new aussie member with a few Q's

[xy4v]

g'day all, i'm new here and from the "land down under"

first question of many; where are all you other aussie guys getting your 240V vac motors from?

[Tony]

Welcome to the Forum.

I am located in oZ, but cannot really help. My previous benches all use a large single industrial blower, not multiple vacuum motors.

[xy4v]

hey tony, thanks for the welcome.

i've just contacted godfreys so i'll see what they say..

[jsa]

[xy4v]

john: thanks for the welcome mate!

i've purchased a set of bruce's plans and will begin construction on it once I am happy I understand the whole concept...

hopefully you can help with my next few questiosn.. I want my bench to be able to handle approx 350 CFM @ 28" with 4 motors.. I'll upgrade it to 8 motors down the track, but 4 will do it for now (I hope)

I'm currently looking at the domel 462-3-541-16 which is a single stage motor. Here are some specs of the motor from domel's sight:

Normal operation: Pm >= 1150 W
Vacuum: pmax >= 27,8 kPa / 96,5 in H2O
Air Flow: Qmax >= 52 dm3/s / 95 CFM
Air Power: P2max >= 570 W
Efficiency: ηmax >= 45 %
Mass: m = 1,58 kg

Voltage: 230 V
Frequency: 50 Hz
Nominal Power: 1350 W

link to the specs:

based on your experience, do you think they will reach my inital target of 350 @ 28"? also, should I be worried that they are only a single stage motor, do you think I should be looking at the dual stage range?

the heads i'm looking at working on are Ford Small Block (mainly 4V Cleveland heads).

[Tony]

Probably not.

The full open flow (at zero back pressure) is rated at 95 CFM.
As you place more restriction on airflow, differential pressure rises, and flow falls.
At the full rated maximum pressure, flow will be zero.

At 28" back pressure the flow will be somewhere between zero and 95 CFM, but what it will actually be, cannot even be guessed at. That is unless you have the specific flow curve for that particular blower.
The shape of this curve will vary hugely from one blower type and model number to another.

You will need more than four blowers to reach 350 CFM at 28", but how many is difficult to say.

Best bet is to test one blower all by itself in a test rig. Try loading the blower against various orifice sizes until that blower can manage around 28". Then use the orifice formula to calculate the actual flow through that sized hole at the measured pressure differential. From that you can figure out how many similar blowers working in parallel will be required to reach your target flow.

Realist too, that the blower has to supply not only the test pressure, but the design pressure drop across the measurement orifice. So the blowers will need to develop 350 CFM working against more like 35" to 42" inches of total back pressure, not just 28".

[xy4v]

[Tony]

Oops, no I didn't open the PDF, but yes, that is the exact information you need.

It says 103 CFM at 33" and 81 CFM at 62" that is the range you will be working in. So yes, four blowers should meet your needs.

Usually blowers are simply specified for max flow, and max pressure, but it is never possible to achieve both at the same time. Sorry for any confusion.

[xy4v]

thanks for the clarification mate

last question for now (I hope :p); without using a variac or dual stage motor, what are my options for depression control in a bench built to bruce's plans/specifications?

[Tony]

Don't even think about using anything other than motor speed control !!

Having the motors continuously screaming absolutely flat out, and then throttling the air, makes no sense. It just creates massive heat, and unbelievable noise, and consumes bulk electrical power. The noise alone will quickly drive you crazy. And your motors will wear out or blow up much sooner than if running at vastly reduced speed and power most of the time.

But there are really two options. A variac as you suggest, or a commercial electronic motor speed control module of some type.

[xy4v]

ok, motor speed controller it is then!

i'll start looking into wiring schematics soon, are there any on this board?

edit: forgot to mention, i'll be using the FP1 with this bench I build..

[106-1194218389]

[Tony]

The vacuum motors have to pull (or blow) air through two restrictions placed in series, one after the other.

The total pressure differential the blower has to work against will always be test pressure plus the measurement orifice pressure drop.
There is simply no way of getting around that with an orifice flow bench.

[jsa]

Total pressure drop the motor must produce is the test depression plus orifice metering (6" or 12" or whatever chosen manometer rise) plus the internal ducting losses within the passges of the bench.

For the Tractor Sport bench Bruce might be able to take some measurements and come up with the ducting losses for various flow rates.

XY4V, the single stage motors you linked are falling off their efficiency peak at the 62.6"/81.4cfm point. You would be running between that point and the 33.8"/103.7cfm point. An alternate motor selection with peak efficiency around the operating point you want would give you better energy efficiency, so a well selected alternate can save your power bill. Without knowing ducting losses I suspect 4 motors might be borderline.

[xy4v]