My RIX SA3-E

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FYI - The Solberg intake filter cans are the same size whether you order the large or the small... I know because I mistakenly ordered the large one first. It required an adaptor and kept vibrating loose. The smaller 1/4" model fits directly into the RIX SA3 port. The cans are the same size and take the same #07 filter. I think its the size if the intake hole in the compressor that dictates the flow rate capacity of these filters.

We can reply in two parts I hope.
First are you sure about 1/4" it's proberbly a typo as the air intake fitting on the SA-3 is 3/8" NPT female not 1/4".
The only 1/4" NPT ports on the 1st stage head is on the discharge side and for the relief valve.

I will look up the Solberg can numbers (and filter number) later suitable for the SA-3 at 3 ACFM flow but it is not a direct fit into the 1st stage head. Again from memory if a Solburg is used it's bigger both taller and wider and has a 3/4" male thread and intake hole. Hence you need to reduce down with a PTR adaptor, a brass fitting 3/4" female one end and 3/8" NPT male the other. Also as the 1/2" threaded Solberg thread limits out for a 2.2 SCFM flow with the paper element from the design point we have to calculate for all options.

I also note that the Rix Mil Spec filter is much better but I appreciate too expensive for you guys hence my explanations but you all need also appreciate that this information is more from the "Custom Shop" end of the compressor build and that these parts are not available from Rix so while there may be alternative we need also to understand the complex application.

Having said that I would proberbly also settle for a 1/2" thread reduce to 2.2 SCFM and split the difference.

Now if you really whant to see the difference. Measure the head temperature with an infrared gun as see the difference the increased port size makes going from 3/8" to 3/4" . Also test with and without the polyester and the paper filter as it makes my point way better than I can describe in text.

Also consider that using the 10Mu polyester filter is much better for ease of flow for a given cross section area of filter than the same size 2Mu paper element but the finer 2Mu paper element attracts more particulate and for example parking the thing in your garage with the air intake under a tree will result in burnt sap and pollen cooked onto the discharge side of the discharge valve over very little time using polyester but be clean as a whistle using paper.

I know your not pumping nitrox so I cant pull a safety warning but these are application aspects not covered in the manual or at the factory at the customer level.

If an extension hose is used as per the yellow "Gas Bag" reclaim pump in the photo then its a 3/4" OD by 1/2" ID food grade non off gassing hose. The other material we use is called Tygon Tubing.
For pulsation dampening and pressure drop problems using too long a hose length is another problem. 10 foot is the maximum length for the 1/2" bore intake hose at 3 SCFM and the "penalty" can again be demonstrated by the infrared gun test.

Lowering the RPM and flow from 3.0 SCFM to 2.2 SCFM also shows some clear benifit.

But making the minimum of presure restriction at the intake side of the pump is critical.
Even more in hot climates, the Dessert Chiller version of the miltary SA-6 has a monster Air intake filter, granted more for the reasons on fine dust clogging all and sundry
Compared with a SA-6 Navy Built for the navy applications in clean air at sea.

But you raise an important aspect of the compressor design that maybe needs a better fuller explanation than I have given so far but I hope we all get the drift. Iain
 
Here's a Topic I've been interested in:

There are two "Erics" at RIX. Eric Zenius was who I would speak to 4 years ago. But more recently I spoke with and emailed back and forth with Eric Connally. He was very knowledgable and helpful with my broken cylinder replacement. Our conversation evolved a bit and that's where I learned some about the Back Pressure Setting of 1500 psi that the RIX manual specifies.

The first Eric (spelt) Eric Zensius the principle sales engineer for the the SA-3 and SA-6 since they were in Emeryville. 30 odd years ago. The second Eric is Eric Connally he is the warranty engineer who's job it is to get blood out of a stone, give nothing away for free to you lot and if you touched the thing last its your fault you broke it. LOL . Just kidding.
 
I had increased my BPR setting to 1800 psi and then 2000 psi because I read about the higher pressure squeezing 99% of the water out of the air. But I was getting moisture to drain out of the BPR that I thought would have been squeezed out in the moisture separators.

This is going to take way more than one post to explain fully even then I dont think we can do it
fully in writing but here goes.

1. If you position the BRP straight after the compressor (before the filter)
Then for the purposes of holding the floating piston against the piston rod
You can set the BPR pressure setting as low as it can go 180-400 psi is just as
good as 1800 to 2000 psi and it's no better in doing the job of holding down the float
or chatter any more than if you went all the way up to 3000 psi

Pick a number they are all good. Try it as an experiment.
No difference the pressure setting is irrelivent over a couple of hundred psi and no time lag regardless of the BPR setting. But here comes the kicker..........

For the purposes of holding down the piston and reducing piston chatter damage only.
However that is not its only purpose and here is when it gets very complicated.

In bigger Rix compressors say the 2J model its a 100 SCFM flow at 5000psi reducing free float of the 3rd and 4th stage floating piston with a BPR would be huge lump of metal so just before start up a pre load is introduced into the 2nd stage with a small pressure loading PMV so that just prior to start both floating piston are safely "locked" onto their rods. On the SA-3 a small pressure into the 2nd stage separator works just as well.

But the next complication is when compressing ambient air and using a back pressure regulator
to compress the ambient air to a pressure greather than the "Charging Pressure" of the cylinder to "knock out" moisture condensing out of the gas due to increasing pressure P1 in a decreasing area V1 but at an increase in temperature T1
 
@SurfLung

BPR and PMV are the same thing. They won't let gas thru until a certain pressure is achieved.

Yes but no but. LOL

Heck this really is complicated to explain more than I first thought. A BPR while true it wont let gas thru until a certain (pre determined set) pressure is achieved it has to be big enough to flow the entire contents of the compressor thru its components.

While with a PMV this can be a tiny device as strictly speaking it does not have to see the entire flow fluid content of the compressor to effect a pressure control. I know its words and meaning, The cloud or a cloud but its important to get the groundwork in place as I fear we are going to do later in this thread what we all mean again by Compressor Balance again and again and again (Until we all get it right I guess) LOL Iain
 
My mistake on the Solberg. I originally bought the 3/4" (I think) and replaced it with the 3/8th. Sorry for leading you on a wild good chase. As you can see from the photo, the cans are exactly the same size.
Solberg01.jpg

Solberg FS-07-038 Air Inlet Filter Silencer
Follow the link and the description give a flow rate of 8 SCFM for 3/8" connections. I figured 8 SCFM is more than enough for my 3 cfm compressor.
 
Hi SurfLung. Good to see someone else making air in the land of 10,000 lakes.

It's a long run at 2-3 cfm but beats driving across the state to get fills.

I have 4 bank bottles and am going to have to take them in to Airgas to be revalved soon. The packing and seats are shot and no one will sell me valve parts. I'll probably have them hydro'd while they are there since they're halfway through the hydro period already and it's such a hassle to take them in.
Thanks 2airishuman. Yes I'm really liking having my own compressor
BTW - I found a new place for hydrotesting and tank/valve service. It's called Hydrostat and located in Rice, MN. The contact man is named Mike and he gives wholesale pricing ($13/hydro) to walk-ins. Check their website at
Hydrostat, inc. a leading hydrostatic tester and requalifier of industrial cylinders.
- They might be able to service your valves.
 
@SurfLung BPR and PMV are the same thing. They won't let gas thru until a certain pressure is achieved.

@iain/hsm can correct me on this, but this is my school of thought on this. You want one IMO as close as possible to the outlet of the final stage so the piston seats quickly where the pressure really doesn't matter. In terms of seating the valve, as long as the pressure is set to somewhere higher than the pressure required to seat the piston, the pressure is irrelevant. You want to be careful in terms of how close you put it because you want moisture to come out somewhere between the two, but that's why you don't want to oversize the moisture separator since it will be that many more revolutions before it seats. Volume is everything. It's a fun balance.
A second one should go after the filter assembly, and that pressure should be set to whatever pressure you feel the filters need to work properly. The higher the pressure, the more the compressor has to work. IMO that pressure needs to be the "balance" pressure of the compressor. Up to a certain pressure, the compressor is out of balance, and over that pressure it is out of balance in the other direction.
I don't know what that pressure is for the Rix, but it would be ideal if it was around 4000psi for compressors hooked up to bank bottles, and 3000psi for compressors filling tanks directly. This puts the compressor in balance for all but the final high pressure run. With banks, that is 4000 up to 4500psi, and for tanks that's 3000 up to 3300-3800psi depending on tanks. The compressor has to work harder the whole time in terms of work required since it is compressing against a higher pressure, but the system as a whole is stable during that whole time instead of having big pressure fluctuations.

Sounds like 1500psi is the ideal BPR for the piston to seat which is good, and hopefully Iain can outline what the "balance" pressure is when the compressor is truly in balance, and whatever that pressure is, is what the filter PMV should be set to.
Thanks T-Bone. I'm planning a new plumbing configuration that should get the BPR closer to the moisture separator out port. I'll keep a watch out for that "balanced" discussion.
 
Thanks 2airishuman. Yes I'm really liking having my own compressor
BTW - I found a new place for hydrotesting and tank/valve service. It's called Hydrostat and located in Rice, MN. The contact man is named Mike and he gives wholesale pricing ($13/hydro) to walk-ins. Check their website at
Hydrostat, inc. a leading hydrostatic tester and requalifier of industrial cylinders.
- They might be able to service your valves.

Thanks much! I was using the place in Wyoming (MN) and have not been entirely pleased. I've been using Weber and Troseth now who are OK but they don't have shot blasting capability and I have to go through a local dive shop which gets expensive.
 
I figured 8 SCFM is more than enough for my 3 cfm compressor.

Surflung you have a SA compressor rest assured every "nut an bolt" on that compressor has been fully engineering designed. But just to tie up an engineering aspect of the SA breathing air compressors air intake filter choice. In many ways if we use our own brand of aftermarket air intake filter type we are on our own with the consequences of that choice. That said two additional aspects need to be considered in using aftermarket choice.

First is that the size of the filter should be based on “blocked flow” i.e. when at the end of its life expectancy not based on the flow charts given by the manufacturers for a brand new filter. Its important that we understand the distinction when applied to breathing air applications.

Additional heat generated by restricted flow will reduce performance and damages component life expectancy.
I gave the example earlier that the SA compressors we build for Army for use in a hot desert use a different air intake filter design than those SA units for use for the Navy on a open deck at sea in a clean (but humid) atmosphere with additional consideration for the additional salt laden atmosphere. Resulting in the design life of one air intake filter being half that of the other.

In addition Delta P or pressure drop accross the filter medium also need very careful consideration Futher I suggested 10Mu for the polyester while for Soglburg its 20Mu with polyester and 2Mu for the paper pleated. Yet this is ony half the consideration it is the pressure drop or Delta P that is the critical performance factor when the surface re of the filter medium is increased to compensate for the loss of flow capacity for the finer medium against the pressure restiction or flow, added to the performance at blocked flow condition.
Yep all this for cheap throw away $10 filter LOL Iain
 
https://www.shearwater.com/products/teric/

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