 16"H be a good size box? This will be an orifice design, hopefully 2-way flow. The head adapter would mount on top of the 'box'. I am just wondering if the roughly 6cf of internal volume will be enough? Can I go smaller?
If there has been a discussion on this, can someone point me in the right direction?

Thanks
Rusty

[86rocco1]

How about something like this? It's sort of styled after the SF120. Two sets of orifices with stoppers, eliminates the need for any internal valves or moving parts other, the large deck plate provides access to the orifice stoppers. The small deck plates on the side are for flow direction control. To test on the intake side, remove the deck plate on the exhaust side and put all of the stoppers in on the exhaust side orifices. A couple of speed controllers for the motors could be used for depression control.

[Tony]

Screwing the manometers permanently to a wall is an excellent idea. It takes up zero space and there will then be no problems with spills or levelling. I have done this myself.

An external blower box, or multiple shop vacs can be removed and stowed somewhere else well out of the way. It also allows simple flow reversal and is a great way to allow future flow upgrades.

The flow measurement part of the bench should have as large a settling volume as possible. The only disadvantage of a really compact bench will be air turbulence around all the tight corners inside. Size is one factor, but flow is another. A small low flow bench, should work, but as flow volume increases, the problem of internal flow turbulence also increases as internal bench velocities rise.

Turbulent flow inside the bench can cause unstable flow measurement which makes precise and repeatable flow measurement more difficult.

Big is beautiful. A smaller bench may need to have a lot more thought go into it to avoid problems of internal turbulence..

[106-1194218389]

Here is another approach. I did this to use the 2 shop vacs I had at the time. It was as you say just a learning experience and I wanted to see how it worked first. It worked beyond my expectations. Here is my bench for now I basically just built the chamber side of Bruce's bench plans. It is 24" square and 33" tall. I then hooked the shop vacs to the bottom chamber with PVC Van Stone flanges. It's not pretty right now but it is accurate. It flows my SBC heads 263 CFM at 10" H2O. One shop vac is a Craftsman 6.5 HP and the other a 4.5 HP. I have a space problem right now also so this fits nice. When the time comes to move it out of the basement it will not be as hard as it will be modular. I am in the process of building the motor side of the cabinet with 8 motors and I will hook the two cabinets together with 2 3" PVC pipes going through Van Stone flanges. This is just a differnet way to go. There are some pictures at that link.

John

[rusty105]

[bruce]

[106-1194218389]

[rusty105]

[106-1194218389]

[rusty105]

OK with the speed controllers

Ok, here is a sketch, not the best, I have been using CAd too much and I am a little rusty with the pencil. But I'll work on a CAD file once I get some ideas sorted out.

The 2 ports on the right side are for the vacs, the hole on top is for the hear adapter, the square hole is for an orifice plate, and the baffle plate is to the left of that. I was thinking of having the baffle plate to be about 2-3 inches smaller on all sides to allow air to flow around it. Most likely 2 deck plates in front to gain access to orifice plate.

Any comments??

[106-1194218389]

You are going to flow exhaust by blowing aren't you? I did this with my shop vacs just by reversing the hose. If so you will need a baffle on the other side of the orifice also. Looks good though I would try it for sure. I had also built an orifice in a tube using 4" diameter PVC and it was getting close. The ones with 6" PVC were getting pretty darn good also as the bigger tube was acting like a chamber and we were putting 24" on wither side of the orifice. I think yours would definitely suffice. That what this forum is about, building for your needs. I would say DO IT!

John

[rusty105]

Yes, blowing. I have an idea for the baffle on that side. I was thinking of using two PVC "Tee"s on the inside of the box, and having a 3", or so, PVC pipe running between the Tees , cap each end, and drilling 1/2" or 3/4" holes to perforate the 3" PVC. Sort of like a header. I think it would spread out the flow quite a bit.

[FPV_GTp]

[rusty105]

Sorry it took so long, no updates, yet. I have been working on the plans a little in Autocad, so I should have some nice looking models next time I post some designs Got side tracked a little $$ wise, but starting to get back on track now. While I was off track I was looking at how to buy/build a inexpensive head adapter, but it looks like that is going to cost more then the whole bench minus the electronics.

As far as the website it needs a good kick in the pants to get going again. I am upgrading the forum software in the next week or so, and that should help with stopping the unending flow of junk registrations that have me deleting 100's of users at a time I had to set it so that I have to activate each and every new user to keep the rif raf out. it seems that I delete far more then I activate. But thanks for the good word. When I am done upgrading stop by again.

Rusty