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Check Valve Over-Kill?

Posted: Tue Jul 17, 2018 10:10 am
by SurfLung
Check Valve Over-Kill?
- I've filled quite a few tanks since I rebuilt the Back Pressure Regulator (aka PMV) and have some observations and questions.
- First, you can see by the photo below that I installed the air outlet on the top and an additional drain/bleed valve on the bottom. The hose from the air outlet goes up about 3 feet vertically to my filter array. And my filter array has a check valve/PMV that keeps the filter array at or above 1500 psi to squeeze water out of the air. So the entire length of the hose from BPR to filter array acts as a moisture condensing tower with a drain at the bottom. ().
- This is essentially a second moisture condensing system. The RIX has two moisture condensing towers of its own that are positioned before the BPR in the air flow. Surprisingly, there still is some moisture in the air as it passes beyond the BPR. So, that drain at the bottom does let out some water even though a bunch was squeezed out by the two primary moisture condensing towers.
- But I am almost never seeing any moisture coming from the condenser on the filter array... So, I thinking I'm getting the moisture out.

- My question is whether the extra check valve that's installed just before the BPR might be affecting the efficiency of the BPR in a negative way? The RIX manual and diagrams indicate that the BPR serves as a check valve. They don't show any additional check valve before the BPR. I'm wondering if the check valve might be compromising the seal of the BPR, allowing moisture to make it though?

Re: Check Valve Over-Kill?

Posted: Tue Jul 17, 2018 11:39 am
by tbone1004
that looks like a Rix. You need a priority valve right on the outlet of the Rix BEFORE the filters, but AFTER the moisture cans. That should be around 2000psi which is th efactory setting and that drops most of the moisture out before it gets to the filters, and because it is a short section allows the compressor to get up to balance pressure quickly which it will appreciate. Higher pressure is more moisture reduction.
With the Rix, it's perfectly fine to use something like a QF4 quick disconnect right after that BPR that you can then connect to your filter stacks if you want them separate. If they are hardlined, that's fine, but you still need the BPR before the filter stacks.

After the filter stacks, you want another BPR to keep the filters running most effiectively and for that, I like to run them at whatever pressure I set my pressure regulator to. 4500psi for me so they are not pressure cycling when I'm filling my banks. After I'm done filling, I will bleed them down to 2000psi or so which probably doesn't matter, but makes me feel better.

Re: Check Valve Over-Kill?

Posted: Wed Jul 18, 2018 9:31 am
by SurfLung
- Thanks tbone.
- I just edited my original post to explain the RIX moisture condensing towers positioned before the BPR in the air flow.
- My RIX manual says to set the BPR to 1800 psi. The Bauer BPR that's identical to my BPR comes pre-set to 1800 psi. See the description at ... .asp?bc=no. So 1800 psi is what I have mine set for.
- Couv asked me about why I didn't set it for 2,000 psi like it says in Compressors 101 and I really didn't have a good reason other than, that's what it says in the manual and maybe it has to do with the limits of the compressor?
- Anyway, I see no harm in trying it adjusted to 2,000 psi. I'll try that and report back my results.

But the Question Remains... Does the extra check valve just before the BPR reduce the efficiency of the BPR? Look at the picture of my arrangement. There's a one way check valve mounted between the 3600 psi OPR and the Back Pressure Regulator. Since the BPR already acts as a check valve, why have another one in there? And, could that extra check valve somehow screw up the air flow so that the BPR doesn't seal properly?

Re: Check Valve Over-Kill?

Posted: Wed Jul 18, 2018 10:01 am
by tbone1004
The BPR functions as a check valve, so having a BPR at the outlet of the compressor, then one at the end of the filter stack, like you should, is sufficient. I have a check valve on my whips, but that's not to protect the filters or compressor, it's to prevent tanks from mingling with each other

Re: Check Valve Over-Kill?

Posted: Wed Jul 18, 2018 10:43 am
by antique diver
I can't see the check valve in it's current location actually being an issue concerning moisture, but would be interested to know if anyone has other thoughts. It can actually be a good thing installed either as you have it, or after the PMV/BPR/BPV/whatever-they-call-it-today. Reason is that the BPR, having a metal-to-metal seat, generally does not seal as well as as a dedicated check valve does, and when compressor is off air can seep from your stored air in the filters back through the BPR, and be lost past the piston rings (which aren't very efficient when static).

Now about the BPR setting... this is just my opinion, based on my experience, (BUT I am open to friendly debate). Tom, I can see that you are well versed in compressor operation, and I don't mean this as a contradiction to your method... like I said, just the way I like to do my fills! I do agree that to a certain degree the higher the air pressure remains in the separators and filters the more moisture will be dropped out of the final air produced. Even so, I prefer to run my BPR's at 1600 - 1800 PSI due to the following reasoning:

1. The rate of elimination of moisture is not linear as pressure increases. In other words you don't remove twice as much moisture volume at 3200 psi as you do at 1600 psi. Probably because you have already removed such a large percentage by then. I have been satisfied with the resulting filter life at my lower settings such as RIX has suggested. I normally use the Lawrence Factor filters with the clear plastic tube and the moisture indicator strips, and visually check them at regular intervals.

2. If you run the BPR at 4500 psi you may drop a little more water out in the final separator and in the filters, but filters are cheaper than compressor parts. By that I mean the compressor heat and wear is greater at higher discharge pressures. Whatever pressure yours is set to is the pressure that your compressor is pumping for the whole fill time. Set at 1800 allows the compressor discharge pressure to average out over the fill cycle, resulting in a little less total heat and wear on the final stage piston, rings and valves. An admittedly small difference here can potentially be a lot of parts dollars compared to the slight increase in the life of a filter which costs a lot less than the aforementioned parts. Just something to think about, and I look forward to more discussion on the subject!

Re: Check Valve Over-Kill?

Posted: Wed Jul 18, 2018 10:49 am
by tbone1004
auxiliary cooling is nice. Removing the stock fans and putting an electric fan on there works well. I have a 2 speed fan out of a volvo that I use which helps a lot when running at higher pressures. I let it run for a few minutes after the compressor is done to help any latent heat buildup.

oh, of important note, make sure to "listen" to the compressor when setting the first BPR. The compressors are imbalanced at too low and too high of a pressure and they have a sweet spot that you want to stay in. That "sweet spot" is where your BPR should be set to. It will go out of balance as it goes higher, but then letting it fall back down will make it happier which is why you don't want to fill a big cascade system in one go if you can help it. Mine seems to be happy at 4500psi so I let it stay there, but it's also rated to go past 5000

Re: Check Valve Over-Kill?

Posted: Thu Jul 19, 2018 10:18 am
by SurfLung
antique diver wrote:
Wed Jul 18, 2018 10:43 am
I can't see the check valve in it's current location actually being an issue concerning moisture...
Now about the BPR setting... I prefer to run my BPR's at 1600 - 1800 PSI...
Thanks Bill, I was hoping you would respond. :)

And Tbone you gave me a compliment awhile back on the Fill Rate Challenge, "...but I do think that you are pretty bloody close to "ideal" running conditions with this thing."

All of the condensed moisture from my RIX is coming out of the two condenser towers before the BPR and the bleeder valve after the BPR at the bottom of the hose leading up to the filter array. The condenser on the filter array hasn't drained a drop much less even some mist. I am due to check the indicator strips and so I should be able to confirm whether I'm running dry enough the way things are.

Thank you both for your help and advice! :)

Re: Check Valve Over-Kill?

Posted: Thu Jul 19, 2018 10:26 am
by antique diver
tbone1004 wrote:
Wed Jul 18, 2018 10:49 am

...oh, of important note, make sure to "listen" to the compressor when setting the first BPR. The compressors are imbalanced at too low and too high of a pressure and they have a sweet spot that you want to stay in. That "sweet spot" is where your BPR should be set to....
Tom, you have a good ear for machinery! What kind of compressor are you running?

Re: Check Valve Over-Kill?

Posted: Thu Jul 19, 2018 11:33 pm
by tbone1004
which one :-P I have three 2500cfm, 500hp Ingersoll Rands, and a "baby" 700cfm, 150hp IR at work. The maintenance and engineering departments reports to me and as an engineer/gearhead I try to keep up. I'm starting to design a PLC system to monitor everything that will be a generic/more complete version of what Bauer has because one of my PLC guys is currently not fully utilized so he's helping with that.

Right now I have a 6cfm Hamworthy that I'm going to be selling since I can't slow it down as slow as I need it. I'm hemming and hawing on either rebuilding one/both of my Rix SA6's *which is painful because they need some parts that I don't really want to buy on top of the normal maintenance kit, or get a Walter Kidde 2.4cfm so I can run them on a standard wall outlet. Either will end up with a voltage doubler and VFD though so I can plug it into a standard outlet with the VFD and run it slow, or I can bypass the VFD and get full speed with 230v if I have it.

On the actual ear thing, it's more "feel" it and you can feel when it starts vibrating a bit more from the imbalance. I actually put a vibration meter on it, but I have them around the plant so it's convenient to borrow one of those. They aren't that expensive, but more expensive than they're worth when you can get close enough by touching the frame of the compressor and feeling for the vibe

Re: Check Valve Over-Kill?

Posted: Fri Jul 20, 2018 5:16 pm
by antique diver
I don't think I have ever even seen a compressor as large as those IR's. I assume they are screw type. Where do you work that uses that much air (if it's any of my business)?

What's the issue with running your Hamworthy slower. Does lubrication (splash lube?) become a problem?

Re: Check Valve Over-Kill?

Posted: Sat Jul 21, 2018 10:06 am
by tbone1004
they're centrifugal which is adorable because they actually need to be jump started by a smaller compressor if they go down and we lose air pressure but by God they are powerful, sound like a jet turbine.
Big textile operation with air-jet looms for composite fabric production and they are thirsty buggers with each taking about 80cfm to run. We have converted a bunch over to a rapier style loom, but prior to doing that the plant was running the air at capacity. 3x 2500cfm, 1x 1500cfm, 3x 1200cfm, and then the baby 700cfm that runs when we shut down for extended periods of time *typically the week of 4th of July and Christmas*, 24x7x365 it's rather impressive. They're in phased retirement now and we are usually only running one at a time for about a month at a time on rotation.

Hamworthy is splash so slowing it down is problematic

Re: Check Valve Over-Kill?

Posted: Sat Jul 21, 2018 10:53 am
by captain
At work we had a 17,000 cfm @ 80 psi Demag centrifugal compressor driven by a 3500 hp synchronous electric motor feeding an air separation plant. Starting it was usually an adventure.

Re: Check Valve Over-Kill?

Posted: Sun Jul 22, 2018 6:34 pm
by Bryan
I did a due diligence report on a plant that had an 800 ton centrifugal chiller with a main contactor that was so wonky they engaged it by pulling it closed with a 6 foot piece of rope.... I asked them WTF they were doing and was told.. That's just the way we do things round here....

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