Film-Tech Forum ARCHIVE: Xenon Pearling

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Posted by Chris Byrne (Member # 1563) on 01-16-2003, 09:40 PM:

Firstly (as this is my debut posting), a big thanks to all the guys on this site for sharing their wealth of knowledge. I have learnt a lot from reading the various threads over the past couple of weeks.

Now on to a concern I have had with xenon pearling:

Lamp house: Xebex IIIR _ RS model.
Xenon Bulb type: Ushio 3000 HK-O
Rectifier: Ushio U4 KCX100

Lately I have had a couple of xenon bulbs discolour(or pearl) on the anode metal end (where the lug is connected between bulb and spring nut.) My first concern was a high resistance join between the lug and the end of the bulb, however I have replaced all anode leads and even went to the extent of using multi-grips to tighten on a lead while bulb was free of the lamp house.

I have tested all the exhausts and they comply with the standard set in the manual (180cfm.) Everything seems to be working as normal (clean, etc), except for leads darkening closer to lug. The pearling I mention has affected the past 3 bulbs in one cinema only at around the 1000 - 1500 hour mark (bulb is warranted for 1500 hours.) They have all died from seal failure at around the 2000 hour mark. I find it highly unlikely early failure is due to poor bulb quality.

To finish off, my technical support has suggested that I cut the power to the safeties while the xenon is struck to prove they are working efficiently and extinguish the bulb immediately when the fans stop. My latest thought is to replace the lug style fitting with a clamped one that slides over the xenon end.

If anyone has any ideas - please throw me a lifeline?

[ 01-21-2003, 08:21 PM: Message edited by: Chris Byrne ]

Posted by Tim Reed (Member # 137) on 01-16-2003, 09:49 PM:

Hi, welcome aboard! Have you checked the lamphouse alignment, to be sure the beam isn't being focused on the end of the bulb? It's possible to have this condition if a bulb is adjusted out of kilter, to compensate for a misaligned lamphouse.

It's remotely possible you could have a bad run of bulbs, especially if it's an odd size.

Other than a loose DC connection or exhaust fault, as you have already mentioned, I can't think of anything else.

Posted by Michael Schaffer (Member # 1204) on 01-17-2003, 10:31 AM:

The lamphouse fan should also run for a while AFTER the xenon lamp is extinguished!

Posted by Jack Ondracek (Member # 1466) on 01-17-2003, 12:21 PM:

quote:
from Chris Byrne:
...my technical support has suggested that I... extinguish the bulb immediately when the fans stop.

Chris, what do you mean by this? Are you able to run your lamp without the fans being on? This should not be possible under any circumstance. If possible, you should have some form of safety that prevents it. Many systems have vane switches in places like the entrance to the vent stack or in front of a blower. These are connected to the same circuit that prevents the lamp from running if you open the door. After you turn off your lamp for the last time, you should run your fans at least an extra 5 minutes or so.

If you can run your bulb with no fan, you'll most likely find the problem there.

In any case, considering you've had trouble with this lamp on more than one occasion, it sure sounds like you've got a problem with either the fans or the tightness of your connections.

Posted by Adam Fraser (Member # 1074) on 01-17-2003, 12:34 PM:

We let the fans blow until the lamphouse is room temperature. 15 minutes or so is a small time to wait around if it saves an expensive lamp.

Posted by Gordon McLeod (Member # 33) on 01-17-2003, 01:01 PM:

Also most xebex's have a flat heat filter make sure it isn't blasting the heat back at the end of the lamp
Also 150cfm is low from the inof I have on the Supersol and Hibeams we have in use up here

Posted by Michael Rourke (Member # 1142) on 01-17-2003, 03:08 PM:

I would say 300-400 cfm is the range you would want to be in for a 3000 watt bulb. When my exhaust fans went a while without servicing my bulb life reduced and I had a problem with bulbs fusing into the threaded negative clamp. I never had a problem with seal failure or any discoloration to speak of, but it sounds to me that you have a cooling problem, and if you don't have much cfm you will want to leave the fans on after the last show until the lamphouse is cool to the touch, not a set time limit.

Posted by Tim Reed (Member # 137) on 01-17-2003, 08:29 PM:

quote:
I would say 300-400 cfm is the range you would want to be in for a 3000 watt bulb.

A 3KW lamp? Duh! I didn't even notice that.

THAT'S the problem!

Silly me. [Razz]

Posted by Chris Byrne (Member # 1563) on 01-17-2003, 08:37 PM:

Thanks for all of your help, guys! I will keep this info handy should I encounter any further problems _ Touch wood [Wink]

In response to Jack's reply regarding the confusion with the safety vanes working or not. The answer is yes (as in the lamp will not strike without them operating properly), however I have never tried testing them while the xenon is struck to ensure they extinguish the lamp quickly and efficiently. Just recently I found that all these emergency cut-outs we have around the box (in case of fire) had all been disconnected [Frown]

All things being equal, it shouldn't matter, however it is a viable test that I should carry out given the circumstances.

I've ran RP40 for best picture result, however haven't tested the lamphouse alignment since problem first reared its ugly head, so that is a good start and one in which, I'll post any discrepancies if found.

I have also asked for a delay timer to be included as part of our air conditioning system on the exhaust switches. That is so they continue to run for 15 - 20 minutes after the night projectionist leaves. Does everyone agree this is adequate?

I am fairly certain the exhaust is pulling enough air on that particular lamphouse (307cfm.) What service can I carry out on it besides ensuring it is clean and tightly fitted to stack?

Finally, Gordon, I am particularly interested to hear about the heat filter. I have a couple of new ones in stock, as the original ones (fitted with a gauze cover) have holes in the gauze presumably from excess heat. The new one is without the gauze covering (which I think contained asbestos?). I have had little to do with these. In my shoes, would you consider replacing this?

Posted by Gordon McLeod (Member # 33) on 01-17-2003, 10:05 PM:

The xebex heat filters where are all a single pane of dichroic glass that sits in the snood and if mis angled can reflect straight back at the lamp
never seen one with absetoes on it

Posted by Jack Ondracek (Member # 1466) on 01-18-2003, 01:32 AM:

quote:
from Chris...
I have also asked for a delay timer to be included as part of our air conditioning system on the exhaust switches. That is so they continue to run for 15 - 20 minutes after the night projectionist leaves. Does everyone agree this is adequate?

It sure couldn't hurt, Chris... especially if your night operator heads for the hills as soon as the last show drops. I've never seen such an installation in an indoor house, but I did run into delay relays at some drive-ins.

Posted by Chris Byrne (Member # 1563) on 01-18-2003, 01:54 AM:

Sorry Gordon ... my mistake. I meant the black heat sink that sits just below the exhaust stack.

Posted by Scott Balko (Member # 438) on 01-18-2003, 03:20 PM:

I had this problem when I first took over at my current theatre. The lamphouse fan had a sail switch on the intake side for the automation and when the automation closed at the end of the film, it would shut the fan off to kill the power supply. While the large booth fan was still exhausting the air from the housing, the bulb was loosing its cool air supply. Once I got the lamphouse fan and the booth fan to run after the bulb was powered down, bulb life got better and the discoloration was cured also. I never had the problem at home when I controlled all the fans manually. Since the lamphouses at the theatre are identical to the ones in my screening room, the problem was fairly easy to identify as a lack of cooling after the bulb was shut off.

Posted by Chris Byrne (Member # 1563) on 01-18-2003, 08:20 PM:

Scott, the blower fan is another thing I have been contemplating. While it is not linked with the automation and remains on 15 hours a day (approx.), there is a slight waver in the vane. Not enough to trip the switch it is attached to, but no other lamp house has this inconsistency.

I think I have a few checks I can carry out in the meantime. A brush out of the impeller inside the blower won't do no harm neither.

Posted by Michael Rourke (Member # 1142) on 01-20-2003, 12:41 PM:

quote:
I am fairly certain the exhaust is pulling enough air on that particular lamphouse (307cfm.) What service can I carry out on it besides ensuring it is clean and tightly fitted to stack?

Make sure that the squirrel cage is clean, and the motor is oiled, most exhaust fans require a SAE20 oil, there is a 3 in 1 oil made especially for 1/4 hp motors. When the exhaust is on, trace the duct from the lamphouse to feel if there is any air leakage. If there are any 90 degree bends in the stack that's like adding 30 feet of duct, greatly reducing the air flow. You want the duct from the lamphouse to the exhaust to be a straight shot, but two 45 degree bends is much better than one 90 degree bend. Another option is to add a stack booster fan which could add 50-300cfm depending on what size you get.