questions about air tanks

[melkite]

We have a pd4501.  It appears that the previous owner rerouted the air lines to the airbags, bypassing the air beams.  It also appears that we may need new tanks.  We also have another air tank under the old restroom area.

what determines the size tanks needed?  Can we move the tanks? Right now they are in a baggage compartment on the street side, and there is room in the engine compartment on the curb side.

We are remodeling this bus, so we need to find room for propane tanks, a water heater and a generator.  The holding tanks were oriented to the curb side, so that needs to be changed, plus we need to put in a fresh water tank.  Moving the air tanks would help.

[TomC]

Repositioning the air tanks is no problem as long as everything is rehooked up correctly.  If you do replace the tanks (looks like you should) use equal or larger tanks-not smaller.  Make sure you have an air/water separator, if not, install one (goes between the compressor and the first or wet tank). Good Luck, TomC

[akbusguy2000]

Things to consider when moving air tanks:

Ideally air tanks should be placed where they are exposed to the outside atmosphere for cooling.  This is a must for the "wet" tank at the very least.  If the tank is not exposed to cooling air it will not condense sufficient water from the charged air supplied by the compressor.  This is why these tanks must be drained regularly.  An air dryer will help, but it will not change the dynamics of the wet tank.  For this reason the wet tank needs to be exposed, equipped with a drain valve, and located as far as possible from the compressor.   The dry tank is less critical, but it too will accumulate water by virtue of condensation.  And as we know, water is the enemy of all downstream air systems, and can be disastrous in freezing conditions. 

I think to relocate either wet or dry tanks, or both, to the engine compartment would not be too wise in view of the heated surroundings.


my opiinion


tg

[kyle4501]

Hey Melkite!
It looks like your air tanks have already been relocated once before. Originally they were over the street side rear tires in the parcel package area. Get a good air schematic & redo your air system so that the tank location suits your needs & the air is routed where it needs to be. If an air line is lengthened too far, you may need to oversize that line to get required flow.

The air beams on -092 have been bypassed too. & it rides very well 

Do you still have the factory heat? If you're not using that, remove the blowers & you will have lots of space for tanks there.
I'm assuming the factory A/C is gone from the engine compartment. You can mount the tanks back there & put a heatshield (just a piece of sheet metal) between the engine & tanks if heat is a problem.

New tanks would be best since lack of air pressure makes it difficult to go far. Check truck salvage yards to see if they can offer a better price for air tanks that are only a few years old.

BTW, the air tank under the washroom was full of pinholes in mine.

Good luck!

[melkite]

Thanks for the replies.  Explain to me the 'wet' and 'dry' tank.  I imagine that the tank on top in the photo with the drain would be the 'wet' and probably first in line from the air compressor, and next would be the 'dry' tank.  So what is the tank under the washroom, and would that be for front air lines?

I've printed this out and will let Dave look at it, and we'll probably have more questions.

thanks again.

[kyle4501]

When air is compressed, it heats up. As the compressed air cools off, the cooler air can't hold as much moisture, so it condenses out. This usually happens in the first tank after the compressor, hence the name 'wet tank'. The cooler this tank is, the more water will condense out & this is why this tank doesn't need to be in a hot area. This water needs to be drained after every use of the coach. Water can condense in other tanks too, so you will need to keep an eye on them & drain them too. If the air dryer is working properly, there should be very little water in the wet tank.

As far as the tank under the washroom, I think it was used for flushing the original chemical toilet. I think it supplied pressure to a chemical tank & pushed the chemical to the toilet when flushed.

I believe the sink's water supply was pumped from a tank behind the seats infront of the washroom. You pushed the button & got a timed amount of water.

Do be carefull with these old air tanks. There is tremendous energy stored in compressed air. Usually air tanks fail by pinhole leaks, but by this time, there is significant rust elsewhere in the tank too, so it is a waste of time to try to repair them. If you have seen the damage caused from an air tank rupture, you would understand why the law requires code certification for welding air tanks. If they are questionable, replace them.

BTW,
Do you still have your original washroom intact?

kyle4501

[buswarrior]

Hello melkite.

The location of tanks, the diameter of the piping, the lengths of run, the elbows, this is all carefully calculated to ensure the brakes function as intended.

Now, it seems that your set-up has been messed with by the previous owner... so all bets are already off!

The critical thing is that you do not unwittingly change the speed of the required flow of air, unbalance the volume of the tanks you require, or fail to include a variety of safety valving, check valves, pressure protection valves, etc.

Bendix is a great resource, and considering the vintage equipment you are working on, the area rep near you may take a special interest. Let him use your coach as an educational tool? Does the local school of higher learning have an enginneering level pneumatics program that needs a practical exercise?

Might as well design that new air system to be an updated dual circuit one?

happy coaching!
buswarrior

[Tom Y]

Melkite, I parted out a 97 Ford over the road truck this summer.  I saved the air tanks, 1 steel tank 35 L and 11 dia. 2 aluminum tanks 31 L and 8.5 dia. I don't think there is anything wrong with them. I plan to put them and some other parts on the garage sale page. Cheap or free, 5.00 each + shipping maybe.  Intrested?  Let me know.  Tom

[TomC]

The one critical positioning of the tanks is the service brake supply tanks.  You want those tanks to be very close to the drive and tag axle so it doesn't have pressure drop when you push on the brake pedal to open pressure regulator at each axle.

For those that don't know about air brakes, in a nut shell, the brakes have two circuts- application and service.  When you push on the brake pedal (which is a pressure regulator in itself) you are letting X amount of pressure into the application circut that leads to the pressure regulators or pop valves at each axle.  When the pressure from the pedal is sensed, these valves open up letting in the air pressure straight from the air tanks.  This is done since it would take a long period of time for just the pedal valve to fill up the brake chambers making for undesireable lag in brake application time.  The maxibrakes, on the other hand, only use one valve at the tandem since application time is not important on the parking brakes.  Good Luck, TomC

[melkite]

Our bus was converted, so we don't have the original washroom, thank heaven.  We don't have the original A/C, but we have some sort of heating, probably from the webasto.  that needs to be checked out also.

Tom, I don't think, since we are on the west coast, that we will be looking for tanks far from home.  the shipping would cost more than the tanks.  Our friend and mechanic has resources for truck items.

The tank in the front may or may not be linked to our air brake system? 

Thanks for the replies - very helpful.

[RJ]

Melkite -

Are you talking about the air tank located in the tool compartment underneath the driver?  If so, at least on the 4104 and 4106, that tank supplies air to the suspension, air horn and air windshield wipers.  Not sure on the Scenic, but is probably similar.

FWIW & HTH. . .