Oil or oil-free compressor needed to operate RTS rear door when isolated?

[Kevin Warnock]

Hello,

I got the wheelchair lift out of my RTS bus yesterday. It took about 16 hours of full time, hard work. Now I am turning my attention toward getting the back door operation controllable via a wireless remote key fob like found on automobiles. The keyless entry system I have in mind is described here:

http://www.commandoalarms.com/itm100033.htm

I wonder what kind and size of air compressor I should get to pump into the air system that powers the rear door. It would seem best to isolate the door air supply from the rest of the bus, and run the door exclusively off the compressor I buy and install. I take it I don't need a large compressor, and that the smallest Sears model, for example, would be more than adequate. The unit I am considering is described here:

http://www.sears.com/sr/javasr/product.do?cat=Compressors+%26+Air+Tools&pid=00915312000&vertical=TOOL&subcat=Air+Compressors+%26+Inflators&BV_UseBVCookie=Yes

The price is $99 and it comes with a lot of fittings, some hose and other accessories. It is small, and probably doesn't draw too much power, though the specs don't say.

The compressor is oil lubricated, and I don't know if that's a problem or not. I read that oil lubed compressors are quieter, which is a plus here.

I also don't know if I need an air dryer, or if such a thing is practical. The air dryer for the bus is big and looks expensive. If I forgoe the air dryer, does that mean eventually the air system will fail or rust out? What are the consequences of water in the air system? Can I get the water out manually with a dump valve? If so, how often would I need to remember to do so?

Is the following a potential strategy that I might pursue? Hook the air compressor with permanent air fittings into the isolated door air system, and plug the compressor into my inverter, and keep the air compressor switched on all the time? Then, after a certain number of door openings and closings, the compressor comes on for a few minutes to fill its tank? How much power, if any, does an electric air compressor use when it's idle? I presume there is some kind of a mechanical pressure switch that causes the pump to start when the air tank pressure falls below a set level... is this right? If so, does that mean there is really zero electrical use when the compressor is not pumping? If so, that would be great. Do some models of compressors draw electrical power even when 'idle?' Anyone know how many open/close cycles I might expect with a 1 gallon capacity compressor like the model I am considering? I would hope for at least dozens of operations between cyclings, but it's not a requirement.

If you don't like the Sears unit I mentioned, can you please suggest another brand and/or model?

Thanks very much for your thoughts and advice.

Kevin
San Francisco, CA
1994 TMC 80286 'RTS' Series 50 40' x 102"

[kyle4501]

The compressor is oil lubricated, and I don't know if that's a problem or not. I read that oil lubed compressors are quieter, which is a plus here.

Oiless = cheap construction, Oil lubed can be much better & usually more durable



I also don't know if I need an air dryer, or if such a thing is practical. The air dryer for the bus is big and looks expensive. If I forgoe the air dryer, does that mean eventually the air system will fail or rust out? What are the consequences of water in the air system? Can I get the water out manually with a dump valve? If so, how often would I need to remember to do so? 

The less it runs, the less water to deal with



Is the following a potential strategy that I might pursue? Hook the air compressor with permanent air fittings into the isolated door air system, and plug the compressor into my inverter, and keep the air compressor switched on all the time? Then, after a certain number of door openings and closings, the compressor comes on for a few minutes to fill its tank? How much power, if any, does an electric air compressor use when it's idle? I presume there is some kind of a mechanical pressure switch that causes the pump to start when the air tank pressure falls below a set level... is this right? If so, does that mean there is really zero electrical use when the compressor is not pumping? If so, that would be great. Do some models of compressors draw electrical power even when 'idle?' Anyone know how many open/close cycles I might expect with a 1 gallon capacity compressor like the model I am considering? I would hope for at least dozens of operations between cyclings, but it's not a requirement.

Depends on the condition of the door system. The size of the cylinder also effects how much air is required per cycle. The actual cycle rate will determine if running it off the inverter is a good idea or not. It'd be bad to ruin your house batteries    due to an air leak when you weren't there to hear it run continuosly (depends on how good your inverter is at low voltage shut down)

[Hartley]

I ran a door on one of the $49 12 volt compressors. Had a relay that turned on the compressor when door open
was needed and on again on door close. Hooked to the original door operator cylinder system. Took the bus air system out of the circuit.

The little low volume high pressure units would open and close the door with about 10-20 seconds operation.

Just modified one of the cigarette lighter units to hardwire and left it in it's factory case, shoved it up in the overhead
door operator mechanical bay.

I did have to change the air solenoid coils and relays to 12 volts on one I worked on, But the last one was already 12 volt bus.
Most have Potter-Brumfield plug in relays anyway.

[Don4107]

I just picked up the next bigger model in a dinged box for $90.  Same motor/compressor with bigger tank that works out better where I want it in the 4107.   Took about 15 min to air up the 07 from zero. 

ID plate on motor says 10.5 amp. Did not put the amp probe on it yet.

I would hook it up so you can open a valve to air up the whole bus.  Would also keep a chuck so you can hook up a hose for whatever.  I am going to mount mine so it can be removed without too much trouble to keep it available for other uses.

I think the noise will be a lot less with a little extra foam around the intake filter or maybe a length of rubber hose between the compressor and the filter.  If it is close maybe plumb the intake into the engine air filter. 

And of course it is made in China.

Tank has it's own moisture drain built in.  It will need to be drained like any compressor.  Just a pipe plug, but could easily be changed to a valve.

[buswarrior]

Hello 1967

On draining... whatever moisture the electric compressor makes will be found in the first place the volume of air is stored, so if you use the stock tank that comes with it, you just have to drain its tank periodically.

With experience, you will find the right interval/duty cycle for draining. I expect it will be quite long, if you isolate the door system.

You may want to upgrade the drain to something automotive, like a cable drain. The stock drains in these little compressors are hard on the fingers, need access to get an arm in there, etc. A cable drain would be really nice.

happy coaching!
buswarrior

[Kevin Warnock]

What is a 'cable drain,' may I ask? Where might I get one?

Thanks,

Kevin

[buswarrior]

Hello.

A cable drain is a drain valve that you pull on the rope and it drains. Available at a good automotive supplier near you. Makes inaccessible drains easier to drain.

happy coaching!
buswarrior

[TomC]

Before you spend all that time and effort on the rear transit door, most transit doors leak alot of air.  I had bi-fold doors on my transit and they weren't even close to sealing out the air.  Maybe the RTS is different. Good Luck,TomC

[HighTechRedneck]

Before you spend all that time and effort on the rear transit door, most transit doors leak alot of air.  I had bi-fold doors on my transit and they weren't even close to sealing out the air.  Maybe the RTS is different. Good Luck,TomC

I imagine when my RTS and it's seals were new, they doors sealed up pretty good.  But now, the seals are 25 years old and they don't even come close to sealing.  But for now, my budget is going to more critical conversion needs.  Some day I will pop $1000 on a door, but not today.  I am looking at how I might be able to supplement the door seals to improve them.

I've found this thread interesting and may try it myself.  It would make for a cheap and functional solution for now.

[TomC]

I had camper doors made for my bus-both in the front and the back.  I just made a door frame from wood screwed into the metal, and have had really good luck with that setup.  Granted you hear some wind noise at freeway speeds (thats why highway buses have the air pressure cylinders applying pressure to the closed door) but they do what they are supposed to do.  Even though they are straight and the bus has 3 angles to it, I think it is acceptable looking.  Maybe one day I'll attempt to make a custom door to follow the contours-but now they work well.  Good Luck, TomC

[Kevin Warnock]

I know there will be lots of wind noise if I retain the back RTS door. That's why I intend to put in a residential entry door just behind the door mechanism, at the height of the middle step. That door will have normal weatherstripping, and will fit tightly. This should keep out the hot and cold when stopped, and muffle the wind noise from the OEM door. I don't want to mess with the sleek OEM look, which is why I am keeping both the front and rear doors unchanged. The front door will be sealed from the inside with silicone, or something like it, so there should be zero wind noise there if I do it correctly. I think even with a new R & M door up front, I would still have had some wind noise. What I am shooting for is none, like the driver's side front, where I can't detect any wind noise, even at 75mph.

Kevin