PTS Flowbench Forum

That feeling when your stuck and getting brain fog and time is whistling by, Days go by,Months go buy. Project is dieing.

Need to bring it to life. Desperate.

The bench is built.

I place a 54mm hole plate on top of the bench. Reading are taking with this on.
3 motors on full blast.

Manometer reading on the test chamber is around 9 inch H20
Manometer reading when plugged across the 63mm orfice in the wooden box is 5.3 inch H20

Did you download and use Ed's spreadsheet to figure out your ranges on each plate?

A 54mm orifice @9" should yield 183cfm

A 63mm orifice @40" gives you a range of 0-527cfm assuming you are using 40" digital manometers?

So my quick math will go like this:

Using Ed's spreadsheet you get a 19% on your 0-40" scale around 5.5" (you are seeing 5.3" again just do some rough math on my end) your scale length is 0-527cfm so 527/.19 and come up with 100.13cfm@9" (9" being your static test pressure)

With your 54mm plate you should be in the range of 34% when it's flowed 183cfm@ 9"

This is just some quick math to give you an idea of what direction you need to go in . . .

1) I am not using 40" manometer. I am not sure what I am using. I think I am using digital manometer that goes up to 55 inches water pressure. Because on the box it says max pressure 2psi

2) I was disappointed to see that using the test plate 53mm, I could only achieve a test pressure of 9"! I have 3 x Ametek 119666 motors. Shouldn't have this been atleast 18 inches water pressure?


3) Also why was the water column pressure fluctuating i.e 8.8, 8.5, 9.0, 8.6. If this fluctuation is happening every tenth of a second then how can you know you are improving the flow when making minor changing when grinding out a port on an engine.

4) Remember the plate you supplied me 63mm orfice. The measurement H20 is being taken when one tube of the manometer is on one side of the orifice and the second tube is on the front side of the office.

Thanks for the prompt response.

damunk wrote:1) I am not using 40" manometer. I am not sure what I am using. I think I am using digital manometer that goes up to 55 inches water pressure. Because on the box it says max pressure 2psi

2) I was disappointed to see that using the test plate 53mm, I could only achieve a test pressure of 9"! I have 3 x Ametek 119666 motors. Shouldn't have this been atleast 18 inches water pressure?


3) Also why was the water column pressure fluctuating i.e 8.8, 8.5, 9.0, 8.6. If this fluctuation is happening every tenth of a second then how can you know you are improving the flow when making minor changing when grinding out a port on an engine.

4) Remember the plate you supplied me 63mm orfice. The measurement H20 is being taken when one tube of the manometer is on one side of the orifice and the second tube is on the front side of the office.

Thanks for the prompt response.

1) You will have to base your calculations on the range of your manometer then.

2) You can not predict the motor output as there are to many variables in flowbench design. If I recall you added a filter or baffle in your design? (Sorry I can't keep up with everyone's builds anymore, I do scan through the posts but try to let others answer as I'm not the "Flowbench Guru")

3) Yes, digital will work that fast without some type of averaging you will see pulses, with water gauges it dampens out due to the weight of the water reacting to the pulses you can't see it happen digital makes it much faster reacting. The accuracy of your digital sensor then comes into play also.

4) I machine so many plates for various customers it is hard for me to recall everyone's plate dimensions so I always ask when I talk to people what it is that they have, at any given time I am probably dealing with 4-5 people building flowbenches not all are PTS builds.

Right I think it's my understanding of the manometer is lacking.

1) You asked if I was using a 40" manometer. Did you mean am I using a manometer that has a MAX limit of 40"?


2) On my digital manometer it is set to 0. When I run the bench flow the reading on the manometer goes from 0 up to 9" as explained. There is no calculations to do apart from using ED's spreadsheet to work out the CFM.

Is this right what I have said?

3) P.S I wonder if liquid manometers are better than digital because they don't show the fluctuation in reading like the digital too. The liquid way would be easier to read as it is if you are seeing an average reading per second.

1) Yes, you need to know your manometer range for the differential across the internal orifice plate

2) Yes

3) I'm kinda partial to digital, all comes down to what you want out of your flowbench? Nothing wrong with water other than all the math required, which you also have with a hand-held digital, computer based digital opens up a whole different experience in flowbench use.

I do not want to get in the middle of this educational process but it looks like you are close

The DP across the test plate is 9" at 54MM @.62CD is 184 CFM +/-

The DP across the internal plate 63MM is 5.3" @.62 CD is 192 CFM +/-

So first things first are both plates made of the same material? Thickness ? Edge Treatment? How was the ID measured ?

You are close enough that you will have to refine your numbers and determine the CD of your two plates, you see the (Looks like 5mm) on top of the Bench with a square edge will not have a .62 CD so you will have to Regress your plates to determine what CD you manufactured them at (why we use Bruce's Plates). It just time and iterative testing and understanding what CD is.

Also it looks as if you do not have a open chamber below your test orifice and thus the round pipe will play a roll on the CD as there is a partial Beta factor that will affect flow into the pipe.

Last if pressure is fluctuating it is a good chance you have a leak.

Just some thoughts.

I really needed that help guys. cheers.

Right. Time to paint it all up from inside and get rid of the leaks.

@1960FL

The 54mm was just a wooden plate

The 63mm was Bruce's plate.

I just made the wood one because I was rushing to check things.