What makes an older compressor drop cfm?

[msanderson]

Hi all,

I have an older compressor (Poseidon P100 a.k.a. Bauer Jr II from what I'm told). I just had it serviced and the report came back with the following text:
"Unit in very good shape. Unit was manufactured in 1990 and was originally rated to pump 3.5 cfm. Upon measuring the unit, it is currently putting out 3.2 cfm or running at 91% of original capacity which is extremely good for a unit that is 20 years old."

And the report goes on to say that the actual CFM is 3.2 at 1800psi

So, my question is just how does a compressor age and what does this indicate? Does it mean that there are some leaks round some seals somewhere? I wouldn't have thought so because then it wouldn't be likely to get up to pressure (I have the relieve valve set to 3,600psi so I can fill HP steel tanks at 3,500 with no problem.)

I figured the likelihood was that it was the gas motor (Honda) that wasn't spinning as fast, but by not saying anything like that, to me the report implies that it's more a function of the compressor (the bit about it being pretty good for an older unit).

One other option was that it never ran to its rated cfm and this in fact doesn't indicate anything.

I'm asking because I'm interested in changing the gas motor out for an electric motor and then doing some continuos blending, but am thinking if there is something old and worn out on the compressor itself that I should probably look for a different compressor for that job.

Cheers,
Mike

 

[Hank49]

I bought a used Bauer Jr 2 and the pistons and cylinders, like in a car engine, were worn. You get blow by, or air that passed around the piston rings instead of moving to the 2nd or 3rd stages which reduces your CFM.

This is assuming that your drive engine rpms have not reduced.

 

[Wookie]

What Hank49 said. Another thing to consider is the condition of the valves and valve seats. Little chips and nicks are a fact of life and allow pressure to bleed back into the stage before.

Not very likely that you have a seal leak, they get worse quickly.

A warning. If you intend to CB nitrox you will want to consider the oil you use, and the condition of your final stage piston. It gets mighty hot in the final stage and lower flashpoint oils can flash in high O2 environments. Take it from someone that has spent many thousands of dollars rebuilding air compressors.

Frank

 

[veriqster]

as said above, internal ware and tear. it's probable that it has small leaks as well but those are easy to identify by pressurizing an looking / listening. it's also possible that the motor does not spin as supposed to, as internal engines loose compression they also loose power which might limit how fast it can spin the pump. test the rpm to narrow it down, if the rpm are correct than it's something in the pump, most probably rings, if rpm is low test compression on the engine. depending on what's wrong with it, it might actually make sense to service and keep it. best of my knowledge rating of the pumps does not account for draining the water out of the separators, which actually lets out some air and might account for some differences as well.

 

[DCBC]

If you're getting lower air pressure at the point of use the low pressure can be caused by a number of factors. You may have air leaks in the distribution piping or clogged filter elements. The pressure at the compressor discharge may not be sufficient to overcome system pressure drop. Check the lines, connections and valves for leaks and make sure you clean or replace filter elements.

 

[veriqster]

forgot to mention, quick way of finding out if you have significant blowby on some of the stages is to see how much air you are putting out the crank vent, not sure this spump has one(not familiar with it) but if it does it will give a pretty good idea on condition of the pistons / rings.

 

[msanderson]

Hey, thanks for the insight and ideas, I really appreciate it!

I'll measure the RPM of the motor this weekend and see where that leaves me. The compressor does reach my desired pressures (in fact the service tech said that the unit rated to 5,000 psi and that he'd expect that it would reach there. I probably should have had him check that at the time, but instead I had him put on a 3,600 psi relief valve.

If I'm not too worried about time for fills, is slowing down the compressor a little actually a "good thing"? Am I right in thinking a slightly lower rpm will allow the block to cool a little more between strokes? I guess if the pistons are leaking then slower is probably worse - more time during the compression cycle for the blow by?

And in the spirit of keeping heat down (especially for working with EAN), has anyone every thought of trying to put a fluid jacket and small radiator on any of these small compressors? It seems that it might not be that hard a hack - maybe you'd just do it for the 3rd stage?

Cheers,
Mike

 

[veriqster]

slowing down a splash lubricated compressor is NOT a good idea, they rely on the speed to "splash" oil for lubrication, a compressor that has an oil pump is a different story. contact a bauer representative to find out the minimum design rpm, don't go lower.
water jackets are too complex for a system that vibrates as much as a compressor. if you want to you can fit an interstage water coller, basically a coil of stainless that is placed in a water bath for cooling. it will improve the filter life and reduce output air temperature.
also, test for both engine and pump rpm, just in case you have belt slip. fill a tank without draining the separator (if capacity allows), calculate your output and compare to specification charts for the compressor.
once you go EAN you want to keep the temperatures down as much as possible to avoid oil flash. also, switch it to synthetic oil before you do that. look this up on the forum, it's not too complicated but is not as simple as a car oil change, especially if there are carbon depposits.

 

[Wookie]

And in the spirit of keeping heat down (especially for working with EAN), has anyone every thought of trying to put a fluid jacket and small radiator on any of these small compressors? It seems that it might not be that hard a hack - maybe you'd just do it for the 3rd stage?

Cheers,
Mike

water jackets are too complex for a system that vibrates as much as a compressor. if you want to you can fit an interstage water coller, basically a coil of stainless that is placed in a water bath for cooling. it will improve the filter life and reduce output air temperature.

once you go EAN you want to keep the temperatures down as much as possible to avoid oil flash. also, switch it to synthetic oil before you do that. look this up on the forum, it's not too complicated but is not as simple as a car oil change, especially if there are carbon depposits.

Yup, what he said. You can easily build your own cooling jackets for the interstage coolers, or you can buy them from a compressor re-manufacturer like Stark Industries. Cooling the first stage output will result in removing most of the water from the compressed air, resulting in longer final filter life. Cooling the final stage is the safest for making EANx. Cooling all of them is a great idea if you have essentially limitless amounts of cool water.

If you are changing from one diesther oil to another the change isn't that big a deal. If you are switching from a petroleum-based compressor oil, the procedure is long, but not difficult. There are lots of intermediate steps. I recommend UltraChem's Chemlube 800 for high flashpoint.

 

[IyaDiver]

Hi Mike,

The Bauer junior is rated at 2,300 RPM for the newer ones and 3.6 CFM , I don't know the older one and comes with 5HP Honda. There is a name plate on the frame that will tell you such spec.
Its good for low usage but don't push it to hard, 2,300 RPM is too fast for heavy duty work.

When you remove water from the separator during a fill, watch for the colour and the oil content in the water. If piston rings or liner are worn out, I used to get the water from milky white ( usual ) to yellowish ( mineral oil used not synthetic ). Yellowish means high oil content in the air production. If your compressor oil color turn dirty fast and also a bit whitish in under 200 hours of operation, that is a lot of piston blow-by happening.

At the filter housing where the filling hose is connected, that is a small alumunium block next to the base of the filter housing, that is the Pressure Maintaining Valve ( PMV ). Make sure it is set at 2,200 psi and this is very important for proper dwell time of the air within the filter housing hence proper filtration. I ruined this PMV often by using the compressor on boats ( salty - wet ) and over due filter change because I back then do not understand filter life correction factor for hot climate.

I once asked a Bauer tech during a seminar, asking him why there are build up of whitish residue like salt on my PMV ? I always thought it was salt from heavy used at sea but it was not all salt.
I was told that once the filter media is over saturated ( forgot which one of the media ), there will be corossive by-product bleaching out. I do not know if this is the sulphuric acid from over saturated carbon charcoal as what one article I remember reading. The PMV aluminum housing will be pitted internally and that was what happened. Once it pitted and jammed up, the PMV will stop working.

You can easily tell if a PMV working well ( but wether the pressure is set correctly or not is another story ) by dumping air out of the filling hose assembly. If the dumping air from the filler hose also empty the filter housing, your PMV is jammed open.

My older compressors when used on the boat, they are always aging so fast due to high ambient temperature, direct sunlight exposure ( very hot ) , salty air wave splashinh sea water on the comp and what I did not understand about filter life back then.

Good luck with your diving fun with that compressor.

Regards,
IYA