Planing a new bench - rubber plugs and orifice range

[larrycavan]

[thomasvaught-1]

Long Post Quote:

"You 2 guys do whatever you like but one thing is certain. If you go damaging the edge of your measuring orifices, your calibration will be off, plain and simple."

I always like having discussions with Larry and Tony as I typically learn from each discussion.

This is just my opinion:

I protect the "calibration orifices" that go on the top of the bench carefully. I store each one in a specially modified felt lined layered wooden cigar box. Those orifices are my "STANDARDS".

Every day (and sometimes more often if I see a weather change) I compare the flow numbers for each orifice in the multiple orifice plate to the "standards" readings. This tells me where I am for that day's testing.

I realize that according to the SF people that an orifice bench "is a ratiometric bench and the readings should be the same every day, no matter what the weather". Whatever the percentage is for that test point for that day, you multiply it by the SF chart "range" number and that is your flow number. Simply! Not quite.

I have noticed after working on several SF 300 & 600 benches at Ford over the years that the actual orifice plates "get dirty". A fine varnish builds up on the id and the edge opening of those benches. I assume that this "varnish" is from never getting the heads totally clean or the cleaning fluid itself evaporating out of the pores of the metal during the flow test and mixing with the air. Whatever, when you measure the orifice diameter (vs what the "known dimension" is supposed to be) there is a small change. The edge of the plate is "smoothed out" by the varnish therefore the "sharp edge" is not as sharp. I do not see this situation on the SF110 type bench as much as you have to take the top orifice plate off to see the bottom edge so maybe it is there but I missed it. With the SF-300 and SF-600 benches and a good flashlight it is easy to see looking down the test hole.

So here you have a orifice type bench and maybe your Delta P orifice is very slightly changing over time. With the daily corrections from the Calibration plates, it is a non issue.

Back to the rubber stopper deal wedged into the orifice hole. I have personally never seen the buildup of the varnish in the orifice hole on the SF1200 series bench. Maybe the rubber stopper rubbing it off keeps it from happening. You would think that because a SF1200 bench is a CARBURETOR bench of all of the benches it would have the most chance of seeing varnish from the fumes and dust in the air as it moves the most air and carbs are never totally clean typically when they are tested on that bench.

So which is the "worst character" the varnish or the possible "knocking the perfect sharp edge" off of the orifice plate?

Bruce made some very nice "sharp edged" plates for the plate study. He tried to get them to an exact flow number based on his mathmatical calculations and his equipment.

When we tested them on the "Big Buck" bench there was a small difference. So who was right? The 3 million dollar bench or the calculation? Even the 3 million dollar bench is corrected to some standard temperature/pressure/R.H. and an assumed Lbs per cfm of air. That 3 million dollar bench is in a climate controlled room so the numbers vary less but it is still recalibrated often.

Larry mentions "a stickler for details" which is great but how many realize that you can only get so far with what you have for available resources. That is why a worry about my "standards" much more than my actual flow measurement parts which with have "noise" in them from the weather, the wear on the orifice edge, varnish, measurement error from the set-up of the port adaptors, the radiused edge being duplicated perfectly for each type of head flowed, etc.

With the "Standards" I can always get back to a certain ASSUMED flow. may not be perfect but is one method of doing it.

We make assumptions on everything in life everyday. That a 9/16" drill bit is truly a 9/16" diameter from the factory. That a machined part on a lathe is centered perfectly. That a chemical in a pill is exactly the correct ratio. In every case you have Quality Control measures that try and keep you with-in a certain standard. JMO

Tom V.

[larrycavan]

[thomasvaught-1]

Busting my Chops Again, huh Larry! Man, this is a tough crowd.

Just passing on my thoughts.

I suppose that you could make "tee" rubber stoppers that would slip into the orifice opening without actually having to "wedge" them in place and you could then use a weight on the top of the stopper like my buddy does to keep them from being blown out on exhaust flow testing.

Maybe I will take a known flow orifice plate and jam a rubber stopper in it several times a day for a month and then reflow it and post the results using the "Big Buck" bench.

Tom V.

[larrycavan]

[200cfm]

The discussion of rubber stoppers had me reviewing my stoppers. I notice "etching" marks on the rubber stoppers caused by the pressure pushing on the orfice edge. It is a very fine etch line or cut. It is on all three stoppers. The stoppers and plates have been used a good full year and I estimate I have removed and reinstalled the stoppers a good 100 plus times. Looks like it is time for a total bench recalibration. I periodicly check the manometers to each other in parallel to make sure the incline has not shifted. I suspect I have some orfice cd change. Hope I don't have to order new plates.