New here - thinking of building my own Flowbench

[saltfever]

I am a new “wana-flo-be” as well. I saw the title of this thread so I hope I am in the right place.

I can see there are a ton of valuable posts on the forum and it will take me a long time to assimilate everything and come up to speed. I won’t bug you with a lot of inane questions until the neurons have at least grasped a few nuggets. However, as I am moving through the forum, I would like to at least be headed in the right direction. With the collective wisdom here, you can instantly tell me if I am wasting my time or should be taking a different approach.

I have a 4-71 Roots blower in good condition and I was planning on driving it with a small 6 or 10HP Honda motor. The 4-71 will give me 493 CFM (in free air) at 3,000 RPM. I plan on working on a small motor with port flow less than half of that. Everything I have seen so far is focused on electric motors which make sense since they are clean, quiet, and controllable. But is my idea workable? Do you see any problems?

[saltfever]

Repeatability of FB numbers is paramount. My understanding is the PTS design removes the influence of power variables while David Vizard’s design does not. If a FB is immune to the variability of a power source there is greater choice. Kilowatts are expensive and there is usually no 3-phase in a residential neighborhood. 3-Phase converters add even greater inefficiency and cost, and high horsepower electrical motors become even more problematic. A gas motor has none of these limitations. RPM on a gas motor can be precisely controlled with a PID loop.

Is a gas motor design a bad decision right from the start?

[Brucepts]

Is a gas motor design a bad decision right from the start?

No just different

Electric offers convenience of use and compact space requirements.

8 motors in a box will flow ~600@28" and sit in a space the size of a desk and use roughly 30-40amps of 220v

It all comes down to what your end goal is . . .

[jfholm]

Repeatability of FB numbers is paramount. My understanding is the PTS design removes the influence of power variables while David Vizard’s design does not. If a FB is immune to the variability of a power source there is greater choice. Kilowatts are expensive and there is usually no 3-phase in a residential neighborhood. 3-Phase converters add even greater inefficiency and cost, and high horsepower electrical motors become even more problematic. A gas motor has none of these limitations. RPM on a gas motor can be precisely controlled with a PID loop.

Is a gas motor design a bad decision right from the start?

Here are my thoughts on the subject. We will give you suggestions from our experience and "opinions". Ultimately you have to make a choice that is "best" for you. Most of run our flow benches in our small garages or shops that are a little tight and cluttered. Or even in our basements, like mine was for awhile. I could not use a gasoline engine in that case. A gasoline engine has a lot of advantages that I can see. Here are some things that may make it feasible. If your shop is out in the south 40 acres and not enough electricity to it then the gas engine, even diesel, would be the choice.

Here are some thoughts though. With an engine like that you will need a cooling system. If it is in the shop with you expect some heat build up. Our dyno room would get pretty darn warm running just small 4 cylinder engines. Also all the GMC blowers I have been around are incredibly noisy. If the heat and noise is of no consequence to you then the gasoline setup is probably a match made in heaven for you.

I personally picked vacuum motors as they are the most available and the easiest for me to setup. I will have 60 amp 220v outlets in my garage so for me that is the logical choice. For you the choice is what is the best for you not for me. So the gasoline engine may just be the way to go. Just sit down and figure out the things like cooling system, power transmission to drive the blower, area available.

The PTS style flow bench takes up little room, about the same as a small desk. I have seen other high pressure, high flow benches that would fill my house. Good luck and keep us informed on your progress as we are all more than willing to help. This is a great forum.

John

edit: I was digging around to see if I could determine if 10 hp would be enough to drive that blower or not. I do not know, but the top fuel guys claim it would take all the horsepower of a stock 426 Hemi to drive one of their blowers.

I did find this link to an online supercharger book that looks pretty good: http://books.google.com/books?id=190v57 ... er&f=false

[Tony]

Funnily enough I am putting together a 7KVA standby power generator for out in the garage right now myself.
Main issues are size and noise.
Flow benches are pretty noisy from air roar anyway, and having a gas engine and a roots blower all running together will be deafeningly loud unless you think the whole thing right through and plan the noise aspect very carefully.

But I see no reason why it would not work, and work very well.
I would mount the gas engine and blower remote from the actual bench, at least on the other side of a solid wall somewhere, and run some very large diameter plastic pipe to the bench.
And as you suggest, throttle the engine from a PID loop that works directly off flow bench test pressure.

The simple way would be to get one of the the Forum automatic test pressure controllers from Bruce.
This already has the tunable PID loop that you need, and outputs a dc control voltage.
That could be used to run an ordinary analog servo to operate the carb throttle on your engine.
As far as I know you will be the first person to do it this way, but I see no insurmountable problems.
This whole idea actually makes a lot of sense.
Dare to be different !!

[1960FL]

Ok, I got a hook in my mouth and will try to spit it out as a pseudo neigh sayer, but now one of the older members here.

We all start off dreaming to build a 1000CFM at 100” depression bench, then we read and learn and think and dream and read and research and add up dollars and so on and so on. The next thing you know it’s been two years since you started the process and still no bench. Me I was gong to build a 16 motor servo reversing valve monster all to flow some heads that may flow 300CFM at 28”. After years of helping other build great benches I invested in Bruce’s plan to have panels cut by CNC cabinet makers, I think my panels are set #’s 3 & $ but who cares there not signed by Bruce so they wont be worth anything in 100 years like if it were Smokey of Grumpy or… But I digress; My recommendation to you is to build a PTS bench with 8, 10 or 12 vacuum motors, get it done learn the basics and start flowing…. Your data will be good as the PTS bench is accurate and repeatable and I personally would trust the data from most any person with a PTS bench and DM with Bruce’s plates.

Now for the kicker, After about 12 months of working on that PTS bench your head will be spinning and if you are addicted to flowbenching and improvement you will “WANT MORE!”. Here is where your 471 and gas engine come in, the way I see it your will have a great foundation in which to build a full on WET FLOW bench without electricity and able to even pump out the waist fluid if you so desire…. In this configuration depression control is not all that critical as you are looking for the visual and with the power you would have “If constructed properly” you could wet flow at some pretty high pressure differentials and maybe see even more.


This is my silly opinion.

Rick


PS. I like different

[saltfever]

Thanks to all for the very quick replies. I was going to quote individually, but to save space; I’ll sum it up here. Actually, I see I didn’t save any space with this long winded reply. But this is a onetime reply to get my idea on the table. Future posts will be more streamlined.

Thanks, Bruce. I’m in learning mode here . . . and I am slow and busy, so it will take me weeks of forum education before I start building. I changed the title of this thread from “Building” to “thinking”. Don’t want to disillusion anyone to actually believing I am sniffing the PVC glue just yet. Can you edit the title?

JF and Tony, thanks also for the quick reply and your wisdom. Glad to see a gas motor is not outright rejected. With that in mind it will keep up my enthusiasm during the learning curve.

I think we are all focused on power density. Very loosely translated . . . “it’s the greatest amount of power packed into the smallest volume, with low noise, lowest heat, least pollution, best controllability, with good durability, for the lowest cost”. OK, admittedly a very loose definition, but you get the idea
.
I’m in a residential neighborhood and I am in continual stealth mode regarding noise pollution even though the neighbors seem to care less about their barking dogs. I like the whine of the roots blower but doubt neighbors do. I plan to package it in a box lined with Dyna Mat (or whatever it’s called). It’s that silver, sound-deadening stuff you see being installed in Hot Rods and custom cars. Decibel reduction will be a goal. In a former life (25 years ago) I worked with roots blowers (we called them roughing pumps) in a high vacuum environment. They were driven electrically in town and by gas engines in the desert. We used them to pull down extremely large volumes to a few millitorr quickly. I have forgotten a lot of that experience but they were extraordinarily reliable and require zero maintenance except for an oil change.

I don’t mind paying for a good tool that helps me accomplish my goal. But at the same time I like to use up stuff that’s been lying around for years and already paid for. Some of the FB electrical horsepower numbers I see are problematic. The KW, amps, and electric motor costs don’t compare to the “free” gasoline (or E-15) stuff I have laying around. 10-50 gasoline HP is irrelevant for me compared with a 10-15HP electrical motor. With gas, my power density is great; electricity scales up too fast.

I too have limited indoor floor space. My plan is to have both motor and roots pump outside the shop, well muffled and sound insolated. With a DIY dyno in my future I also have a sound deadening idea with a concrete-block-tunnel muffler.

This just in: Thanks Rick for chiming in. I was just about to send this reply. As you know I am a newbie but my assumption is the PTS bench is rather immune to the vagaries of the power supply. How else to guarantee repeatability? If that is true what difference does it make if it is coupled to 8 vacuum motors or a quiet, clean, injected, E-85, Falcon or Vega motor? (Rhetorical question). Thanks for your advice. Ok, forget the Vega motor. Yes, I will buy Bruce’s plans shortly.

[Tony]

I have neighbors nearby, and noise is a serious issue for me too.
My Wisconsin 12Hp single cylinder air cooled engine is not too bad. But if I was doing it all over again I would much prefer a multi cylinder water cooled engine.
The reason being very efficient sound insulation and high volumes of engine cooling air are not really compatible.
A water cooled engine can be fully enclosed with the radiator located outside of the sound proof box.

The biggest problem will be exhaust muffling with minimal exhaust back pressure.
Forget about automotive mufflers.
What I did was use a tuned length of one inch thick wall water pipe (63 inches, 500cc cylinder, 3,000 rpm) leading into about a fifteen gallon compressed air tank. This tank has about 1/4 inch thick steel walls, and definitely keeps the sound in. Exit pipe is half inch diameter. This compressed air tank has a removable inspection plate, and I stuffed the inside completely full of chunks of fiberglass insulation for sound absorption.
It is huge ugly and heavy, but is almost totally silent and offers minimal exhaust back pressure.
Probably a 100 Lb propane tank would be just as good.

Roots blowers can drone at high pressure, but at our lower flow bench pressures should not be too bad. I have seen (heard) electrically driven roots blowers used as vacuum pumps in both a small desalination plant, and for air flow research in a laboratory. The nature of the noise should not be too difficult to screen with a simple acoustic box.
A large bore and reasonably long air pipe to the flow bench should also reduce any pulsing.
I suggest you buy a set of Forum flow bench plans to adapt to your needs.
You wont be using the vacuum motor half of the bench, but the flow measurement half is very well developed and a well proven design, and well worth copying.

For a dyno exhaust, the concrete tunnel idea is exactly what I have in mind myself for my own dyno.
What I thought of doing was buying a couple of lengths of that concrete storm water pipe, maybe about two feet in diameter. Divide it up into several separate chambers with two foot steel blocking plates with a central hole, and then fill the whole length with old car tires for sound absorption.
Buried under a lawn with a tall vertical exit pipe, it should be pretty silent with minimal back pressure.

[Old Grey]

I was thinking about going petrol, but with 4 vacuum motors off the mains and 4 motors off a petrol generator - it gets around the 40 amp problem -.

I was also thinking about sound deading by lining my porting room with this foam

[Tony]

The generator idea is certainly practical.
I know someone that does a lot of metal casting at home. He bought a really big commercial induction furnace and runs it of a diesel power generator trailer, 50 KVa !
That spiky pyramid foam looks like really good stuff, and a bit of old carpet on the floor will help too.