Rix SA-6 Rebuild - winter project

[iain/hsm]

As is typical with a project like this, two steps forward, one back.

You probably know this already, but on that filter shell IMHO you need a non return valve on the inlet side of the filter shell and a bleed valve down stream of the NRV (fitted on either side of the shell. Whichever side has the least plumbing I guess)

One to avoid loosing cartridge pressure when draining those water separators, as this disrupts the chemical, the other is to drain the filter shell when you want to change the filter cartridge.

With all those gauges also I would also add one on that BPR (downstream side) that way you can easily set up the the BPR pressure setting and also monitor the lift pressure of the BPR with the gauge marked No:3 when the shell is charging up

You also need two bolts on the filter top cap and fit a "rain cap" cover, or you have to unscrew the whole filter shell to change a cartridge, instead with two small cap head set screw bolt stubs you can use a small bar or spanner and remove just the top cap. Iain

 

[maniago]

Excellent, thanks Iain!

I have a check valve on the input side of the 3+ coalescer (its my "2nd" 3rd stage coalescer) with a BPR on the output, so I going to use the bleed down from that for the filter. Jim suggested this instead of another bleed in the line, though now that you point it out, the flow will be backwards through the filter stack and coalescer, and that does now strikes me as less than desirable. Thanks for pointing that out.

So I'll put the check on the input of the filter, then the moisture eye, a bleed, then the BPR . I have another BPR already on the output of the 3rd coalescer to keep the 3rd piston seated, and so it doesn't spend a lot of time hammering while the entire down stream line to pressures up. Maybe over kill (ie 2 BPRs), but it doesn't hurt.

The gauge on 3+ is measuring filter stack pressure - its actually the 4th gauge in the line - there is a "3rd" gauge before the BPR for the 3rd stage piston pressure, but its just off the top of the pic (above the electric cut out switch). I'll have to move that 4th gauge though to continue measuring the filter pressure. That 4th gauge in the filter stack is meant to also act as my final fill pressure.

I have the rain cap, but this pic is right after I took the filter end caps out of the ultrasonic cleaner and its just partly assembled the filter for measuring. Its got no orings or 1801 installed. I still have to wash the filter shell itself...

 

[maniago]

So lots of plumbing work later, and I think I've got it nailed now. No filters inside the stack, or disk in the moisture eye, but that was academic up to this point. I still need to weld up a bracket to support all the crap hanging off of my 3+ coalescer tower, but that's something to do tomorrow. Good news, the LDS owner that I DM for is going to let me use his Trace Analytics gear to do my air tests, so score one there. Should be able to get a good baseline without breaking the bank, then I probably wont bother thereafter.

Here's what it all looks like. I changed from compression fittings to flare fittings on the high side of things - two fitting blow outs scared the piss out of me - 3000psi projectile tubing flying around is no joke.

 

[iain/hsm]

SNIP

I have another BPR already on the output of the 3rd coalescer to keep the 3rd piston seated, and so it doesn't spend a lot of time hammering

but it doesn't hurt.

I have the rain cap, but this pic is right after I took the filter end caps out of the ultrasonic cleaner and its just partly assembled the filter for measuring. Its got no orings or 1801 installed. I still have to wash the filter shell itself...

1. Just a point using a BPR prior to the filter chemical IMHO it can hurt especially when you start up from scratch. The pump fills up to the BPR pressure setting say 1500 psi then it opens allowing the HP gas to "rush" the chemical disrupting the chemical and shunting it up the cartridge tube, I have some old MDE filter cartridges that this has happened to I will photo tomorrow from work and post it shows clearly the white moly sieve really blasted up into the black activated carbon and the internal felt pad blasted out at 45 degrees

Depending on the spring rating and BPR design they really open with a "blast" like a shotgun especially if deltaP downstream is at atmospheric, most are cheap so have a huge hysteresis, It is something I would check out with a bare empty filter first see if you are happy. They can also "stick" shut over time and again this is not really what you need.

2. That empty 4 inch grey anodised filter shell looks like a Bauer type that you need the 0-rings for. If it is and you need both an 0-ring and a back up ring the size is AS 333 nitrile 70 shore hardness. A look at the base would verify. Iain

 

[maniago]

1. Just a point using a BPR prior to the filter chemical IMHO it can hurt especially when you start up from scratch.

Depending on the spring rating and BPR design they really open with a "blast" like a shotgun especially if deltaP downstream is at atmospheric, most are cheap so have a huge hysteresis, It is something I would check out with a bare empty filter first see if you are happy. They can also "stick" shut over time and again this is not really what you need.

2. That empty 4 inch grey anodised filter shell looks like a Bauer type that you need the 0-rings for. If it is and you need both an 0-ring and a back up ring the size is AS 333 nitrile 70 shore hardness. A look at the base would verify. Iain

Well I think I'm in the blind luck territory on the BPR. With a gauge on either side of it, I can watch as it unloads downstream into the filter stack, and it actually seems agonizingly slow (but consistent) to come up to pressure. I am using 1500psi as the unload threshold - I think someone earlier mentioned that as a good dwell-time (pressure) for the mechanical water separation, though that could have been for the MS dwell instead. Any clarification on those numbers?

WRT the filter tower, yes its an oring and backup ring setup, though I gather it to be not a Bauer produced unit (no markings). Maybe a Bauer copied design - it is 4"x15.5" though. I need to ask Jim Sheldon on its origin. Not a huge deal to turn out if you have a big-assed Bridgeport to do it on - quite out of my league though. But thanks for the oring info - it did come with the appropriate rings, though no data on their material or sizing. Another question for Jim...

 

[iain/hsm]

Well I think I'm in the blind luck territory on the BPR. With a gauge on either side of it, I can watch as it unloads downstream into the filter stack, and it actually seems agonizingly slow (but consistent) to come up to pressure. I am using 1500psi as the unload threshold - I think someone earlier mentioned that as a good dwell-time (pressure) for the mechanical water separation, though that could have been for the MS dwell instead. Any clarification on those numbers?

WRT the filter tower, yes its an oring and backup ring setup, though I gather it to be not a Bauer produced unit (no markings). Maybe a Bauer copied design - it is 4"x15.5" though. I need to ask Jim Sheldon on its origin. Not a huge deal to turn out if you have a big-assed Bridgeport to do it on - quite out of my league though. But thanks for the oring info - it did come with the appropriate rings, though no data on their material or sizing. Another question for Jim...

Slow? not surprised with all those separators to fill, makes a "spare air" look like a twin set LOL

As for timing you need to check the charging rate of the build. Fill all your filters and separators to 3000psi with the dive cylinder turned off, then time filling it up also to 3000 psi, or you will loose time filling up the filter and separator
You also need to know the volume size of cylinder to work out the charging rate.

Also check the RPM at start up, at 1500psi and at 3000rpm, if you have a clamp meter also check the Kw draw over a cable at same above points.

2. I was thinking you checking the BPR with the filter lid off so you can gauge the in rush. Its the dP inrush from 1500psi off your BPR set point to ambient thats the consideration, too high a setting and too large (or many) the separators then the blast of air into an empty filter can disrupt the chemical when charging up.

Conversely too large a pressure drop on the discharge side from say filter to an empty cylinder can also disrupt the chemical and can destroy molecular sieve into dust by the freezing of the water particles trapped in the matrix expanding as ice with a rapid pressure drop destroying the fine internal chemical matrix

Photo enclosed shows what a disrupted cartridge looks like, easy to see on those clear cartridge tubes.

Further folk who use a wall mounted filter downstream of a HP storage bank as a secondary filter for pretending to clean for nitrox can also achieve this rapid chemical
destruction and the fine dust you sometimes see inside nitrox cylinders and valves

3. IMHO you really need more information on that filter if you bought it new.
For starters what is the WP would help. You need some paperwork. Just an invoice with the WP and the cycle loads stated IMHO would be great.
How much did it cost? always a good indicator.

I agree its maybe not a huge deal to turn out a 4 inch alloy tube but when you expect it to cycle load at 5000psi working pressure and by your photo its only
got a 0.5" half inch thick wall. IMHO you need 7075T6 alloy and not some commercial off the shelf 6063 T0 alloy from some local stockholder. Iain

 

[maniago]

Cool pics!

Its actually agonizingly slow watching the filter tower come up to pressure, not the 3rd stage and the coalescers. But the comment on rpm is on point - I have a variable pulley on the motor and I have it set to the lowest point, so the compressor is not running at spec speed yet ~1200 rpm - on purpose testing wise, though I might just leave it there if the fill rate isn't much slower. I'm only filling for myself anyway.

The filter tower was about $600, so not much less than what I might get from a named supplier and Jim has a very good reputation in the compressor rebuild industry, so I would be surprised if anything of his is not top notch. Same if I was in the UK buying from you, eh ol'bean?

Thoughts on what BPR pressure points I should set at for the coalescers and 3rd stage piston; and the set on the downstream filter stack?

 

[iain/hsm]

Cool pics!

Its actually agonizingly slow watching the filter tower come up to pressure, not the 3rd stage and the coalescers. But the comment on rpm is on point - I have a variable pulley on the motor and I have it set to the lowest point, so the compressor is not running at spec speed yet ~1200 rpm - on purpose testing wise, though I might just leave it there if the fill rate isn't much slower. I'm only filling for myself anyway.

The filter tower was about $600, so not much less than what I might get from a named supplier and Jim has a very good reputation in the compressor rebuild industry, so I would be surprised if anything of his is not top notch. Same if I was in the UK buying from you, eh ol'bean?

Thoughts on what BPR pressure points I should set at for the coalescers and 3rd stage piston; and the set on the downstream filter stack?

Agreed if the filter stack is new and from a known source then quite agree its good to go, although with forums you have to points out all the pitfalls just in case.
Although "old' bean" in the UK for $600 (£375 GBP)we would have to have included the BPR with integral check valve and enough 1/4" ports for two charging take offs and a pressure gauge.

The BPR setting is a bit of a balance, 150 barg 1500 psig is about right balance wise. However if you increase it to say 200 barg 3000 psig then your filter chemical lasts longer as more moisture is "knocked" out at the separator rather than have to carry over to the filter chemical. Great sale pitch for the filter boys, however the pump has to run up to 3000 psig all the time and this has a knock on effect with higher and more frequent service and maintenance costs, Not so great for the pump boys.

Hence the 150/2000 pressure balance, enough back pressure to knock most of the moisture out while the pump runs up around half way on the charging side.

While I'm at this just a comment on your adding that 1st stage discharge separator, and this small condensate your collecting, Now while there is nothing wrong per say with it although you should realise that all that moisture you collected would have dropped out anyway at the 2nd stage separator, for less parts.

Conversely we have built SA pumps for special air applications that we inject distilled water into the 1st stage head to reduce the head discharge gas temperature and
the interstage approach temp this reduces the discharge gas temp by 50%, yet the same moisture is knocked out by the same separators 2nd and 3rd, just auto drained more
frequent using the same dwell just a shorter pulse.

Your 1200 rpm also is fine, reducing RPM reduces flow and cooling fan RPM but again its just about equals out.
Half the speed is half the flow but also half the heat required to dissipate.
Again have done them as low as 300 rpm 1.1 scfm Iain

---------- Post added March 21st, 2014 at 02:45 PM ----------

I do like your blue air intake hose, very very nice almost like "Cooper hoses"
Its a bigger bore, therefore less pressure drop and less pulsation, almost temped to try a metre or two LOL

Much better than our stock 1"OD 3/4"ID PVC reinforced tubing, less prone to collapsing and kinking when you have to roll out the 15 foot stock length.

The air intake filter at the end is also very interesting, looks like an automotive part

The Rix stock air filter is custom built ugly can of tin, built special to a mil spec for USN its hugely overpriced and still only a plated tin shell, with a pleated element.

This is an area I think we should explore further. Even with a lower dP the larger bore intake hose compensates acting as a pulsation dampener. It looks good too.
On the performance side the 3/4" bore Rix tube with a one meter 3 foot tube length will give a higher charging rate than either no intake hose air filter direct mounted or any other length up to 15 foot.

There is a good article here if we ever need get sidetracked from compressors LOL

Exhaust System Technology: Science and Implementation of High Performance Exhaust Systems

All the best. Iain

 

[maniago]

While I'm at this just a comment on your adding that 1st stage discharge separator, and this small condensate your collecting, Now while there is nothing wrong per say with it although you should realise that all that moisture you collected would have dropped out anyway at the 2nd stage separator, for less parts.

I do like your blue air intake hose, very very nice almost like "Cooper hoses"
Its a bigger bore, therefore less pressure drop and less pulsation, almost temped to try a metre or two LOL

Iain

Thanks for all this Iain!

I know you're not a fan of the 1st stage coalescer I have - youve sent me the numbers on why and I get it, but I've gotta tell you that I'm getting the same amount of water out of it as I do my second stage, and its not trivial. That and the two "old" second stage heads I acquired were locked up solid with rust - one an old AL head, the other a SS head tells me something. In anycase, given that it does nothing sitting on the shelf, and it doesn't wear out in use, well, you can see my point.

Funny on the intake hose - its standard swimming pool plumbing hose. And the intake filter? $7 HEPA filter for a Dirt Devil vacuum. Can't beat that with a stick!

I'm tracking with the tuned pipes - just like we used to keep our old 2stroke bikes "on-pipe" when scrambling. Maybe I'll chase that animal with the lower 1200rpm just for $hits and giggles! Cheers!

 

[iain/hsm]

Again just another thought on that automotive air intake filter, try again the charging rate time test with and without the air filter fitted
just to make sure its not starving the pump at full 1500 RPM. That way you have covered all your bases.
Some automotive air filters are much too fine an element for air compressors and use a paper pleated element that can clog up easy
as opposed to the fibre element. Not an issue indoors and dry but outside on a deck it can be a source of problem.

Again its a huge debate on the pump design side (or should be) the choice of intake filter, most of us will at some point compromise
cost over efficiency against failure when wet or clogged. In 25 years building Rix blocks the small amount of replacement service air intake
filters we sell is a sad reflection on its perceived lack of importance with users. Iain