PTS Flowbench Forum

Good afternoon,

I have found my self needing a flow bench. I have a small ATV performance shop, and porting heads is a pretty important part in the performance side of stuff.

A few questions.. I'm sure these have been spoke of many times over, I have spent a couple hours now reading through the threads and have not found the answers yet.

First, what type would best suite my needs? The most I should ever <em>need</em> is about 350cfm. Accuracy and consistency are very important to me. I also want digital read out. I understand this will add a additional $300 ish to my total.
I am not swimming in pools of money, so I would like to spend the minimum required to reach all of the above.
Orifice, Pitot, or the MAF type?

Second, I have located some vacuum motors. They are 120v and each use less than 8 amps. They claim to do 135CFM @2inches. Four of these would put me at a total of 540 total CFM. Is this correct? Or is there something I am not aware of? They are dual ball bearings. And a flow bench I repaired once seems to have the same style of engine.
Using 4 it would keep my amperage below 40, so I could keep it on a 40amp breaker and get to stay away from 220.

Third, How do you switch the direction of flow from intake to exhaust? I can imagine using two separate "valves" to do this. But that seems like it would be too complicated.


If all goes well, and I can get the correct motors located I will be building one within a month. I will be using Bruce's plans.

Thanks in advance for any/all info and advice given.


Kasey

Kasey,

First of Welcome to the forum,

Now for your bench and its requirements, Motor selection is critical and the numbers you posted on the motors you have found truly have no value what we need to know is what if the CFM flow at or around 44” of water. 28” of test pressure plus your 16” of delta P assuming you would be building an orifice bench such as the PTS Plans.

As for a bench I would just build the PTS bench look at the tread on my latest build and you can see actual costs for what is pictured and there is a lot of fat in that cost. For power you will be best suited to just use 8 motors from the start and unless you are going to do some tricky extension cord routing you will need to wire the bench for 220VAC.

http://www.flowbenchtech.com/forum/view ... ?f=8&t=565


Rick

Hi Kasey, welcome to the Forum.

As Rick says, the Forum bench plans will get you off to a very good start, and the low cost of the Forum digital manometer now make water manometers not worth the effort to put together.

As to selecting motors, there are really only two ways to go.
Do some actual testing of the motors that you already have before fitting them into the bench, or buy new motors that have a known specified CFM flow at around 44 inches.

Testing your own motors is not that difficult.
Cut some round holes of various sizes into light gauge scrap metal sheet.
These will stick "by suction" to the intake of the vacuum motor, and just measure the developed suction depression behind the hole with a very small hollow probe (blunt hypodermic needle).
From the developed pressure, and the hole diameter, you can then calculate CFM.
A series of readings with different hole sizes will enable a flow curve to be plotted, that is inches of pressure on the vertical axis, and CFM flow on the horizontal axis.

Even if none of the measured pressures ends up being at exactly 44 inches with the selection of hole sizes available, you can pretty well eyeball what the flow will be at 44 inches from the overall shape of the curve.

This does not all need to be super accurate, just an indication to weed out the good motors from the bad motors.
You will quickly discover which motors are wimps, and which motors can really pull some air.
If you also measure motor amps at the same time, a figure for CFM per amp will tell you which are the most efficient motors when running at around 44 inches as they will be in your bench.

All this can be fun, and quite instructive, and need not cost a cent to do.
But you can pretty well anticipate the final flow and total amps of the finished bench, and be certain it is all going to work.

1960FL wrote:Kasey,

First of Welcome to the forum,

Now for your bench and its requirements, Motor selection is critical and the numbers you posted on the motors you have found truly have no value what we need to know is what if the CFM flow at or around 44” of water. 28” of test pressure plus your 16” of delta P assuming you would be building an orifice bench such as the PTS Plans.

As for a bench I would just build the PTS bench look at the tread on my latest build and you can see actual costs for what is pictured and there is a lot of fat in that cost. For power you will be best suited to just use 8 motors from the start and unless you are going to do some tricky extension cord routing you will need to wire the bench for 220VAC.

http://www.flowbenchtech.com/forum/view ... ?f=8&t=565


Rick

FL,

First thanks for the welcome and the response.

I have to say, that is the nicest bench I have seen in a very long time. Great job!

In the link below it the motor i was referring too. It is the same design as the bench I worked on had. It also is two stage. Your price sheet shown $80, was that each or for all eight of your motors?
With your advice considered I will go ahead with the 220. I will do some further research for some good priced 220 motors.

http://www.kleen-ritecorp.com/p-32541-l ... -120v.aspx

Now for another beginner question; I understand that the "standard" level of test is 28 inches of water.. But what does this mean? "Of water?" And the other 16 inches you mentioned?

Again, thank you for all of your input!

Kasey

Tony wrote:Hi Kasey, welcome to the Forum.

As Rick says, the Forum bench plans will get you off to a very good start, and the low cost of the Forum digital manometer now make water manometers not worth the effort to put together.

As to selecting motors, there are really only two ways to go.
Do some actual testing of the motors that you already have before fitting them into the bench, or buy new motors that have a known specified CFM flow at around 44 inches.

Testing your own motors is not that difficult.
Cut some round holes of various sizes into light gauge scrap metal sheet.
These will stick "by suction" to the intake of the vacuum motor, and just measure the developed suction depression behind the hole with a very small hollow probe (blunt hypodermic needle).
From the developed pressure, and the hole diameter, you can then calculate CFM.
A series of readings with different hole sizes will enable a flow curve to be plotted, that is inches of pressure on the vertical axis, and CFM flow on the horizontal axis.

Even if none of the measured pressures ends up being at exactly 44 inches with the selection of hole sizes available, you can pretty well eyeball what the flow will be at 44 inches from the overall shape of the curve.

This does not all need to be super accurate, just an indication to weed out the good motors from the bad motors.
You will quickly discover which motors are wimps, and which motors can really pull some air.
If you also measure motor amps at the same time, a figure for CFM per amp will tell you which are the most efficient motors when running at around 44 inches as they will be in your bench.

All this can be fun, and quite instructive, and need not cost a cent to do.
But you can pretty well anticipate the final flow and total amps of the finished bench, and be certain it is all going to work.

Tony,
Thanks for the reply.


With the testing of the motors, that will be a issue for me. I don't have any! Lol
I hate to spend $50+ on different motors to test them. Is there any you have used and can suggest?

I really want to use a digital display. I would like to be able to go straight from my porting bench, to my flow bench. With out having to pick up a calculator or a pen and pad. What is the price of the digital manometer you are talking about?

Thank you for the reply and the info!

Kasey

Kasey, you may be able to score a bunch of old vacuum cleaners free from the local rubbish tip.
At the very worst, you can take them all back !!

Pressure (and vacuum) is measured here in inches of water.
Get a bucket full of water, stick one end of some clear plastic pipe into the bucket.
Suck on the free end of the pipe, and the water rises up the tube.
However many inches the water rises, is a measure of suction pressure.
A decent vacuum motor can pull maybe 120 inches maximum, but we only need around 44 inches, and that is the sort of suction pressure we should be testing the flow of our motors at.

This is the performance chart of the particular motor. Now let's say you're building an orifice bench that maxes out at 350cfm @ 28"WC with 4 of these motors, that means you'd need a flow of 87.5 cfm per motor, now if we look at the chart we see that these motors will pull approximately 34"WC of vacuum when they're moving that amount of air so at a depression of 28", you'd need to size your orifice so that your differential pressure is at most 6"WC and that works out to a 3.246" (assumes a Cd of 0.62).

The PTS digital manometer use a differential pressure sensor with maximum range of 16"WC so this set-up wouldn't make maximum use of the PTS manometer's capabilities. Now let's say you wanted to use the full range of the PTS manometer, your motors would need to draw 44"WC of vacuum again referring to the chart, when drawing 44", these motors move about 67 cfm each or 268 cfm for the 4, the appropriate sized orifice that that set-up would be 2.223" (again assumes a Cd of 0.62)

Tony wrote:Kasey, you may be able to score a bunch of old vacuum cleaners free from the local rubbish tip.
At the very worst, you can take them all back !!

Pressure (and vacuum) is measured here in inches of water.
Get a bucket full of water, stick one end of some clear plastic pipe into the bucket.
Suck on the free end of the pipe, and the water rises up the tube.
However many inches the water rises, is a measure of suction pressure.
A decent vacuum motor can pull maybe 120 inches maximum, but we only need around 44 inches, and that is the sort of suction pressure we should be testing the flow of our motors at.

Thank you for the info on Inches of Water. I will try to get my hands on some old vacs to get this bench going.

86rocco wrote:This is the performance chart of the particular motor. Now let's say you're building an orifice bench that maxes out at 350cfm @ 28"WC with 4 of these motors, that means you'd need a flow of 87.5 cfm per motor, now if we look at the chart we see that these motors will pull approximately 34"WC of vacuum when they're moving that amount of air so at a depression of 28", you'd need to size your orifice so that your differential pressure is at most 6"WC and that works out to a 3.246" (assumes a Cd of 0.62).

The PTS digital manometer use a differential pressure sensor with maximum range of 16"WC so this set-up wouldn't make maximum use of the PTS manometer's capabilities. Now let's say you wanted to use the full range of the PTS manometer, your motors would need to draw 44"WC of vacuum again referring to the chart, when drawing 44", these motors move about 67 cfm each or 268 cfm for the 4, the appropriate sized orifice that that set-up would be 2.223" (again assumes a Cd of 0.62)

Sorry for yet again, another beginner question. You say 34"WC. Is this 34 Inches of Water?
I think I'm missing something, this seems like gibberish to me for some reason.

Thanks to everyone for the explanations and for your patience of my lack of knowledge.

Yes, 34"WC means 34 inches of water column. I write it that way because in some circles it's very common to use inches of mercury when talking pressure or vacuum so I use WC to indicate that I'm talking about inches of water not mercury..