Flow Meter Location - Help finding an old post.

[PFM]

All,

I think I read a post about error in a flow bench caused by placement of the measuring device too close to the part under test. I did some searches but have not been able to find it. Any help would be great.

Thanks in advance.

PFM

[larrycavan]

I think you're referring to the placement of the manometer pickups [probes]....

Pitot benches have different requirements than an orifice bench. Bruce or one of the other Pitot guys can better explain the Pitot system setup.

For an orifice bench, their locations are dependent on what's going on inside the bench. Turbulence issues can make the meters bounce. Velocity sensing will throw the meter off. You want to be sensing pressure changes and not reading velocity impact.

Last summer I tested different locations of the top plenum pickup location and found that in my bench, I could slip a length of tubing over the metal probe and no matter where I placed it in the top plenum I got the same pressure readings.

As long as it wasn't pointed directly into the air stream.

My test pressure pickup is located on top of my baffel plate and the manometer pickup is located a few inches away from it. It works. You may or may not have similar results.

Hope that helps.

Larry C

[PFM]

Larry,

Thanks for the reply, my bench uses a Flow Performance flow element, so I guess you would call it pitot tube flow element. I know there is quite a post here on the subject of placement and turbulence etc. I just wanted to review it.

Just trying to get the last little detail and gain a bit of repeatability etc. from the bench.

Thanks again,

PFM

PS I have a little / large spread sheet to add to your Excel area, after I clear off a shop name or two I will post it. I is designed to be printed op a large format printer / plotter say 36" wide, it is a nice TQ / HP spreadsheet.

[larrycavan]

Spreadsheet sounds good...can always use more of those...

[The Silver Bullet]

[larrycavan]

Here's a sketch showing how the manometers should be hooked up. You have to reverse the connections when you reverse flow through the bench or hook them up with valves that perform that task. I would suggest staying away from the valves until you have calibrated your bench, then go back and add them if you like.

There are different opinions on specific probe locations. Some guys put them right next to the orifice plate and get good results. I put mine away from the orifice plate and get good results.

I use a probe with static holes drilled around the cirumference for the test pressure pickup.

Both top plenum pickups effectively sense the same pressure reading. The MSD article calls for the test pressure probe to be located in the test adapter cylinder. I tried that way back when...I would not advise using that method. I got best results when I moved it to the plenum

[The Silver Bullet]

That is how I thought they went, but it is good to be 100%. Thanks a million. Now I need to get some orfice plates.

[trader]

I posted some pic's of my project in the readers flowbench projects, so that I could add a question to this post. I will probably T off the LFE like Meriam suggest, but want to add another static pickup in the plenum. Suggestions???

Also I have a bimetalic temperature guage, and would like suggestions, of where to place the 6" probe in the plenum. Looking at my project, would it be unwise to place it directly in the path of the flow below the test hole?

I intend to remove the hook and temp sensor fitting from the top of the LFE filter, and silicone a stainless mixing bowl to the top of the filter, to smoothe out the flow. I also intend to install a deck plate to the plenum cover, inside the cabinet, so that I can change the filter..trader

[trader]

On the SF 600 and 1200 I see a temp guage in the front of the plenum. Can someone tell me if the probe is in the direct path under the test hole? Or is it just reading the temperature inside the plenum, out of the way? thanks...trader

[Thomas Vaught]

Temp probe is well away from the orifice and is reading air from the discharge tube that has hit the baffle plate.

Tom V.