blower speed correlation to actual testing

[williamsmotowerx]

Ok, I've been reading this on and off for a bit... purchased some pitot tubes from bruce and have decided I may build a bench to upgrade my sf110, and buy the plans from bruce here.

this is what is driving me crazy though. i'll put it in perspective for people reading this forum that haven't had a lot of experience actually running a bench but planning on building one.

when you first start out using a bench it's so much fun... but after awhile it gets to be like work... so anything to speed up the testing will make you keep up on the fun part.

when testing on my orifice type sf110 i found out that in my head testing from the different manufacturers of the same size motors i have to adhere to my "range selection" to be able to compare heads at the different valve lifts.

this is where i need advice:

i build a orifice bench use 4 motors. all running at the same time with a speed control.

lets just say i'm in range 4 orifice on head "A" mid-lift 28" water and i'm adjusting the flow control and motor speed control. the motor speed control ends up being 50%.

now since i adhere to my "use the same ranges for different brand heads of same motor size" i'm testing head "B" in range 4, mid-lift 28" water, adjusting flow control and motor speed control. this time motor speed control ends up being 75%.

my question... is the flow between the two heads still apples to apples even though the blower motors are spinning at different speeds?

[DWC]

Hi Williamsmotowerx,
Although I dont claim to be an authority on flowbench tech it seems to me that the flow between the 2 heads will still be apples to apples as the test pressure both heads are seeing is still the same which is what is determining the volume of air they are flowing. I have a SF110 with a variac for motor speed control and i have the flow control for intake if thats what im flowing opened right up i dont balance between flow control and motor speed control. Im not sure why you would need to balance between the two as i have good control over the test pressure with just the motor speed controller (variac).
regards,
DWC.

[bruce]

Since you mentioned my PTS bench design let me add this . . . my design does not have a flow control and a speed control. It only has one moving part and that's the slider plate for direction change. You can either go manual (not in the plans, you have to add, support found here on the forum) or electrical control for static pressure/flow depression.

If you go digital gages and add on digital motor or valve control for your static depression then you set it and forget it and the bench will control your depression. Now this adds to the initial cost of your flowbench, but it's still going to be way less $$$'s than a commercially produced bench. I'd say a fully spec'd out flowbench like this would cost roughly around $1500 depending on blower selection and qty. Try and even find a new let alone used commercially produced bench for that money with all those features?

My design is also upgradable, so say you start out with 2,3 or 4 blowers and find later on you'd like to test at high cfm volume. All you have to do is add more blowers (bench design allows space for 8 blowers) update your power (220v 50amps) add a new orifice plate or two. And you have a new larger bench.

[49-1183904562]

[color=#000000]Mr. Williams,

Lets say you have a compressor at home and you fill the left front tire of your care with 32psi of air using a Camel tire gauge you keep in the glove compartment. Later that same day your wife goes to the gas station and notices the right front tire is low she puts air in it 32psi using the same gauge out of glove compartment.

Can I assume both tires have same amount of air YES

Can I assume they have exactly 32psi of air NO (don

[williamsmotowerx]

DWC hit the nail on the head, 28" is 28"... doesn't matter what i'm using to acheive that... as long as my orifice plates are consistent.

bruce... now you brought up another question. if you just use variable speed control... how do you perform the leakage test of the head/valves to baseline start your head test? on some cases when i'm doing this now... my flow control is just barely open. i can't see that much sensitivity in a variable motor control? (DWC are you just opening the flow control all the way, and using the motor speed to do what i just described here?)

I already have a performance trends black box that i'm using on the sf110, was just going to carry that over to the homebuilt.

1960, I just read your post again... and now understand it some (gonna have to re-read it a few, lol) but good post and informative.

[bruce]

I would see no problem with the speed control running one motor for leakage testing. I am currently using a Harbor Freight router control and have had no problems leakage checking on my bench. I purchased a different type of control and plan on controlling 2 motors at a time in the very near future on my bench.

Most of the specifics of the workings of my flowbench design are discussed in more detail in the PTS Plans area which unfortunately is only open to members who purchased a set of plans. Hope you understand why I don't go into a lot of details in the public area of the forum.

[Tony]

It seems to me, that the blower has to work against a total pressure, that is the 28" test pressure, plus whatever the pressure drop is across the measurement orifice at the flow you are measuring. So the load on the blower will change with flow, even if the test pressure remains constant.

The other thing is that the shape of the blower curve will be radically different from one type/brand/size of blower to another.

Some blowers deliver almost constant pressure at constant rpm over a very wide flow range.
Other constant speed blowers develop huge pressure at low (blocked) flow, and the pressure dies away to almost nothing at the high flow end.

Your blower might well be very sensitive to pressure change, and require a fairly large rpm correction for even quite small changes in flow.

[DWC]

(DWC are you just opening the flow control all the way, and using the motor speed to do what i just described here?)

Yes that is what im doing and as im sure you would know the SF110 has 4 vacuum motors 2 for intake testing and 2 used for exhaust testing. So my motor speed controller (variac) is controlling 2 motors at one time and i try to keep this type of testing as brief as possible due to the fact that there is very little airflow to keep the motors cool. As for the sensitivity of the speed controller being a problem at these low flow levels i can say that i have no problem whatsoever at least not with the setup i have using a variac but i couldnt comment on other types of speed controllers as i have no experiance with them. The reason you only have your flow control just barely cracked open for say a leakage test with your current setup is that your 2 vacuum motors are running full bore and they will easily go waaayyy above your normal test pressure associated with that bench due to no real airflow through your test piece.
regards,
DWC.