My Rix SA-6 Diesel

[rob.mwpropane]

I noticed some minor leak through when I was setting up the back pressure. I didn't think it was enough to have any effect on it's function providing the whip was not bled. I think I read that it was not unusual for them to leak a bit in the same place I saw the tip to tap the ball. Not sure where I read it but it might have been the Oxygen Hackers Companion.

I sent an email to August, they've been great about any questions I've had. I'm sure they'll respond with something. Odd that a PMV doesn't maintain pressure

 

[rob.mwpropane]

I work with the sweat of my brow for who ever wants to pay me I'm not that fussy. But thanks for the magazine suggestion. Now as for "this can work itself out" nonsense that my friend is the sort of junk advice that belongs in a womans magazine. Hope dies last with the wishful thinking.

If you can't hear it leaking anymore there is a simple answer: You've gone deaf with the noise its been making.
Take it out inspect the rings and replace the o-ring if required.

Now you do have one advantage if you still have that 2nd stage pressure gauge fitted, check the interstage pressure
while running.

1st group in barg and psi line is at FINAL PRESSURE
2nd group is 2ND STAGE @ SEA LEVEL
3rd group is 2ND STAGE @ 1500 M 5000 FT ELAVATION
Done in BARG and PSIG just to confuse the heck out of everyone

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.
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 back into the
Worn 3rd stage rings.

Warning: Running the compressor for long periods with low interstage pressure may cause
overheating of the 3rd stage resulting in reduced ring life and probable 3rd stage 0-ring failure. Your call,

Really watched these as the pressure was rising. Everything matched spot on to these pressures.

I also read this in the manual;

 

[iain/hsm]

Really watched these as the pressure was rising. Everything matched spot on to these pressures.

I also read this in the manual;
View attachment 664651

The piston rings are dynamic in other words they "energise" and seal against the cylinder bore on the compression stoke and "relax" on the return stroke due to a small o-ring fitted under each of the compression rings on each stage. Further a weep hole is machined at a degree angle to allow higher pressure gas on the compression stoke to be forced under the oring expanding it out and with it the compression ring to effect a seal. This light force contact area reduces friction load forces and this "Tribology" effect reduces power required to gain pressure, the reduced contact area reduces friction and heat creation, allowing a more effective cooling effect with no small advantage of not having to cool the bucket full of hot oil with conventional scuba compressors or the contamination hot oil creates and the possible CO creation that friction causes.

In addition as each ring in the compression ring stack behind the first contact ring out front is not energised
until the 1st ring at the front wears away creating blow by from ring 1 then up onto ring 2 and so on until the last ring blows by and the compression rate reduces. This extends the ring life and TTUP.

Now when you switch off the compressor the 0 rings behind each of the compression rings are no longer being energised and the oring "relaxes" creating a leak path around the spiral ring allowing a mild discharge of pressure on each stage over time.

It also aids high rod loads and high motor starting current if restarting the compressor without draining the system in what is called re starting on load.

As an edited note the latest MITP manual does not agree that large leaks will be indicated by a large hissing noise as this is confusing. The largest leak you can get is from a sheared cooling coil and if that happens you get no noise what so ever over the general running noise. Switch off and there is no leak and soapy water has no effect when running unless you sheep dip the thing. Iain

 

[iain/hsm]

Does anyone have pictures of the 1st or 2nd stage pistons pulled out? I found pictures from Ian that showcase the 3rd stage, but I can't find any of the others.

I'm in the works tommorow and we have SA-6's in for service if I remenber I will take the photos you require.
Also a nice example of one that had never been lubricated since new showing a very worn thrust rider.
Normally we measure wear with a micrometer with this thing you could measure the wear with a bent stick. Iain

 

[iain/hsm]

PMV is steady leaking through.

It's a brand new Bauer PMV. I don't think it should be doing that... any remedies?

Beggers the question why use a Bauer BPR on a Rix. But you wont like the answer I give.

 

[grf88]

Beggers the question why use a Bauer BPR on a Rix. But you wont like the answer I give.

Could it be the added cost of the MIL SPEC documentation that comes with the Rix part that needs to be covered.

 

[rob.mwpropane]

The piston rings are dynamic in other words they "energise" and seal against the cylinder bore on the compression stoke and "relax" on the return stroke due to a small o-ring fitted under each of the compression rings on each stage. Further a weep hole is machined at a degree angle to allow higher pressure gas on the compression stoke to be forced under the oring expanding it out and with it the compression ring to effect a seal. This light force contact area reduces friction load forces and this "Tribology" effect reduces power required to gain pressure, the reduced contact area reduces friction and heat creation, allowing a more effective cooling effect with no small advantage of not having to cool the bucket full of hot oil with conventional scuba compressors or the contamination hot oil creates and the possible CO creation that friction causes.

In addition as each ring in the compression ring stack behind the first contact ring out front is not energised
until the 1st ring at the front wears away creating blow by from ring 1 then up onto ring 2 and so on until the last ring blows by and the compression rate reduces. This extends the ring life and TTUP.

Now when you switch off the compressor the 0 rings behind each of the compression rings are no longer being energised and the oring "relaxes" creating a leak path around the spiral ring allowing a mild discharge of pressure on each stage over time.

It also aids high rod loads and high motor starting current if restarting the compressor without draining the system in what is called re starting on load.

As an edited note the latest MITP manual does not agree that large leaks will be indicated by a large hissing noise as this is confusing. The largest leak you can get is from a sheared cooling coil and if that happens you get no noise what so ever over the general running noise. Switch off and there is no leak and soapy water has no effect when running unless you sheep dip the thing. Iain

So given that my loads on both 2nd and 3rd stage match up what do you recommend? If I shut the unit off it's a slow leak that takes a good bit of time to release the pressure built up in the lines. I usually give the coalescers one last open to get moisture out and bleed it down to zero and of course the leak stops.

I'm in the works tommorow and we have SA-6's in for service if I remenber I will take the photos you require.
Also a nice example of one that had never been lubricated since new showing a very worn thrust rider.
Normally we measure wear with a micrometer with this thing you could measure the wear with a bent stick. Iain

That would be great!

Beggers the question why use a Bauer BPR on a Rix. But you wont like the answer I give.

I don't like most of the answers you give, you're always trying (and succeeding) to get me to open my wallet ...... but I sure am learning a lot!

 

[rob.mwpropane]

Does anyone have any insight on what best to set the PMV @? I have read 1800-2200, but someone at August said to set it higher, like closer to 3000. That they set it closer to the lowest pressure tank they have?

Does anyone have any pros or cons to setting it higher or keeping it lower? I believe mine is set right around 2000, which is what it was set from the factory. I don't really have any tanks that I would fill below 3300, so I was thinking about setting it @ 2800 or so. Thoughts?

On a good note my tower is holding pressure. It's been 4 or 5 days and the needle hasn't moved at all.

 

[Tracy]

It doesn't matter than much, somewhere between 1500 and 2500 should be fine. The idea to is keep pressure on the compressor so it doesn't run unbalanced and allow adequate dwell in the filter stacks. You aren't going to notice a diference by changing it 500 psi.

 

[Curious_George]

1500psi is NOT enough according to this page: Compressor Filter System Theory - Scuba Engineer. It needs to be set to at least 2000psi in order to remove 99.3% of the moisture (assuming 95f ambient and 10 degree rise from there in the filter tower) and avoid trashing the MS prematurely. Higher the better, but anything over 2500 is likely putting unneeded work load on the compressor.