High Capacity High Depression bench

[zane bates-1]

I am ready too redo my Bench.
I need a bench that will pull 50+ inches of depression through a 2.5 inch orifice will equate too about 600 cfm at 50 inches.

I have plenty of vac motors.

My question is will it be better as a orifice bench or a pitot bench?

I question whether or not a pitot flow tube will cause a restriction at the higher depressions negating the benches efficiency.

Most of the larger commercially available flow benches are orifice styles I assume?

I am thinking a min of 12 motors will be needed?
I like the looks of Bruce's bench plans and I am sure they can be modified for more capacity?

[2seater]

Being a pitot bench user, I believe the pitot style has a lower overall restriction factor, particularly if digital data aquisition is used. Actually the digital helps both styles as it seems to provide reliable data at lower velocities than with water manometers. Back to back comparison would be interesting. The orifice operates on the pressure drop across the opening, and the pitot measures velocity, but it requires a restriction to increase the velocity to a readable level? I'm sure there are more definitive answers out there.

[zane bates-1]

Thanks 2seater.

I have been using the the Audie Flow quick for about 4 or 5 years.
I like the Pitot style because of simplicity but I am ready too redo it and I want too make the right choice.
I have yet too see a Pitot bench that pulls 50 to 60 inches of depression at 400 to 600 cfm range of flow.
I would like too get the bench rebuilt and try Bruce's electronics .

Thanks again

[bruce]

A few things I can comment on; my bench plans are not recommended for static depression over 28". You would have to make some structural enhancements. The PTS digital manometer currently is only capable of ~38" of static pressure, we will be looking into higher static pressures, the sensors are available but right now we need to "walk before we run". This upgrade would be limited to the amount of people who would need this feature so it's not priority #1 (we currently have ALOT of people waiting on what we are offering now).

As most know I have always been a pitot bench fan . . . but after building an orifice style bench and using it for a few weeks now there is no way I'd go back to the pitot style of bench! The ease of use and changing of ranges, cost factor of more plates as apposed to flow elements. Do a cost comparison of what it would cost you to build a bench using flow elements or orifice plates and it's a no-brainer in my book!!

I think though if you want to go higher depression you need to get away from the multiple blower bench and go with a single blower as has been discussed in the past on the forum. Power requirements for multiple blowers can reach close to 100amps but for a large single blower you could be less than 50amps?

Tony has a very nice single blower bench, I'm sure he will weigh in on this subject . . . he has been a big help with my single blower design that is collecting dust in my shop at the moment.

Someday that design might even become a reality! With plans to follow.

[bruce]

. . . but the pitot style bench would be much easier due to the ease of use of pipe that can withstand pressure/vacuum. If you made the flow elements easy to change and you didn't have to pay $$$'s for them ie you did the work yourself it could be a toss-up as to the direction you go?

Oh crap now you got my mind thinking . . . those little guys are on my shoulders . . . orifce . . . no pitot . . . orifice . . . pitot ???



Edited By bruce on 1224944647

[zane bates-1]

My projects take years not months.LOL

My bench now pulls 50amps so I know what you mean.

The problem with a pitot would be that I would need a sensor that is accurate without alot of pipe too straighten the airflow.
Orifice benches do not have that issue.
The more pipe the more loss of depression.

I have been looking for a high capacity blower but I have not purchased one yet.


I could modify the plans for added depression.I have busted 2 cabinets already.



I will search more posts.
Thanks for the help.

[evil16v]

[zane bates-1]

3/4" MDF.

I used what I could get easily.
I prefer too used plywood now.It is more flexible and forgiving.

[2seater]

I can't argue with others on the ease of use, I have only used a pitot style bench. The reason I mentioned efficiency is the experience I have had with my own. It is about as simple as it can be. Under my bench top is a stainless steel stock pot used as the settling chamber with a 4" pvc flange bolted to the bottom and a short drop to a single 4" x 3" reducing elbow. My motor box is a seperate unit mounted on casters, and it is reversible. The motor box is connected to the elbow below the settling chamber with the various diameters of pitot tubes. Since the motor box is movable, the pitot tubes can be only the minimum length required for laminar flow. My maximum diameter pitot tube is 3" but a larger 4" tube would have less flow loss and still get good accuracy with the electronics you have. There is a single elbow in the system and the motor box can be build as stout as it needs to be without pressurizing the whole bench. It's not elegant, but it is efficient in the low flow loss department. I have pulled over 80" wc without problem.

[Tony]

Vacuum motors are a pretty good way to get started building a flow bench, but they do have some disadvantages. The biggest probably being high power consumption, high noise level, and the relatively short life of the high rpm brush type motors.

If you are planning something from the start to have well above average flow or pressure capability, a single large diameter industrial blower (or supercharger) will very likely be more power efficient, and produce vastly less noise, and it should run for years without any motor fires or explosions.

When building your bench, realise it has to withstand considerable air pressure over some very large areas. The forces involved can easily reach many thousands of pounds, so bursting or implosion of the main bench structure is always a risk under blocked flow conditions.

That is another disadvantage of vacuum motors. A large diameter industrial blower will put out fairly constant discharge pressure, even with completely blocked flow. Some two stage vacuum motors can spike to well over 120 inches with completely blocked flow, and that could burst your bench.

It is always much easier for the structure to withstand high vacuum than high positive internal pressure. Leaks are less likely under vacuum, as all the joints compress. My own preferred method of bench construction these days, is a welded steel angle frame, with MDF panels bolted to the outside. If I ever get around to building yet another bench, I would do it this way again without hesitation.

[zane bates-1]

I went too plywood and used 2x4 throughout for support.
I would have used metal(for the frame) but I already had the lumber.

I have been looking for a better blower so too speak.
Just have not found the optimal setup.

Tony what are you using for air movement?

[Tony]

Currently I am using a single large centrifugal blower with an 18 inch diameter rotor run up to 6,000 rpm. That gives me fifty to sixty inches of pressure at around 600 CFM with a 10Hp motor.


But for some future use I have something far larger. This monster has a 42 inch rotor and a 28 Hp direct coupled motor that should easily deliver well over 1200 CFM at ninety inches of pressure. I may never use this blower, but it is something I bought during a mad moment at a very low price, and I knew that if I didn't buy it at the time, I would later regret not having done so.

[106-1194218389]

Tony,
I really like your frame work for your bench! Strong and yet removable panels for maintenance and repair. How did you seal the panels to the frame work?
John

[Tony]

John, The welds on the outside of the frame were ground flat, and a thin smear of silicon sealer between the frame and MDF gave a perfect leak fee seal first attempt.
The close bolt spacing pulls everything together really tight.
I am very pleased with the results. The access panels come off easily, and always go back leak free too with a wide sponge gasket.

[49-1183904562]

Tony,

Is three phase mains standard in AU at a residential location or are you converting ?

Rick