orifice dimension

[86rocco]

I posted a spreadsheet in that you might find useful.

[proto]

thanks for the answer

[86rocco]

The formulae in my spreadsheet assume that you are using a sharp edged orifice. I'm not sure how things might change if you were the use a smooth radiused edge.

[bruce]

Your edge on the orifice must be dead sharp. Not a sharp edge on one side of the plate and a sharp edge on the other side of the plate. You will be making a cut on an angle from one side of the plate to the other side of the plate until you come to a sharp edge at the dia you need. Hope that makes sense? Not as easy to machine as it sounds to end up with the correct orifice dia

[Mouse]

.62 Cf is a general value and seems to be a popular value for a sharp edge orifice. Any plate thickness or rounding of the edges will increase the Cf, how much is difficult to estimate. A section of round tubing will have a Cf close to 1 (but never 1 because turbulence is always present and reduces the Cf). That is why sharp edges are used, they are easy to estimate the flow rates under "ideal" conditions as there are fewer variables.

[84-1074663779]

I believe the point here is that an orifice should have as large a ratio of diameter to thickness as possible. For large orifice diameters that is easy, but for the smallest sizes the thickness of the orifice plate itself may start to become significant.

One way to get around this problem is to bevel the down stream side as shown above, to make the apparent orifice plate "thickness" appear less. Maintaining a very high diameter to thickness ratio over a large range of diameters enables all the hole sizes to conform to similar flow coefficients.

At least that is how I see this. I doubt if the actual angle of departure is critical, but a wider included angle will be more effective at making the orifice plate appear thin.

Quite obviously this is only going to work if the design of the bench never requires a reverse flow through the orifice.

[Thomas Vaught]

Super Flow benches have a sharp edge on both sides, Bruce, with no bevel as the orifice sees flow in both directions.

I have mapped the flow coefficients of discharge and on the Superflow range from .59 to .56 depending on the hole diameter.

Course they calibrate their benches for this deal and provide a calibration chart to go with the bench.

The calibration is everything.

Tom V.

[proto]

thanks

[maxracesoftware]

i just checked out my SF-600 FlowBench orifice calibration
and it averaged = .61911 discharge coefficient

[gofaster]

I was working on my orifice plate and I thought this would be an appropriate place to share this info.

My plate is 24" x 24" x 1/8" stainless steel. I chose stainless because it wouldn't need any further surface treatment when it's finished. Originally I considered using aluminum and having it hard anodized, but after I got a quote from my plater, that idea was canned. I intend to mount the orifice plate between the test opening and the flow control valves and use rubber stoppers to change ranges. I feel that in a set-up like this the aluminum would need to be coated with Ni-Tuff (Brand name?) to prevent wearing out the top edges of the orifices.

I had some cobalt hole saws that gave me good results in the past, but they were a bad idea for stainless. The holes were neither sharp nor round. I ended up going back and recutting the openings with a boring head to true them up, round, sharp and square.

Please understand, I am not making "Sharp Edged Orifices", these are straight cuts with a sharp 90 degree edge on both sides.

This was the result:

1.250..became..1.283"
1.500..became..1.546"
1.750..became..1.860"
2.000..became..2.089"
2.500..became..2.552"
3.000..became..3.050"
3.500..became..3.562"

I don't think the difference in sizes (the nominal sizes that I determined I would need using Larry's spread sheet, and the slightly larger sizes I ended up with in the truing process), are going to be a big problem.

Somebody correct me if I'm wrong.

I think once I get the bench running, I'll be able to determine what the actual flow of each orifice is when I place a test orifice on the entry of the bench and record the resulting manometer readings at given test pressures for each orifice.

A shop tip: after boring the holes, there will be a need to debur them. To remove the bur without damaging the sharp square edge, place a square honing stone flat on the orifice plate, square to the hole, and carefully stroke it radially outward from the center, keeping the stone absolutely tight and flat on the plate. After each stroke of the stone, pick it up and place back over the edge of the hole and repeat until the bur is worked off all the way around the hole. Do Not Stroke it Towards the Center! That will only push the burr into the hole and ruin your edge. This is a die makers technique for deburring punch press dies before they get heat treated.

My afterthoughts on this experience:

I decided to drill and tap mounting holes to install a holder for Bruce's sharp edge orifice plates over the 3.5+" opening, just in case my orifices don't perform to my satisfaction. Bruce's plates "just fit" through a 6 deck plate in the front of the bench.

If I had it to do over, I would have done a few things differently. Regardless of the material, the cobalt hole saws were very fast, and relatively inexpensive. My mistake was in not choosing a smaller nominal size for a rough cut, and then finishing to exactly the size that I originally intended with the boring head. I think I might have reconsidered materials, used aluminum, and spent the money on Ni-Tuff.

I think I would have thought more about using Bruce's plates at the beginning, instead of at the end of the project.

There were a few other things on my mind, but I'll hold on to them until I do some more research.

Can anybody direct me to a post that explains posting pictures? I'm having trouble with that and wasn't finding it through the forum's "search" feature. Otherwise I seem to recall a way to post on the web and direct a link here. Like Dave Mc did.

[bruce]

Use the add reply button not the quick post for adding pics directly. There is a place that asks for attachments when you use the add reply. Or you can use the image button to add outside hosted pics. If you don't have a host let me know and I can host them for you. Plenty of space on the website host.

Future reference, my orifice plates can be machined for any size smaller than 6" square, to include being round if someone needs that for their bench.

[larrycavan]

[Thomas Vaught]

One suggestion on building the orifice plate, I had the 24"x24"x.125" plate laser cut with mounting holes around the perimeter and also with the 5 holes I used for the orifices. I then had to remove very little material to clean up the orifice holes.

Tom V.