Metal Fatigue vs More Frequent Bleeding
Ray C., how does metal fatigue of the filter enclosure work into your recommendation for more frequent bleeding?
I know Bauer has a pretty conservative cycle limit on their filter enclosure before recommending replacement. It’s something like 4,000 cycles for compressors operating at typical airgun tank pressure of 4500 PSI. At the lower SCUBA pressure (3200 PSI) Bauer allows 35,000 cycles. Wouldn’t trying to save on the filter by bleeding more often accelerate reaching the metal fatigue limit? At every 15 minutes, the service life would be 1,000 hours. Every five minutes and we’re down to just 333 runtime hours before Baur recommending replacement of the filter housing.
On the other hand, as a lone air gunner, i”m probably looking at 10 hours a year run time. 33 years is still longer than I am likely to last. I guess by the numbers, it is OK to vent every 5 minutes if you are a light user.
This assumes the metal in the assembly is good quality aluminum stock. I have my doubts regarding the metal quality of the MrodAir Airmax’s water separator. That little unit needs to be bled down every 3-5 minutes and no one mentions an estimate for its cycle limit before fatigue. Would you trust something whose interior looks like this to handle 1,000’s of high pressure cycles?
Mrodair Airmax water separator interior when new
The more I learn, the more I respect what it takes to build a safe compressor.
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The inside of that separator tube appears to be 5-10 years old from the surface corrosion. Is that about right?
All your fixes and add on costs are still a lot cheaper than if you went with one of the “real” high pressure compressors since I couldn’t get you going for less than $2900.
So, you wouldn’t count a bleed of the water as a full cycle? Don’t we dump most of the pressure in the separator during the blast or is a fair percentage of the pressure kept with a short blast? I should pay attention to keeping the venting shorter and not lose a much pressure.
As for your question about the picture, thankfully, the inlet isn’t opposite the outlet. What you see are the outlet and pressure gauge holes. They are part way up the separator. The inlet is at the top. Air goes down through a tiny, inner cylinder about 1/2 inch diameter x 3 inches long. That is supposed to be filled with drying or filter media. At the bottom of that is a bronze sintered pieced.
The whole separator is maybe six inches tall. It does work, but I think it is too small. The design also puts a nearly useless amount of drying media in front of the physical water separation. So, the media gets instantly saturated and rendered useless. That leaves it as merely a means of changing air flow, not absorption. Overall, it’s a dubious design. That’s why I put an Alpha filter after it. The Alpha has a PMV and is large enough to act as a second stage water separator in addition to its filtering. The stock separator on the Mrodair Airmax compressor is pretty scary if someone is using just it alone to dry the air and filling a tank. The compressor does just over 1 CFM, but the separator is really tiny. With an Alpha filter, you do get enough drying, but you have to bleed the Airmax’s separator and the Alpha every 3-4 minutes. Otherwise, you risk pumping frank water into the filter.
Metal fatigue really isn’t a concern when bleeding condensate since you only leave the valve open for a few seconds until the moisture is gone. A cycle is from pretty much full to pretty much empty as far as pressure is concerned.
I do have a question on the picture, though. Is that the inlet tap directly across from the outlet tap? If so, it really isn’t a very efficient separator since you need to change direction of the air to “knock” the moisture out of the air flow. The old school way of making a separator out of a pipe was to fill it with marbles that are way too large to fit in the outlet fitting. The air flowing around the marbles would change direction several times and that would allow the moisture to drop free. Another was to fill it up with stainless steel pot scrubbers that did a similar job. However, if the chamber is aluminum, the scrubbers needed to be pulled and the chamber cleaned/inspected often (we did ours every quarter) to make sure there was no corrosion due to dissimilar metals.
里面是腐蚀了吗
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Ray, that is what it looks like brand new from Mrodair. Scary isn’t it? The Airmax comes with the metal looking like this brand new and has no info regarding expected lifespan and replacement cycle. Meanwhile the much more massively built and cleaner looking metal of the Bauer Junior has the following warning in the manual and you are advised to log your usage cycles.
The max. number of load cycles for the P21 Central Filter Assembly is 4,000 if operated at the max. allowable pressure difference range of 330 bar (4,700 psi). For a pressure difference of 225 bar (3,200 psi) the max. no. of load cycles is 35,000.
To avoid exceeding the max. number of load cycles the operating hours should be recorded in the service manual. On condition that a max. number of four cycles per hour is not exceeded (condensate is drained every 15 minutes) the max. number of operating hours is 1,000 for 330 bar units, and 8,750 for 225 bar units.