Thoughts on a large Devilbiss air compressor build

[Smellypirate]

It just so happens I had a low hour Devilbiss 445 pump and a 200 gallon Devilbiss tank, not from the same unit. I really didn't need a compressor this big, just seemed like something that needed to happen. The first rendering was with a test engine of 13 hp with a 4" sheave. I'm on the real motor now and is a 28 hp diesel and an 8.25" sheave. With both engines, I have severe belt slap. Went to a banded 3BX belt, made a spring loaded tensioner and even added three fixed idlers at one point. It gets closer to usable but I'm really just failing to cover up the issue. The slap is on both the coast and load side. I'm pretty good at alignment of sheaves and such, and this is the first time I haven't been able to solve a belt drive problem. It's almost like the pulses from the pump are at war with the pulses from the engine. Any ideas?

 

[The Tool Tyrant]

I assume you are tensioned correctly according to Devilbiss recommendations?

 

[Smellypirate]

They have nothing on belt tension, but ive even tried making it on the far end of what a 3BX belt should be. While some slap will go away, again its seems to be more of doing something to mask the actual problem.

 

[930dreamer]

what are the rpm's on the output shaft/pulley of the engine?

 

[Smellypirate]

Slap is there anywhere from 800 to 2300. There is only a mild change in slap with RPM change, there is a slight brake in it but its about impossible to maintain. That happens around 1500. The pump must spin a minimum of just under 400 rpm for lube reasons, and cant be spun over 1000 rpm. With that in mind, under load the engine must spin at 1000+ rpm. The pump sheave is 20" and the motor sheave is 8.25.

 

[Smellypirate]

Correction, 300 rpm is the minimum pump rpm. So 800 engine rpm is still in spec. Not that it matters, slap is everywhere. But so you know the ranges.

 

[930dreamer]

Can you post a pics of your setup and a pic of the belt tension-ed?

 

[Smellypirate]

Pic of the first setup with test engine, then with the diesel. Belt is lose on the second casue its not engaged.

 

[930dreamer]

If you push the belt down from the top and bottom how much deflection do you have? Are the new engines closer to the pump then the original? Is this the factory tension setup? Lastly does the idler pulley look worn down/out?

Max rpm is 1000 rpm's;

http://www.mpsindustrial.com/docs/445 Jun12.pdf

 

[The Tool Tyrant]

Sheaves grooves are clean, uniform grooves, double check alignment and both sheaves run true? Are you using a belt tension gauge to check tension?
Sorry, I know these are basic questions, but gotta ask to eliminate possibilities.

Just for S&G's have you tried using 3 separate belts? may just be as simple as uneven tension across the belt...maybe worth a try.

 

[Smellypirate]

Original setup for the pump was a three phase electric 10Hp. Id like to see it with about .4" deflection at furthest span, which i get slap at. Ive ran it with less and more, and with too much and bare bones and still got the same slap. When i did that youd be lucky to get .2 deflection. No id never run it at that, was just for testing reasons

 

[Smellypirate]

Yes sheaves clean and true. Alignment is dam good, everything is on the same plane. I might see if i can grab a video tomorrow. You really have to see the wave even on the drive side. Beings i had two engines with their own sheave setup, in my mind that kind of eliminates drive sheave or engine. That would leave flex or something strange with the pump. Whats stranger, its a v-4. A big and small slug per bank, so it should be pretty dam smooth. But when you watch the belt, youd think its the pulses from the cylinders loading and unloading. On the other hand, pump is fairly fresh and makes air like mad.

 

[Smellypirate]

Idler is not worn, but i made it. Devilbiss didnt make this pump non electric and never with a tesioner. If i do away with it and just tension the belt, even over tension, slap is still there. I have worked on these as from factory, even the newer 2 belt ones didnt need much tesion. In my opinion, any less then .4" is too tight with this belt, distance and sheave size.

 

[American Locomotive]

How many cylinders is the engine?

 

[Smellypirate]

Sheaves grooves are clean, uniform grooves, double check alignment and both sheaves run true? Are you using a belt tension gauge to check tension?
Sorry, I know these are basic questions, but gotta ask to eliminate possibilities.

Just for S&G's have you tried using 3 separate belts? may just be as simple as uneven tension across the belt...maybe worth a try.

First go around I used standard B section. That was with the small engine and 4" sheave. I couldnt keep them on and figured with the tight bend of a 4" sheave it would be a good idea to go BX. I went banded because it almost always reduces issues, and it did a tad.

 

[930dreamer]

Pump is 4 cylinder

 

[Smellypirate]

How many cylinders is the engine?

Inline 3 cylinder Diahatsu

 

[md21722]

There really isn't a difference in compressor pumps gas/electric except all gas engines compressors have head unloaders & some electric do. Have you ever tried to run this pump with an electric motor?

 

[WittHay]

i have seen setups like that on farm equipment and they use 4 individual belts, with a fairly large diameter idler and a heavy spring. The tension bolt for the spring is 1/2"

 

[finn]

I'd guess it's torsional input into the belt from the fired engine vs the electric motor on the original setup.

Running multiple belts , i.e. two or more belt sheaves, will effectively stiffen the drive and reduce slap.

 

[American Locomotive]

Inline 3 cylinder Diahatsu

I think that's part of the issue here. 3-cylinder diesels do not have overlapping power-strokes. So you actually have a period in-between each firing event where the engine's crankshaft has no power being applied and actually starts to slow down.

That coupled with the heavy compressor flywheel and crankshaft is going to setup a lot of pulsing in the belt-drive.

 

[Smellypirate]

I think that's part of the issue here. 3-cylinder diesels do not have overlapping power-strokes. So you actually have a period in-between each firing event where the engine's crankshaft has no power being applied and actually starts to slow down.

That coupled with the heavy compressor flywheel and crankshaft is going to setup a lot of pulsing in the belt-drive.

This kind of where I'm at, I'm just not sure of the solution. I'm considering slightly restricting the intake so the flywheel doesn't over run after a compression. I'm just not real big fan of all this guess work.

 

[930dreamer]

You build a rotary phase converter for a 10hp 3 phase electric motor.

 

[American Locomotive]

Higher engine speeds with a smaller sheave might help. I'd try to step down the pulley size and run the engine right at governed speed.

I've also seen this compressor pump with a 5HP electric motor, so there's that option too.

 

[moriboy]

Just throwing this out, would the height of the motor make any difference? Meaning that if you had both the pump shaft and motor shaft in the same plane. That would make the angle of the belt equal as it rolls on and off both sheaves.

 

[Smellypirate]

Just throwing this out, would the height of the motor make any difference? Meaning that if you had both the pump shaft and motor shaft in the same plane. That would make the angle of the belt equal as it rolls on and off both sheaves.

I wouldn't think so, though at this point, who knows. The test motor was much closer to that, and I had identical slap.

 

[Smellypirate]

Higher engine speeds with a smaller sheave might help. I'd try to step down the pulley size and run the engine right at governed speed.

I've also seen this compressor pump with a 5HP electric motor, so there's that option too.

The test 13 hp had a 4" sheave and I spun that at 3000. Same slap.

 

[American Locomotive]

The test 13 hp had a 4" sheave and I spun that at 3000. Same slap.

The test motor was also a single cylinder. You should see how much the belt on my V Twin mower deck bounces around. That automatic belt tensioner gets a workout.

Your idler pulley is also very small. I would add a larger spring loaded idler pulley with a fixed v-groove idler near the tensioner on the other side of the belt. Thar way the belt is supported on both sides.

 

[Smellypirate]

The test motor was also a single cylinder. You should see how much the belt on my V Twin mower deck bounces around. That automatic belt tensioner gets a workout.

Your idler pulley is also very small. I would add a larger spring loaded idler pulley with a fixed v-groove idler near the tensioner on the other side of the belt. Thar way the belt is supported on both sides.

Good point, I'll see if I can enlarge the tensioner.

 

[MacMcMacmac]

Are you sure all of your pistons and valves are working properly? If you have unbalanced forces on the compressor side it will run rough.

 

[slow_mow]

Just throwing this out there, but what is the rotation of the pump? It looks to me like you're tensioner is on the wrong side of the belt. You always apply tension on the slack side of the belt, otherwise the pulling of the engine will cause the slapping you're experiencing. Try putting your tensioner underneath and see what happens.

I could be completely wrong, it all depends on rotation.

 

[454ragtop]

You should probably set up a dial indicator and check both pulleys for runout. If one of the pulleys isn't running true, it will load and unload the belt as the high spot goes around.