Alkin W31 3.7 or 4.9 cfm?

[lastfrontier]

I am strongly considering the Alkin W31 vertical model.

Does anyone have any thoughts on the 3.7 vs 4.9 cfm model? Is the 4.9 cfm model worth the additional cost?
I would be filling between 2-8 tanks per week, mostly 100 - 130's.

Thanks in advance!

 

[NAM001]

do the 4.9 as it gets older and reduces the output you will appreciate the extra ability.

 

[tbone1004]

The pump is the same on both of these, the 4.9cfm model just goes faster. You can make a 4.9cfm slower with a pulley change, you can't make the 3.7 go faster without a motor change.
You can get the 3.7cfm model in 110v if you don't have easy access to 220v

Faster is usually better from a convenience standpoint, however I don't know what the cost differential is. If it's not that bad, then I'd go to the 4.9, but if it's more than say $200 or so, I'd put that money into a bank bottle or two which will help you out a lot more than going 30% faster.

 

[lastfrontier]

Faster is usually better from a convenience standpoint, however I don't know what the cost differential is. If it's not that bad, then I'd go to the 4.9, but if it's more than say $200 or so, I'd put that money into a bank bottle or two which will help you out a lot more than going 30% faster.

$1200 more is the amount I was quoted. Beyond the obvious, the only difference seems to be that it includes a 2nd whip.

 

[tbone1004]

$1200 more is the amount I was quoted. Beyond the obvious, the only difference seems to be that it includes a 2nd whip.

I'd get the smaller one and get a couple of bank bottles with the difference.

The math
8x 130's filled from 500psi to 3500psi is roughly 900 cubic feet of gas.
The 4.9cfm will take roughly 180 minutes to fill.
The 3.7cfm will take roughly 240 minutes to fill.

Is one hour a week worth $1200?
Alternatively, you can buy say 4x 4500psi bank bottles which all in will probably cost you $2k with the hoses/fittings. $3k if you put line valves, gauges etc on there and go fancy, but $2k if you manipulate them by the tank valve. That will let you fill a couple of those 130's without having to turn the compressor on so you can fill a couple of them whenever you want to without having to turn the pump on.
$1200 would also allow you to build a nitrox stick with regulator/solenoid/etc and get several bottles of O2 so you can dive nitrox whenever you want for basically free.

 

[broncobowsher]

Doesn't a slower running compressor last longer as well? I just remember that from an old farmer, Got a compressor off a nearby dairy and was telling me that it works just fine if you run it slow but the dairy took it out of service because it was spitting up oil after a couple years of running it fast. That was just an industrial 2-stage for running dairy equipment. It was running happy inside the farmer's shop.

I'm going to guess the 4.7 also has a higher HP motor as well? I recently went the other way around for a local shop. Put a lower HP motor in and ran it slower with reduced output. But that was due to lack of available power into the building. Old building just didn't have the wiring needed to run the higher HP option.

As for the price, might be tied in with the warranty. John Deere makes a tractor with different HP levels. the higher HP costs more. Some of the tractors the only difference is the HP programmed into the engine computer. But the higher HP costs more, because it is calculated that the higher HP will create more warranty claims in general.

 

[tbone1004]

@broncobowsher lower RPM is always better for heat and wear.
yes, the 4.9 has a higher HP motor.
be careful slowing down splash lubricated compressors though, they can only go "so slow" before you stop lubricating, which is IIRC somewhere around 75% of their rated speed, i.e. don't try to slow the 3.7 down any more than it already is.

 

[SurfLung]

Some big name compressors will claim 3.9 Scfm fill rate which is filling an 80 cf tank that already has 500 psi and counting the full 80 cf. So you really get something like 3.0 true cfm fill rate. I think Alkin gives you the true charge rate from 0 psi to full. That said, 3.7 cfm is plenty fast. And if you ever want to upgrade, you can buy a new 5 hp motor for as low as $299 at Northern Hydraulics. BTW - I've heard Alkin makes a heck of a good compressor.

P.S. If you do the math on a big name 4.9 Scfm compressor from 500 psi to full, what you are really getting is 3.75 cfm of true fill rate from 0 psi to full. So the Alkin 3.7 is just as fast as the big name 4.9 compressor.

 

[lastfrontier]

Update - I pulled the trigger and ordered the 3.7 cfm model.
I would like to thank those of you that replied to my post. Your help is appreciated!

 

[SurfLung]

Update - I pulled the trigger and ordered the 3.7 cfm model.
I would like to thank those of you that replied to my post. Your help is appreciated!

Me Too! Wow its a beast compared to my little RIX SA3 and Coltri MCH6. I bought the vertical model W31. It's only been warm enough to use it a couple of times. But it works great.