Lets talk Air Dryers for SEE

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peakbagger

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One of the design features of the SEE that can be blessing and curse is the use of air assist for all sorts of systems. Brakes, 4WD, Diff Locks, Air Splitter, remote throttle and probably one of two I missed. Add in low pressure air pressurization of the brakes and axles and there is a lot of air usage. When the systems work right they make the SEE easier to operate, unfortunately when they do not work its a very complex system made even more complex by the addition of a trailer air brake system

Air comes from the engine compressor and one of the byproduct of compressing air is water and carryover aersols that condense into oil. SEEs have an unloader with a spit valve to drain out some moisture but its only partially effective as any one that has torn into the air system has discovered. While the SEEs were being built for the US military, the Germans decided they wanted a clean sheet design for their services and they were having the 1300L built. One of the many design improvements was an air dryer system. The air dryer serves a two fold purpose, its keeps the water and oil out of the system and it captures solid contaminants in combined filter/desiccant unit. The dryer periodically empties itself via a spit valve type assembly. Eventually the replaceable filter craps up and it needs to be changed. Thus crap that could have got in the air system is instead thrown away with the filter. Water is also an issue in under freezing conditions as it will build up in low points and freeze. The SEE is equipped with an alcohol injector that requires it to be turned on in winter and filled with alcohol. The design of the alcohol bottle was flawed and it can be smashed by someone stepping on its cap. Even if my tank could be replaced the actual injector body is corroded and not rebuildable. It is no longer available. Alcohol absorbs the water vapor and hopefully the mix goes out the spit valve or the tank drains. Unfortunately is also carries the various condensed aerosols past the spit valve on occasion leading to even more potential crap buildup downstream. The net result is a air dryer is a potentially good retrofit for multiple reasons.

Air dryers are pretty much standard on newer trucks including Unimogs. Atkinson and VOS sells surplus takeout units but with shipping there are better alternatives. Meritor Wabco have the Supersaver line of air dryers which seem to be popular. There are many sellers of them. The trade off is they are not a direct fit. The other issue that has been raised is that the engine mounted compressor on the SEE 352 engine is located differently than the newer 1300L designs. The 1300L has a belt driven compressor located at the front of the engine. The engine also sits higher in the chassis. The combination of these two differences means the air line from the compressor is longer than on the SEE. The air dryer cartridges are only rated for 175 F so the shorter air line on the SEE can mean that the air from the engine mounted compressor can be too hot for the air dryer. One member of a forum has suggested lengthening the air line to allow more cooling. I will probably put a spot of black paint on my air line and take some surface temps the next time I am running the engine on hot day to see if its concern.

So the next issue is how to plumb it up. Wabco supplies a couple of variations of the Supersavers. I am no diesel pro but the standard configuration of a "standard" air system looks a bit different than the SEE design

1594471170076.png

The SEE does not have a governor at the compressor that controls the air pressure, the governor is combined with the unloading valve ahead of the rear wheel. There is no wet tank. The wet tank can be replaced with a variation that has a separate purge tank. that is piped directly to the air dryer and the wet tank goes away. I picked up an air tank used for air horns with the right pressure rating. The thing I am missing with the supersaver is a governor. I am stuck on the governor as I am just not that familiar with Diesel trucks. it looks to me like its a pressure regulating valve with the bleed piped to the dryer. My assumption is instead of bleeding, it has a spring valve in it so it builds up pressure and then sends a puff of air to the dryer when it exceeds the setpoint pressure?. They do offer a deluxe version of the supersaver with a built in purge tank and govenor but its a lot more expensive. larger and seems to be rarer.

So my question is do I understand the governors function correctly and if so any recommendations on a standalone one?. One thought was leave the old unloader valve in the system upstream of the air dryer and plumb the spit valve outlet to the air dryer to supply the air pulse but would prefer something simpler.

My SEE has an generally inaccesible toolbox between the frame rails with a piano hinge top that is rusted to the point where the sheetmetal flexs when I try to open it. Even if the hinge was not rusted I expect its not very waterproof. I dont use it so am considering taking it out and mounting the air dryer and purge tank in that location. It looks like its bit less prone to abuse and extends my air line a bit longer before the dryer.

So any comments, suggestions or warnings?

BTW after writing this I found a YouTube video on Bendix D2 governors. Looks line I need one of them or something similar
 
Last edited:

joeblack5

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State College PA
Thank you for starting a thread about this.
I am about ready for digging into the air system a little further.

I have a desiccant filter on my shop air compressor line. It has a clear housing so you can see from the color how saturated it is. As far a I know you can just reheat the pellets to 350F to drive the moisture of and reuse.

Could we use a vehicle automatic transmission cooler as air cooler. If the out put is lower then the input all condense would collect at the lowest point of the cooler. Seems that would cool better then the normal truck air dryer.

Not sure that i understand why the desiccant filter would be before the wet tank, seems to be a waste of the desiccant / filter use. I would think an air cooler before the wet tank so that the tank can collect most of the water and then the desiccant dryer to bring the humidity down another notch for the system.

Johan
 

peakbagger

Active member
547
46
28
Location
northern nh
Thank you for starting a thread about this.
I am about ready for digging into the air system a little further.

I have a desiccant filter on my shop air compressor line. It has a clear housing so you can see from the color how saturated it is. As far a I know you can just reheat the pellets to 350F to drive the moisture of and reuse.

Could we use a vehicle automatic transmission cooler as air cooler. If the out put is lower then the input all condense would collect at the lowest point of the cooler. Seems that would cool better then the normal truck air dryer.

Not sure that i understand why the desiccant filter would be before the wet tank, seems to be a waste of the desiccant / filter use. I would think an air cooler before the wet tank so that the tank can collect most of the water and then the desiccant dryer to bring the humidity down another notch for the system.

Johan
I think the coalescing filter on the truck air dryers work different, they just dry out by blowing air back through them. Probably less efficient? I am unsure if the wet tank is that "wet", its downstream of the air dryer in the diagram so its not that "wet". That said the dryer I bought a few years ago was set up for an external purge tank that is plumbed directly to the dryer (not shown on my clip). I think the dryer fills it up with dry air and then when the governor sends an impulse the dryer pulls air out of the purge tank which can be plumbed in remotely. I have looked at the air line going from the compressor to the alcohol injector. I was considering options for lengthening it. Its tricky as its definitely not a place for low point as water could build up and freeze. Of course I could put a low point drain and just blow it off on occasion but ideally better to have the spit valve as the low point. The Wabco dryers have a optional electric heating element in the base that is controlled to turn on at low temps to keep freezing from being an issue. I havent looked if my 1300L has that feature. One of the reasons for moving it to in between the frame rails is to get a bit longer line and possibly put a coil of tubing in there to get some additional length. I ordered a governor valve yesterday after I posted so I should have a bit more info when it gets here.

BTW I was on the EI website searching for air dryers and they offer an air dryer retrofit for a 404. A 404 is smaller truck with less air volume so I think I am on the right track.
 
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