Rix SA-6 needs priority valve. Owner needs guidance.

[RayfromTX]

I am the proud new owner of a fill station at my home. It is based on an old but mostly upgraded Rix SA-6. That is followed by a Lawrence Factor filter tower. I have spent lots of time learning as much as I can about this subject and that is it's own reward. It is my understanding that I need to have a priority valve set to around 3000 PSI at the output of the compressor to help it run balanced as soon as possible. I also need to have a priority valve set to around 2000 PSI at the output of the filter stock to protect the filter cartridge from ambient air and prolong it's life.

The filter stack has the required priority valve although it apparently needs to be rebuilt because it does not hold pressure. The compressor does not have a priority valve and it seems to me that relying on the priority valve at the end of the filter stack is not the best approach because the pressure is set too low and when when I drain the pressure off of the mechanical filter I have created quiet a bit of runtime before the compressor comes up to a pressure that it likes.

Am I completely off base in this thought process? I am including a picture of the set up and if I I'm correct in my thinking I should add an elbow where the hose now comes off the compressor and install the priority valve at that location and tie the hose back into that. I am considering a Lawrence factor priority valve which I can adjust to around 2800 to 3000 PSI.

I have seen some great threads on these issues going back many years but they have only gotten me this far and I need a little guidance before I fire this thing up. I'd appreciate any help I can get. I will be getting a safety chain for the t-bottles soon.

 

[grf88]

I have a priority valve after the filter stack and a one-way valve before the filter. This way the filter stack remains under pressure except when I am changing the filter or if the compressor is not used for a month or more which allows the pressure to bleed down. I have a valve between the priority valve and the filter stack to allow me to bleed it down for filter replacement. I have set the priority valve to 2400 psi.

 

[RayfromTX]

I have a priority valve after the filter stack and a one-way valve before the filter. This way the filter stack remains under pressure except when I am changing the filter or if the compressor is not used for a month or more which allows the pressure to bleed down. I have a valve between the priority valve and the filter stack to allow me to bleed it down for filter replacement. I have set the priority valve to 2400 psi.

Thanks for your reply. Are you using an SA-6?

 

[grf88]

Yes, there is a lot of good information in the archives here on Scubaboard especially posts by iain/hsm.

 

[RayfromTX]

How long does it take your SA-6 to get up to 3000 when you are filling up your mechanical filter from 0 and your stack filter from 2,400?

 

[grf88]

Not long but I only have the separators that the Rix comes with plus a 16" filter stack. I could time it if the weather warms up this weekend but I would guess not much more than a minute or two.

 

[RayfromTX]

Mine runs out of balance for a little while which is why I'm considering a priority valve mounted to the compressor to shorten the time spent below 3,000.

 

[NAM001]

run one prior to eh filter bank to max the moisture separation on the rix. I believe it is to be set at like 1900-2100. have another on the filter output set to perhaps 2500-3000, the 2500 setting should allow for the compressor to run balanced.

 

[Andrew Donn]

For starters 3000 psi is a bit high for a back pressure regulator or priority valve as they are also called. The RIX recommends a BPR set to 1500 psi directly at the compressor outlet after the dryer cylinder. The BPR performs two functions. The first is to maintain enough back pressure to seat the floating piston used in the third stage. Without back pressure the follower on the third stage will slap repeatedly into the floating piston causing wear and eventually damage. This can be heard as a clacking sound as the compressor starts up but should even out and quiet down quickly. The back pressure seats the floating piston against the follower and keeps them moving together. Approximately 300 psi is the minimum back pressure to keep everything seated properly. The second function of the priority valve is to keep the moisture separators working efficiently. The higher the pressure the better the efficiency of the moisture separation. Ted Green has an excellent article explaining the functionality of the moisture separators over on the Deco Stop. (Understanding SCUBA Compressors and Filtration). In there he recommends setting the priority valve to 3000 psi but for clarification he is referring to the priority valve at the outlet of the filtration stack not the compressor. You could add a BPR set to 1500 immediately after the compressor and one set to 2500-2800 after the filter tower.

 

[RayfromTX]

Andrew- Thanks for your post. I just found the back pressure valve recommended settings in the manual that I had missed earlier. It says 300-2,200 so perhaps I'll take the easy way out and leave it at the factory setting of 2,000 and set the valve after the filter to 2,800. Ted Green's article is one I've read several times and I was reading it to suggest the higher pressure valve after the pump to maximize the percentage of the time that the pump runs balanced. I have read it from a few credible sources and it sounds right to me. I understand that the priority valve after the filter will serve the same function but not as soon if the large coalescer is flat on startup and having one on the compressor will also pressurize the second and third stage separators sooner. Perhaps these are trivial amounts of time but I suspect the benefits are worth the expense of a second priority valve. I think your suggestions are on target and will serve to quiet my worries. I also remember Iain to have said on Mani's thread back in 2014 that a higher setting on the first prority valve can lead to a surge of air into the filter stack which can disrupt the media but I assumed the large coalescer ahead of the filter chamber would alleviate that concern. Again thanks for the inputs so far and if anybody sees anything dumb in the picture I posted or in my description, please call me out on it.