Chamber shades not fully closing

[rjsilva]

I’ve been playing at a church and wanted to see if I could fix a few things about the organ. One of those things is the shades. I’m mechanically inclined (I’ve rebuilt an automobile engine, for instance) but don’t really know how the shades work so any help someone could give would be appreciated.

These shades are operated by a bellows inside a pressurised room/windchest. The shades move, they just don’t close all of the way. The swell is maybe about an inch from shutting and the great is probably 4 inches from shutting.

Is this an issue of cable slack, or is there some way of configuring those bellows to pull further, etc.?

[Pipeorganbuilder]

Not seeing a picture of your shade motor, I am suggesting you look at the chest magnets that activate individual bellow inside the box. Your swell shoe will send a voltage to these magnets and will cause a series of magnets to close the bellows which is tied to the linkage controlling the shades. Sounds like you have one magnet not operating one of the enclosed bellows. May be something as simple as a dirty swell shoe roller contact dirty or even trash in the magnet on the action box. Hopefully it won't be a blown bellow inside the box.

Michael

[rjsilva]

Not seeing a picture of your shade motor, I am suggesting you look at the chest magnets that activate individual bellow inside the box. Your swell shoe will send a voltage to these magnets and will cause a series of magnets to close the bellows which is tied to the linkage controlling the shades. Sounds like you have one magnet not operating one of the enclosed bellows. May be something as simple as a dirty swell shoe roller contact dirty or even trash in the magnet on the action box. Hopefully it won't be a blown bellow inside the box.

Michael

Really helpful reply, thanks! Cleaning the shoe contact is easy enough. The bellows look good visually and they both felt identical when I compressed them by hand. I’m not sure where the magnets would be but I’ll have a look. If I can’t figure it out I’ll take a photo and post it here. I think it may be an Austin part but that’s just a guess.

[rjsilva]

Ok, I forgot to bring my Deoxit products to clean the shoe contacts today but I did get a photo of one of the shades motor. I also saw a work order saying they needed to be rebuilt because they weren’t fully closing/opening the shades, at a cost of $3000+ each. The work was apparently done a year or two ago (and they look in good condition), but they’re still doing exactly what the rebuild was supposed to fix.

On a side note, is it safe to be inside the wind chest room when it’s pressurized? I didn’t want to damage my ear drums or something else.

[AllenAnalog]

I'm no expert on Austin swell shade motors but it seems like those pillow pneumatics would need some kind of frame to keep them from blowing out sideways. Lots of lost vertical motion with that free-standing arrangement.

You need to get a two-way radio and have someone operate the swell pedals while you are inside the wind chest to observe what is happening.

[twnelson]

Ah, the Austin UniChest. Makes it easy to observe and service the action while operating. Probably not more than 6" of wind so you should hardly notice the pressure.

It appears that the magnets are on the board in front of the bellows.

--- Tom

[rjsilva]

So what would I be looking for with the magnets?

Since they’re still not opening and closing the shades fully after being rebuilt, maybe it was the expression shoes all along (or some other issue) and the church spent thousands unnecessarily…

I was concerned about pressure because I tried opening the door when the blower was on and it seemed like it needed a lot of force to open. I can be in there before someone turns it on, I just didn’t want to get stuck and not be able to get out in case I needed to :)

[AllenAnalog]

I take it your Universal Wind Chest does not have an airlock? If it does, you use your finger through the hole in the door to move the flap valve and equalize the pressure on both sides of each door as you enter and exit. Otherwise use a radio to have someone turn the blower on and off.

[Coenraads]

So, knowing nothing about Austin swell engines, I'm trying to intuit how the mechanism works just by looking at the pictures. First of all, I assume we're under the organ in the wind room that is under pressure.
On the left, I see a stack of nine or ten little white control bellows that are progressively exhausted through the black tubes as the swell pedal activates the exhaust magnets one by one. Have someone operate the swell while you are inside watching and confirm that they all fully exhaust and refill as the swell pedal is worked. If not, you may have a faulty exhaust magnet or a bad swell shoe contact.
These white bellows have a rod at the top that connects to a short wooden bar at the other end of which is a rod that controls a valve that exhausts the main (blue) bellows which do all the work. As the main bellows collapse the angle of the cantilever is altered until the main exhaust valve closes again. Thus the main bellows "follow" the motion of the small control bellows. How clever.
On the right side of the cantilever is attached a metal bar with a counterweight. Could it be that this weight has slid out of position and needs adjustment?
A rod attached to the top of the main bellows goes up to the actual swell shutters and pulls them closed against the pull of a spring outside the wind room. In this way, when the organ is turned off, the main bellows no longer experiences any downward pressure and is free to float up as the spring pulls on it making sure the shutters are open when the organ is turned off. I assume this is the state we see in the pictures.
Make sure that this return spring is free to move and does not get hung up as the bellows pull on it.
I think that if you get inside and watch this mechanism in action it should quickly become obvious where things are going wrong. If the blue bellows actually fully collapses (shutters closed), then a simple adjustment of the control rod length may be all that is needed.
I'd love to be inside the wind room of an Austin organ as it is being played and watch the very clever stop action in"action."
There is only one downside to having such a huge air box. There is no way to build a tremulant that can actually "shake" the wind. Am I right that Austin organs use rotating vanes, like in a reed organ to get a vibrato effect?

And yes, six inches of water sitting on a surface the size of a door would make it difficult, if not impossible to open. So make sure there is always someone around who knows you are inside and can turn off the organ should you need to get out. In a pinch, just pull down on a few of the larger pipe valves. The resulting ruckus should bring someone running.

[Pipeorganbuilder]

It is safe to be inside the chest with the pressure on. You have a four stage swell engine(4 bellows covered in black on right side of photo). The chest magnets for Austin organs look very different to other builders. Your magnets are the devices with the copper windings to the left of the large black pneumatics. You should be able to trigger them with you finger on each one to see if the pneumatics open and close.. Since the air is pressurized around the system, you will activate each to open and close by sending 12vdc from the swell shoe contact roller to each magnet. While looking inside the console, use a piece of wire to short across the contacts to see if shade closed. Do not worry about getting shocked.

Michael

[rjsilva]

Thanks for the replies and for Coenraads well
thought out ‘intuit’ and Pipeorganbuilder. That definitely helps a lot. I’ll report back when I get back in there.

[rohrlover]

Yes, Austin did use "paddles" to get a tremulant effect. IMO, not very effective.

[rjsilva]

Ok, I was in the chest today with the organ/blower on. In comparison to the swell motor the great didn’t move nearly as much. It’s not an issue of the linkage.

I was trying to touch the magnets to see if anything happened (nothing did) and I wasn’t sure where or how to touch them. Could someone explain with the image where to touch?

[Coenraads]

These are not your typical chest magnets which can be easily "tickled" to make them operate. Austin magnets are unique. Here is a cross section courtesy W.H. Barnes.



You want to activate the armature R but there is no way to do so short of twisting eyelet S and removing cover T. But then the armature may just fall out. Better to observe if the main bellows completely collapse and fill when the swell pedal is operated. Also observe the little white bellows and make sure each one collapses when activated by the electromagnet.

[Coenraads]

During the day, atmospheric pressure varies up or down by about 0.3%. But a change in the weather, such as a storm coming can result in a 0.7% change. Stepping inside an Austin universal wind chest at a pressure of 6.0 inches of water would compare to a change in atmospheric pressure of about 1.47% i.e., equivalent to a heavy storm coming. But 6.0 inches of water still translates to 31.2 pounds per square foot. So a 2 ft by 5 ft door would still require a force of 312 pounds to push open against atmospheric pressure.

Calculation in Newtons and and kiloPascals available for Canadians, and the rest of the world, upon request.

[rjsilva]

Really helpful coenraads, thanks!

Could I also use a multimeter to test at the magnets? If so, where would I test?

Next time I’m in I’ll clean up the shoe contacts but it would be nice to have another testing option while I’m there.

[Coenraads]

One thing I'm not certain about is whether the magnets get power when the shutters are open or closed. Normally, opening the swell sends power to the magnets but the Austin mechanism is unfamiliar to me and I want to allow for the possibility that it operates in reverse.

With the organ on, again observe the little white pouches. If they all deflate and inflate as the swell pedal is operated, then everything is fine electrically.
If one of them fails to operate properly, check which magnet is not operating by tracing the black tubing back to the magnet panel. Then that magnet is is (1) not getting power or (2) the circuit is open or (3) there is a physical problem.

1) Wth the power on, and the swell shoe either fully open (or fully closed, I'm not sure which) measure the voltage between the bare solid copper common wire and the connection(s) to the blue feed wire. You should read organ voltage (typically around 15 volts). If power is not present, check (and clean) the contacts at the swell shoe.

2) With the power off, measure the resistance, again between the bare copper wire and the connection to the blue wire. The reading may be anything from 50 ohms (or less) to over 100 ohms. Any such reading is OK. If the meter reads open, carefully check the fine coil wires to see that nowhere is there a break. If you find a break, some careful scraping of the wire and some soldering might salvage it.

3) If everything checks out OK electrically, I would take the cap off the magnet by turning the eyelet through 90 degrees so that it lines up with the slot in the cap. Check the armature making sure there are no foreign objects blocking any of the openings.

In the case where there is still no happiness, with the wind on and the shutters as closed as they will go, does pulling down on the control rod close the shutters more completely? At least that would tell you that the shutters are not physically obstructed and that adjustment of the mechanical linkage may be necessary. Best of luck.
John