To drain or not to drain

[supergaijin]

When shutting down my Bauer Poseidon I have been draining both condensates and bleeding air from the filling whips to approx 80bar as per the Bauer Manual. However recently I was advised to keep pressure in the 2nd condensate drain (below the filter) to keep dry air in the chamber and thus prolong the filter life.

Any advise?

 

[p1p]

If you can, keeping air in your filter is advisable.

 

[divingtactics]

Yes, you should always keep some pressure in your final filter. If you wish to bleed your whips down completely, you can put a Pressure Maintaining Valve after the filter but before the whip lines. Aqua Environment have a low cost version called the 211 but they tend to bleed down over time and I ended up replacing mine with the Lawrence Factor one: http://www.lawrence-factor.com/Library/ServiceItems/VL-530141-TG.pdf These ones are bulletproof and don't let anything through once they have shut off as the pressure drops. I have mine set to open at 2000 PSI and when I bleed the whips down, it shuts off around 1300PSI. So you are keeping the filter at a minimum of 1300PSI all the time. Because you are in such a humid environment, your filter life is always going to be considerably shorter than a cooler environment, so anything you can do to increase the filters dessicant life is a good thing and money well spent if you want high quality air. I would actually recommend that you put a humidity sensor immediately after your filter output, then a check valve, then a micronic filter, then a 33-inch additional filter stack, then another humidity sensor and finally the LF Pressure Maintaining Valve (Priority Valve), then you connect your whip to that.

This way you can see exactly where your filter dessicant is at. I have this system in place and prior to installing it, was repacking my main cartridge every 15 hours and thought it was okay. After a lot more research, I moved to repacking it every 10 hours, then after fitting the humidity sensor, I am now repacking it every 5 hours. My ambient temperature is 25 degrees C and my main compressor filter is a P21/P0. I have also fitted a 33-inch tower and this has made a huge difference to my air quality.

Finding out about correct filtration becomes an expensive exercise but what price do you put on your life?

If you can't afford all of that, then at least put a humidity sensor after your final filter.

 

[supergaijin]

We have t an average day time temp of 30C. I fill in the evenings to avoid the more extreme temps.. I use a P-31 and change at 15hrs with OM cartridges. Extra filtration is always a good thing, and as my operation expands I intend to re-invest in another larger compressor and keep the Bauer 250 as a backup.

Thanks for the info.

 

[divingtactics]

I use this spreadsheet, which I have found to be quite accurate. http://www.scubaengineer.com/programs/compressor_filter_lifetime_calculator.xls

If you look down at the bottom table, it advises you how much of each chemical is in each Bauer filter cartridge - there is no data on OEM cartridges. You then enter that data in the boxes mid way down and change the values above it to suit your compressor and environment.

According to this, in a 30 degree Celsius ambient temp, with a flow rate of 250 litres per minute and are using the two chemical filter in your P31 + have your PMV set to 140 bar, you will get 9.15 hours.
If you are using the three chemical filter, which contains 70 grams of Hopcalite for CO removal, you will get 7.77 hours.

Average ambient temp of 25 degrees gives you on the two chemical filter cartridge: 11.9 hours
Three chemical filter gives you 10.12 hours

Average ambient temp of 20 degrees gives you on the two chemical filter cartridge: 15.6 hours
Three chemical filter gives you 13.3 hours

A good way to test your cartridges, is to take one apart when you have changed it out and put a teaspoon full of the 13x Molecular Sieve in the palm of your hand, then add a few drops of water and see if it heats up.
Good 13x will heat up to about 60 degrees C
Spent 13x will generate a little heat but you will still be able to easily hold it.
Destroyed 13x will not generate any heat and should have been changed earlier.

Note that any old cartridges that you have lying around will be destroyed within a few days, so you really need to do this test as soon as you can upon removal of the spent cartridge.

Adding a humidity sensor paper disc allows you to change at the right time, when the cartridge passes 10% humidity.

Once the 13x Molecular Sieve gets a coating of oil and water on it, it will stop removing, moisture as it is fully saturated and then the Activated Carbon will stop removing all of the nasties that it removes. If you are using the 3 chemical filter with Hopcalite, the Hopcalite will not function at all if it is damp, so CO (Carbon Monoxide) will be passed straight through the filter cartridge. If the Hopcalite is dry, it will convert CO to CO2.

Really good sources of information on filtration are: Mike Casey of Lawrence Factor in the USA, Ian Middlebrook from this board and others and IyaDiver from this board also. These lads really know their filtration. Plus of course there is a heap of theory on the Scuba Engineer website and the Lawrence Factor library: http://www.lawrence-factor.com/Library.html

 

[supergaijin]

Interesting and alarming- the Bauer Manual gives me up to 16hrs for the P31 at 30C.

 

[divingtactics]

One of the dependents will be what your Pressure Maintaining Valve is set to also, the higher it is set, the more time you will get out of the filter. Typically, they are set to between 130 and 150 bar, I have my two set to 150 bar. So:

Changing the PMV and all of the conditions above with a two chemical filter......
PMV=1Bar or faulty PMV, filter life = .07 hours
PMV=130Bar, filter life = 8.49 hours
PMV=140Bar, filter life = 9.15 hours
PMV=150Bar, filter life = 9.80 hours
PMV=160bar, filter life = 10.45 hours

I wouldn't recommend setting it any higher than 150 bar, but you can see how it changes slightly. Of course if you are running the 3 chemical filter, the hours will be less as there is less room for the Molecular Sieve to make room for the Hopcalite. 150 bar is generally a nice balance point for your crankshaft too.

It's interesting to see what a faulty PMV will do to the values.

The best test you can do if you are concerned is to do the Molecular Sieve test on a just spent cartridge - then you will know where you are at in real terms as all of this information and Bauer's information is theoretical only - well theory based on chemical science.

For my system, and using the calculation spreadsheet, it is right on the money. It tells me to change at 5.16 hours, and when I do the Molecular Sieve test, which I do every filter change to the used MC and the new stuff I repack it with, it generates a little bit of heat in the old stuff and the new stuff is too hot to hold as soon as the water hits it.

 

[neutrino]

Interesting thread. I drain my compressor completely at the end of the filling session. Is it possible to permanently leave the 4th stage and filter towers under pressure at 3000psi over night or for a day or two?

Cheers
Rich

 

[divingtactics]

Interesting thread. I drain my compressor completely at the end of the filling session. Is it possible to permanently leave the 4th stage and filter towers under pressure at 3000psi over night or for a day or two?

Cheers
Rich

It sure is possible providing you have no leaks in your valves, connections or PMV.

Of course, it is ideal to have the filter under pressure of 130-150 bar for beyond just a couple of days.

The pressure that a vessel is under is not the issue, but the pressure cycles are, as in how many times it is pressurized and then depressurized. It is the number of pressurize/depressurize cycles that will eventually fatigue the filter stacks and separators. At 230 Bar/3335 PSI the limit of cycles is not something you would probably achieve in the entire life of the compressor, but if you are pumping banks to 330 Bar/4785 PSI, this figure is substantially reduced and needs to be monitored.

 

[neutrino]

So basically when I finish filling for the day I should just shut off the compressor. The auto dumps will drain for me and then leave the filter and whips charged ready for the next filling session?

Cheers
Rich