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Author Topic: T80 Issues - Rebuild  (Read 5617 times)
Jr. Miner
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Posts: 496

« on: September 24, 2015, 04:16:53 PM »

Hey Guys - Air is life and when your sucking air through your long yellow straw you want as much clean air as you can get. 

I recently had a bad air day on my T80 and what I found got me REALLY concerned.  I could get one breath and then I'd get nothing.  Of course I was on the bottom and it took some effort to fight the current to get there so I was needing as much as I could get... and one breath wasn't cutting it.  I jumped out of the hole and started checking everything.  Engine Running - Check, T80 Chugging - Check.  I checked my reg and it was clear - flowing only a little air on the purge.  Checked the quick disconnects between the T80 and the reserve and those were good.  Checked the disconnect between the reserve and my hose and it was good.  I bypassed the reserve and connected the hose directly to the T80 and I was getting what I needed.  That of course pointed me to the reserve and filter.  I was using a 5 micron inline air filter immediately after the reserve tank.  That's the recommended setup by the way.

I pulled the filter element out of the inline filter and WHOA!  It was completely black and the pores were packed!  I could have salvaged the day/weekend by leaving the element out and working on unfiltered air but my OCD would have killed me.  I also put my finger over the output of the T80 and it was making my finger black and not just a little bit - so there was no way I was comfortable breathing on that. 

If you are doing this as your normal operation - I recommend that you reconsider!   

I called RockDoc to see if they had a rebuild kit for the T80, or a new T80 or a new Gast... struck out. 

I went into town and I wasn't near any big box or specialty shops so TrueValue was my only option.  They didn't have a replacement element for my filter so I bought a new filter, luckily it was also a 5 micron filter but I don't like the bulb filters because they aren't very robust and a busted filter makes for a bad day - YA THINK?!  Anyway - I got back to the dredge and got everything installed.  MUY BUENO!!  Plenty of clean air and of course I had a lot more than I was getting all summer on a slowly plugging filter.  It's amazing how much better your day goes when you aren't tired from sucking air.  HOWEVER, by the end of the weekend the once white filter element was completely black - I have a stash of extra filter elements now. 

But installing a new filter was only solving half of the problem.  The other half was "why was my T80 putting out so much crap?"  Incidentally, I had my regulator serviced back in May and the tech commented on how dirty it was... HMMM 5 micron filter wasn't really cutting it.  I also noticed that CGC's T80 was putting out more pressure than mine - his PRV was popping off and mine wasn't.  It is possible that his PRV was lighter than mine but I'm pretty sure mine has the 50 PSI spring in it and those are pretty standard so I assumed that mine wasn't putting out as much pressure.  Time to rebuild!

I ordered replacement parts from  Parts got here and I tore into the T80 - I had rebuilt it once already about 3 years ago so I was already familiar with the innards.  Here's the parts list and assembly diagram.

  The first things I noticed on the tear down was that the rubber diaphragm was wearing on the connecting rod plate and it left a ring of really fine caked up rubber on the plate.  The surface finish of the plate wasn't all that great.  I think a finely polished surface will help with this (future rebuild - I wanna dredge not polish).  The belly of the beast also had a fine layer of black (rubber I'm assuming) so I cleaned all the surfaces really well.  The bearings were all good and there weren't any signs of metal wear (others have reported this).  I replaced the diaphragm, reeds and both reed plates after cleaning everything really well.   Got it all assembled and it works great.  I'll dredge this weekend on a new filter element so I'll report what the results are and I'll see if my PRV actually pops off. 

Couple of other observations - The snorkel on the T80 just sits in the intake socket and so there's a leak path into the T80.  I sealed mine up on the previous rebuild with RTV (3M 5200 actually).  I also have a screen and carbon filter on the top of the snorkel.  Could the carbon filter be the source of the fine black coating?  Certainly could be but I pulled that all apart and none comes off on my hands so I'm thinking it's not the source.  There's also no black stuff in the snorkel tube - even at the 90 that goes into the T80.  Gotta be the wearing diaphragm.  Not only did the 5200 seal up the snorkel, it doesn't rattle around anymore. 

5 microns filters are pretty darn fine.  The Gast PCA-10 (263) has 40 micron filters and those are a staple for dredgers.  If you are having issues with your regulator - Have it professionally serviced ($25 + parts at most dive shops), and you'll likely learn that you had crud in there causing it to act up. 

In addition to the new 5 micron filter element, I also just installed an in-line scuba filter between my hose and the reg hose.  It's an AQUATEC AF-100.  It doesn't have a micron value associated with it but at this point, it will be a secondary filter and hopefully I won't need to replace the filter element as much as the primary.  I'm probably being a bit anal about my air but peace of mind is cheap and breathing issues are not. 

Grade/Class D breathing air doesn't have a particulate limit.  It only defines the limits of oxygen, gas contaminates and condensed hydrocarbons (I doubt they considered rubber particles), so when you see adverts for particulate filters for Class D Breathing Air - they are trying to sell you some bunk.  Some filters have catalysts for removing gaseous contaminates and condensed hydrocarbons, desiccants for removing water while also removing particulates; those can meet the Class D requirements but particulate alone = bunk.  Just an aside... Air Filters don't typically have micron ratings, those are typically for the liquid filter industry, but I'm not caring to argue the point with my filter manufacturer.  You'll have to decide for yourself what level of particulates you will accept - it's not just the size but the quantity (ppm of air) that you should consider.  I'm ok with changing filter elements more often now - changing out lungs is a much more painful and time consuming process.  If you are a smoker - everything I just went through won't really help you. 

Tidal breathing (resting) and Vital breathing (working) are very different and most dredgers will be Vital breathing most of the time.  We all come in different shapes and sizes and your O2 requirements will depend on your fitness level as well but most people are Vital Breathing 3-5 Liters every breath at a rate of 15-20 breaths a minute.  I'll do the math for you...  That's between 1.6 and 3.5 CFM at a consistent rate but there are times when we are well above that when we are really huffing.  Let's say your reserve is 5 gallons (damn unit conversions), you'll have between 3 and 6 breaths, plus one in your hose so if your compressor quits, you've only got a few breaths left to get to the surface.  Most of us lose suction before losing air, but losing suction could be because of a plug so we don't leave the bottom immediately (couple breaths maybe) before we feel the reduction in air.  There may be 5 gallons of reserve plus your hose but if your engine quits then the pressure will drop in the reserve and you'll have to suck that last bit of air out at considerable effort.  Why is this important when discussing filters?  In fact why are you even reading this - I'm bored, what's your excuse?  Here's the down side of filters - they restrict flow.  So your compressor needs to supply more than 3.5 CFM, but pressure is important.  All filters have a pressure drop across them and their efficiency (pore density-contaminates) determines how much restriction there is.  As the filter plugs, the flow rate decreases and the pressure drop increases.  While both change as the efficiency changes, filter designers use a fixed pressure drop to determine what filter is necessary for a minimum flow rate.  For liquid filters the pressure drop is a function of the flow rate squared, for air filters the pressure drop is linear with flow rate.  I found it curious that most air handling systems design in a reserve of 1 gallon per CFM to handle changes in demand.  Anyway - I now have two filters inline and I may have to drop to one - we'll see. 

Now this is where it gets interesting - you are still reading right?  The T80 compressor is AKA Thomas Model 80AX33 and Thomas is now a Denver-Gardener Company.  I pulled the spec sheet.

Take a look and see that it's not rated for 50 PSI - it has a 40 PSI max constant pressure - OK so that explains why my 50 PSI PRV doesn't pop-off.  But what's most interesting is the performance curve.  At 0 PSI it can put out 4.25 CFM but we can't really breath off of 0 PSI air and that drops to 1.6 CFM at 40 PSI.  WOW!  Now realistically, as we are breathing we are dropping the system pressure significantly but lets assume it's running at 10-20 PSI while breathing.... it's only outputting between 2.6 and 3.3 CFM.  No wonder some of us can out breathe the compressor, reservoir and airline.

I suppose it's time to put a pressure gauge on the system somewhere and measure what I'm actually breathing on.  Perhaps a Tee off my harness and have a gauge underwater with me - at least for testing things out.  But not before tomorrow!!!  I'll be underwater all weekend wishing I had data but oh well. 

My guess is that I'll have used but rebuilt T80 for sale sometime after dredge season.  Until then.. Happy Pans!!

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