Flowbench design

[Brendan]

Hi
I am looking at building a flowbench to flow around 600-700cfm @ around 28'' my budget it $2000 or less I would like to the flowbench to be electronic rather that the traditional manometers.
Electric is not a problem as we have 400 amp 3 phase power.
I also have a procharger blower that could be used or should I use
Ametek electric motors(that I would have to purchase).
I want simplicity and repeatibilty, way to many options to choose from, I also purchased the Mercdog plans.
Lets hear the opinions on what is the best design considering the requirements?
Thanks!!!!!!!!!!!!!!!!
Brendan

[ThomasVaught]

First off, welcome to the board.

Quote:

"Hi
I am looking at building a flowbench to flow around 600-700cfm @ around 28'' my budget it $2000 or less I would like to the flowbench to be electronic rather that the traditional manometers."

If you are considering ametek motors, a few comments:
1) The best ones to use are the 115923 Two Stage motors (Same ones the Blue Bench guys use). 2) They are about $100.00 each but at times you can get them cheaper. 3) They are 110 volt units.

If you use your procharger unit, you need to post which unit you have
as most of their units are for race cars and are over capacity for what you are doing and not very efficient at low rpm. Say you wanted a bench with 1000 cfm capability: The actual "Boost pressure" out of the blower for 68" of water (5" Hg) would be 2.456 pound/square inch. It probablywould require a 15-20 hp electric motor to drive the thing too. Most centrifugal blower set-ups in the old days were at least 10 hp three phase (208 volts).

Quote:

"Electric is not a problem as we have 400 amp 3 phase power."

See above

Quote:

"I also have a procharger blower that could be used or should I use
Ametek electric motors(that I would have to purchase)."

See above

Quote:

"I want simplicity and repeatibilty, way to many options to choose from"

With electric Vacuum motors, once in a while one goes bad. You need to
design your bench so that you can service the bench when you need to.

Repeatability is more of the measurement strategy that you use.
Orifices will work with either manometers or electronics. Same deal for
pitot tubes.

Quote:

"I also purchased the Mercdog plans"

Here you are probably not going to like the answer I post. The plans are based off of several FREE magazine articles on the web. The plans are not very good compared to the vast info on this board. IMO you made
a mistake but now you can easily correct it by being a member of this board with minimal loss of funds (cost of the "plans"). The members here have built a variety of excellents benches vs the M bench plans.

Quote:

"Lets hear the opinions on what is the best design considering the requirements?"

You have my opinion.

Quote:

"Thanks!!!!!!!!!!!!!!!! Brendan"

No Problem, again welcome.

Tom V.

[Tony]

Welcome to the Forum Brendan.

Thomas has summed it up very well, and there is little I can add. As you already have the procharger, I would first either try to either get some flow curves for your exact model, or just do some tests.

As you have an "unlimited" power supply, efficiency is not as large an issue as it would be with very limited power. But Thomas is right, it will probably require about 15+ Hp to drive the thing, but a suitable three phase drive motor should cost almost nothing of you hunt around.

The design of the bench is entirely up to you, there is no "best" way to do this. Spend some time going through past threads, there are some vastly better and truly innovative ideas here. The Mercdog design has some fairly serious shortcomings which you should research here before starting construction.

It is all here on this Forum, you just need some stamina to read through it all, but your patience will be well rewarded.

[Brendan]

Thanks for the great responses, so if I go with the Mercdog design what changes would you make?
Fixed orifices with plugs?
easy motor access?
and what other changes?
I think I will use the FP1 for measurements.
Thanks!
Great information!
Brendan!

[tweaks]

Hi Brendan,

as Tony said there are a few shortcomings with that design... it would be best if you looked up mercdog bench in the search engine and read the various articles from the members...that way you will be able to understand the various short falls with the bench and see what other members did to rectify them

Best of luck

Lynds

[larrycavan]

Hi Brenden,

I have an MSD bench that has been tweaked to work properly. 2 problems with the bench were the MSD orifice disk and lack of a baffle. They're easily cured.

If I were to do it over again, I'd go wider with the cabinet design.

Vacuum motors [especially the number you'd require for your goal] are extremely loud and annoying.

I have electronics on my bench. They were by far, the single biggest advancement in DIY flowbench technology.

Pitot or Orifice....doesn't really matter. Both work equally well for most purposes. If I were heading down the road toward 700 CFM capacity @ a minimum of 28" and using orifices, the one thing I'd make absolutely certain of is to have plenty of cabinet volume and offset the test stand from the measuring orifice by a good margin.

Look over the different designs you'll find here and take your time with the project. Careful planning and accurate workmanship is the ticket to success without pulling your hair out.

Larry C

[bruce]

[Tony]

Larry raises an interesting point. If the maximum airflow is planned to be on the high side, there is no real substitute for scaling up the size of everything. Flow areas and internal volumes should be made larger, there is no disadvantage in doing this.

On the other hand, there may be some real problems created within the bench if everything is made too small to do the job.

Put another way, a huge bench is likely to avoid many problems that a mini bench design may encounter at very high airflow. Size is important!

Another thought to bear in mind is structural strength. Twenty eight inches is 1psi, or 144 Lbs per square foot. There can easily be thousands of pounds of force on those wooden panels, so it needs to be built very strongly.

As for hair, bald heads are definitely are more aerodynamic, and that can be an advantage.

[larrycavan]

[ThomasVaught]

Superchargers are not quiet! LOL!

Lots of gear noise in their set-up transmission, some belt noise, etc
so nothing will be perfectly quiet.

The best blower for a quiet flow bench in my mind (using an automotive
supercharger) would be the Powerdyne (internal belt step-up) unit. Very
quiet and enough airflow for most benches. (more than the old Paxton
ball drive units used many years ago).

Some of theblower units like Tony has and Bruce is building might work even better with their high tip speeds due to their large diameters.

Vacuum motors work but as was said have terrible nvh.

Tom V.

[Tony]

If you want silence, begin with a three phase induction motor driven off a VFD. Direct couple that up to a large diameter, low rpm pressure bower. Apart from the unavoidable roar of air movement, there will be no additional mechanical noises at all. Feed the exit air from the blower outside, or as far away as possible. The bench will be no noisier than a small window airconditioner. Normal relaxed conversation is easy with the bench running absolutely flat out, and your hands on the controls.

[Brendan]

Thanks for the great responses!
Still not sure if I should use the procharger the electric motors sound like less work!
I read that Bruce was working on some plans for a new flow bench an word on when they will be avaliable?
Thanks!
Brendan

[bruce]

I'm working on the plans but have a little "glitch" that I'm trying to workout with the gauges . . . additionally, I'd like to build one first and make sure it works as designed before offering the plans but that might take a week or two. I'd hate to have it "field tested" and then find problems with the design.