My RIX SA-6 Conversion and Setup

[iamsharky]

That's a great looking set up you have....I think I will try the in line bleeders....Where is the best place to purchase those? Thanks!

---------- Post added November 19th, 2013 at 10:44 AM ----------

That is also interesting that you have a pressure gauge mounted on the 1rst tower.....Is that so you can have an idea of the pressure the compressor is making?? I have a pressure gauge on my fill whip....

 

[maniago]

I hope you still have the two little black separator towers?

Iain, can you comment on why there is no 1st stage coalescer tower ie prior to 2nd head?

I'm in the middle of rebuilding a junk SA6 (done a lot of chatting to Eric, but forgot to ask this question), and I'd like to improve on the packaging. I have 20' of new AC/R tube for all the stages so I'm contemplating running it all and wringing out as much water as possible prior to 2nd and 3rd heads. Why? I'll eventually run nitrox and He (I know I know caveats understood) and want to keep the 3rd head well below the teflon critical point....

FWIW, I've already cut new cylinders, and am cutting a new crank as mine is warped out .010", but that's another story....

Thanks
Mick

 

[iain/hsm]

Iain, can you comment on why there is no 1st stage coalescer tower ie prior to 2nd head?
SNIP Mick

No problem.

On the standard SA-6 the compression ratio (CR) of the 1st stage head (3" inch, 76.20mm diameter piston) is 5.76:1 and too high for any appreciative moisture condensation to form.

Assuming ambient inlet the discharge pressure off the 1st stage is 100.11 psig

It is therefore easier and cheaper on component cost I guess to use just the 2nd stage the (1.24Inch 31.25mm diam piston ) and at a 4.94 CR as the "knock out" point for any water separation. The second stage pressure being 628.22 psig

Besides there is also little risk of water condensing out after the 1st stage due to the high CR therefore the Calculated gas temperature is 493.5F (256.3C)
Second stage gas temp calculated is 447.95F (231C)

This is the calculated gas temp and NOT the measured gas temp so purely an adiabatic gas loading and so no cooling factors are included, heat dissipation, fan cooling etc etc.

I have assumed a 70 F (21C) ambient air temperature and a 25F (35C) approach temperature in the above and a maximum 5000 psig (350 barg) output pressure
The average CR for all three stages is 6.99:1 and at 5.5 SCFM flow 1500RPM your using 4.87 BHP efficiency calculated at .72

Enclosed below are the calculations for a standard SA-6 at 5000 psig
If you like I can also work out your nitrox and Helium gas loadings. Just let me know your required discharge pressure and some idea of ambient air temperatures and the gas at inlet temp

For Nitrox and helium you can also put say a 5 psi pressure loading on the 1st stage head this will give a big improvement. Also if its helium your pumping then no water condensation out the separators.

Also factor no filtration is required unlike an oil lubricated pump so you design in a by pass of the filter tower when compressing dry clean gases. Iain Middlebrook.



---------- Post added November 20th, 2013 at 12:29 AM ----------

SNIP I'd like to improve on the packaging. I have 20' of new AC/R tube for all the stages so I'm contemplating running it all and wringing out as much water as possible prior to 2nd and 3rd heads. Why? I'll eventually run nitrox and He (I know I know caveats understood) and want to keep the 3rd head well below the teflon critical point....

FWIW, I've already cut new cylinders, and am cutting a new crank as mine is warped out .010", but that's another story....

Thanks
Mick

Mick.

The heads are well away from the Teflon rings, besides its not Teflon but a proprietary Polycompound material that is used.
So IMHO its the deflection point of the Viton material 0-rings) in the heads you need to consider more closely.

In both stages 2nd and 3rd there are three (3) O-rings, that will get to a point of melting out. Once this happens you no longer have a pressure so in effect its a fail safe, but non the less keeping below the deflection temperature of the 0-rings is helpful. From memory its around 450F but I will need to look it up. an simple RTD (remote temperature device) may help on the 3rd stage discharge side

Same fail safe idea is used on the piston rings and piston 0-rings, overheat them and they melt out and therefore by default cannot retain any pressure and therefore your no longer filling cylinders but making noise. Again unlike an oil lubricated compressor that an overheat causes serious consequence to gas purity.

On your point of .010" warp on the crankshaft, Im not so sure?
Have you checked the alignment adjustment (blue spring) of the two lower (6 o'clock) Thrust rider bearings?
Turn the pump slowly by hand and look at the blue spring, Does it move in and out, if so thats either poor adjustment
or thrust rider plate wear, change the two bearings if required and or reverse over the thrust rider plates to a fresh side.
Adjust the trust plate bolts so the trapeze is parallel.

Also it may be that the main crankshaft bearings are worn out, again yank the shaft by hand and see if thats the play your getting
before making a new crankshaft

Worse case scenario is the outer bearing race is rotating in its housing and has worn out the inside of the block
Note, there are two set screws Half Dog 1/4-20 NF x 3/4" long under the block that hold the main bearings (notched)
from rotating. I hope this it not the case.

Photo 1 shows the two bearings, set screw and adjustment bolt all about 3 inches below crankshaft

Photo 2 the blue adjustment spring, the 2 rider bearings and thrust rider plates.



Iain Middlebrook

---------- Post added November 20th, 2013 at 01:02 AM ----------

That's a great looking set up you have....I think I will try the in line bleeders....Where is the best place to purchase those? Thanks!

---------- Post added November 19th, 2013 at 10:44 AM ----------

That is also interesting that you have a pressure gauge mounted on the 1rst tower.....Is that so you can have an idea of the pressure the compressor is making?? I have a pressure gauge on my fill whip....

Fittings are available all over but depends where on the planet you are I guess for the best deal. No point us sending in UK if your in US

The pressure gauge in the photo is simply an interstage gauge shows the second stage pressure only hence the 60 bar range (800 psig)
However in the workshop we find that compressor condition can be evaluated more quickly and accurately with the installation of a 2nd stage pressure gauge.

Variation of the interstage pressure (2nd stage) indicates a problem such as worn piston rings, sticky valves, or air leaks starving the 3rd stage inlet of presuure, resulting in a higher than normal inlet gas temperature that can reduce the life of the 3rd stage pistons rings and head 0-rings.

Easy to retrofit just remove the 2nd stage relief valve and install a branch tee with the centre leg of the tee pointing down. Refit the relief valve to one horizontal port of the tee. If required also install a small hand valve to isolate the gauge during running.

NOTE: due to compressor vibration it is a good idea if you are going to use a cheap chinese gauge to keep the gauge off the unit when running and use a blank plug. Install gauge only when a pressure check is required. Or buy a quality 316 wetted parts dampened movement gauge.

Normal 2nd stage pressure on an SA-5 are as follows:

FINAL PRESSURE	2ND STAGE @ SEA LEVEL	2ND STAGE @ 1500 M 5000 FT ELAVATION
137 barg / 2000 psig	29.3-32.7 barg /425-475 psig	26.8-30.3 barg /390-440 psig
172 barg / 2500 psig	31.0-34.4 barg /450-500 psig	28.9-32.4 barg /420-470 psig
207 barg / 3000 psig	32.7-36.2 barg /475-525 psig	31.0-34.4 barg /450-500 psig
241 barg / 3500 psig	34.4-37.9 barg /500-550 psig	33.1-36.5 barg /480-530 psig
275 barg / 4000 psig	37.2-41.3 barg /540-600 psig	35.8-39.3 barg /520-570 psig
344 barg / 5000 psig	40.0-44.8 barg /580-650 psig	37.9-42.7 barg /550-620 psig

Low pressure will be caused by one or more of the following:
Worn 1st or 2nd stage piston rings. (Check for blow by)
Leaking 1st stage valves.
Broken 1st stage head gasket.
Leaks in piping or 0-rings.
High 1st stage piston clearances.
Restricted inlet hose or filter.

High pressure will be caused by one or more of the following:
Leaking 3rd stage valves.
Worn 3rd stage rings.

Warning: Running (any) compressor for long periods with low interstage pressure may cause overheating of the 3rd stage resulting in reduced ring life and possible 0-ring failure. Iain Middlebrook

 

[maniago]

Thanks Iain, I'll have to absorb it better over several cups of coffee this morning, but just a few quick thoughts for you while youre having a quick bit of nosh on afternoon break

Just from first principles, would you not expect that with 20' of 1/2" OD copper, I'd be below the dewpoint at ~100 psi and I'll have water that needs removing (same as I do in my 125psi shop compressor)? Sure don't want to slug the 2nd stage....

Re: .010 run out, haha, no my bad. The crank is chucked up in my lathe when I measure it. I have new "everything" to install, but we're at the starting point and the compressor is all, and I mean all, apart. We're talking ground up restoration here. I'm just "lucky" the block isn't cracked (at least that is I haven't found one yet). This is no longer a cost effective rebuild. Its now a project! haha

One other conundrum perhaps you might comment on - I have the old AL 2nd stage head without the center plug. I'll replace it with a new head, but damn - all its guts are frozen in it - no amount of ultrasonic cleaning or heating has loosened it up. I want to get it apart without destroying it so I can perhaps recut one later on.

Is the head design the same as the new one, such that I can drill a center hole in its face and penetrate the inside to punch out the guts with a drift? If so, how deep should I penetrate the cavity without drilling into whatever is on the other side and ruining it?

Thanks

Mick

 

[iain/hsm]

Thanks Iain, I'll have to absorb it better over several cups of coffee this morning, but just a few quick thoughts for you while youre having a quick bit of nosh on afternoon break

Just from first principles, would you not expect that with 20' of 1/2" OD copper, I'd be below the dewpoint at ~100 psi and I'll have water that needs removing (same as I do in my 125psi shop compressor)? Sure don't want to slug the 2nd stage....

Re: .010 run out, haha, no my bad. The crank is chucked up in my lathe when I measure it. I have new "everything" to install, but we're at the starting point and the compressor is all, and I mean all, apart. We're talking ground up restoration here. I'm just "lucky" the block isn't cracked (at least that is I haven't found one yet). This is no longer a cost effective rebuild. Its now a project! haha

One other conundrum perhaps you might comment on - I have the old AL 2nd stage head without the center plug. I'll replace it with a new head, but damn - all its guts are frozen in it - no amount of ultrasonic cleaning or heating has loosened it up. I want to get it apart without destroying it so I can perhaps recut one later on.

Is the head design the same as the new one, such that I can drill a center hole in its face and penetrate the inside to punch out the guts with a drift? If so, how deep should I penetrate the cavity without drilling into whatever is on the other side and ruining it?

Thanks

Mick

On the 20 foot cooling coils, there are another factors you may consider when using such a long interstage coil is that when starting up from scratch your both starving the second stage of inlet pressure (this 100 psi)
and in addition the time taken to build up pressure increases the hammering the 3rd stage floating piston gets before the back pressure generated holds it firm against the rod.

So I guess as short as it needs to be is the answer.

However the cooler the approach temp, the greater the risk of water condensing on the inlet side of the reed valve gets so sometimes in a compressor design gas is allowed to run hotter to avoid this water condensation problem.

Don't forget also your not reducing water vapour by this long coil just removing more water condensate up stream than down.

Again IMHO an efficient after cooler is my preferred option as the high pressure acts as a helpful tool to knock out more of the water condensation due to the higher pressure.

Water being (in effect) non compressible cannot remain in the same vapour form for the same volume of gas. As pressure increases, the higher the pressure the lower the water content by weight. Yet the water vapour is still at 100%

The kicker is upstream water cannot be tolerated yet conversely downstream the separator is there to allow water vapour condensing out into droplets to be collected, the increase in gas pressure is by far the biggest contributor
for this and cooling only aids the process to knock as much water out.

So the design I guess is always for hot heads and cool coils and the main reason why water coalesing mechanical filters are always after final pressure.

On the old aluminium head its the same as the stainless one, a centre drill for a 7/16-20 UNF thread will work as a stainless plug is easily available
Maximum drill down is 0.40" and 0.60" is as deep as you dare.
Drill size 0.3906 (25/64") but check that. Iain Middlebrook

 

[maniago]

On the 20 foot cooling coils, there are another factors you may consider when using such a long interstage coil is that when starting up from scratch your both starving the second stage of inlet pressure (this 100 psi)
and in addition the time taken to build up pressure increases the hammering the 3rd stage floating piston gets before the back pressure generated holds it firm against the rod.

Hmm, yes I've been pondering the hammering issue while doing these mental gymnastics.

The point of all of this piping stuff is to keep the 3rd head (in particular) out of the 400F zone. Whatever the rings are made of (teflon or some other slippery substance), its all over the insides of my third head (and to some extent the 2nd as well), so I know the compressor has seen at least 40% nitrox and well over 400F. And all the orings are shredded as well. Water cooling the 2nd and 3rd heads is an idea, but outside my current rebuild plans.

The fan I have is mostly "blade-less" (read: unusable), so I'm planning using a large ducted electric fan blowing on the head side down the block ie opposite the current direction. Maybe that's all I really need (?)