PTS Flowbench Forum

I would like to find out what the max CFM @28" is for the motors I will be using in my build, they are YDK Dyson DC04 motors, 1600W x 240V and measure 138mm OD with a 33mm ID

I plan to bolt one of the motors onto a chamber with an orifice on the other side and a manometer to measure the vacuum

The question is if I want to find out what the motors will flow @28" on a working bench when using a 16" Delta P through the orifice (44" total vacuum at the motor), should be I testing the motor flow @28" or @44" vacuum when using a single sharp edge orifice to simulate the real bench flow @28"?

A little confusing but I am sure someone will have tested this before

Thank you

44" in the chamber below the orifice plate

Experiment with the orifice size until you find a size that drops very close to 44 inches with your particular motor.

A one inch diameter hole might be a reasonable first guess, then go up or down from that to get 44 inches.

From that, you can then use the orifice spread sheet to calculate CFM using the hole size and the actual measured depression the motor can pull.

The range of typical vacuum motor efficiencies (for a 1,600 watt motor) should place you somewhere between 55CFM and 100CFM per motor, with an "average" motor probably capable of flowing around 80 CFM at 44 inches.

Thank you Tony, that is exactly the conclusion I arrived at, testing the motors at 44" with a suitably sized orifice and lets say that orifice flows 70CFM @28" and the motor is capable of drawing 44" through it, that means the motor will be capable of flowing 70CFM @28" when testing an item on the bench with the orifice in place and 44" at the motor

Will test the motor with a 22mm ID orifice (53.7CFM@28") first and work up from there until the max DP lowers to 44"

Then I will have a good idea of what the motors will flow @28" on the bench and can order orifice plates to suit

That will get you very close.

There is a strange motor proximity effect that lowers the airflow when multiple motors are operating in very close proximity fed from a common air box.
The exact mechanism causing this is not clear.
But it could be turbulence around the motor intakes, or perhaps one motor robbing air from its neighbour.

The result will be that you will end up getting slightly less final total flow than you anticipate by simply multiplying the tested flow of one motor, by the number of motors.
Results vary, but the flow loss people have typically experienced might be in the region of ten percent.

If you have a definite final flow goal in mind, fitting an extra motor should get you there.

That is interesting Tony about the lowered CFM with multiple motors, I imagine power supply levels also play a small role is reducing the max CFM with lots of motors vs one or two

With all of that in mind I tested 2 motors side by side in a chamber, that way the results will be a little more accurate

Orifice test results:

ID --- Inches of Water (lowest In observed)

31.50mm = 54.50 In

35.00mm = 43.00 In

45.00mm = 22.20 In

51.80mm = 14.05 In


I believe the motors are flowing 65CFM @28" + 16" Delta P (44" total at motor)

6 motors = 390CFM @28"

Minus 10% = 350CFM which should be plenty on the conservative side

So now the question is if the motors will flow 350CFM what size orifice plates and calibration plates should I order to work with the DM?


A few questions

1. What is the lowest % flow that the DM/Orifice can accurately measure down to, can it flow down to 15% if I use say 35" water to help raise the orifice Delta P for low lift flow testing for example and correct back to 28"

2. What CFM @28" should the calibration plate be in comparison to the largest orifice plate, should it ideally be 90% or 95% for example of the orifice CFM

If the largest orifice is 350CFM @16" then I could go with a 28" calibration plate that flows 335CFM (95.7%) is this the best way to do it in terms of accuracy?

I would like a 230@16" orifice for testing a particular type of head down to around 35CFM@28" @.050" lift

Let me know what you think, I don't mind getting a few extra plates if needed

Many thanks

A few pics of the motor testing

A few more

The PTS DM has an "official" working range of 450cfm so one plate will be good for 0-450 or 150-600. I sell a set of 4 plates that cover a working range of 0-600cfm@28", each plate can be used internally or as a calibration plate for the next range. If you use the 625 plate you use the 3 smaller plates for calibration, next range down uses the 2 smaller plates and the last range just uses 1 plate.

Personally, (un-official version) I use one plate in my bench that is 625cfm@16".

I go with ~80% range for calibration.

rwdford wrote:That is interesting Tony about the lowered CFM with multiple motors, I imagine power supply levels also play a small role is reducing the max CFM with lots of motors vs one or two

Supply voltage will have a big effect on the available airflow from a given motor.
Those Kemo modules seem to be very popular in Europe, a number of Forum members are using them with great success.

I have never seen Kemo products out here in Australia, so I don't have any personal experience with them.

There are two things to be aware of. The first is that the potentiometer is directly connected to one side of the mains and could present an electrical shock hazard if suitable precautions are not taken.

I have also heard that even when turned fully flat out, those Kemo modules can still drop several volts so you can never reach full mains voltage at the motors.
Just something to keep in mind when motor testing, as those last few volts can make a big difference.