My RIX SA3-E

[tbone1004]

I would recommend you call Eric Z and ask him to clarify the design parameters and compromises of the Rix because you clearly won't believe anything that I have to say. Reliability and field serviceability are high priorities and I was not questioning those, longevity is not something they are often concerned with. The design engineer I talked to was at a conference many years ago and he has since retired.

All you have to do though is look at the scheduled maintenance on these things compared to something like a Bauer to realize that they are designed for completely different things.
50 hours to lubricate bearings, 200 hours to replace the third stage piston vs a comparably sized Bauer that has it's first valve replacement at 2000 hours on it's PM schedule. I don't appreciated you putting words in my mouth saying that they're running on the ragged edge of failure, which they are not. They are running at the maximum safe speed at the sacrifice of longevity in order to give the military the smallest package possible. That interval on a SA6 is 15k cf of gas before you have to lubricate. That's a LOT of gas, and for a compressor that was designed to go on a zodiak and be small, portable, and durable, and that was more than long enough since they were intermittent duty. Go out on a couple missions, come back and lube everything, happy days. Something like 50k cf for the third stage, that's several years for what they were doing. For something sitting in a fire department or dive shop where 200 hours goes by REALLY fast, it gets expensive.

 

[rjack321]

I would recommend you call Eric Z and ask him to clarify the design parameters and compromises of the Rix because you clearly won't believe anything that I have to say. Reliability and field serviceability are high priorities and I was not questioning those, longevity is not something they are often concerned with. The design engineer I talked to was at a conference many years ago and he has since retired.

All you have to do though is look at the scheduled maintenance on these things compared to something like a Bauer to realize that they are designed for completely different things.
50 hours to lubricate bearings, 200 hours to replace the third stage piston vs a comparably sized Bauer that has it's first valve replacement at 2000 hours on it's PM schedule. I don't appreciated you putting words in my mouth saying that they're running on the ragged edge of failure, which they are not. They are running at the maximum safe speed at the sacrifice of longevity in order to give the military the smallest package possible. That interval on a SA6 is 15k cf of gas before you have to lubricate. That's a LOT of gas, and for a compressor that was designed to go on a zodiak and be small, portable, and durable, and that was more than long enough since they were intermittent duty. Go out on a couple missions, come back and lube everything, happy days. Something like 50k cf for the third stage, that's several years for what they were doing. For something sitting in a fire department or dive shop where 200 hours goes by REALLY fast, it gets expensive.

Once, a long time ago (15+yrs), we had a local shop that tried to use the "oil-less" best quality gas as a selling point. They had 2x SA-6s. That was a hard lesson for them. The rebuild costs combined with the time required and the rebuild frequency was brutal on their bottom line. For years they would have one or the other pump down for costly maintenance - in parts and in the time it took to rebuild it which took away from other income generating activities like classes, reg maintenance, tank vips, etc.

Eventually those owners sold the shop. One of the first actions the new owner was forced to do was replace the 2x SA-6s with a Coltri 16cfm model (? I forget this was back in 2007). The new owner also added a super fancy membrane system with a giant LP compressor to drive that. The lease on all that equipment (despite the vastly longer required overhaul interval) eventually bankrupted him similar to how the Rix maintenance costs sunk the first owner. I believe there probably was a viable, profitable, middle road for a tech oriented shop in Seattle city limits in the mid 2000s - but first the Rix and then the giant membrane system weren't on that path.

 

[tbone1004]

@rjack321 thanks for that. I obviously believe in the little pumps because I wouldn't have sold a perfectly working Hamworthy and invested thousands of dollars to rebuild them. The difference is I want to use them outside of their intended design criteria and use them to pump large quantities of gas at a time when I have to fill my banks. Going outside of that criteria requires a lot of engineering work to figure out what the new "optimal" is. Optimal stock is the highest fill rates without sacrificing reliability and the cost of that is maintenance frequency. Decreasing maintenance frequency requires something to be sacrificed, and that is speed. No different than charge cycles in batteries when weighed against depth of discharge and charge speed. Sure you can use the battery to near 100% of it's capacity, but in doing so you reduce its lifespan by an order of magnitude. If you double the size of the pack, you significantly increase the lifespan. Same with running a motor at redline for extended periods of time. Redline isn't the maximum rpm of the motor before it fails, it's the maximum safe rpm of the motor. It requires a lot more frequent maintenance when ran up there, but you can do it safely.

Rix makes continuous duty pumps that use the same oil-less technology in the SA series. The SA series run at 1500rpm. The continuous duty ones run anywhere from 200-900rpm and they specifically say "low RPM for long service life". I want long service life, so I'm running at low rpm....

 

[rjack321]

Oh I hear you. One of the selling points for me on my 3cfm Alkins back in 2007 was the slower RPMs which were likely to lower heat output and overall reduce wear and tear compared to a Bauer junior running at double the RPMs. Seems to have held up so far but we don't have 90+degree days here often - and other harsh conditions.

 

[SurfLung]

Your words were, "...when I talked to the guy at Rix who actually designed the SA series compressors, the discussion was that they are essentially redlined and running at maximum RPM because the Navy needed them to fill as fast as possible, longevity be damned." My translation was "running on the ragged edge of failure." No intention to put words in your mouth but surely you can see why I thought that was an accurate translation. This kind of misunderstanding is why I bowed out of your original discussion on the making your RIX SA6 "better". It made no sense to me and I figured I would end up saying something to offend someone.

I agree totally that the RIX SA compressors work great at full factory spec rpms and give years of service when maintained according to the factory specs. I also think we're moving the goal post when we use a dive shop application to criticize the RIX SA. Since they weren't designed for that, it's irrelevant. And now, I've probably managed to offend you both in one post.

I apologize for turning this into an argument.

 

[iain/hsm]

My idea of efficiency is having my compressor work the way the manufacturer designed it to work. I know you probably have some complicated formula but MY FORMULA is real simple... Filling my scuba tanks as fast as my compressor is designed for is the most efficient use of my time... My time spent filling tanks and my time spent diving. That's what peak efficiency means to me.

I have absolutely ZERO interest in slowing it down to satisfy some theoretical efficiency formula.

With respect we can create a problem on forum when terms are either miss used or miss understood.
For example some time back it was the term "Compressor Balance"

Now with compressor efficiency the recognised standard term for a compressors efficiency is the standard model of thermodynamic isothermal (PV1=C1) and the isentropic process (PVk=C2) with the polytropic process (PVn=C3) to give you either the Polytropic Efficiency or the Adiabatic Efficiency of a compressor. Although you should do it for each of the 3 stages stage but in the case for your SA-3 the compressor effiency it's around (.71) for ambient air at 14.7 psia 1.4K and at 70 degF

 

[iain/hsm]

On the contrary, I think the "true design side" discussions that you and Iain get into are so hypothetical and theoretical... Because its all on paper or in your head. Until you've actually got your RIX SA6 compressors restored to working condition, none of your slowed down, re-designed concepts will be proven workable nor even of any practical value. Like the discussion you guys got into on the poor little Solberg Intake Filter.

I liked our disussions on the Solberg filter, I hope it showed the level of design that goes into the Rix products as opposed to a cheap off the shelf Solberg alternative. The critical difference is the Rix is designed for continued use when the filter is old, blocked or wet and used up, While the other cheaper alternative spec is when brand new and in a clean dry condition.

Look at the Bauer air intake air filter too as another example of good engineering practice

Now although we could have discussed any other part of the Rix SA compressors with equal depth and detail but to my mind the air intake was as good a place to start with than any other. As for it all being (All) on paper or in our heads I wish that were true LOL

 

[iain/hsm]

50 hours to lubricate bearings, 200 hours to replace the third stage piston vs a comparably sized Bauer that has it's first valve replacement at 2000 hours on it's PM schedule.

1. You can't call 4 to 5 simple pumps off a grease gun into a grease nipple and a rub around with a paper towel every 50 hours on a Rix SA-6 anything like the same as an oil change on a Bauer or the cost of an oil filter and the short 40 hour air filter catridges life used up adsorbing the oily stuff.

2. The 3rd stage valve change on the SA-6 is also 2000 hours same as the Bauer, the only difference its 20 minutes work with one spanner and an allen key and a couple of $17 parts with four o-rings. By contrast the Bauer needs a special tool to kick off with.

3. After pumping for 200 hours on a SA-6 at 6 cfm thats about 1000 cylinder fills
So you get to waste another 20 minutes tops for a 3rd stage piston ring change and as you dont need to change the metal piston itself and the rings are around another $17 each you need four of them and two pressure breaker rings at $13 each. Some $100 in parts tops.

Second stage piston rings service at 800 to 1000 hours, around $85
and first stage piston ring at around 1000 hours, around $100 in parts

 

[SurfLung]

Piston Head Puller Tool
- Quite a ways back in this thread Iain/hsm was identifying how old my RIX SA3 is by the style of piston heads and how they come apart. I found a couple of pictures that show the underside of the 2nd stage head and the puller tool that can be easily made up with a machine screw, nut and washers:

The Scheduled Maintenance from my RIX SA3 manual says to grease the rod ends and thrust bearings every 25 hours or every month whichever comes first. I've been doing it every 10 hours of run time. It also says to inspect for leaks, loose fitting, and to clean things up. There is no mention (that I've found, anyway) where I should replace the Head O-Rings, reed valves, or piston rings at a certain number of hours.

I know it becomes necessary. I've replaced Head O-rings a couple of times so far... When I first got the compressor, I opened up the heads and found the O-rings melted and/or extruded. But I replaced them with common hardware store O-rings. Then when I was re-ringing the pistons, I replaced the head O-rings with some better quality O-rings but still didn't put in the Viton 90 Dura that I should have. I shopped around and found the correct rings for the heads at the O-Ring Store (online)... So I have them ready for the next time if and when.

But for a schedule on piston ring and head O-ring changes, I'm thinking to watch my fill rate and when it starts to slow down, that will be my warning sign that it's time to do the changes.

BTW - I filled my Twin 38s from 200 psi to 2000 psi in 26 minutes last night. That's 3.2 "S"-cfm... Probably about 3.0 cfm FAD.

 

[iain/hsm]

There are a number of typo errors in the SA-3 manual that are known about but no one has the heart
to do anything to change them and the 25 hour or one (1) month re grease is one of them.
It also say’s 25 hours or every three (3) months elsewhere.

My consideration would be that the amount of grease in the reserve barrel on the piston rod is very small (compared to an SA-6) coupled with the huge cost if you make a mistake and not grease often enough or grease with too little grease and have to replace a bearing or worse still seize the bearing up and snap the con rod. So maybe now you can see why the typo remains.

Now my firm opinion is to use a good high quality grease gun. Years ago Rix provided a small 8 oz push type grease gun with the SA-3 for the recreational market, it was a $10 part and frankly junk.

By contrast the only grease gun I recommend and supply is the $90 Alemite 555E Pistol Grip with the flexible hose end for a Zerk nipple. Set to volume flow not pressure flow. Never leaks, Never smears grease all over the show and seals on the grease nipples on the piston rods each and every time.

2. You won’t find any official Rix recommending a change out time for the rings or a life expectancy for the compression rings or 0-rings Its an American legal thing to keep the corporate lawyers happy.
One thing I will say is changing just the 0 -rings twice as often as the seal rings will far out live the life of an equivalent pump where both the 0-ring and seals are changed together.
So if you want to extend the life of the compression rings then change just the 0-rings at 100 hours and do the same with the 0-rings in the heads.

Reason its not done is the labour to guarantee costs in the workshop in so far as once you have it apart easier and faster to change the parts for new than to clean and re ring the old parts back in again. All the 0-rings are Viton with only those parts marked with a -90 being 90 shore

Agreed, the only other good option is to fit a interstage pressure gauge off the 2nd stage separator.
If that shows low pressure (or even high) it can really help with trouble shooting.