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BlueDogDozing

Donaldson air filter housing, butterfly valves?

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I have a question about a Donaldson air filter housing on a 96 Mack RD688S with an E7300.  The air filter housing has two different air inlets, one on top under the cap (smaller of the two), and one that draws air from under the hood.  Both of these air inlets have large butterfly valves and they're setup so that when one is open, the other is closed.  The valves are actuated by a pneumatic cylinder that should be bolted onto the Donaldson housing...but my mount broke off...and the pneumatic cylinder doesn't move anyway so I was going to replace it.  

I've called three different service/parts departments at Mack dealerships and have yet to get an answer about what it is, what it does, etc. and when I tried to get a replacement part for it, they told me they had the part number, and that it was made by Bendix (part number 283023N), but apparently they didn't have a price, nor do they show any parts in stock.

Since the little cylinder/mount is broken, and the larger of the two butterfly valves was shut, I temporarily set it up to where the larger valve stays open...seeing as how they likely put this weird assembly in for a reason (I assume it has something to do with operation under different throttle/idle conditions, I have an air throttle so this might work like the air modulator for the auto transmission) I'd like to figure out what it does, and restore the function to factory operation.  Or just remove both butterfly valves so I have more air incoming all the time 😎

I've attached pics of the housing on the truck, the inside of it with the butterfly valves and linkage, and the pneumatic cylinder.  Ignore the red paint on some of the parts that shouldn't have paint on them.  Apparently someone resprayed the cab and for some reason they removed the hose from the air filter housing and sprayed paint into it instead of taping it off.  I guess they figured the filter is there for a reason 😳.  Any help or explanation would be appreciated!

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You have a truck with the inside-outside [engine] air intake option (with in-cab control).

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1 hour ago, kscarbel2 said:

You have a truck with the inside-outside [engine] air intake option (with in-cab control).

That makes sense, there are a few switches without labels in the truck.  

I finally found a replacement pneumatic cylinder, for $435.  Needless to say I won’t be replacing it.  Good to know it’s not necessary so it doesn’t matter if I disable it  

It seems like an odd option.  What is the point of choosing outside vs inside air?  Besides air being cooler outside I don’t really see a difference between the two. 

This was formerly a DOT plow truck so I assume it has something to do with that. 

Edited by BlueDogDozing
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My 95 RD e7 350 has a "cold start only" switch on the dash, operates some sort of intake plumbing that bypasses the intercooler until things get warmed up... We have never had to work on the engine in the 10 years we have owned it, so not real familiar with it. And we never use the switch b/c it's in a heated garage....

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You can get pneumatic cylinders online for cheap, just need to measure the throw and figure out how to attach it to the butterfly valve. 

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On 1/17/2019 at 9:26 PM, JoeH said:

You can get pneumatic cylinders online for cheap, just need to measure the throw and figure out how to attach it to the butterfly valve. 

That is true!  I was hoping to find the correct part off the bat so I wouldn't have to fabricate anything as far as mounting brackets go, but it won't be too hard to do if it comes to that.  However for now I just set it to draw air from outside only so it's cooler than from under the hood.  I won't be using the plow anytime in the near future so I won't need to switch to inside air.

And must be nice to have your trucks in a heated garage!  Every time I work on it in the freezing cold I will think about your warm garage...

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We use waste oil; it's dirty and horrible to deal with but it's free! We have a local shop that gets us about 750+ gallons a year! Our tank for the heater has about 4 inches of sediment in it from over the years.... Can't wait to replace the tank and deal with that mess!

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Why not just pull the cylinder out soak it in PB Blaster, clean it and the bore and replace the o rings?

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