AHS S130 - Fan Disk Position Question

Hi,

I am switching from a direct drive fan assembly to the belt drive option. I am about to assemble my fan disk onto its drive shaft. Two set screws hold the fan in position on the shaft. I want to make sure the fan disk is in the correct position on the shaft. The extremes could position the fan disk with slight clearance from the abrasion shield or with slight clearance from the swirl chamber. The actual range of position between those extremes is 3/4 inch. I am hopeful someone can give me his or her opinion of the optimal position for the fan disk within that range. I failed to measure the original position so I do not have that as a reference.

Best Regards,

Brian

MacCoon wrote

MacCoon wrote:I am switching from a direct drive fan assembly to the belt drive option. I am about to assemble my fan disk onto its drive shaft. Two set screws hold the fan in position on the shaft. I want to make sure the fan disk is in the correct position on the shaft. The extremes could position the fan disk with slight clearance from the abrasion shield or with slight clearance from the swirl chamber. The actual range of position between those extremes is 3/4 inch. I am hopeful someone can give me his or her opinion of the optimal position for the fan disk within that range. I failed to measure the original position so I do not have that as a reference.

When you have the shaft in place (in the bearings) slide the shaft all the way in. MARK THE SHAFT at the shield then slide it all the way out and again MARK THE SHAFT again and measure the haft way point, this point should be set at the sheild and that should do it.

Mazzy

That will split the difference nicely. But if it is like the AA fan, and I'm just guessing here, there may be a critical dimension from fan to housing clearance. If no one chimes in that knows for sure, I would give AHS a call to be sure you don't give up a bunch of suction because you didn't know what the number is.

I don't believe it's critical. The Axeman Anderson simply calls for it to not scrape when flexed. The Axemans are on rubber mounts. If you "lean on it" and it scrapes, move it a bit. I think the AHS is more a rigid mount. I'd shoot for half way & happy sailing.

I bought my AHS S130 with the belt drive option. It just so happens I have the entire assembly removed from the boiler. I'll measure it tomorrow. Any particular dimension you want? I think I'll post a photo with a ruler.

Yanche,

Please take a measurement from the annulus (outboard surface) that holds the gasket within the abrasion shield to the outboard surface of the fan disk.
In my photo attached that distance is 1.55 inch with the fan disk up against the ceramic heat shield.
Note: The thickness of the rule on the square is 1 inch for reference.

Many thanks,

Brian

MacCoon

You need to install the heat shiels assembly on to the boiler, losen the set screws on the bearings and follow the haft way rule I posted earlier. I called tec. support last year and this is what AHS recommends.

Mazzy

Thank you for the halfway position recommendation. However; I have decided to use an imperial method to get some data first. The basic assumption is fan efficiency is proportional to pressure drop across the coal pot. So I will measure pressure drop at various positions. My intuition tells me that the fan should be closer to the swirl chamber than the abrasion shield to obtain efficient operation. I will start the test closest to the swirl chamber. If I had to venture a guess the efficiency will be a second or third order function relative to the distance from the swirl chamber. We will see.

Plan:
Measure pressure drop across the coal pot at various fan disk positions.

Method:
Remove the coal grate thereby emptying the coal pot.
Close off the bottom of the coal pot sealing it from airflow.
Close off the coal inlet tube also sealing it from airflow.
Install a pressure port in the draft inlet flap (e.g. site tube cover.)
Connect the pressure port to a water manometer,
Run the fan at positions across the position range from .025 to 5/8 clearances from the swirl chamber.
Measure the delta-P across the coal pot.

Positon , Delta-P
.025 . ? in Water
1/8 , ? in Water
1/4 , ? in Water
3/8 , ? in Water
1/2 , ? in Water
5/8 , ? in Water

My setup is half done. Will finish Monday.
More to come….

Brian

Here's the photos:

Over all view:

The motor speed is 1750 RPM. The speed ratio is 1:1. The pressure drop was not linear as expected. However; the fan efficiency relative to gap from the swirl chamber was the opposite of what I expected. The knee in the curve is at a distance of approximately .5 inch from the swirl chamber. I set the fan at .6 inch from the swirl chamber to stay safely in the maximum range and have ample clearance (~.265 inch)from the abrasion shield.

My direct drive setup provided a draw of 2.75 inches of water with the ports closed in similar fashion. I plan to change the drive pulley to a 4inch with the driven pulley being a 2 inch for a 2:1 speed increase. I will get the new pulley and belt tomorrow and retest.

Wondering how I closed off the bottom of the coal pot and top of the coal inlet tube? I used 2" thick DOW board. After cutting the basic shape I pressed the board into the pipe to get an impression. Then I cut out a 3/8 wide groove along the impression. The groove was filled with silicone and press fit into position. Yes I will have to peel off the silicone when finished but it will be worth the effort knowing I have a leak free seal for the test.

More to come ...

Brian

Brian,

The reason the results were not what you expected was due to increased turbulence losses between the fan and abrasion/heat shield as the fan impeller was moved away from the abrasion shield and toward the swirl tube.

The recommended position for the fan impeller is based on reasons other than performance optimization. Our concern is fan removal during replacement or other maintenance procedures. We recommend that the impeller be located on the shaft so that there is about 1/8 inches of fan hub sticking out over the end of the shaft. This prevents any of the outside of the shaft from becoming rusty. It also creates a small well for penetrant that can be placed on the end of the shaft for "soaking in" and subsequent loosening when the fan must be removed from the shaft.

Mike

Wouldn't having a burning pot of coal give you different results as the draft (or pressure as you measured)would not be so free flowing? I think rpm changes or fan design would be more useful in increasing efficiency. Or a variable speed, computer controlled of course, based on demands or economy, sort of a "Coaltrol" for boilers. When you get it to the point where you can vent it with pvc, I would be knocking on the owners door. Just rambling

Mike, Thanks for the setup information relative to the Fan Disk/Hub position. I will employ that mounting technique. What penetrant do you use that stands up to the heat in the swirl chamber?

Wanted to clarify that my measured data trend in Test 1 is increasingly increasing up to the knee in the curve while I was moving away from the swirl chamber and towards the abrasion shield. That effect repeated when I increased the Fan Speed.

Update: I miss-stated the draw in my direct drive setup. Earlier I reported the draw was 2.75 inches of water when it actually was 2.0 inches of water. So the nominal difference between the direct drive setup and the belt drive setup (1:1 ratio) is approximately half (e.g. 1.08 in HOH to 2.0 in HOH). HOH = water.

So here is my result for the speed increase experiment, Test 2:

Speed increase %150;
Driver Pulley OD = 3.9 & Driven Pulley OD 2.6, speed increased from 1750 to 2625 RPM.

Pressure increase %243;
Test 1 Pressure1.08 to Test 2 pressure 2.62 in HOH
Notice the knee in the curve occurred much earlier as the fan was moved away from the swirl chamber toward the abrasion disk! This makes the Fan Disk position less critical relative to the swirl chamber than the lower speed.

Note: All data from Test 1 and 2 represent static pressure measured with zero airflow and is effectively a pump suction head test. The airflow dynamics of a burning coal pot with heated flue is a totally different subject. I plan to install an analog pressure transducer so I can track and log Delta-P during burn. That will be sometime in October.

Brian,

Penetrants will not stand up to the heat. They are very unlikely to prevent seizing of the fan to the shaft. Some time of anti-seize would be recommended for that. The penetrant comes into play strictly at removal.