Bench novice needing assistance!

[mattpatt]

Hi all.

First of all, many thanks to Bruce for helping me with registration to this forum. Now that I can get right in there I've found a wealth of very informative stuff.

Anyway, I'd like to introduce myself as a complete flowbench novice, so please don't be surprised if I ask questions that have already been asked a million times, but I just need some help on a few things.

My first flowbench is close to completion. I 'borrowed' the rough ideas from the MSD plans and then modified them to what I wanted. What I've ended up with is a bench almost identical to forum member cfm200's bench. Please don't acuse me of plagiarism, it was purely coincidental.

Moving on, thanks to the info in this forum, I think that I've sucessfully completed the set up of the inclided manometers, but just to be sure I'd be most grateful if someone could just verify the following:

I want to attach a picture of the bench but I don't know how.

My bench has three main chambers (like cfm200's bench). The vertical manometer is probed into the top (1st)chamber, the other end open. The inclined manometer has the reservoir end connected to the 1st chamber (same as vert. manometer) with the other end probed to the 2nd chamber. The orifice plate separates the 1st and 2nd chambers. 3rd chamber houses the motors, which exhaust through holes drilled in the side of the cabinet.

When I run up the motors, everything seems to function correctly.

Next I wanted to verify the incline so I followed cfm200's method of using a hand pump (it was 11.30pm last night and I didn't want to upset the neighbours!), and connected the 1st chamber hose end from the vert manometer and the 1st chamber hose end from the incline manometer to a 'T' joint and then to the hand pump. I pulled 12" differential on the vert manometer, and this corresponded perfetly to the 12" height on the incline. As I slowly relesed pressure 1" at a time I noted the height change on the incline and it matched up nicely, all the way to zero. Incline length is as shown in the drawing, and I'll use the spreadsheet on this site to make the percentage scale.

So....my first main question is; is that the correct way to do it?

A very quick (suction) leak test showed almost nothing at 12". Not very accurate or scientific at this point but it was late and I was tired!

Then, just for fun and to wake everbody up, I fitted my home made 2.05" orifice, and then another 2.05" on the top of the bench and ran up to the 100% point that I'd marked. However, the vertical manometer was showing approx 11", not 12".

I do have another orifice hole in the cabinet that I was going to use as a blow tester, but that's sealed off.

I know that there's going to be some leaks, and I'll nail these in time. I'm also going to have to fit some valves for the vacuum motors as I'm sure I'm pulling back through the motors as when I get 4 of the 6 motors fired up, then remaining two are spinning, which is not good.

Sorry for my long first post. I'm just a little excited

[mattpatt]

Thanks to Bruce again for helping out with the attachment process, so here's a rough diagram of my bench.

[mattpatt]

So what I was basically saying in the first post was that I connected ends B & D to a T joint, and then to the vacuum pump. Ends C & A were both open to atmospheric.

With 12" difference on the vertical manometer the inclined manometer rose from zero setting up to the 12" height.

Just for info, I then connected A & C to the pump and applied pressure to 12" difference on the vert, but the incline only rose about half way. No idea what that means (if anything at all).

[200cfm]

It's been a while since I calibrated my manometers to each other. I will have to refresh my thinking by reviewing some notes. Once you mark up your incline scale % flow you can use the marks as a reference but it is quicker, easier, and more accurate to go directly to the formula to calculate the CFM air flow. Use the formula: CFM = square root of the ratio of the delta incline rise to total incline length times the CFM rating of the selected orifice plate.

I notice your manometers are marked in inches. That's fine but you can have greater accuracy and easier tube reading on the manometers if you go with a CM and MM scale. Example: An incline rise to 37.5 cm or 375 mm. Much easier to read the total rise more accurate than using inches, halfs, quaters, eights, etc. At least for me it was.

[mattpatt]

Thanks for the reply.

As for the scale being in inches, I've really only gone imperial because of the fact that everyone else in the flowbench game seems to talk inches.

From what I can see so far, If I select my 52mm (2.047") orifice, and then put another 52mm orifice over the bench inlet, pull 12" on the vert, with the incline at 100%, I can say that I'm pulling 197.4cfm if we call the Discharge coefficient 0.62.

If I then obstruct the top plate, reset the vert to 12" again, but the incline has dropped to 70%, then I'm pulling 138.2cfm. Correct?

This is of course assuming that my setup is correct in the first place.

Oh, and just got hold of a bunch of 2" water pump valves. These will definitely do the trick in stopping backflow through the motors. And at only $5 a pop I could hardly refuse.

[200cfm]

Your vertical test manometer is marked up to 30 inches. Are you building to test at 28 inches wc or 12 inches wc?

Yes, if the incline goes to 100% incline rise with an angle that positions it 12 inches up and you have selected the 2.047" orifice, you are moving 197.4 cfm through the orifice.

The total pressure drop from head opening to exhausting would be 28" wc vertical test manometer reading plus 12" wc incline manometer pressure drop for a total of 40 inch wc pressure drop from the top of the bore bench to exhausting port.

But if you are setting the test vertical manometer at 12" wc you are going to flow less and the incline is going to rise far less. Hope I am not wrong on my theory here. It has been several months since I have had time to work the theory and my bench. Will get back "into to flow" this winter though.

[ThomasVaught]

The vertical manometer because he has a "U-Tube" arrangement may be 30 inches tall but one leg will be going down and the other leg will be going up. Adding the two legs will equal the total test pressure or 30 inches maximum but most likely he will be able to read about 28" of test pressure accurately. Read the "up leg" at
14" from the "Centered Zero point" and multiply by 2.

The test pressure manometer is reading the delta P across the TEST PART.

The Inclined manometer is reading the delta P across the FLOW ORIFICE and reporting the test part reading vs a maximum 100% flow reading for that given orifice.

The combined pressures; Test pressure and delta p across the flow orifice are only valid when sizing the vacuum motors/ blower for maximum
test pressure of the bench.

Tom V.

[Tony]

If you are going to be testing at 28" it may pay to make the test manometer a lot higher than 30".

The reason being, that if 30" is exceeded all the water will be blown out instantly from the manometer. It will be remarkably easy to reach thirty inches while adjusting the test pressure. Make the manometer legs as tall as you possibly can.

If your vacuum motors can pull a hundred inches with completely blocked flow, the test pressure could conceivably go that high in an instant if you drop a valve during testing.

[mattpatt]

Hi All,

Thanks for the replies so far. I'd like to just clarify exactly where I am with this.

On the vertical manometer I'm tesing the difference between ambient pressure, and the pressure drop in the chamber immediately after the test piece. I set that at 12" difference, so 6" above zero on one leg, and 6" below on the other. The vertical manometer will read up to 28" difference because that's the way I made it. No other reason.

The incline is set at 12" vertical height between the zero and 100% point.

If I select the 2.047" (52mm) orifice between the first and second chambers, and then fit another 2.047" orifice over the top bench test hole (which is 4" incidently), and then set the vertical manometer at 12" difference I should read 100% (or 12" difference) on the incline manometer right?

That's exactly what's happening now, and I'm assuming that I've done it right, but we all know that assumption is the mother of all...ahem...mistakes!

On to the leak test. Covering the top hole and pulling up to 12" makes no conveivable difference to the incline. At 28" I would figure no more than a couple of %. However, my scales at the moment are not very good, and I am actually at the office at the moment printing them out properly using SolidWorks so that I can be a little closer to the truth.

'Other' problems so far:

The water pump valve I got needed modifying a touch, so I turned them down in the lathe, then fixed them in position. I then discovered another 2 problems. The spring controlling the valve is a little too strong as I checked the vacuum on each motor with and without the valve and the valve difinitely caused a drop in power, so I will need to modify this.

Next problem was that the valves are obviously causing a problem with the flow of air into the second chamber. There's not enough room to get the valves away from the orifice, so I'm thinking that it's causing grief with the incoming flow. This was sort of verified by running the 2x 2.047" orifices (as tested above). With valves assembled I was getting 100% flow on the top plate, but at 11", but with valves removed I was back to the 100% at 12". My presumption here is that the valves are retricting the flow through the 1st/2nd chamber orifice, so it's potential flow rate has been lowered, meaning that the top plate (even though it's the same size) essentially has a greater flow rate.

As for blowing water everwhere, you weren't the first, and I bet that I'm not the last to do it My plans for today are to increase the size of the incline reservoir, so less drop of fluid and more accurate incline reading, and also add reservoirs to the top of the incline and also the vertical (that one's for you Tony!). It was an interesting observation that when you get flustered and fire the water out the top of the incline, even when you hit the kill switch the water continues to flow into the 2nd chamber thank to the syphoning effect. It's also a useful way (although not recomended) to find a split in door seal when the blue dyed water starts dripping on the workshop floor :;):

[mattpatt]

An update.

Changed lots of litle things on the bench, such as increasing the diameter of the reservoir pot for the incline manometer. Also reduced the ID of the incline manometer from 6mm vinyl (floppy) tube down to 4mm acrylic (rigid) tube. Then made a pair of 30" tall vertical manometers out of ID 6mm acrylic tube. Rigged all this up and seemed to be getting some sort of result.

Checked for leakage. Fitted a 30mm orifice plate, blocked the test hole and cranked up the volume to 12" DP. The incline crept up to around 4% I would guess. This would tell me that I have approx 2~3 CFM leak.

Is that a correct assumption? If I leave it at this should I then take say 3 CFM off subsequent results, or should I take 4% off?

Next I stuck my 52mm plate in with a 52mm plate as the test plate and dialed in 12". The incline went up beyond the 100% mark to about 102%. If I took the 3 CFM off this result I would end up with a reasonable close number to what the 52mm plate is supposed to flow.

How am I doing so far.

I then went through my other plates, keeping the 52mm plate as the reference, and flow rates seemed to be within a couple of CFM to what I had calculated from the spread sheet on suplied on this forum.

This pleased me, so I hope all is ok so far.

I then went and switched the 52mm plate for the next size down and tested the smaller plates again compared to the new reference, and again came up with some very close results.

What do you reckon? Am I somewhere on the money?

Just for fun I then made a velocity probe usine 1/16" & 1/8" brass tube. Bending it was fun (NOT), as was drilling the little holes. I sealed the business end with some epoxy. At the separation end I drilled a hole in the outer (1/8") tube, soldered on another length of 1/8" tube, and then stuck some fittings on for my tubing using epoxy. Then covered the soldered joint in epoxy just to be on the safe side. I was rather sceptical as to whether my first attempt would work or not, but I connected it up to the vert manometer and jumped for joy when it did what it was told.

As for it's accuracy I don't know. The inner hole diameter is 0.7mm (dynamic), and I drilled 4x 0.7mm holes around the outside of the 1/8" tube. How important are these hole dimensions? I mean, if the vert manometer goes to 12" can I confidently say that the velocity is around 229 ft/s, depending on ambient temp and pressure?

Looking forward to hearing what you have to say.

[ThomasVaught]

Apparently you are coming up to speed quickly on your bench.

At This point some might say just go electronics and eliminate the water manometer issues.

I personall think that if you totally understand the "physics" behind the bench you can get your bench to be very accurate with manometers.

Unless you are doing the deal as a fulltime job,
I would say the time factor with the electronics
is balanced with the "Physics" knowledge you gain.

JMO

Tom V.

[mattpatt]

Tom,

Building my flow bench was basically just a project to test myself with. I'd read a bit up on it and there seemed to be a lot of for's and against's, with some saying (especially commercial flow bench retailers) that it was impossible to modify an engine without the assistance of a flow bench, and others sying that if the head looked right, it probably was right, or at least close.

I've modified mainly two stroke engines, but in the last few years have worked more and more on fourstrokes, and have found that very few have responded well to actually opening up the ports and it seemed to me that they seemed to improve as the velocity increased by reducing the ports, or filling in "dead" areas. So I decided that enough was enough, I needed to know what was really going on in there and wanted some solid numbers to back it up.

Since getting into this I've read through a lot of very interesting info regarding flow numbers, flow velocity etc., and can see that a flow bench is quite a valuable tool to have on hand. And it's also been good fun (and frustrating) building it and trying to figure out what's going on and how it exactly works. I don't like buying things like this if possible because I really do like to know how they work, not just that they do work.

The flow bench isn't a tool for my job as such, but it does tie in nicely, and it's quite amusing and satisfying when a customer walks into my workshop and says WOW, you've got a flow bench, and I can say, Oh that old thing, something I knocked up in my spare time

Anyway, time's always at a premium, and I still haven't had time to get anything onto the bench worth testing yet, but I will, and you guys will be the first to know if it's all been worth it, or just a waste of time.....the former I hope!

[106-1194218389]

Hey I am sure glad I joined this forum. I love to build things myself and I am glad to see the inclined manomets are working. I just got a quote on a Mariam 30" with a 12 inch rise and it was $1056.00 WHEW! So that makes the effort of building much easier.