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Thread: Compressor questions. How 'bout it guys?

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    Compressor questions. How 'bout it guys?

    Hi all,


    I have a little problem and I can't seem to find an answer. I know there are some compressor gurus on here, so here goes:


    First, a few basics: I have a Bauer Navy model, 6cfm, diesel driven portable compressor. When I got it, it had been sitting for several years in storage. No filter cartridge or fuel. I cleaned off the dust, added fuel, and it cranked and ran perfectly on the first pull! I let it run up to final pressure, the pop off opened as set at 4950, and I shut it down. I didn't run it any longer than that as it didn't have the filter cartridge installed.

    I don't want the hassles of an engine driven compressor, so I immediately set about converting it to electric. I won't be moving it around anyway. It is quite large for a portable, and takes up a lot of space, so I built my own frame. I basically cannibalized the stock unit and put it all in a smaller space, roughly about half of the original size. I'm in the last stages of fabrication now, and all that's left is to take it apart and get the frame sand blasted and painted, then re-assemble.


    It is for personal use, so it won't see a lot of use. I won't be filling 100's of tanks a year. Also, for the most part, 3100psi will be my max pressure. I will add a nitrox stick. I may eventually get a big tank to store nitrox, and take it up to 5000psi, but for now just straight fills to individual tanks.


    When I started trying to decide which motor to use, I looked at the 3 compressors I have access to at work. A Mako, a Scott, and a Hypress. I also looked at the Bauer we have at the shop I teach through. The Mako, Bauer, and the Hypress all had 1725 rpm motors, and the Scott has a 3450. I'm a Scott tech, so I know their reasons for the increased rpm motor. It's a 2 cyl/4 stage, and generates a lot of heat. Most of the compressors I've seen use lower rpm motors, so I figured 1725 was the most logical choice. I went with a 5hp Baldor motor, a magnetic starter, and I added a pressure switch so I can set the cut out pressure.


    At first I could not find a manual for my compressor. I figured it's a 6hp diesel, probably running in the 1500 -2000 rpm range, so a 1725 motor should be fine. After I had all these parts bought and paid for, I found the manual. Turns out its rated for 3600 rpm WOT. Idle speed is 800-1000 rpm. Now I'm wondering if I should've used a 3450 rpm motor.


    At 3600 engine rpm the compressor is driven at 1250 rpm. I've put the largest drive pulley I can fit on the motor, and my final compressor speed is only 700 rpm. On one hand it seems like that's good. It will lessen the load on the compressor. It should still make the proper pressures, just take a little longer to get there. I figured I'd be ok. A buddy of mine has a Bauer Jr, and he only runs his at half throttle to extend compressor life (that's what he says).


    Then I got to thinking about cooling, which is what I'm worried about. I will install the compressor inside my dive shed, which is insulated and heated/cooled. It will be easy to keep the ambient temps down. My concern is that with the reduced rpm, the flywheel/fan might not provide enough air flow for the compressor. I'd sure hate to burn it up over something like that. Also, if this matters, I was thinking about adding a large outside air vent near the compressor. My thinking is, I'll have a removable door in front of the fan. If it's cool out when I run the compressor it can suck in outside air to assist in cooling. If it's hot, I'll leave the door shut and crank the A/C down in the shop. Not sure if this is really necessary, just a thought. Again, with the low fan rpm, it might not pull enough air to matter. I could also use a shop fan to provide additional air flow for cooling if necessary.


    As I said, the motor is paid for. I can't return it, so I'd really like to make what I have work. Worst case, if I absolutely had to, I could order a 3450 motor, but that's another $500 or more.


    So, long story short....


    Go with what I have and leave the compressor rpms at 700, or get a 3450 drive motor to bring the rpms up to the 1250 range?


    Is the only major drawback to the slower rpm the increased fill times, or am I missing something?


    Anything obviously flawed with my approach?


    Hope I wasn't too long winded, but I wanted to give a clear picture of what I'm dealing with. Alright guys.... have at it!


    FD

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    RBW Member AzTek Diver is an unknown quantity at this point AzTek Diver's Avatar
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    Re: Compressor questions. How 'bout it guys?

    At the lower speed the oil pressure and oil splash will be alot less, it would a concern for me. Why not increase the size of the drive pulley to get compressor speed up to the 1000 rpm range. I've had several small Bauers running on 5 and 7 hp motors, all were 3450 rpm.

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    Re: Compressor questions. How 'bout it guys?

    ok its an easy one, fill a tank and check the filter for temperature if it is boiling hot that's bad if not your good to go.for oil pressure well it probably not have an oil pump and if it has the pressure is low.also oil splash there is plenty at 700 rpm.the only reason to run at top speed is time so unless your filling 60-70 s80 a day take it slow

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    Re: Compressor questions. How 'bout it guys?

    My thoughts...
    It wants to run 1250, you have the HP to drive it at 1250. Run it at 1250.


    HP is nice in that RPM is factored out. The same HP can be created from low RPM and high torque, or from high RPM and low torque. So just run a larger pulley and trade some of the torque for some more RPM.


    HP = (torque X RPM) / 5252
    (torque rating in ft-lb)

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    Re: Compressor questions. How 'bout it guys?

    I stated in my post....


    I can't put a bigger pulley on it. I have the largest diameter pulley I can fit installed.


    I thought about the oiling too... it is a splash lubrication and has an oil pump. I think I'd be ok in that respect, but again...just a guess.


    I'm still looking for a definitive answer.


    Thanks, FD
    Last edited by firemandiver; 9th February 2015 at 16:18.

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    Re: Compressor questions. How 'bout it guys?

    When I was looking at the coltris in the 9,11,13,16 sizes, as try were generally the same unit (ish) running at different speeds, I checked the parts books, and saw thy there is a selection of the pulley/fans on the pump side. It may be worth looking at various Bauer models to see if there is perhaps a smaller fanwheel on a slightly different model that may go on it? Did you figure out what the compressor block is?

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    Re: Compressor questions. How 'bout it guys?

    If it's a 6 cfm Bauer running diesel, it is almost certainly a Bauer Mariner running derated to about 170LPM due to the diesel motor.
    Normally it will pump 190LPM as an electric compressor using either a 2950rpm (at 50Hz) or 3450rpm (at 60Hz) 4KW electric motor with pulley size matching the motor.

    An easy fix for not being able to put a bigger pulley on your electric motor is to install spacers between the motor mounting plate and your electric motor. For every inch you raise the motor the maximum pulley diameter increases by 2".

    Mariners use an oil pump and are rated for continuous use, no cheap sh*t using splash lubrication involved. Use either 150wt mineral compressor oil, or for demanding applications including cold temps a synthetc di or triesther 100wt compressor oil.

    Michael

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    Re: Compressor questions. How 'bout it guys?

    one website I looked at said the 6cfm navy was a capitano.

    bit confusing as the Capitano is an IK100 block and mariner is an IK120. The IK100 block is used in the utilus 100lpm (3.5cfm) @ 900 rpm and capitano 140lpm (5cfm) @ 1280 rpm. The mariner is the IK120 block delivering 200lpm (7cfm) @ 1270rpm.

  9. #9
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    Re: Compressor questions. How 'bout it guys?

    Thanks for the input so far. A little more info:


    Yes, it is a Capitano. From what I've read the Capitano became the Mariner. In reading the service manual it is a combination type lubrication. There is an oil pump that pressure feeds the 3rd stage, and the bottom end is sump/splash. The manual also provides details for adjusting the oil pressure regulator. It says it's adjusted at the factory and should not need adjusting. On one hand I could bump the pressure up with the regulator, but I'm sure Bauer set it for a reason, so there's no need to mess with it.
    The manual also says that because of this type of lubrication system and heavy duty construction, the compressor is rated for continuous duty. That leads me to believe that it can run in some fairly wide parameters. Just a hunch, nothing solid to back that up.


    At this point, unless I can get some concrete information that running at lower rpm is fine, it's looking like I'm gonna have to man up and get a 3450 rpm motor. I know the desired range can be achieved with pulley combinations, but I am restricted to what I have built. I would have to redo it all to change pulleys. It's too much trouble. The motor change is a direct swap.

    Here are a few pics of what I have, before and after. It may be a little hard to tell, but the size difference is considerable.
    Attached Images
    Last edited by firemandiver; 9th February 2015 at 16:21.

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    RBW Member PeterVICEG is a glorious beacon of light PeterVICEG is a glorious beacon of light PeterVICEG is a glorious beacon of light PeterVICEG is a glorious beacon of light PeterVICEG is a glorious beacon of light PeterVICEG is a glorious beacon of light PeterVICEG is a glorious beacon of light PeterVICEG is a glorious beacon of light PeterVICEG is a glorious beacon of light PeterVICEG is a glorious beacon of light PeterVICEG is a glorious beacon of light PeterVICEG's Avatar
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    Re: Compressor questions. How 'bout it guys?

    You may run into heating, or rather cooling issues. It looks as if you are doing a very nice job, but I suggest you monitor very carefully the temps of all the components to be certain to not have any component over heat. The motor is now running over the heat of the compressor and the compressor will possibly be hotter due the compactness of your layout.

    It may of course be just fine, but it would not be hard to keep an eye on this at least initially.

    Peter

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